NOTE: 18000MFD 75VOLT UNITED CHEMI-CON OR 19000MFD 75 VOLT CORNELL DUBILIER MAIN FILTER CAPACITORS, .5 OHM 30 AMP MIN INRUSH LIMITER , 35 AMP DIODE BLOCK , AND NEW POWER SWITCH ARE INCLUDED WITH THIS PURCHASE. INSTRUCTIONS AND
PICTORIALS WILL BE DELIVERED VIA A USB FLASH DRIVE. THIS FORMAT INCLUDES COLOR
PICTURES AND THE ABILITY TO ZOOM AND PRINT. IF YOU DO NOT HAVE ACCESS TO A
COMPUTER OR PRINTER AND REQUIRE A HARD COPY OF THE INSTRUCTIONS, PLEASE CONTACT
ME VIA EBAY EMAIL BEFORE PURCHASING FOR ADDITIONAL PRICING AND SHIPPING CHARGES.
HAFLER
DH-220 ULTIMATE UPGRADE KIT. THIS UPGRADE ADDRESSES MANY ISSUES PERTAINING TO AUDIO
AMPLIFIER DESIGN PRACTICE. THIS SIMPLE UNIQUE JFET CASCODE DESIGN OFFERS CLEAR
AUDIBLE IMPROVEMENTS AND INCREASED POWER OUTPUT. INCLUDES GOLD PLATED COPPER
RCA INPUTS, LARGE GOLD PLATED OUTPUT BINDING POSTS CAPABLE OF ACCEPTING .154
INCH DIAMETER WIRE WITH SPECIAL INSULATING BUSHINGS TO FIT 1/4 INCH CHASSIS
HOLES , TWO PC-1 DRIVER BOARDS WITH ALL COMPONETS, ASSOCIATED WIRING AND
PARTS, AND DETAILED INSTUCTIONS
INCLUDING COLOR PICTURES AND PICTORIALS ON A USB FLASH DRIVE.
THIS PACKAGE
IS DESIGNED FOR INTERMEDIATE TO EXPERIENCED KITBUILDERS. YOU MUST HAVE GOOD
SOLDERING PRACTICE SKILLS AND BE ABLE TO
FOLLOW INSTRUCTIONS. YOU MUST BE ABLE TO READ COLOR BANDS ON 1% RESISTORS
(MATERIALS SUPPLIED) AND INSTALL AND
SOLDER SMALL PARTS ON PC BOARDS. YOUR TOOLS SHOULD INCLUDE THE FOLLOWING:
A 40 TO 60
WATT SOLDERING IRON WITH 3/16 OR 1/4 TIP WHICH CAN REACH 600 DEGREES F.
ROSIN CORE
SOLDER (SUPPLIED)
A DAMP
SPONGE OR CLOTH TO WIPE THE TIP OF THE IRON
A WIRE
STRIPPING TOOL FOR REMOVING INSULATION FROM 16GA TO 24GA WIRE
A
MEDIUM-BLADE SCREWDRIVER
NEEDLE-NOSE
PLIERS
SMALL
DIAGONAL OR SIDE CUTTING PLIERS
A 1/4
SPIN-TITE NUT DRIVER
PLIERS, NUT
DRIVERS, OR SOCKET SET FOR INSTALLING INPUT AND OUTPUT JACKS
YOU WILL
ALSO NEED BOTH AN AMMETER CAPABLE OF RESOLVING 250MA DC AND A DC VOLTMETER
CAPABLE OF RESOLVING 10MV DC. A VARIAC
WOULD ALSO BE A PLUS BUT NOT REQUIRED.
*18000MFD UNITED CHEMI-CON OR 19000MFD 75 VOLT CORNELL DUBILIER MAIN FILTER CAPACITORS, .5 OHM 30 AMP MIN INRUSH LIMITER , 35 AMP DIODE BLOCK , AND NEW POWER SWITCH ARE INCLUDED WITH THIS PURCHASE.
POWER
OUTPUT, DISTORTION, AND NOISE SPECIFICATIONS OF ORIGINAL DESIGN GUARANTEED TO
BE EXCEEDED. SEE PICTURES OF TYPICAL
DH-200 MEASUREMENTS. AS WITH ANY HIGH
POWER APPLICATIONS, QUA-CO LLC ASSUMES NO RESPONSIBILITY FOR IMPROPER ASSEMBLEY, FUSING OR
INSTALLATION CAUSING AMP OR SPEAKER FAILURE.
