Hafler DH-200/220 Mods

[GRollins]

Originally posted by anatech


There is a cult status these parts have achieved also that you are only feeding. I can not allow you to misled people in this way. As you know, this is absolutely not personal. It has only to do with many, many years of observed failures.

Chris,
Cult status?
Yep, we live in different worlds, all right. Not once have I ever talked to another DIYer who advanced the idea of a multi-turn pot--I came to use them on my own. There certainly hasn't been the huge groundswell of support for multi-turn pots here that you seem to imply, as it would have erupted in numerous threads over time. And presumably would have evoked the same "Repel the heathen invaders! Kill them all--let God sort them out!" response from you.
'As you know, this is absolutely not personal.'
Actually, I was thinking about your behavior as I drove home last night and the only apt comparison I could think of was the tirades that Fred D. used to unleash on anyone who dared disagree with him.
I will now bow out and let you continue your anti-multi-turn rant by yourself. But please restrict yourself to things that I have actually said; not things that you have imagined.

Grey

[anatech]

Hi Jack,
Sure, sorry.

-Chris

[Variac]

I think that we have learned enough about pots for the moment and I agree- lets move on.

Realistically, I think that the high voltage transformer of the US version Hafler is what discouraged me about the PLH . The Hafler that Nelson had seen was an international version that he thought could be wired for 220 to run on 120 and put out half the voltage. When we discovered that the US version didn't have the 220v leads I kind of dispaired- even though Nelson felt that it could be made to work..

I really hated to replace the transformer, because then you are pretty much just using the case.

Also, as was mentioned, it is tough to rip apart an amp that works fine and puts out a decent amount of power...

Incidentally, I have another orphan amp - a BK ST 202 Does it have any virtue or is it another candidate for upgrading?

[Sze]

Hello everyone,

Merry Christmas. Finally had sometime to finish modifying my Musical Concepts modified DH-220GXB. Hard to get spare time with 1 and 3 year old boys.

I added a separate transformer and a regulator for the driver boards and placed it above the MC toroid transformer. To the right, just above the power switch I also installed a soft start circuit. This is the amp that got me started on the DIY path. IMO the GXB mod was the best of the original DH-220 mods from Musical concepts. I started with the original M mod, then DX, FX, GX and finally end with the GXB.

[Sze]

another view

[Sze]

and another

[Dick West]

Congrats on your impressive work!!

Can you characterize for us the before and after differences in the sound of the amp with the regulators? Does regulating the voltage to the PCBs make much difference?

[fab]

Originally posted by Sze
Hello everyone,
..
I added a separate transformer and a regulator for the driver boards and placed it above the MC toroid transformer. To the right, just above the power switch I also installed a soft start circuit. ...

Hi

Very nice integration and available space optmization !!


What is the voltage you used fro the driver stage?
I see you used IC regulators but which one?

Thanks

Fab

[Sze]

Originally posted by Dick West
Congrats on your impressive work!!

Can you characterize for us the before and after differences in the sound of the amp with the regulators? Does regulating the voltage to the PCBs make much difference?

Hopefully I can notice a difference for all the work that went into this little project. The amp has not been used in my system for over 6 months during this latest work in progress.

I'll report on sound at a later date. I'm letting the amp burn in for a lititle while.

Sze

[Sze]

Originally posted by fab


Hi

Very nice integration and available space optmization !!


What is the voltage you used fro the driver stage?
I see you used IC regulators but which one?

Thanks

Fab

The front end circuit is set at 60v regulated and the driver transistor and output stage is at 65v unregulated. A 55v+55v transformer provides 80v+80v to the regulators.

Actually Fab, there are no ic used in this regulator. It is all descrete components. There are 2 sets of pass transistors. The prereg uses TIP 122/127 and the main regulator uses K216/J79 mosfets.

regards,
sze