Hafler DH-500 DH-220 DH-200 PC-1 High-End Audiophile Driver Boards Only Upgrade

$685.0 Buy It Now or Best Offer
free,30-Day Returns

Seller Store 7houses
(177) 100.0%,

Location: Brunswick, Ohio
Ships to: US,
Item: 273749175535

All returns accepted:ReturnsNotAccepted
DH-500, DH-200, DH-220 QC-600, QC-280:DH-500, DH-200, DH-220 QC-600, QC-280
Country/Region of Manufacture:United States
Type:Power Amplifier
HAFLER, FANTASIA AUDIO:HAFLER, FANTASIA AUDIO

*Please contact me BEFORE BUYING so that I can determine your exact needs.* ** Depending on your version of DH-500/220/200 and whether or not it was built properly if it was originally a kit or if it has ’user’ installed mods, there may be additional costs to properly interface the new Driver Boards. ** *** Turn-around time for this set of upgrades, is typically 2 weeks once I begin your project. I do this work part-time and never rush my work as this is very detailed, custom work. I want to make sure that everything sounds just right before sending your amp back to you. As time allows, I contact my buyers as to their position on my list as I move through my projects. The wait may be long, but it is SOOO worth it- just read my Customer’s Testimonials below. *** Because the demand for my upgrades has been growing in popularity, I have 3 projects on my ’Waiting List’. Some of these projects are ’boards only’ which only take me a couple nights to complete. It typically takes me 2 weeks to complete each project, so do the math on the wait. I apologize for the long wait. To reserve your place on my Waiting List, I am only requiring a partial payment(the cost of my PS Upgrade – varies by model). Of course, you can always pay in full as some have done. I will require the Balance Due prior to shipping your amplifier back home to you. As I move through the list, I send out updates as to your position. When I begin the project in front of yours, I will let you know to ship me your amp so I can begin work on your project. I also will send you regular progress updates with pictures so you can see how things are coming along. **** Parts price increases is unfortunately here in 2024. Parts have become more difficult to find and in some cases have quadrupled in price! The specific Power Supply Capacitors I have been using have reached their ’end of life’ from the manufacturer. Other parts have seen a 100-400% increase because of supply chain shortages and increased tariffs. Even with the increases, you will find that these upgrades are a great value when you consider the increased performance & reliability of these upgraded Hafler Amplifiers. **** I will advise you if anything unexpected reveals itself that will affect the upgrade. I ALWAYS open, and inspect your amp when I first receive it BEFORE doing anything. I check the fuses, then power it up. I check the Power Supply voltages ’as-is’ and Bias & DC Offsets before I run some music through it for a preliminary sound check to verify that your output MOSFETS are working. I will notify you if I find anything that we don’t already know about. This upgrade utilizes your existing Power Supply – IF – it is in good shape. Remember, it is 30+ years old! If your Power Supply needs restoring/upgrading, see my listings for my ’Complete High-End Audiophile’ Upgrades which includes the PS upgrade along with (2) Larger Filter Capacitors, a new upgraded 35A Rectifier/Disc Capacitor & a 16A Upgraded Power Switch and an Inrush Limiter if your version doesn’t have one. ***I do have a very limited amount of good, NLA stock Hitachi MOSFET ’matched’ pairs that have been recovered from other amplifier upgrades that I can possibly use to replace any bad ones in your amp if needed & if they match the series used in your amp.*** IMPORTANT: If your Stock MOSFET’s are good, there’s no real need to replace them. They are among the best ever made and should last a lifetime as they RARELY fail. Additional MOSFET Servicing: I can, however, pull & test them along with cleaning them and the MOSFET sockets plus install all new MICA Insulators under them and apply fresh, better formulated, Heat Paste to ensure maximum heat transfer. Cost: $70 for the DH-200 or 220 and $90 for the DH-500. See additional Services below. Thanks for looking! Please take the time to read through my customers’ testimonials below. See what others have experienced!——————————————————————————————————————————- So you really want to revive & upgrade your prized Hafler Amplifier, but don’t have the technical knowledge, skills or time to do your own installation? Or maybe you’ve priced the other high-end ’boutique’ Mod Shops and found them to be a little out of your price range. Let me affordably and professionally upgrade your amp for you. I have been an Engineer in the Broadcast industry for 30+ years and have worked as a Studio Recording Engineer as well. I take great pride in the quality of my work. Being an Audiophile has been a lifelong passion of mine. If you have one of the above mentioned Hafler Amplifiers that has become old and tired, but still works and needs some new life breathed into it OR you are still searching for true High-end Audiophile sound quality without the high-end price tag, then I have the upgrades you need to get you to that next level. I exclusively use QUA-CO Audio’s(now FANTASIA AUDIO) upgrade parts and kits. I have had nothing but FANTASTIC results using his upgrade kits. These upgraded Hafler Amplifiers have NEVER sounded better! After listening to my first modified DH-500 I did for a guy who worked many years for several ’high-end’ audio equipment companies, we were both immediately convinced that the designer at FANTASIA AUDIO had truly designed something really special. Ed spent more than 20 years working at Hafler and knows these amps as well as Hafler himself. Ed has been developing his own Driver Boards to work specifically in these Hafler amps. They are a culmination of his years of experience. His driver boards sound SO much better than the original Hafler design. I believe your FANTASIA AUDIO PC-1 Modified amp will go head-to-head with amps costing several thousand dollars or almost anything commercially being made today. ——————————————————————————————————— Here’s what you will get: Once I receive your amplifier, I will give it an initial check and then run some sound through it to make sure it has no unknown issues before I begin. If I find anything unusual, like a ’sagging’ Power Supply, I will contact you and discuss your options. I have another listing for a complete Power Supply Upgrade that I highly recommend to get the most benefit from your amp upgrade. If it passes the initial check, I will hand-assemble a pair of FANTASIA AUDIO’s ’state-of-the-art’ PC-1 Driver boards designed specifically for your Hafler Amplifier model. QUA-CO uses Murata 1000 VOLT 5% Con-formally Coated Ceramic Capacitors, Electrolytics are Nichicon Audio Grade Gold or better. All other capacitors are Xicon, Rubycon, or Cornell-Dubilier 250V to 630V 5% or 10% Polypropylene’s and ’matched’ transistor pairs. I use industry standard, high quality, Kester ”44” 63/37 non-corrosive Rosin Core Solder when assembling your new driver boards. Each and every solder joint is visually inspected. I will remove the original driver boards and install the new PC-1’s and optimize the Bias and DC Offsets for each channel. I will replace your old Input & Output connectors with new Gold RCA’s and Gold Binding posts. As part of my installation service, I will clean your Frame & Heat Sink as well as take apart the Fan Motor(DH-500) and clean and lube it with a non-gumming, Liquid Bearings Synthetic lubricant it so it is ready for many more years of service. I will simplify & re-organize wiring paths (where needed) and make sure that the Star Ground System is properly done to reduce noise. If your amp was originally a kit built or ’tinkered with’ by someone, they may have used the wrong wire type/size (I have seen this before). I may replace that wiring(where possible/needed) with the proper wire type as well to neaten the wiring paths to further reduce the chance for noise induction. These amps are ’dead