Hi schubert,
So ... what is the amp then after a different driver board is installed?
Also, those old filter caps are often fine. I rarely need to replace them and I do both measure them and look at the waveform across them under load.
Just say'in. Been restoring them for decades.
So ... what is the amp then after a different driver board is installed?
Also, those old filter caps are often fine. I rarely need to replace them and I do both measure them and look at the waveform across them under load.
Just say'in. Been restoring them for decades.
Well if you can verify that the caps are OK by measuring, you're way ahead of me. You can see a description of the boards here. I've used them a couple different times (on a DH220 and a DH500) and have been very pleased with the results. Unfortunately qua-co's prices have escalated a bit.
Anatech, you are my kind of tech. Wish I had someone like you in DC metro area to do my solid state stuff; I do have a tech that does tube stuff (used to work at Conrad Johnson).
I did two of these amps - one with the qua-co boards, and the other I replaced almost all the parts on the original board, along with the power caps. On a DH-500 I replaced parts first then replaced the boards. The difference the boards made was pretty dramatic with the 500, less so with the 220, but still an audible improvement. Don't get me wrong, the original 220 is still a mighty fine amp.
It looks like its wired correctly for 240V
The manual says F405 4A, Slo-Blo MDX
The thing to do is to pull all four fuses, F402,F403, power up using a variac or DBT measure the voltages on C403,404,
if okay then turn the bias down to zero, you can sub 100 ohm/5W in for the fuses as a first test and power up again, test one channel at a time.
Before any power is applied you could test the o/p fets in ckt with DMM in diode test mode to check that they are not D-S shorted.
Should be open in one way and then you measure the parasitic diode in the other direction.
Makes you wonder why Hafler never wrote up a short troubleshooting blurb or a theroy of op.
Oh well above is a start, good luck
The manual says F405 4A, Slo-Blo MDX
The thing to do is to pull all four fuses, F402,F403, power up using a variac or DBT measure the voltages on C403,404,
if okay then turn the bias down to zero, you can sub 100 ohm/5W in for the fuses as a first test and power up again, test one channel at a time.
Before any power is applied you could test the o/p fets in ckt with DMM in diode test mode to check that they are not D-S shorted.
Should be open in one way and then you measure the parasitic diode in the other direction.
Makes you wonder why Hafler never wrote up a short troubleshooting blurb or a theroy of op.
Oh well above is a start, good luck
It's a Qua-quo MOSFET amplifier. Without looking at a schematic, I am assuming since it says, it uses 2sk170 or 2sk117 ( which are different jfets) and not any p-channel jfets, it's assymetrical topology, not symetrical or push-pull like the original design.
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I don't have both boards, but I have seen Rick's boards. I'll support ticknpop and Rick.
A properly redone Hafler is a nice amplifier.
Hi Buckapound,
The problem with every cap kit I have seen is this. The capacitor choices aren't the best, and that is if they are not fakes (yup, those are out there). On major issue is that I see almost no one installing capacitors correctly. If you have to ask what's wrong, you don't know how. There are also better choices out there in technology for some.
Often, leaving it original is better than "recapping it". I've come to hate the term in fact. So unless you do have a defective capacitor (and how would you know?), leave the poor thing alone. If it does need rebuilding, then please let someone who actually does know parts and what they are doing handle the job. Of course, everyone is an expert these days.
A properly redone Hafler is a nice amplifier.
Hi Buckapound,
The problem with every cap kit I have seen is this. The capacitor choices aren't the best, and that is if they are not fakes (yup, those are out there). On major issue is that I see almost no one installing capacitors correctly. If you have to ask what's wrong, you don't know how. There are also better choices out there in technology for some.
Often, leaving it original is better than "recapping it". I've come to hate the term in fact. So unless you do have a defective capacitor (and how would you know?), leave the poor thing alone. If it does need rebuilding, then please let someone who actually does know parts and what they are doing handle the job. Of course, everyone is an expert these days.
The cap kits are ridiculously expensive; you can get better caps for less from Mouser or Digikey. Ticknpop, I haven't looked into this in a while but I think I've heard of Cordell's design. There was a reason I didn't go with his boards at the time but I don't remember what it was (getting old).
Anatech, maybe leaving it alone may be best at times, but these amps are getting pretty long in the tooth and electrolytic caps have a limited lifetime, so sometimes it's "better safe than sorry", especially if the amp has been sitting idle for a long time. That being said, I've only been hit by a cap failure once - I sold a NAD preamp that had been sitting for a while. I checked it out before I sent it, but the buyer said it didn't work - he sent it back and I found that an electrolytic cap had pooped all over the board and obliterated a few traces. What a mess! I did get it cleaned up and sent it back to him, though. And that one wasn't nearly as old as these Haflers, so I guess that's why I'm a little skittish about this.
