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Hafler DH-200 refurb questions

Thanks David

Your advice seems very sensible. And of course, whether my old ears will hear any subtle changes is highly questionable. I "may" add those caps at some point simply because I have a bunch on hand and part of this hobby is the fun of tinkering. Right now the more pressing question is whether to replace the semiconductors. I see ebay seller Qua-Co has a PC-6 semiconductor kit that replaces "every diode and transistor used on one pc-6 driver board. (D1 thru D14 and Q1 thru Q13 --- 27 semiconductors total) Input devices are screened for noise, and beta is matched for low offset and distortion characteristics". I had originally balked at paying $50 for what is probably $20 worth of parts but I don't have the knowledge or inclination to match transistors and besides, I'd have to buy a bunch of them to try to find matching pairs so.... maybe just go with the kits.

So here's what I've done so far:
  1. Replaced input jacks with gold-plated (purely cosmetic IMO)
  2. Ran ground wires, through 2.2 ohm resistors from both RCA jacks to ground
  3. Replaced 5-way binding posts with gold=plated (also cosmetic although Blue Shadow doesn't like the ones I used)
  4. Replaced C1 10uF 16V NPE with 3.9uF mylar film cap
  5. Replaced C5 470uF 6.3V NPE with 470uF 25v NPE
  6. Replaced C10 100uF 80V lytic with 220uF 160V
  7. Bypassed C1, C5, C10 with Vishay MKP1837 0.01uF caps
  8. Replaced C16/17 10,000uF 75V 'lytics with 18,000uF 75V
  9. New 35 amp bridge rectifier
  10. 16A 0.5 ohm inrush limiter (may change this to CL40)
  11. replaced disc cap on the power switch with an X1/Y2 safety cap
  12. Replaced flimsy 18 ga non-polarized power cord with 16 ga polarized
  13. Replaced the twisted pair wires from RCA jacks to PC boards with shielded cable
So I fired it up and it works :biggrin:. Didn't want to take any chances with my good speakers so I used a pair of Infinity Entra Ones I found at GW for $13. So I haven't done any critical listening but it sounds good. I always take things like amps to a real technician after I've mucked around inside so I'll do that with this too but I'm thinking I may as well spring for the Qua-Co kits and install them first so I can have the tech adjust the bias and check the offset.

-Kent

PS: Pete, I didn't see your reply until after this was posted but thanks. As I mentioned, I don't want to really use this until my favorite tech has been over it. I "may" use it to power my AR-3a's and I don't want to take any chances. Right now I'm using a McIntosh MAC-502 which is certainly a beautiful little amp but it's on loan so before I plunk down the cash to buy it I'd like to see if the relatively cheap DH-200 will do the job just as well.
-K
 
Well I ordered the semiconductor parts so I'll be tearing into the amp again ;)
If I knew what I was doing I could just order new transistors from Mouser and save some money but this way I let someone else do the work of matching. Will post more after the next surgery.
 
I would not replace semis, there is no reason to do it and who knows if those
are real that you are getting. Have you ever done this before?
Do you know how to current limit the rails so that you do not blow up the
output devices? Modern transistors do not just go bad unless there is a
good reason. One mistake and the amp and unobtainable outputs go up
in smoke.

I'm going to stop posting here, I can't stand to watch this.
 
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A few years back I bought one of the quaco semiconductor kits for my right-channel driver board. I had retired my DH200 about 10 years ago when the right channel started popping. Turned out one of the drivers was bad (don't recall which now). I found the kit nice and I didn't begrudge the price. However, I probably could have fixed the problem for a couple of dollars. I have also used quaco's capacitor kits for both my DH110 and DH200. I like to tinker and I just added a CL80 between the fuse and the power switch. The DH200 gets rotated with a couple of nice tube amps. I should mention that outputs for th DH200 CAN be had if needed.
 
Pete B said:
I'm going to stop posting here, I can't stand to watch this.
Click to expand...

Don't do that. Helps to have folks add tech comments.

About qua-co on the bay, there is a post on AK that indicates he used to work for Hafler. It is on the internet, I don't know if it is true. Not supporting qua-co but just mentioning some info found here about him. Most comments seem to be positive. Parts would be cheaper buying from Mouser, but...

With the DH-200, the DC offset is controlled by the matching of the diff pair of transistors and in the case of buying them from qua-co, they are matched, probably at least as good as if one were to purchase a dozen and try to match them at home. Probably need to buy a couple dozen to get enough to do the amp. I'm not saying that all the semis need to be replaced and don't know if what is supplied is just the stock parts or something a bit better. I know that the diff pair, 2N5401 and 2N5550 had recommended but NLA replacements a few years ago but those two are still available. Additionally, the supplied transistors would probably match left and right as well as NPN-PNP, not that that is necessary but it would be less trouble if all 5401 supplied were the same as all the 5550s, less chance for the home hobbyist to make mistakes.
 
eickmewg & Blue Shadow (BS??) Thanks. I think Pete must be having a bad day.