silent’ with no signal present when wired properly. Once completed, I put each amplifier through a minimum of 2 days of rigorous ’in-system’ testing to make sure everything sounds just right. Your modified amp will sound so good, that you’ll be tempted to crank it a bit more than you did in the past. So you will want to properly protect your precious speakers and renewed amplifier with the correct speaker fuse rating. These are a VERY high-current amplifiers capable of up to 30 Amps into a dead short! For most speaker systems, 2 Amp to 3 Amp Fast Blow Fuses are more than adequate for even very loud listening levels. Replacing fuses is way cheaper than replacing blown speakers and/or expensive amplifier repairs! I will also make sure you have the correct speaker fuses(and internal Power Supply fuses) installed at no additional cost based on the speakers you will be driving. I will include a Speaker Fuse Selection Chart to guide you if you feel the need to increase the rating to safely suit your listening habits. Once completed, I will send you all of the upgrade documentation that includes written PC-1 assembly & installation instructions, schematics, pictures and diagrams. I will upload them to a free large file transfer service called WeTransfer. Also included is a letter from the PC-1 designer, Ed Fantasia on his design theory, best performance tips, specs and a Speaker Fuse Selection Chart (to guide down the road should you ever change your speakers). WeTransfer will send you a download link that expires in 7 days. This way you’ll have an electronic version and can print what you feel you need in hardcopy. ———————————————————————————————————–Take the time to read the NEW and IMPROVED specs provided by the FANTASIA AUDIO PC-1 Upgrade: PC-1 DESIGN GOAL REALIZATION:A. Precise PC board layout with no track crossover.B. First stage single ended JFET/bipolar cascode differential amplifier with CCS regulation. JFETS incorporated are genuine Toshiba 2SK170BL devices with IDSS closely matched. If you know anything about this JFET, I need not say anything else. High input impedance, high gain, tube like presence, and eerie low noise in listening tests makes it a no brainer. Cascode configuration reduces Miller effect, drastically increasing bandwidth and lowering distortion. This all important first stage configuration eliminates the need for massive gain and feedback used in many amps to cover up distortions and design flaws.C. Second stage also uses SE bipolar cascode amplifier with CCS regulation. Again, Miller effect is reduced and bandwidth is not compromised.D. Simple bias control and emitter follower circuit to drive output stage is added and all that is needed to complete the design goal. E. High Quality Polypropylene Capacitors throughout with all HE Electrolytic Capacitors bypassed with Polypropylene’s.F. Vital Star Grounding realized with pictorial showing proper wiring arrangement. UPGRADED SPECIFICATIONS:DH500: Clipping now occurs at 335 watts into 8 ohms instead of the 270 watts from original PC-10 or PC-19.XL600(still in development): Clipping now occurs at 400 watts into 8 ohms instead of the 360 watts from the original PC-40.DH220, DH200, P220 & P230: Clipping now occurs at 150-160 watts into 8 ohms instead of the 110-115 watts from original PC-6 or PC-19.DH120: Clipping now occurs at 80-90 watts into 8 ohms instead of the 65-70 watts from original PC-25.Signal to Noise Ratio, unweighted:103 dB TypicalTypical THD at Full Rated Power into 8 ohms:20 Hz: 0.0025%1 KHz: 0.0025%20 KHz: 0.008%Input Impedance: 33,000 ohms.Frequency Response into 8 ohms: 4.8 Hz to 225 KHz at 1 watt, – 3 db,——————————————————————————————————————– And if all those specs are a little too technical for you, your ears will tell you the rest of the story! I was blown away the very first time I heard an upgraded DH-500 and you will be too! You will have a deeper, wider sound stage, better dynamics, better sound articulation(higher resolution) and a cleaner, quieter, much more ’musical’ sounding amp. The one comment I get most often from every one of my customers is: ”I’m hearing things I’ve never heard before!” QUA-CO uses only the highest quality components and closely ’matches’ all critical semiconductors to ensure that the best specifications are achieved. These Driver boards are not mass produced. They are carefully hand-assembled by me and each solder joint is visually inspected. These upgrades will make the single most significant improvement to your sound system than anything else you could do. Better Architecture + High Quality Components + Professionally Hand-built = Better Sound. ———————————————————————————————————– Additional Available Upgrades/Services: 1) You can also have your Power Supply rebuilt with new Nippon Filter Capacitors, Inrush Limiter and a new, higher current, 35 Amp Rectifier Bridge at an additional cost. I HIGHLY recommend having this done if you still have the original 30+ year old caps installed. THIS should be your FIRST priority upgrade as you will not reap the full benefits of ANY upgrades down line. If your Power Supply is not solid or balanced, your sound quality will suffer even with the new driver boards and may even cause premature failure of the output MOSFETS! Increased filtering & current capability make big improvements in Bass & Transient response and reduce clipping. If you plan on doing any upgrades and plan on keeping your amp running properly for the next 30 years and sounding its absolute best, Get your Power Supply rebuilt. I charge an additional $185 or $225 for this (depending on amplifier series – includes parts and labor). See my other listings for this upgrade. 2) If your amp version (some early 500’s & 220’s & all 200’s) did not include a factory installed Inrush Limiter to protect the Power Switch & Rectifier from turn-ON current surges, then your Switch may have taken a beating over the years. Hafler started to eventually add these because of the many prematurely failing 10A Switches. Maybe the Switch no longer illuminates (very common) or you may just want the upgraded Switch version for your amp, then add $25 for an upgraded 16A Power Switch, fresh 1KV Disc Cap and (Inrush Limiter $10, if needed). 3) If your Output MOSFET Transistors are blown in either channel, a new complete set (6 matched pairs per channel for the DH-500 – Quantity & Price varies by model) will need to be installed at an additional cost. *** Because our supplier of the EXICON MOSFET’s is currently unable to provide devices that meet our specification requirements, I AM NOT OFFERING THIS OPTION until we can source MOSFET’s that are reliable. *** ***HOWEVER, I DO HAVE A VERY FEW ’MATCHED’ SETS OF THE GOOD EXICON BATCH IN STOCK FOR THOSE THAT NEED OR WANT THIS UPGRADE- if needed – if they happen to ’match’ yours.*** 3) MOSFET Servicing: This important routine is something that I can do when asked on upgrades that don’t include this. It involves removing all the stock Output MOSFET’s, testing them, cleaning off the 30 year old, dried Heat Paste, cleaning the MOSFET Sockets, Replacing the all (8 or 12) old, brittle MICA Insulators under the Stock MOSFET’s and reapplying fresh, better-formulated Heat Paste for better heat transfer. This really should be part of this upgrade in my opinion, but its not required. However, its the perfect time to do this while I have your amp completely disassembled. I have made this MOSFET Service ’standard practice’ in my Complete Audiophile Upgrades because I want to give you the best, most complete upgrade possible. Cost: $70 for the DH-200 or 220 and $90 for the DH-500. If you decide to have ’the full set of upgrades’ done to your Hafler Amplifier, including these newly designed PC-1 Driver boards ($685) + my Power Supply Upgrades ($225 or $175 – model dependent), you will have one of the finest sounding stereo amplifiers one can own! For less than $1000, you will have an amplifier that will rival amps costing several thousand dollars and almost anything being commercially built today! Contact me for details about your model. Ed and I have now made true, High-end, High-Resolution Amplifier Upgrades within reach of many more audiophiles than just the few with the financial resources. The other mod shops do great work too, but can cost a bit more. We have worked hard to keep our mods affordable. Yes, it’s still a major investment, but its sooo worth it. Message me with any questions about my other upgrades.