Anatech, maybe leaving it alone may be best at times, but these amps are getting pretty long in the tooth and electrolytic caps have a limited lifetime, so sometimes it's "better safe than sorry", especially if the amp has been sitting idle for a long time. That being said, I've only been hit by a cap failure once - I sold a NAD preamp that had been sitting for a while. I checked it out before I sent it, but the buyer said it didn't work - he sent it back and I found that an electrolytic cap had pooped all over the board and obliterated a few traces. What a mess! I did get it cleaned up and sent it back to him, though. And that one wasn't nearly as old as these Haflers, so I guess that's why I'm a little skittish about this.
Hi schubert,
Well, been doing this for close to 50 years. Most capacitors are not in stressful service and unless the seals are bad, they will be fine. Some tend to go bad in certain locations. In case you're wondering, I test caps with an HP 4263A and a 4192A, plus a digibridge and a number of other testers, including the 4195A with impedance test fixture. I test all pulled caps in case you're wondering.
Often, a new capacitor has it's seals damaged upon installation. It takes a few years for this to show up. So everyone is convinced they did a great job. That and some capacitors are better in certain locations than others, and this has zero to do with popular opinion. Knowledge of parts is critical.
From what I see coming across the bench, unless you know exactly what you are doing, you'd best leave stuff alone. I have to redo most work I see. Customers aren't happy, then when I show them, they are highly displeased with those that came before. It is a pain in my butt explaining this stuff. So the entire concept of improving performance by replacing everything, especially with the darling cap of the time, falls flat when you actually look, listen and measure. Listening is problematic since you are presupposed to hear what you hope or think you will hear.
All I can hope for is that people do not damage the PCB.
How many people fine tune an engine in their driveway and actually get the best performance? Almost no one. Same with anything.
Well, been doing this for close to 50 years. Most capacitors are not in stressful service and unless the seals are bad, they will be fine. Some tend to go bad in certain locations. In case you're wondering, I test caps with an HP 4263A and a 4192A, plus a digibridge and a number of other testers, including the 4195A with impedance test fixture. I test all pulled caps in case you're wondering.
Often, a new capacitor has it's seals damaged upon installation. It takes a few years for this to show up. So everyone is convinced they did a great job. That and some capacitors are better in certain locations than others, and this has zero to do with popular opinion. Knowledge of parts is critical.
From what I see coming across the bench, unless you know exactly what you are doing, you'd best leave stuff alone. I have to redo most work I see. Customers aren't happy, then when I show them, they are highly displeased with those that came before. It is a pain in my butt explaining this stuff. So the entire concept of improving performance by replacing everything, especially with the darling cap of the time, falls flat when you actually look, listen and measure. Listening is problematic since you are presupposed to hear what you hope or think you will hear.
All I can hope for is that people do not damage the PCB.
How many people fine tune an engine in their driveway and actually get the best performance? Almost no one. Same with anything.
Testing with the right equipment and skill will take you a long way. Listening is also important and the two keep you on the right track.
If you haven't used the right equipment or don't know how to interpret it, well you're maybe not going to look at the right things. BTW, we are looking at a spectrum, not a needle. People without the skill and / or equipment always claim listening is superior. This is 2023 people, not the 1980's.
If you haven't used the right equipment or don't know how to interpret it, well you're maybe not going to look at the right things. BTW, we are looking at a spectrum, not a needle. People without the skill and / or equipment always claim listening is superior. This is 2023 people, not the 1980's.
FYI. See attached schematics of PC-19c vs PC-6 where components and/or junctions are denoted as follows: a) yellow = common function; b) purple = new and/or different component/topology junction; c) unshaded = tbd. Note: differences in OEM component values are not noted/identified (i.e., only presence, lack of, different topology junction are noted/identified).yup got you!
what are your thoughts on the AC wiring side of things and the primary connections I described?
Looking for input to arrive at a concise/accurate listing/sketch of what's required to mod a DH-200 with the DH-220's offset adjust circuit.
Q: Why?
A: Why not?
Attachments
Starting my DH-220C journey and am impressed with the amount of supporting information that is included with the PCB's. I find chassis preparation and BOM building to be the most time consuming aspects of DIY projects. Having the BOM's already completed is a huge time saver! Well done Rick, thanks. 
Yes, I set bias per the build guide. Heatsinks settle at about 50C. Toasty but not really hot.
My SMPS measured +/- 67VDC unloaded, so my implementation may be a smidge more voltage than the original power supply, but all is well. I have faint hum at the speaker, but undetectable by ear more than a foot away.
My SMPS measured +/- 67VDC unloaded, so my implementation may be a smidge more voltage than the original power supply, but all is well. I have faint hum at the speaker, but undetectable by ear more than a foot away.