Qua-Co is in Blackwood, NJ, home of Hafler, so I think it's very possible Ed (the seller) did work for Hafler. Anyway, I don't mind paying his price for the semis and it appears there will be detailed instructions. I'm a hobbyist but not a total noob (I've rebuilt dozens of KLH tube radios, a Mac 4100, a few Scott tube tuners and amps, AR receiver, Advent radios, etc. Also have built several kits and re-built an old Dynaco ST-120 with new Akitika parts). So I doubt I'll blow anything up. And if I do screw up? I only paid a hundred bucks for the Hafler, so no huge loss.

I'm thinking along the same lines as you, Blue. Everything in the Q-C kits will be matched and I won't have to needlessly buy dozens of extra parts. I'm a big Mouser fan, but in this case I'm paying for someone else's expertise.

Now, I'm surprised no one commented on my thought of replacing a Mac-502 with this Hafler. The Mac is on loan and if I keep it I'll have to pay for it. The Hafler will end up being about 1/4 the price. But the Mac is nice.....
 
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The hafler has more power and since it is 25% the cost, you can spend 2 times the cost and make it much better than the 502 with the Musical Concepts upgrades many like.
 
I for one am curious to hear how the Hafler compares to the Mac. Mind you, I haven't heard the Mac. My DL 200 compares nicely with a similar powered HK PM665 and a DIY mosfet SKA GB150 powering modded MMGs.
 
Blue Shadow said:
make it much better than the 502 with the Musical Concepts upgrades many like.
Click to expand...
OK Blue. I had not wanted to spend the money originally but you make a good point. I just spoke to John at Musical Concepts and ordered the boards. I did not go with the TOTL $500 PA-6 but rather the $200 PA-4 closeout. Seemed like a good compromise. Won't have them for a couple weeks though.

I'll be sort of sorry to see the Mac go. It IS a beautiful machine, but too expensive for my workshop and probably not powerful enough for the AR-3a's.
sfox52 said:
I for one am curious to hear how the Hafler compares to the Mac.
Click to expand...
Don't know if I'll get to do that. Since I'm not keeping the Mac I want to return it to its owner.

So now I'll have a spare set of original boards with new caps and the Qua-Co semis. Should have just gone that route in the first place--woulda saved some cash (yes, Blue, I know you suggested it in Post #2). Guess I'll just have to look for another DH-200 to play with ;)
 
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Just a comment about the DH200 vs. some tube amps. My DH200 has had some meaningful rehab but still I am using the original driver boards. I currently also have a kit-built Latino ST120 KT88 tube amp and a 9300-series Magnavox 6BQ5 amp with the full Dave Gillespie modifications. At the volumes I usually use, they all sound very similar. If I really concentrate, I think I can hear a difference between the Hafler and the tube amps; reed instruments, such as a saxophone, on jazz recordings simply sound better with tubes. I also can hear very subtle differences using the pentode/triode switche on the ST120, with the triode operation again being slightly "better" on jazz stuff. The Hafler seems to have better channel separation and can be quite noticeable with my Polk SRS SDA 2.3 speakers. I am happy to have all three and all get used. I have frequently heard that the DH200 is very "tube-like," whatever that is supposed to mean.
 
JKent said:
Guess I'll just have to look for another DH-200 to play with ;)
Click to expand...
It is AK we do that. Get more than one. When I purchased my Hafler DH-200s, I got three of them in anticipation of going mono on one pair. Traded on for a pair of tube mono amps, half the power and still have the other two with original hafler DH-202 bridging kits unused. No maintenance needed, no caps on those boards.
 
OK. It's been a couple of weeks so here's an update:
The DH-200 is finished, not without some problems. I changed out the capacitors etc. as described in earlier posts, then set about replacing all the semiconductors with the Qua-Co kits, despite advice from some guys here and even my trusted professional tech friend, but I had the parts, so.... it IS a hobby.
Made very sure to install all the transistors with the correct CBE orientation, even though some "looked" upside-down. And full disclosure: I did not bother with the diodes.
Put it all back together, brought it up on a Variac and checked the DC offset. All good.
Then I checked the bias and it was all screwy. Just for giggles I hooked up a garbage speaker and got nothing but noise.
Convinced I had screwed up the semis I took it to Tim at Bristol Electronics and confessed all my sins.
Well today I got it back and it works perfectly. Turns out I did not screw up the transistors. There were a few things wrong:
  1. Slo-blo fuses for speaker protection. They were in there when I bought it and were not the cause of the "no sound" problem, but they had to go
  2. A couple of broken wires! Tim tells me this is not unusual in the 200s. Apparently crappy quality wire and when it's repeatedly bent back and forth while working on the boards, they break (and I didn't notice).
  3. There was one open resistor. I never found it. Replaced 90% of the parts but not that.
  4. A couple of iffy solder joints. Tim is always chiding me about not using enough solder.
Tim installed fast-blo speaker fuses, repaired the wires, replaced the resistor, adjusted the bias, re-checked the DC offset, ran it for 6 hours. It's all good. Tomorrow I'll hook it up in the system.
Meanwhile, I bought another 200 (this is an addiction) and a set of Musical Concepts boards. When I finish building the second 200 I may bi-amp my AR-3a's or maybe just sell one amp. I'll probably lose some money if I do that but it's a hobby and a learning experience. Cheaper than golf! ;)