————————————————————————————————————————————— Shipping: (Please Read Carefully) – Buyer Pays Shipping Costs to and From Me. This listing says ”Free Shipping” because you are only responsible for shipping your amp to and from me so I can upgrade it. Buyer will specify shipping method if other than UPS Ground. Estimated shipping cost each way: $28.00 – $90.00 (cost varies by buyer’s location, weight and shipping method. Please include a PREPAID RETURN SHIPPING LABEL inside the box along with your amp so that there will be no delay in returning your amp to you once its completed. If your shipper will not do this, we can settle this later. NOTE: Insuring your amp will increase the cost of shipping somewhat). You MUST make sure that your amplifier is packaged properly as they can weight upwards of 50 lbs.! I suggest having it double boxed with Heavy-Duty Cardboard boxes. It would be a shame to have it damaged in shipping. Please, refrain from using solid Styrofoam panels as they do not absorb shocks very well. I’ve seen too many bent heat sink fins & front panels and extensive internal damage because of poor packing. If you are going to use shipping peanuts, put them into bags and make small pillows out of them so that your amp will not bottom out if your amp is tumbled in shipment – and they do get tumbled! Thick-walled Foam Tubing for Pipe insulation that you can find at Home Depot, works really well and is very cheap. I will be using YOUR packaging to return ship your amp once completed. Buyer assumes all responsibility. If I have to repair shipping damage & repack your amplifier, there will be additional charges for time and materials. Thanks for looking!———————————————————————————————————- Please, take the time to read my customer’s testimonials: Jim, First off I would like to thank you for the efforts you go to in keeping vintage amps like my Hafler 500 (which has become a QC 600) up and not only running but exceeding all expectations. My Hafler was tired and needed some help….man did you ever come through! The little tweaks that you kept my informed of were great, but the fact that you have been through so many of these amps that you know them like the back of your hand really made me feel confident in using your skill for my amp’s upgrade. It is nice that your efforts are not lockstep, but rather if you see an opportunity to improve upon your process, like in my amp’s case using the non-shorting, heavy duty, gold speaker binding posts that you take that opportunity and tweak your process and the customer and amp is better for it. The sound from my amp with the new PC-1 driver boards is as you mentioned……..dead silent on power up and super clean and detailed through my Polk SDA SRS2 speakers. I am really looking forward to the years ahead with this amp……money very well spent. Finally, I was very impressed with the return packaging on my amp……..my packaging effort to send it to you couldn’t hold a candle to how you returned it……….thank you so much Jim and good luck in your endeavors in the future…. Lou Hello Jim. Just got my Hafler. It sounds like never before. Lows have more warmth, highs more crispy and mids have a beautiful presence too. The frequency spectrum is much wider. Great job!Thanks again!Mario Hi Jim, Your work is impeccable. So clean and sanitary looking. I have had a few weeks to listen to the DH500 after the rebuild process. Before I delivered the amp to you, it had a lifeless, almost flat sound. The bass was weak, and the mids/highs were muddy-sounding—typical for a 40-year-old amp, I suppose. The sound now- defined, clear, authoritative bass, very musical is what I would describe it as. If the recording is good, wow! If the recording is less than ideal, it shows. I attribute that to the amp letting all the detail through. I am using a very nice tube pre-amp. The system just sounds incredible. It was worth every penny! I would put this amp up against any Bryston, Krell or McIntosh; it’s that good. What a powerhouse. I don’t always listen to Steely Dan, but when I do so do the neighbors! Best regards, Kurt D. Ristow Jim, Got the amp set up last night. One word: Magnificent! More thoughts to come… Don B. Don B’s follow-up thoughts: I am extremely pleased with the work done. I was hesitant at first because of the price, but then found out what it would cost to replace with a similarly powerful amp of the same quality. I went from hesitancy to no-brainer. The sound quality is like nothing else I’ve heard from ANY system. Visitors to my rec room are blown away by it. Most say the same couple things: 1) That they are hearing subtleties of the music they’ve never heard before, and 2) It sounds like they are in the recording studio, as if the band is right in front of them. Best $1000 I’ve ever spent on my system. Thank you very much. Don B. Music lovers. Champagne ear on a beer budget? Anyone looking to upgrade a legendary David Hafler vintage power amp should strongly consider a Jim Settecase rebuild. (200, 220, 500) High quality improved circuit boards designed by former Hafler amp guru Ed Fantasia. Outstanding build workmanship quite reasonably priced. Jim provided precise progress notes and photos during the rebuild. Post build documentation too. In summation; I sent Jim a glass of tap water. He sent back a bottle of San Pelligrino. Superb sounding amp with effortless power. (Power rating upped from 220 to 280 wpc) Highly musical. Brought my already very good system up to outstanding. Chris MorehouseHouston TX Jim, After having plenty of time to do some serious listening I have concluded that there is a dramatic improvement in the sound of my Hafler 500 after the audiophile upgrade. I hear detail like never before. The vocals jump out with such presence I am able to clearly hear the lyrics where before the upgrade on some recordings the vocals would get lost and muddled. I never thought my speakers were capable of producing the sound I am hearing. A perfect example of this are recordings in Dolby Atmos. Prior to the upgrade Dolby Atmos recordings had virtually no difference in sound. I now hear depth, clarity, detail, separation unlike anything I have heard. I have no doubt the investment was well worth it. My experience with the process is not the first time having Jim work on my Hafler 500. About three years ago he did a PCB upgrade and I thought there was no way to improve on the sound until I had the Audiophile upgrade. There is no-one else I would trust to work on my 40+ year old amp. He is a true professional that takes pride in his work. His detailed updates along the process is unusual in today’s world. I highly recommend the upgrade for anyone who would want to make a major improvement in the sound of their system.Stephen G. Hi Jim:Just a note to say that Hafler #2 arrived in perfect condition last week. Thanks for the expert packing to insure safe travels for the return trip. Alway appreciated!I also wanted to say thanks again for all your hard work on both of my Hafler amps. I’ve set one QC-600 up in a dedicated media room and the other in the main livingroom. Both are performing flawlessly and sound awesome paired with my Benchmark DAC3 HGC Ref. DACs. Happy Thanksgiving Jim.Ed Jim, January is on it’s way out the door but my Hafler amp is staying put! It sounds great. I have it driving a pair of Vandersteen 2Ce speakers using a Rotel CD11 Tribute, Everything sounds so good, friends just can’t believe the clean signal, the separations and the sheer quality of the entire system. I have played several types of music ranging from the Acid Rock of my youth to the quieter sounds of wooden guitar music and all sound superb. I have put this amp thru several days of intense listening and I have not heard a flaw in any of the tunes I have played. Separation between instruments has been spot on and each