IF YOU ARE INTERESTED IN HAVING THIS UPGRADE INSTALLED
PROFESSIONALLY BY A QUALIFIED ENGINEERING SERVICE, PLEASE EMAIL ME FOR CONTACT
INFORMATION.
Being
intrigued with audio since 1973 has given much insight on the topic of
amplification and proper design practice.
My interest in audio continues to be both my hobby and my passion. Employment at both Dynaco as a technician and
Hafler Company as a project engineer was not only enjoyable but allowed me to
work and converse with some very accomplished audio engineers. I continue to work on many audio projects,
but will discuss my views on power amplification here.
So what is
it that allows a power amp to excel in its ability to reproduce music? Why does Brand A power amplifier sound better
than Brand B power amplifier? Let us
assume both have similar power, distortion, noise, gain, slew rate, etc.
specifications. Brand A is proclaimed to
be an exceptional amp. It certainly
looks better cosmetically. Does that
mean it sounds better? It costs $1,000
more than Brand B. Does that mean it is
better? We read or hear about terms like
triode sound, no coloration, more natural, less fatiguing, cleaner, neutral,
transparent, precise imaging, superb stage, etc., but what does it all
mean? We cannot measure these terms
quantitatively with standard test equipment.
We can make standard measurements as set forth by The Institute of High
Fidelity but that is as far as it goes.
Double blind listening tests are the only way to proceed at this point,
revealing the truth about your $500 amp or your $1,500 amp.
Of course all testing of this nature is now deemed subjective, but a
trained ear will fairly consistently pick the superior amp.
So what can
we surmise at this point? Why does Brand
A amp own the preferred sound? We can
agree that it is surely not because it looks better or costs more. So what is it? What is the solution? I have concluded after years of listening
tests, circuit analysis, and endless bench testing, the answer is not as
elusive or fleeting as I once felt but really what one would expect as a now
seasoned engineer.
1. Simple circuitry - This means not
pushing the audio signal through more semiconductors and capacitors than
needed. We are dealing with non-linear
components and need not compromise the audio essence with more ingredients than
needed. This will only lead to
unnecessary phase shift, distortion, and loss of clarity.
2. Good design practice - This is where
many amplifier designs fall short. The
first problem area overlooked is PC board layout. It is crucial that 2 layers or multi layer PC
boards have minimal or no track crossover from layer to layer. This will tend to inject capacitance into
unwanted areas and cause instability. In
turn, this leads to the addition of more capacitors to stabilize circuitry, effectively robbing
bandwidth and introducing additional phase shift. The amp design is now flawed by poor PC board
layout. Amps that have multiple small
value pF caps or caps tacked on to the foil side would by suspect of this
flaw. The second problem area and one
that will corrupt the sound of even the best amp designs is proper grounding
technique. Input, output, and power
supple ground must follow the star ground scenario. For some reason, many manufacturers still to
this day do not seem to get the importance or take grounding serious
enough. Ground is ground. Period!
It drives me crazy when I see resistors in the ground path to balance
out ground loop situations or daisy-chaining unrelated grounds to save 12
inches of wire. These acts will muddle
the audio content and ruin what we are trying to accomplish. If you have any of these situations, correct
them or save your money and go buy a $159 receiver. When evaluating a design, look at the B+ and
B- rails in relation to power supply and signal grounds. Then, try to visualize the circuit backwards
where the grounds now become the B+ or B- and the B+ and B- become the
grounds. This look can be very
revealing. Would you insert current
limiting on power supply rails and expect music to sound dynamic and
accurate. I already have a problem with
fuse resistance in the rails skewing dynamic capacity and incorporate bypassing
measures when required but that is a topic for a different discussion.
3. Quality parts - Audio engineers are
often limited to the final costs requirements of a new design. Unsurprisingly, the first parts to be
downgraded to save on cost are capacitors (except for their own unit of
course). This is a poor choice. Even under the double blind listening test,
most audiophiles can consistently pick out the difference between quality
polypropylenes and inexpensive metal films.
Semiconductors should also be of good quality with low noise and
distortion characteristics. Now all that
is needed is a properly sized power transformer and main power supply filtering
capacitors along with some desirable bypassing.
Pure amplification does
not have to be elusive. Listen to
simplicity and enjoy.
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
2SK170 or 2SK117 devices with IDSS closely matched.
If you know anything about these Jfets, 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. Clipping now
occurs at 150-160 watts into 8 ohms instead of the 110-115 watts from original
PC-6 or PC-19.
E. Polypropylene capacitors throughout
with all HE electrolytic caps bypassed with polypropylenes.