Now here's another question for you guys: On the first amp I replaced the 10,000uF 75v output caps with 18,000uF 75v. I'm looking at what's available on Mouser and there are some 22,000uF 80v caps that should fit. Too much? They're about twice the price of the 18,000 so I wonder if it's worth it.
 
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Guess I'm addicted ;)

For the 2nd DH200 I decided to take Blue Shadow's advice and get the Musical Concepts boards. John Hillig is a good guy to deal with and the boards arrived quickly, even though he had to put together a new kit. As mentioned, these are the PA-4 boards. I figure they "were" TOTL at one time and should be an improvement over stock. The PA-6 may be even better but they're 2 1/2 times the price.

So for the 2nd amp:
  1. New Musical Concepts PA-4 boards
  2. Inrush Limiter
  3. New 35A Bridge Rectifier
  4. Nichicon 22,000uF 80V PS caps
  5. Gold-plated RCA jacks (came with boards)
  6. New power cord (only because the old one was dry)
  7. And just on a lark; cascaded some bypass caps on the PS caps: 10uF mylar, 1uF PIO, .01uF Vishay MKP1837. They were in my parts drawer, so why not?
I left the original binding posts. They seem perfectly good.

Fired it up with some trepidation (actually, brought it up slowly on a Variac). Adjusted the Bias and DC offset according to instructions from Musical Concepts, attached some cheap speakers and an MP3 player. All good! :thumbsup: Will post some photos soon.

A couple of thoughts on the MC boards:
  1. This is a good upgrade from a good company. As mentioned, John is a good guy and easy to deal with. He answered a couple of (dumb) questions and was very helpful.
  2. I'd say this project is for the advanced kit builder. I built Dynakits back in the day as well as my now long-gone DH220. I've recapped a few receivers and dozens of tube radios. Last year I installed several of Dan Joffe's updatemydynaco mods in an old ST-120. So as far as ease of building/quality of instructions, I'd place the original Dynaco and Hafler kits first, updatemydynaco a close second, and MC third. The instructions aren't bad but they can be a little ambiguous. John tries to cover every amp the boards work in (200, 220, 280, 500, etc) in one set of typed instructions so there is some skipping involved. The drawings are very helpful, but I would have liked clearer or larger and again--one unique drawing per amp model. Finally, I find photos very helpful. I suggested to John that he put some photos of the assembly process and finished product on the web site.
Those nits aside, the Musical Concepts kit is really nice and I expect the modded amp to last a long time. And I may just buy another DH200 and do even MORE mods. Maybe a toroidal transformer.......
-Kent
 
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Go for it. I've rebuild at least 6 of the Hafler amps - 2xx and 5xx series - with MC boards of various generations in the past 20 years. Have also recapped quite a few as well. They all work well when done up. The MC boards are _very_ nice.

Next project is an XL-600 with the semi-conductors to be replaced. Have recapped it, which helped, but have at least one noisy transistor in there.

Yeah, they're addicting, aren't they?

Cheers,

David
 
I'm giving dshoaf the blame for you grabbing the MC upgrade parts. He is the main proponent of those mods and you can see above why. He keeps doing it. Glad you have a couple working units and I look forward to your discussion of the sonic differences which would pit a few MC mods against a recently Qua-co new parts unit, close enough for those that are looking at redoing some of these aging amps. The bypass cap stack, might give the MC unit an advantage in addition to the new boards.
 
I did the PA-4 upgrade to an XL-280 a while back. Can't remember the stock sound, but compared to my completely restored DH-200 (with DH-220 PC-19C boards) the MC PA-4SE is more clear and warmer sounding. My stock XL-600 sounds similar to the MC PA-4SE, but the PA-4SE still seems the best. Tempted to try the PA-6, but I don't have $500 lying around. The PA-4SE was $249 when I bought it, and the PA-5 V2 is still similar enough so I'll just wait for the PA-7 and buy a PA-6 for cheaper...
 
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