sound as I believe they should. Most importantly the program being played is smooth and not in your face (that’s the Mosfet system at work I believe). This now brings me to a crossroad. Do I go back to collecting vinyl and buy a good turn table or buy a good used reel to reel for extended listening time when socializing? Either way my wife will think I’m nuts!!!Thank you again for doing a wonderful job in restoring this amp. It makes it impossible to NOT listen to the system, it’s a real joy.I really hope you enjoy the great work you do.David L. What an amp!! Music is my first love – listening, playing, and performing. To me, the best quality home stereo equipment reproduces the original signal as accurately and invisibly as possible, i.e. without adding or subtracting anything. A straight piece of wire with gain, as the saying goes. My Hafler sounded excellent before shipping it to you, and sounds stellar after receiving your upgrades. I’m using an Emotiva pre, with the QC-280 driving a pair of 1978 vintage Klipsch Cornwall’s and couldn’t be happier with the sound at all volume levels – warm, punchy, dynamic, detailed, revealing, deeply enjoyable without fatigue.Additionally, your customer service is second to none – the amount of communication and the detail therein along with all the documentation provided, is truly exceptional. It is very clear that you love what you do, which is immediately evident from your level of workmanship. Being the electromechanical systems technician and lifetime nerd that I am, I was obligated to open the case and have a look – inside I observed some of the most perfect wiring and soldering that I have ever seen performed by human hands. Meticulous, careful, patient. I am confident that this now heirloom quality audio component will function flawlessly for at least another 40 years.Lastly, I don’t think there is a power amp out there anywhere close to the price point of the QC-280 that can come within a country mile of its performance. Thank you Jim, I am very pleased with my investment!Jesse Stunning, phenomenal, accurate, precise, I could go on describing the sound!!!! Top notch impeccable build quality. Parts quality spot on . Jim stayed in touch with me every step of the way. Phone, email, text message every method was used. This was an awesome experience all the way around. If you are on the fence about doing this to your amp. I can’t stress enough DO IT !!!! You will be glad you did. Sonic purity !!!! You will hear things that you didn’t before.Capt. Mark L. Hey Jim,Well, I’ve been having a marvelous time with my QC-280, and so have a friend or two. We’ve thrown a variety of speakers at it, both bookshelf and floor-standing, as well as different amps and preamps. I’ve gotten to know its sound pretty well and am convinced of its long-term reliability. So here goes the testimonial I promised. I hope it isn’t too corny as I tend to wax. When referencing you and your service, I just used the name ”Jim”. Here goes…I’m a repeat customer of Jim’s Hafler Amp upgrade service on eBay. So, I think I can speak with some authority on Jim’s overall professionalism, reliability, timeliness, and quality of the upgrades he offers. If you appreciate true high-end sound and can do without the boutique looks and exorbitant prices of today’s new amps, then I urge you to get in touch with Jim on eBay. I’ll explain why.Jim’s first upgrade for me was a complete recap of a Hafler DH-120 that I built from a kit in the mid 1980’s. Along with some new hardware for more solid connections, this upgrade also included a new switch, surge protection and higher value power supply filter capacitors. I was completely stunned at the improvement in smoothness, bass slam and overall musicality Jim brought to this little medium power amplifier.While no circuit mods were performed on my DH-120, the overall improvement in sound quality whetted my appetite for what Jim could do with his ”audiophile upgrades” to Hafler’s higher power amplifiers. So, I patiently waited and watched on eBay for a used DH-220, that was still in working condition, had the cosmetics I was willing to live with and at a price I was willing to pay. I didn’t have to wait long and snagged my 220. I immediately contacted Jim. He went over the upgrade options and prices with me, and I didn’t hesitate to opt for the full audiophile circuit upgrade, speaker protection circuit and the other hardware component upgrades to transform my amp.Jim supplies instructions on how to safely pack your amp for shipment to his location. So, I sent Jim the agreed upon down payment and shipped him my amp with no consternation at all. These upgrades are getting pretty popular, so Jim let me know my place in his working queue and the approximate time it would take to complete the upgrades on my amp. Once that started, Jim provided me with an overall assessment of my stock amp, made a few adjustments to bring it within spec and started the upgrades. He sent me photos each step of the way so I could see exactly what he was doing. He also sent me a link where I could download the new circuit schematic and a description of the new circuit’s operationas well as other useful technical information. My amp was completed within a couple of weeks of Jim starting work on it, tested in Jim’s own listening environment, and promptly shipped back to me.I’ve been listening for a few weeks to the upgraded 220, now called the QC-280, as these upgrades add an additional 20 watts of power to each channel and wanted to provide a few thoughts on its sound. I’m not a professional reviewer, but I’ll use the power of 3 and summarize my thoughts into 3 categories. I’ll call these Slam, Space and Soul.SLAM: Jim advised me beforehand that I might no longer need to use a subwoofer in my listening setup as the QC-280 could provide all the bass power, slam, and testicles that anyone could want. He was so right! I’ve already reassigned my subwoofer to home theater duties. The difference the upgraded 280 makes is actually startling. And that’s not all – bass notes now have quality and texture – something I had not heard before out of my Nola Contender speakers.SPACE: With a good preamp, in my case a Benchmark LA4, the QC-280 will reveal all of the spacial queues that are captured on your recordings or streaming services. Individual instruments are precisely located in space and provide separation from other instruments in that recorded space. The stereo image is 3D with great front to back depth and lateral spread. I think this is a hallmark of the new circuit design and a quality usually only heard in very expensive amps. It really puts the high in high-end and creates a listening experience that you wouldn’t think possible at this price-point.SOUL: Ok, so this is the hardest part to describe in words, but you will certainly know it when you hear it. I like to go to a lot of live performances of Jazz, choral, orchestral, and small ensembles around where I live. This helps keep my ears attuned to what live instruments and voices really sound like. Real, live music has texture, tones, overtones, and ambiances that help make a live musical performance such an emotional experience. We want that in our home music systems too, but it’s hard to obtain. The QC-280 gets you a long way there. You can hear the husky growl and sexiness in Diana Krall’s voice, the sweet and lush string tones of the Vienna Philharmonic, the hall ambiance of Severance Hall and the Cleveland orchestra, the bite of Coltrane’s horn, and all the percussive effects of Fourplay and today’s modern music.Needless to say, I’m completely happy with my upgraded QC-280. It has provided me with much musical value and happiness at a price I never imagined possible. I urge you to contact Jim soon. Jim,I’ve been letting your upgrade of the DH-200 soak into my musical brain for a few weeks now. Wow! I never imagined how profound an improvement it could make in my system! It’s hard to stop listening and yes, I’m rediscovering my music collection all over again!! I’m driving a pair of DefTech BP-10s and it’s handling the 6 ohm nominal very well. Everything sounds so