Hafler DH-200/220 Mods

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stenks

stenks

Member
Joined 2011
Stormrider said:
Hello all,

This DH200 is on my bench currently. It was given to friend of mine, and he passed it to me for some simple work. He had no idea it was modified, so I was pretty surprised when I opened it up and saw that it had been completely rebuilt (see attachments).

The filter caps are 75Vdc Nippon Chemicons, and they dropped the rails to +/-56Vdc with the new toroids. The bridge rectifiers are IXYS FRED 68A/600V. They added bypass caps on the mosfets, and upped the value of the on-board bypass caps, as well as the feedback cap using Muse parts. They removed and jumpered the VAS pre- devices, Q7/Q10, and re-did the output wiring.

This, IMO, is all going to far with one of these amps, and the extra noise and hum on the output says this amp was not treated with care. I intend to return the circuitry back closer to stock, as well as fix the DC offset problem with the left channel.
Click to expand...


Good job just a suggestion, try that instead of the input capacitor putting something better BENIC sounds desperate but DAYTON however sounds much better I don't know how possible it is to say that the same producer if I'm not mistaken something, try something else you'll hear a big improvement.
 
P

pidigi

Member
Joined 2003
Dear Fab and Djk,

thank you for the hint about the different poles in the amlpifier.

Please, help me to understand how the story goes: it makes sense that we don't want to send to the amp a signal that is not going to be seen by the feedback loop, so the input pole should be higher than the feedback pole. Why this doesn't apply for the ps pole?

Ciao

Paolo
 
fab

fab

Member
Joined 2004
fabaudio.online
Paid Member
Caps value

pidigi said:
Dear Fab and Djk,

thank you for the hint about the different poles in the amlpifier.

Please, help me to understand how the story goes: it makes sense that we don't want to send to the amp a signal that is not going to be seen by the feedback loop, so the input pole should be higher than the feedback pole. Why this doesn't apply for the ps pole?

Ciao

Paolo
Click to expand...

But it applies too.
I suggested to increase the power supply caps to 3 times the original value.


Fab
 
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stenks

stenks

Member
Joined 2011
Hi pidigi ,Fab,djk!

This intrigued me a lot because I'm also looking for the ideal solution value input and feedback capacitors, I found something interesting this is a post written by Dick West 683 quote:

"Then, I replaced each channel's C1 (10 uF electrolytic) with A 4.1 uF + 1.2 uF combo of polyrpop Solen film caps. This last mode was the icing on the cake. It did make a considerable difference!"
pidigi said:
Dear Fab and Djk,

thank you for the hint about the different poles in the amlpifier.

Please, help me to understand how the story goes: it makes sense that we don't want to send to the amp a signal that is not going to be seen by the feedback loop, so the input pole should be higher than the feedback pole. Why this doesn't apply for the ps pole?

Ciao

Paolo
Click to expand...
 
stenks

stenks

Member
Joined 2011
Hi pidigi ,Fab,djk!


I tried with 2.2 uf PP (Mundorf Mcap) and 1000uF (Nichicon MUSE) feedback capacitors, I can say imaging is much better in the upper range but the bass is noticeably weaker. I have been thinking a lot about changing the feedback resistor in the circuit and the input stage but would like to I hear what you think and if anyone tried anything like that.

Best regards S
 
fab

fab

Member
Joined 2004
fabaudio.online
Paid Member
Poles

stenks said:
Hi pidigi ,Fab,djk!


I tried with 2.2 uf PP (Mundorf Mcap) and 1000uF (Nichicon MUSE) feedback capacitors, I can say imaging is much better in the upper range but the bass is noticeably weaker. I have been thinking a lot about changing the feedback resistor in the circuit and the input stage but would like to I hear what you think and if anyone tried anything like that.

Best regards S
Click to expand...
Hi Stenks

Nichicon Muse cap usually needs some burn-in time before judging the end result.
Also , more muffle bass is not better than weaker precise bass in my opinion.
Regarding the resistor, after burnIn is practically complete, you could try to change 22k input and feedback resistors for 47k to lower the input pole and preserve dc offset. but if you do that You will have to lower the feedback pole ( changing 2k2 feedback and input to 3k3 and 100 ohms feedback to 150 for example. It will change also the higher poles of the amp but it could still be ok. Otherwise you may have to decrease input/feedback higher pole frequency caps. Input cap could also be 3.3 uF. You can look at the DH-220 schematics for values.

Good luck

Fab
 
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R

Rick G

Member
Joined 2013
Hello all, newbie here. I recently bought a DH-200 on Ebay. It does work, but upon inspection, R39 on Both Chl's is blown. Can any one tell me what is the function of R39 on PC-6. It is supposed to be R2.2 1/2 watt.

I have been reading thru this thread and plan on making most if not all of your collective mods.
Thanks,
Rick
 
Stormrider

Stormrider

Member
Joined 2006
ouimetnick said:
Guys, I'm sad to report, but diyAudio member Dick West (Richard Westenskow) has passed away at 82.

diyAudio - View Profile: Dick West

He will be missed by the community and I will miss him deeply. He knew everything that there is to know about Hafler amps. I learned a great deal from him! He also was the guy to go to if you needed your MOSFETs tested and matched. He had a rare Hafler MOSFET Checker/Matcher. He was a very kind person.

Rest in peace.


Rockford Register Star

Obituary Notices: Week of Feb. 27-March 5, 2013 | The Rock River Times
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This is sad news indeed. I purchased three Haflers from Dick, as well as learned a great deal about Haflers, amp design, and troubleshooting in general from him. I can say that he alone got me into the hobby, as well as helped propel me towards a career that I now enjoy in Electrical Engineering.

Good bye friend, you will be missed.
 
H

humble

Member
Joined 2007
Hiya Rick G please look at Page 40 and post number398 this resistor R39 simply joins the input earth to the output earth, it has varied in value i think from 0.5 ohms to the later 2.2 ohms, it has a nasty habit of burning out as the amplifier can go unstable which increases circulating currents at high frequency around the earth paths, best way if you can follow the advice given in previous posts about isolating the I/P earth and the O/P by taking wires separately back to the main earth star between the main reservoirs, the whole explanation is in those earlier posts, if you feel unable to cope
just increase this 2.2 ohm resistor power rating but don't use any inductive types
wirewound etc you can use two 4.7 ohm in parallel of the 0.6 watt variety which will survive somewhat better best wishes Humble
 
R

Rick G

Member
Joined 2013
Humble,
Thanks for the insight. i have made all the gnd corrections on my dh200 as well as most of the other mods as far as caps & wiring go, and it sounds 100% better to my ears. I think i will use this Ebay amp to try some of the more to me anyway 'advanced' mods. Also as you have said, i adj my bias with meter leads and sure enough, that board is not working now.! will use the blown fuse with resistor from now on. Guess i was lucky first 2 times i did it that way. Now have to figure what all got blown.

Regards
Rick
 
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