F. Vital star grounding realized with
pictorial showing proper wiring arrangement.
SPECIFICATIONS
Signal to Noise Ratio, unweighted:
Exceeds 100 db referred to 100
watts into 8
ohms
106 dB Typical
Typical THD at 100 watts into 8
ohms:
20 Hz: 0.002%
1 kz: 0.002%
20 kHz: 0.006%
Input Impedance:
33,000 ohms.
Input Sensitivity:
1.285 volts rms for 100watts into 8
ohms.
Frequency Response into 8 ohms:
- 3 db, 4.8 Hz to 225 kHz at 1
watt.
Semiconductor Complement per board:
9 transistors, 2 Jfets, 5 diodes, 4
zener diodes
FEEDBACK:
Item
as advertised. Well packed. Very fast shipping. Great transaction!
Excellent
service and support
Fast
shipping. Amp adjusted and tested. This is an an outstandiing product.
I
listened to the JFET cascode kit in the DH-200 today. Holy cow !!!
I compared it against an original DH-200 using one channel from the
original design and one channel from another DH-200 amp with your new driver
boards with the preamp in mono and adjusting the balance back and forth.
All I can say is WOW ! I didn't expect to hear that much of a
difference. Stereo Imaging is better. switching both channels to
the new amp you can close your eyes and place some sounds in a very, very
specific front/back left/right space. There is a sense of ease and the
music seems to have more depth and space. It's hard to believe how
good the DCM TF350 speakers sound with this new amp. They are pretty good
speakers but nothing that exotic. The lows are quite a bit better as well
maybe some of which is due to the original amp having original power supply
caps. The original amp is one that you repaired for me and has a capacitor
upgrade kit so I know it's working correctly and is a good comparison.
D***, now I won't want to use the old amps until I upgrade them.
Many
thanks, again, for your excellent designs. I just installed the Hafler DH220
get cascade boards and upgrades, filter caps and inrush suppression. The result
is spectacular. This will force retirement of my EL34 upgraded ST-70 type amp.
The upgraded DH220 has I ncredible resolution and transparency without some of
the fatiguing qualities of bipolar designs. Took a scant 2 evenings to complete
the work.
Wow it gives me goose bumps its
amazing performance. Not only did I install your cards but added 4 Nichicon
33,000uf power caps with soft recovery rectifiers along with dual mono torodial
transformers. This jumped several levels in performance believe I'll have
this amp until I die.
What a slap of my face when I heard the first
tracks compared to the DH-220 !
None of the personal tweaks I had done (recap,
transformer etc...) made a significant sound change. But your design is
absolutely amazing, I feel like dancing again listening to my tracks !
Got the amp back Wednesday. Couldn't do
anything with it until today. (had shows Thursday and Friday). All I can say is
HOLY S#@T! I have been hearing small things in everything I have listened to.
Am particularily impressed by how tight the bottom end is. Some of the bass
riffs sounded like I was sitting in front of an SVT. Great detail in the upper
ranges. You were right , it's got some grunt, little afraid of it yet, but not
for long. Great work! At some point send me another sticker that you put on the
front, as I have a rack mount plate for it, and I want everyone who asks to see
who built it. It is remarkeable how this sounds to me. I am used to a big
concert rig, but I'm just floored by how detailed it sounds. I will
definetly send a testimonial for your work. If it gets better after a burn in,
well, I just don't know what to say.
Ed,
Just letting you know, I paid Jim to build me
a set of pc-1s for my dh-220 and it sounds amazing. Thanks!
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.
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!”
Just FYI, your Haflers are replacing two
Counterpoint SA-100s, one expensively upgraded and one stock...with no
reservations.
Ed, I have been A-B ing your upgraded dh200
with amp switch box against my upgraded Counterpoint and a Classe Model Ten. I
got the upgraded amp early.
Hands down it outperforms the very detailed and
nice sounding Classe...in all areas. Against the Counterpoint with brand new
Electroharmonix 6dj8 matched and balanced set of tubes there is hardly a
difference. What difference there is, is a matter of preference. I would say
the two are a 95-98% match across the spectrum, musically and dynamics. I
get the same results above across three different preamps too. What a wonderful
job you have done.
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
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
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.
Yours in the love of music and high fidelity, 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 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 runs super quiet thanks to your work getting the fan to run correctly. I was really impressed with how fast you responded to questions I had and the level of detail to questions and to the repair process itself. I wanted to let you know how pleased I am with the process and the end result. Your attention to detail is tremendous and your fees are really reasonable!