tight, so much more detailed with a good soundstage even for the bipolar speakers. As an acoustic guitar and banjo playing nutter, I’m especially impressed with how “real” acoustic instruments appear…the attack, decay and resonance are amazing. Also, the transients and percussives are so tight! High quality recordings like my re-mastered Miles Davis will lock me in my chair and I can’t stop smiling!! Thanks again for your guidance, your outstanding workmanship and the value you built into this amp!! I’ve got several musical instruments and this amp may be the best one I’ve got! Highly recommend!Dave Hi Jim,Below are a few comments for anyone considering having you work on their Hafler DH-200 or DH-220 Amplifier.If you are an audiophile enjoying audio equipment that simply disappears and allows you to thoroughly enjoy music, then you will be interested in (7houses) out on eBay. I found 7houses on eBay upon searching to upgrade / improve my Hafler DH-200 amplifier. Jim, the tech that does the electrical upgrade has been an Engineer in the Broadcast industry for 35+ years and has been working on Hafler amplifiers for years.Jim is truly a professional, taking great care to implement the upgrade as if the Amp was his own. He sent email notes about his progress during the upgrade implementation to keep you thoroughly informed along the way.You can ship your amp to Jim, but I delivered my amp in person because it was convenient for me living in Ohio and it gave me a chance to meet Jim. After meeting Jim, I can say that you have no worries shipping your amp to him to work on. He is very knowledgeable about audio electronics and definitely knows Hafler amps inside out.I purchased the ’High-end Audiophile Upgrade’ that includes the new PC-1 Driver boards, Gold RCA’s & Speaker connectors, & all PS upgrades. That is the complete front to back upgrade. The only things not replaced is the AC Transformer & output MOSFET’s. But Jim tested the MOSFET’S. With regard to the MOSFET’s, he pulled all of them and cleaned-off the old dried Heat Paste, cleaned the sockets, reapplied fresh paste and new MICA Insulators under all of them.The decision to have Jim refurbish and completely upgrade my Hafler DH-200 amp was easy. I now have an amp that easily competes with amps costing much more and sonically sounds fantastic. Having the old / worn out parts replaced with those made of new modern materials and new PC circuit cards with modern designs simply transformed the sound of my Hafler amplifier. Jim performed the upgrades utilizing the existing chassis. And Wow!, the sound was significantly improved. The bass sound is tighter and more powerful, the mids are outstanding, not forward sounding, but just placed correctly and the high frequencies are still smooth (MOSFET – approaching the silky high frequency – natural sound from tube equipment) , but even clearer. The now 140 watt/channel into 8 ohms Hafler amp drives my Vandersteen 2ce Signature III speakers quite well. The sonic improvements are excellent, especially when one considers the reasonable cost of the upgrade vs. buying a much higher priced amp, which may not perform as well!Going back to Jim, he sent several emails communicating what he found and accomplished along the way. This made me feel very comfortable that my amp was in good hands and progress was being made. You don’t wonder when it’s going to be completed and knew that Jim was performing a thorough job. Basically my amp was in good hands!Would I do it again? Absolutely a resounding YES! I saved a lot of money and acquired an amplifier that competes with other amplifiers costing a lot more money.Jim, thank you very much for the excellent job you completed on my Hafler DH-200 Amp!Best regards,Tom Jim, So yes, I’ve finally fired up the amp. Been listening for almost 2 hours now…. Wow! Freaking awesome! I am amazed at the details and the transparency! No listening fatigue- just “what’s next”? It’s going to be so cool going through and rediscovering my music collection and certainly a reason to find even more incredible music! I’d say the amp woke up the speakers. We listened to quite a variety of music, from Donald Fagan to Molly Tuttle. The biggest surprise was a group that we like from Canton, NC near where Mindy’s dad is. They’re called ‘Balsam Range’…yeah kinda Blue grassy, but a bit more updated in their approach. All their albums are recorded very well. Oh my god the vocals and harmonies sounded incredible! The guitar, mandolin and fiddle had tactile details and the bass was solid. They were in our living room! I am blown away! My thoughts are this is more than an amp, it’s a musical instrument in and of itself. Thank you! Your work and knowledge are so appreciated. Your gift is the music 🎼 Oh yeah!DaveHi Jim,First, all I can say for now is the results of your efforts are ”Simply Unbelievable”. I have never had my Hafler perform like it is now even when it was new. The clarity and crispness have blown me away. The amp is really fantastic!Thanks, Tom Hi Jim,It’s Cam here from Nelson BC , Canada.I have to commend you and Ed’s for your combined work contributing to the rebirth of my DH 200.I am delighted with the outcome and couldn’t be happier!The words that sum up my listening to the rebuilt amp for the first time is simply WOW! I can’t thank you enough for your support to my friend Jim S. who did the install of the boards.It was so worth the wait, the additional power from the upgrade has made my Kef 105.2’s sing to new highs! Many many thanks! Kind regards ,Cam (another happy customer) Hello – my name is Denny. If you’re an audiophile and music lover like me, you’re on a constant quest for better sonics and musical enjoyment. But the cost of high-end audio gear continues to soar, perhaps putting our goals out of budgetary reach. But, there might be another way forward, just as musically satisfying, and well within your budget. Why not refurbish or completely upgrade your existing Hafler amp? Replacing worn out parts components with those made from modern materials or completely upgrading circuit cards with modern designs, can dramatically transform the sound of your Hafler amplifier. And all this can be done in the existing chassis, so you’re not spending money on new metal work or cosmetics that do nothing to improve the sound of your amp. But I was skeptical. Do I really want to ship my amp off to a person completely unknown to me? Would I get it back? Will it get damaged in shipping? Would it take forever and a day for the upgrades to be completed? Would I be happy with the results? With these questions in mind I began looking for upgrade resources on the internet to get answers. Among others I found Jim (7houses) out on eBay. Jim was patient and took the time to explain his upgrade process, detailing exactly how everything would work along the way. He also explained different upgrade options, at different price points, that were available to me. Jim also described the sonic benefits of each upgrade and even made a suggestion for the biggest sonic bang for my buck for my particular Hafler amp. Jim’s been doing these upgrades for years and knows how to coax the best performance from these amps, rivaling just about any new products you can buy today. Jim also sent me detailed instructions on how to pack my amp to prevent any damage during shipping and the approximate time-frame it would take him to perform the upgrade. As a result of these communications I got real comfortable with Jim, decided to move forward with his recommendation and price and shipped my amp off to him. Was it worth it? The answer is a resounding YES. Jim communicated with me during the entire upgrade process, even sending photos along the way with his comments. I got my amp back within the specified time-frame too. Jim’s upgrades not only improved the long-term reliability of myamp but completely transformed its sound in just about every way. These sonic improvements aren’t trivial, and I’m just delighted with the soundof my amp, knowing that Jim saved me hundreds or even thousands of dollars over a new amp. I’d do it again in a heartbeat. Thanks…. Denny Jim, It’s been around 6 yrs+. since you upgraded my amp. It still sounds absolutely fantastic every time we listen to it. Being an old-time audiophile, I have yet to hear a cleaner, attention to detail and clearer sounding amp. I’ve rep’d Adcom, JBL, Hammond and retailed McIntosh, B&0, NAD, Carver/Phase Linear, & Linn along with several others and chose Hafler for the realistic strong sound it offers (even met David Hafler @ a CES back in the day). Your mods make a difference and I strongly recommend anyone who owns a Hafler Amp to invest in your talents.Good Job & thanks!