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Old 27th December 2007, 07:30 PM   #531
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by Sze



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.

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sze

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Old 3rd January 2008, 01:36 AM   #532
pidigi is offline pidigi  Italy
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Default voltage regulator for DH-200

Hello guys!
Very, very nice thread!!!
I'm an Hafler fan from more than 10 years, I don't modify old Haflers, I built them from scratch instead!

Someone could think it is a waste of money but from my experience you end up having a great piece of gear, far better than the original amp and capable of being always near the best (and way more expensive) other amplifiers I've compared to, not to mention the great number of the amps in his price range it killed out.

I include the 2SJ162/2SK1058 direcly on the board, I find it useful since I don't mind using existing mosfets and heatsinks.

The modifications I did are all the "simple" ones that you already discuss here (correct grounding, increased filter capacitors, soft start, mf resistors, etc), except from the regulated power supply. I have a question about this: seems that some of you are worried about the effect of a lower voltage on the "small signal" part of the amp due to the voltage drop on the regulator, but doesn't the R28-R34 already cause a voltage drop in the original configuration too?

Ciao!
Paolo
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Old 3rd January 2008, 01:57 AM   #533
eyoung is offline eyoung  United States
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hello again... i dont think 47 ohms causes much in the way of a voltage drop. easy enough to ck with a dvm, regulating the driver section would cause the front end to clip befor the outputs. several schools of thought to boost voltage for the driver section range from additional transformers to simple diode voltage doubler regulated from there 10+ volts or so above the rail to drive the final outouts to their full potential.
Good luck, let me know how it goes as i have an older dh200 that i am in the process of modernizing some pc 19 driver boards ...

Elwood
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Old 3rd January 2008, 04:22 AM   #534
fab is offline fab  Canada
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Default Regulating driver section

Quote:
Originally posted by eyoung
hello again... i dont think 47 ohms causes much in the way of a voltage drop. easy enough to ck with a dvm, regulating the driver section would cause the front end to clip befor the outputs. several schools of thought to boost voltage for the driver section range from additional transformers to simple diode voltage doubler regulated from there 10+ volts or so above the rail to drive the final outouts to their full potential.
Good luck, let me know how it goes as i have an older dh200 that i am in the process of modernizing some pc 19 driver boards ...

Elwood
hello eyoung

If you require higher driver voltage you can do the same method as Sze in previous post but use a higher transfo voltage. But, in my opinion, this will only give you original maximum power (about 130Wrms into 8 ohms I measured for the DH-200 and DH-220 may be a little higher). Of course using lower voltage for the driver will reduce this max output power. For the clipping concern, for mosfet output stage it is not a problem -as already mentioned by Mr Nelson Pass in another thread a few yeaes ago from what I remember. I also tested lower driver voltage and clipping does not show any major problem.
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Old 3rd January 2008, 10:32 AM   #535
pidigi is offline pidigi  Italy
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Default voltage drop

Quote:
Originally posted by eyoung
hello again... i dont think 47 ohms causes much in the way of a voltage drop. easy enough to ck with a dvm, regulating the driver section would cause the front end to clip befor the outputs. several schools of thought to boost voltage for the driver section range from additional transformers to simple diode voltage doubler regulated from there 10+ volts or so above the rail to drive the final outouts to their full potential.
Good luck, let me know how it goes as i have an older dh200 that i am in the process of modernizing some pc 19 driver boards ...

Elwood

Hi Elwood,

I will check the voltage droop with a DVM, but rougly 47 ohm means 5V per 100mA, and you have also the voltage droop on D12/D11... It is possible to use a low droop voltage regulator instead of the 78XX/79XX versions.
I made a test some years ago, supplying the DH-200 with a variac in order to be able to hear the effects of a voltage variation on the sound. Well, of course I wasn't using all the power of the amp (the room was quite small, the loudspeaker about 89dB, and the listening level for this test was not high), but the difference in the sound was evident.
Was it due to a different bias? Or a different voltage on the VAS? I don't know, but the result has been clear.
If needed, since I use toroidal transformers, I can wind another couple of windings to have the right voltage. Now the only problem is to define "right voltage".... Shall I reference to the voltage measured on C7/C10 at the nominal mains voltage?

I'm in the process now of making some boards, so I wish to include all the important modifications: other suggestions other than this voltage regulator?

Ciao!
Paolo
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Old 3rd January 2008, 02:23 PM   #536
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If you are cloning the DH-200 circuit I hope you are including a circuit to null out DC offset, like the one on the DH-220 boards.

Also, the resistor/diode combo on each power supply rail to these boards is meant to provide some decoupling between the VAS and the output drivers, to help protect the voltage gain circuits from power supply modulation created by heavy transients in the output MOSFETs.
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Old 3rd January 2008, 11:00 PM   #537
pidigi is offline pidigi  Italy
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No, I didn't include the DC correction circuit. I always use matched bjt in the input stage and I believe that this is useful also for lowering the distortion.

Ciao

Paolo
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Old 4th January 2008, 01:52 AM   #538
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YGM
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Old 4th January 2008, 04:07 AM   #539
fab is offline fab  Canada
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Default Re: voltage drop

Quote:
Originally posted by pidigi

...I made a test some years ago, supplying the DH-200 with a variac in order to be able to hear the effects of a voltage variation on the sound. Well, of course I wasn't using all the power of the amp (the room was quite small, the loudspeaker about 89dB, and the listening level for this test was not high), but the difference in the sound was evident.
Was it due to a different bias? Or a different voltage on the VAS? I don't know, but the result has been clear...

Have you tried to change ONLY the driver voltage or the voltage of both the driver and output stage?

Anyway, regardsless of the driver voltage used, lots of today's "hi-fi" power amps have a regulated voltage driver stage so the increase in parts must justify it otherwise peoples are crazy...

Quote:
Originally posted by pidigi

...I'm in the process now of making some boards, so I wish to include all the important modifications: other suggestions other than this voltage regulator?
  • -Double mono power supply (if transfo have 2 separate windings) for the output stage;
    -Cascode the VAS with low Cob transistors

    Why do not incorporate most or all improvements suggested im this thread?

Good luck and keep us posted on your progress
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Old 4th January 2008, 04:12 AM   #540
fab is offline fab  Canada
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Quote:
Originally posted by pidigi
No, I didn't include the DC correction circuit. I always use matched bjt in the input stage and I believe that this is useful also for lowering the distortion.

Ciao

Paolo



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