Best Wishes,
Dave B.
Hey Jim, been meaning to send you a line or two with my thoughts about the "new" DH200/QC280. 😁
I've been giving it some very serious listening sessions since discovering I'd wired the right speaker out of phase. 😝 In a way I'm glad I messed up, I can be confident I'm listening objectively and not hearing what I want to hear.
So what I'm hearing is nothing short of spectacular! The combination of the Hafler and Infinity's is incredible. As you pointed out these speakers have the reputation of being amp-killers. Paired with an amp that took measures to prevent speaker-killing and I think we have a thing of beauty. The amp has the balls to push the speakers and they have the balls to take all it can dish out. I haven't come close to pushing either but enjoy the pure, clean power while listening 'comfortably loud'. I have no doubt the sound will be just as pure at ear-splitting levels as well.
Like you said, some music is better produced than others and I find myself cringing a tad from time to time, but when you hit a well produced song it is absolutely thrilling. I listen to just the Infinity's on 2 channel most of the time, but occasionally I'll kick it into full 9 channel wall of sound and it's really something.
I'm totally happy that I went ahead and had you do the full mod on my amp. It was totally worth every cent not only to have an absolutely top notch power-amp, but the nostalgia factor of having the core of my 30 plus year old hi-fi system back can't be measured. I don't think a modern 2 channel amp can come close to the old Hafler's for the price of this upgrade. This is as close to the warm sound of a tube amp as anybody can possibly hope to come.
I look forward all week to my weekend listening sessions.
Thanks Jim!
Theo
Dear Jim and Ed,I wanted to let both of you know how ecstatic I am with the sound and build quality of my two bridged Hafler DH500s. I am having the same feelings of wonder and awe I got 35 odd years ago when I first bought assembled and listened to them.I've tried several different amps over the years including Carver, Proton, Adcom, Nakamichi, and a few others, but nothing came close to the power and clarity of my Hafler’s. They've been used exclusively with a pair of Polk rta12b speakers bought at the same time, and until recently, the only speakers I ever needed.While Jim was rebuilding my amps, I had the good fortune to acquire a nice set of Infinity rs2b’s. An order of magnitude better than the Polk’s, they also quickly showed every flaw of any piece of equipment attached to them. The Nakamichi Stasis 7 did not sound good on them, a Proton AA-1150 sounded more musical and less harsh. I could tell that it just wasn't powerful enough, the infinities are serious power hogs.So yesterday when my amps returned home from their visit with Jim, I spent the next 12 hours listening. Suddenly, all of the drivers in my speakers came alive, the emims got the power they needed to keep vocals and percussion separate and distinct. Where I once thought I might need a subwoofer, the speakers now extended way down to their bottom end, you could hear bass notes fade clearly as the strings vibrations lessened. Spatial imaging took on outstanding depth as well as breadth.Like I said, it felt like the first time all over again.Kudos to you for the board design Ed, and you've got a real treasure in Jim. He went above and beyond to make everything perfect, I'm really surprised he hadn't changed his phone number.Jim, I can’t say enough about how great it was to do business with you! Thanks for answering ALL my questions and helping me with your advice.Kind regards,A very satisfied customer,Russ Hunsberger
Jim,
My Hafler’s P505’s are exceptional! Between you and Ed at QUA-CO, I could not be happier.
Ed‘s design and your assembly of these boards have put together a remarkable product. The best thing I did was listen to you when you said I should replace the Power Supplies, when all four of these amps were on and running at normal volume they would draw about 5 or 6 Amps when looking at my power conditioners meter, now 3 amps if even.
As for sound quality they are remarkable. I am running a pair of Dahlquist DQ-10’s with the two matching Sub woofers and the Dahlquist DQ-LP1 Electronic Crossover. These speakers are known for their remarkable reproduction of sound, and I thought they were good before, but now, it is unbelievable. I am hearing instruments in songs that I have played for years and never heard.
I went to the Hafler line, because after a lot of searching and reviewing to find the closest sound to a vacuum tube amp, in a solid state, all roads lead to Hafler, I have never looked back. Now I have four brand new amps that could very easily go up against amps costing $5,000 dollars or more.
So thank you for an excellent job! Anyone out there thinking their Hafler amp is shot or too old, contact Jim and bring new life to your system, if you really appreciate high quality sound, and want a high end system do this upgrade, you won’t be sorry.
I love music and you and Ed have given me a great gift of sound. Thanks to the both of you.
Thanks again Jim
Gary S.