- lexovetJim,Got my amp back last night and all I can say is WOW!! Stayed up till 3 AM listening to things on tracks that I’ve never heard before. Stereo separation, soundstage and clarity are vastly improved. Thank you so much Jim!MikeMike’s follow-up comments:Hi Jim……..My name is Mike and you did a Hafler DH-500/QC-600 upgrade last year for me….and it is flawless…. I have hundreds of hours on it now and you may use me as a reference anytime……any prospective clients can come to listen to my Lancaster, PA. system anytime. It will be a lifetime relationship with this amp! Jim,The amp sounds terrific, and your electronic workmanship is top-notch!Thank you!Doug A. Jim,As I promised, I’ll share my impressions and thoughts about the QC600 upgrade that I’ve been listening to for the past couple of weeks. I plugged the amp in and listened as the amp seemed to start opening up after an hour or two of on time. It did sound pretty good, but it really got better after being on for 24 hours or so. Improvements after a day or so are subtle, but noticeable. What I’ve heard is an expansion of the perceived stage. The image is both deeper and wider (more 3-D) than any of the other amps I have that I’ve recently listened to. For me, I’ve discovered that the leading edges of a note, chord or a voice also seem much cleaner. To me, that leading edge reveals a lot about the amp in its ability to direct current in the proper direction in the proper amount of time to make the music sound as I think it should. The amp isn’t “mushy”, nor is it giving a crystalline quality. It just sounds right to me.On well recorded sources, the image can expand beyond the outside edges of the speakers. It’s funny, as in my old house, this phenomenon more often occurred in the right channel, and in the house I’m in now, it happens mostly in the left channel. It’s got to have something to do with speaker/room interactions and how the speaker is situated with room boundaries and listener position. The QC600 is good at presenting a stable image, wide, tall and deep, and you will hear room artifacts if the music was recorded in a larger space or was injected post-recording. I prefer the real stuff, but if it’s there, you’ll notice it.The amp is very good and quite honestly, has exceeded my expectations. It is quiet, clean and has plenty of power to keep the Magnepans singing. This amp really is a quality upgrade.Good job! Thanks for spending the time and energy to get this thing working so well!Regards,Steve Hi Jim,I hope all is well with you and your family. Now that I’ve listened to my upgraded Hafler 500, I just wanted to let you know that I’m super happy with it. It’s more than I imagined! The thing that really sets it apart for me is the way it drives my 1.7 Maggie’s. I was previously using a Hafler 220, and while the sound was good, I noticed that some recordings were lacking in bass. With the upgraded 500 driving them, that issue is long gone. The 500 drives them wonderfully, and there is plenty of bass!I will likely send you a Hafler 220 next. 😊 Thank you Jim, I’m very appreciative!!Rick Hi Jim,I unpacked and plugged in the amp today and it does sound fantastic! Incredibly crisp and clear, with easy power.After more listening:I’ve really been enjoying the QC-280. It sounds great with all kinds of music. It’s nuanced and precise playing The Nutcracker (my 2-year-old daughter’s current favorite), with easy separation of instruments and a wide sound stage. It handles the dynamic range very well, with barely any loss of detail in the quiet parts. The controlled power of the guitar riff on Dire Straits’ ”Money for Nothing” was enough for my Infinity CS-3008’s to knock a picture off the wall–with the volume at 1:00. Ella Fitzgerald and Count Basie sound like they’re playing ”Honeysuckle Rose” right in the room with you. I wish I could say more, but I’m more of a music lover than an audiophile. Joe Hi, Jim: I’ve been listening to my new QC-600, and I have to say all the reviews I’ve read are right on and then some. My Klipsch Heresy speakers sound different than before the upgrade: bass is deeper, highs and mids more out front, instruments more separated, more air around everything. It’s extraordinary. Great job on the amp, Jim. Ed, your design on the PC boards is fantastic. Very happy with the sound. Truly the finest my music has ever sounded. Jim, your communication while I was waiting for my turn in your queue, while you worked on my amp, and follow-up with photos and documentation chronicling the upgrade were above and beyond my expectations. I feel very lucky to have found you guys on eBay. Jim,It sounds fantastic! The day my reworked amp arrived, I spent the entire evening listening to a wide variety of music and loved every minute of it – straight out of the box. No fiddling with the controls on my preamp, no acclimating my ears to the sound – just sonic bliss. To describe this upgraded amp as ”musical” falls short. It lends liveliness and presence to songs that I’ve heard a million times previously but had never ‘experienced’ them like this before. I love it! You can listen to music for hours with this amp, without the fatigue that was an a facet of the character of the original DH-220.Its also important that I mention the communication by the seller was top notch every step of the way. I got daily updates via email on the progress of the upgrade and prompt replies to my email queries before, during, and after the sale. If I owned another Hafler amp, I wouldn’t hesitate to upgrade it.-Jon G. If you own a vintage Hafler amplifier do not hesitate to get the full PC1 upgrade Jim is offering. I’ll break this down into two parts. First is the work and Jim himself. At every step of the upgrade Jim kept me informed including photos of my amplifier as he transformed it. Every picture showed me that this man is meticulous and conscientious in the work he does. Craftsmanship is rare these days and Jim is truly a craftsman. Now how does the amplifier sound. Is this hyperbole or the real deal? To remove any variables I kept my audio system the same as it was, the only difference is I connected my new QC280 amplifier Jim built to the pre-out on my NAD C368 BluOs and reconnected my KEF XQ10’s to the new amp leaving my KEF 400b subwoofer on the sub out. My source material was CD’s ripped with Exact Audio Copy and 32/192 kHz streaming through the BluOs. This amplifier was a revelation! The soundstage was massive, both wide and deep and truly holographic in its’ imaging. Dynamics were crisp and instantaneous. I put on Steve Reich’s Music for 18 Musicians and every instrument was clearly defined and organic in timbre. Next up was Miles Davis In a Silent Way. Again, from Miles’s trumpet to Shorter’s sax to DeJohnette’s brush work on drums and cymbals and McLaughlin’s guitar runs all seemed to be in the room with me. I stayed up until dawn going through every genre, classical, jazz, rock and roll, Afro-Pop, and all of it was like I was truly hearing it for the first time. This amplifier upgrade is the best value I have found in a very long time and Jim himself is a gem. I am currently building myself a pair of CSS 1TD speakers and I can’t wait to hook them up to this amazing amp. Yours in the love of music and high fidelity, Jeff YoungJeff’s Update: Jim,The amplifier has had some time to settle in and keeps getting better. I finished my DYI CSS Criton 1TD speakers and your QC-280 amplifier makes them sing! A great combination. Here’s a photo of the finished CSS Criton 1TD kit. I went with the superior crossover option after my experience with you convinced me that quality parts in every step of the audio chain matters. The Superior crossover uses high end parts instead of entry level parts used in the Standard. The capacitors get changed to Jantzen Superior and Jantzen Cross Cap, inductors are upgraded to heavy gauge Erse air core, and the resistors are Mills. The bass response for bookshelf speakers is incredible. I’ve ended up setting my sub crossover filter at 35Hz. Between the amplifier and the speakers, I’m hearing nuances that were never there before. I can hear the difference between a down stroke and an upstroke on violins or the difference between any early production Gibson SG standard guitar and a later production one. Needless to say, the amp brings out all that these speakers are capable of. The dynamics with large orchestral pieces are breathtaking. Thanks again for being an essential part of this acoustic journey for me.Thanks again.Sincerely, Jeff Young Jim,I have had a chance to put the amp through a wide range of my musical tastes and can only come to one noticeable difference – EVERYTHING!!!I have been able to listen for a long period of time at a high level without any listening ‘fatigue’. I am hearing things on recordings I have been listening to for may years that I never heard before. Especially subtle differences as a song I’ve known for many years now hearing there is some reverb and delay in the recording I never heard. I can clearly hear the differences in how recordings are produced, some very minimally (clean instruments and vocals) and others that sound ‘over produced‘. My wife who is not an audiophile says everything sounds so much more clear with defined presence. I hear complete silence through the speakers where before I would hear a hum at high levels. I thought my speakers were past their prime and ready to replace, but now its like I’m listening to new speakers. I installed a few more cooling fans in the cabinet that my stereo components are in because before your upgrade the amp fan would usually kick on to the high speed. Now the cabinet temperature is at around 10 -15 º cooler and I have yet to hear the fan go to high, and can’t hear it on low because it is so quiet.I have had this amp for over 40 years and about 10 years ago began looking for someone who could diagnose and replace/upgrade what it needed so I wouldn’t have to part with it. It basically has been idle for that time until I came across your ad on eBay. My only regret is not packing the amp as you suggested by double boxing. I believe I had enough cushioning but another box around it with more insulation would have protected it on the way home. The dent it suffered is hidden by the cabinet, so the fact that it works flawlessly is what I care about. The wait time to send the amp and get it back was well worth it. Your attention to detail and meticulous workmanship is hard to find today. It really shows how much you care and love what you do. You have definitely made a big impact on my love and appreciation for a good sound system. I can’t thank you enough. I would recommend you to anyone looking to upgrade a Hafler amp needing some TLC. P.S. The first album I played was Lyle Lovett ‘Step inside this House‘ double album all the way through. It was a good first test because the album although recorded in 1998 is one of my favorite quality recordings of great musicians and well produced. Turn it up loud for ‘Rolin By’. Another favorite is Dire Straits ‘Brothers in Arms’, I was blown away listening to the remastered recording.Thank you.Stephen Grzeszkiewicz Hi Jim, I hope all is well with you and your family. I just wanted to let you know that I finally finished the PC-1 upgrades to my DH-200. It took a while. I only was able to work on it a few hours here and there. On Tuesday I did the final adjustments. The bias pots only need @ 1.5 turns to get a very steady 225ma. The dc-offset pots only needed a nudge and I got -00.3mv and -00.5mv and called it a day. So now was the time for sound testing. I hooked up the QC-280 to my MC DH-101 (never heard since I got it back from upgrading), added my Gamma 20 Tuner and my 30-year-old Philips cd player. On Saturday my wife, using a 1990s Technics receiver and a 1990s Technics cd player was playing some of her cd’s one being Broadway songs. The speakers were about 5 feet apart, on the floor, and were sounding the best I have ever heard them (this being before I heard Ed’s PC-1 boards). I was very happy with the sound to the point that my wife asked if I wanted to hear one of my cd’s and I responded “no, I am very happy just sitting here and listening to the sound coming out of the speakers”. The sound seemed as if you were in the audience of the show. So, on Tuesday, thru the Philips cd player and the upgraded Hafler, I played the Beatles ‘Love’ discs and Eric Clapton ‘Unplugged’. On Wednesday, I played ‘The Essentials of Billy Joel’. The song “The River of Dreams” was unbelievable. I had to listen a second time the sound was so fantastic. On Thursday, I listened to Steely Dan ‘Aja’, a cd of big band songs, and Brian Seltzer ‘Dirty Boogie’. As you know, the sound is phenomenal. It is more than I ever imagined. It is everything the testimonials say. The guitar strings, piano notes, the drums, the horns, the stand-up bass, the chimes, cymbals, the strings, the back-up singers you never heard before, the singers stretching out the notes, etc. You hear everything. I thought the system I bought 40 years ago was a nice sound. But I think the PC-1 upgrade lets thru twice the sound the original Hafler produced. I could not be happier. – Danny Danny’s ‘Follow-up’ Comments: I just wanted to let you know what I have been experiencing. And I would assume it will be things you have heard many, many times. As you may remember, I have some big, old KLH’s for speakers. These QuaCo / Hafler amps are great. As I have said before, its more than I could have ever imagined. This week I have been listening to it for a couple of hours a night. After an hour and half or so, the amp starts sounding very good. The problem is, it is now getting late and I should be going to bed, but I can’t. Last night about 11:00, The Blues Brothers song, “Sweet Home Chicago” came on. OMG, the musical sound you heard! The soundstage / imaging was great. I just closed my eyes and listened in amazement. I could not go to bed yet, I just had to listen to a few more songs. It was great. A few months ago, I never would have thought that from a 30-year-old cd player I got for $100 and 20-year-old bargain basement speakers for less than $200, that they would produce this kind of sound. I cannot imagine what the sound will be like out of a good pair of speakers. My thought is – once the amp gets about 100 – 125 hours of play time, it will be very close to its ultimate sound. Hopefully, by then my ears will be accustom to the much bigger soundstage and I will be more prepared to audition better speakers so that I can hear what the amp is truly able to give. When the time comes, I will start with the speaker companies you have suggested. In hindsight, I am so happy that in one of your earlier emails you commented that you would gladly just refurbish my DH–200, but if and when I wanted, you could take the amp to a whole new level. And I know it took me awhile to realize that the additional cost was minimal (maybe $100 or so), but I am very glad you made the comment and planted the seed in my head. Thank you so much. – Danny Cisco’s ’follow-up’ comments: This IS an important detail: my super thirsty RTi A9 Polk’s have ALWAYS needed to be bi-amped to really get them to open up and sound full and big—especially on the low end. To wit, I had them wired with an Adcom GFA-555SE for the Bass/low end, and either an Adcom 555SE (special boutique upgrade akin to your QC-600, custom driver board, silver solder matched components, etc., etc.) or a Yaquin 100B Tube amp with VERY expensive and exotic tubes rolled into it for the top end/mids/highs. I alternated with solid state and tubes so that I could use the SS amp for movies and theater and the tubes for music just to help conserve tube lifespan. I have bee driving the whole thing with a Krell Foundation 4k preamp, using their automatic room correction. Anyway, when used in this combination, the amps really light up the Polk’s, and the sound is phenomenal, especially the solid state/tube combo. The speakers easily handle around 200-300 watts RMS, and really need that extra power they get from being bi-amped for the bass to appear at all. With this setup, there is no need for a separate subwoofer—these babies shake the house! Now, on to the most important part: with the QC-600, I get the same level of bass and sound, except clearer, cleaner, wider, more open, faster, more detailed, and if you can believe it—even more powerful—FROM A SINGLE AMP. That’s right—the QC600 effortlessly outperforms two other expensive amplifiers COMBINED—both a pure SS and a tube/SS setup. I was able to A/B every possible combination directly, and I can say with absolute certainty that by the end of my experimenting, I was convinced. I literally pulled all the old amps from my cabinet right then and there and replaced them—PERMANENTLY. The results are just that good. And they’re only getting better as the amp burns in and opens up more and more every day. Thanks once again—I wanted to add this extra bit so you can use it in your ads should you choose. I think it’s important for people like me who are naturally skeptical to understand that if they are even a little hesitant about doing this upgrade—DON’T BE. It is the single best investment I have ever made in my long audio career in terms of sheer value. It’s not an exaggeration or hyperbole of any kind to say that this upgraded amplifier can hold its own against amps priced far higher. So to anyone who may read this: ”JUMP. Make the leap. You.. WILL.. Not.. Regret.. It. Audio Nirvana is closer than you think!” Thanks again Jim, and I WILL be back to use your amazing services again very soon! Sincerely,Cisco OH MY GOODNESS!!Is it working? Is? It? Working? IS IT WORKING?????Never in my life have I heard anything like this! Audio nirvana! My Polk RTi A9’s have always been super thirsty, which is why I bi-amp them—till now it’s been the only way to get decent bass. Their sensitivity is garbage. Well, once I finally had time to hook up the amp, I fired up a test song from one of my favorite playlists. I had only intended to verify the amp was working, but an hour later, I realized that the speakers had disappeared and I had just sat there enjoying songs I’ve heard a hundred times like they were brand new. Expansive soundstage—it was just me and the music.Bass was deep and tight, not boomy or loose in any way, but still powerful and commanding. The mids, my god the mids! They stood out on their own with a clarity and smoothness that was astonishing. The highs were so clean and airy—I had not even a HINT of listening fatigue after the hour session—in fact, I had to tear myself away from the music to get some work done. Another awesome thing was that the music sounded fantastic at all levels—even quiet, it still had powerful presence and compelling clarity.Before I quit though, I did an A-B with my Adcom 555SE (a not inconsequential $1400 amp), and a heavily modded Yaquin tube amp I had nearby. The Adcom had great mids, but nowhere NEAR the commanding presence and incredible bass of the QC600. It sounded shrill, hollow and empty, flat and disappointing. (It actually sounded great, but after the QC…well now I am officially SPOILED!!) The tube amp was nice and warm, but just didn’t have the power that the Polks needed. It too, while sounding really great, was greatly disappointing after hearing the QC600.This amp has been one of the most expensive investments I’ve ever made, because now my other amps are all worthless, hahaha! But seriously, NEVER in all my years of audio have I gotten so much value from my investment. This was worth the wait and the money 100x over. Thank you so, so much for sharing your gift with the world, and with me. I can tell you with absolute certainty that I will be back for more in the future! It was an absolute joy working with you. I will remember in the future also your advice about double-boxing, it was an eye-opener just how close I came to having something bad happen to this absolute treasure!With the quality I see inside this amp, I would expect it to play faithfully for maybe 20-30 years with no problems. I’d love to pass it on to my son someday :)Thank you, Jim. I wish you and yours a wonderful year, filled with happiness, health, laughter, family, smiles, friends, and MUSIC.Sincerely,Cisco Hi Jim: I bought my Hafler in the late 1970’s along with a Luxman tube pre-amp. At the time this was a big step up in affordable quality. Eventually I put my gear in storage, which ended up being for 25 years. I decided to resurrect this equipment last January. I happened upon your eBay offering and after giving you a call, decided to move forward with it. I was expecting maybe marginal improvement in performance but I was looking to at least to have an evaluation and replace any aged parts. During this time I also re-tubed my preamp and cleaned it up in anticipation of the audition of 21st century electronics. Your communication was excellent during this process. You provided very affordable recommendations. Just a note, anybody out there, if Jim makes a recommendation for parts – don’t go cheap. Follow his direction. When I received the amp, I hooked up the Luxman, and I was off to the races. The initial impression was the surfacing of music in the tracks that were never clearly audible before. Separation in stereo was markedly improved. The new N.O.S. stock tubes in the pre-amp brought a sound stage to this amplifier that was nothing short of profound. THIS AMPLIFIER IS MADE FOR TUBES. This prompted me to look in the marketplace for new technology in a tube pre-amp. I settled upon a PrimaLuna Dialogue pre-amp. Outstanding performance and build quality. After rolling some N.O.S. tubes, this turned out to be superior to the Luxman. Now I’m hearing vocal back tracks in Jan and Dean that I never heard before. The Doobie Brothers tracks I thought were out-takes because there is so much more music that I never heard before. Jim’s efforts are one of the great open secrets in audio. This quality in sound is the biggest bargain I’ve run across. Thanks again Jim Hi Jim,I can tell you that the original 500 you reconstructed sounds incredible! (more 3D than my other older one, but with the same perfect frequency balance). In fact, the 3D enhanced 500, due to the increased depth of the sound, provides more space between sounds and instruments. I will have you do the same reconstruction to my other 500 at a later date.Kind Regards,Pierre Jim,Thank you for the work on my DH-200, now QC-280. I still can’t fathom the difference that you’ve built into this amp, It’s too much (in a good way)! I’ve only played the amp for an hour or so and am floored by the bass response. I could go on, but you know what you built for me, so I won’t. Suffice to say, I am one very happy customer 🙂 Update: Thank you again for the upgrade work on my ’QC-280’, it’s so clear. And seems to appear more transparent and more dynamic every day (maybe the speakers are finally getting run in too? who knows!). I’m having to weed out the ’not so well produced’ sources, not necessarily a bad thing. This amp is deep (as in, way down the audiophile rabbit hole!!). Regards, Mark. Hi Jim,I wanted to send you an update on how the Hafler 500 (QC 600) has been performing. It’s been a couple of months since the upgrade and I am really enjoying the amp. The Solstice speakers are moderately efficient so it doesn’t take much form the QC 600 to shake the house. What I have really noticed is the increase in sound stage, the clarity of the individual instruments, especially with Hi-Res sources. Bass response is fast and punchy way different than the Adcom amp I used to own. It has been a blast to listen to my collection of music and hear parts of the recordings that I was not able to discern before. The amp run

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