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Old 30th July 2005, 01:25 PM   #11
K-amps is offline K-amps  United States
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Quote:
Originally posted by djk
[B

"Would it be any good to bypass with 1000uF, then 100uF or 47uF then 0.1uF? (I have many 1000uF's lying around) "

That would be OK, but the 0.1F needs to be bigger, more like 0.47F~1F. This may cause the amplifier to oscillate. If it does, try adding about 5 ohms in series with this cap.
[/B]
This was helpful info. Is this oscillation (with the 0.1uF) more an issue with the Hafler or would it be an issue with a 555?

thanks!
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Old 30th July 2005, 04:17 PM   #12
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Quote:
" I still don't understand where you are attaching the 47uf by-pass caps."

Kind of hard to figure out "I usually add four solder lugs with internal teeth on top of the existing lugs. "? There is only one place in the amplifier with four solder lugs. Look at the main filter caps.
Are you being sarcastic? Was my question not clear?
How does your telling me that you add four solder lugs on top of the existing lugs tell me where the leads for the new caps attach?

OK, mine is a P500, so maybe it looks different but I don't see any solder lugs on the filter caps.

Click the image to open in full size.

Let me ask in a different way. Do you wire the 47uf caps in parallel with the filter caps?

Thanks, Terry
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Old 30th July 2005, 10:08 PM   #13
K-amps is offline K-amps  United States
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Quote:
Originally posted by still4given

Do you wire the 47uf caps in parallel with the filter caps?

Thanks, Terry
Yes Terry, if you did them in series, you total amplifier capacitance would be about 44uF...
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Old 30th July 2005, 11:12 PM   #14
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rgulate the PS t the frnt end alone will prob make a huge difference, it did for my dh-200..
cheers
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Old 31st July 2005, 02:23 AM   #15
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Quote:
Originally posted by george a
rgulate the PS t the frnt end alone will prob make a huge difference, it did for my dh-200..
cheers
I completely agree !
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Old 31st July 2005, 08:01 AM   #16
djk is offline djk
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"rgulate the PS t the frnt end alone will prob make a huge difference, it did for my dh-200..
cheers"

I agree, but it is quite a project for many.

http://www.audioxpress.com/bksprods/pcbs/nelsonpass.htm

ITEM # PCBP-10B Pass/Thagard A75 Power Amplifier
From Audio Amateur Issues 4/92 and 1/93. Pass/Thagard A75 2-channel power amplifier power supply board. 3-3/8 " x 5". 1 lb. $8.95

http://www.passdiy.com/pdf/a75p2.pdf
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Old 31st July 2005, 11:47 AM   #17
K-amps is offline K-amps  United States
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Quote:
Originally posted by djk
"rgulate the PS t the frnt end alone will prob make a huge difference, it did for my dh-200..
cheers"

I agree, but it is quite a project for many.

http://www.audioxpress.com/bksprods/pcbs/nelsonpass.htm

ITEM # PCBP-10B Pass/Thagard A75 Power Amplifier
From Audio Amateur Issues 4/92 and 1/93. Pass/Thagard A75 2-channel power amplifier power supply board. 3-3/8 " x 5". 1 lb. $8.95

http://www.passdiy.com/pdf/a75p2.pdf
Djk,

Will the main board work with 90v rails or just use the OSU?
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Old 31st July 2005, 02:35 PM   #18
fab is offline fab  Canada
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Quote:
Originally posted by djk
"rgulate the PS t the frnt end alone will prob make a huge difference, it did for my dh-200..
cheers"

I agree, but it is quite a project for many.

http://www.audioxpress.com/bksprods/pcbs/nelsonpass.htm

ITEM # PCBP-10B Pass/Thagard A75 Power Amplifier
From Audio Amateur Issues 4/92 and 1/93. Pass/Thagard A75 2-channel power amplifier power supply board. 3-3/8 " x 5". 1 lb. $8.95

http://www.passdiy.com/pdf/a75p2.pdf
The PASS is quite a good circuit but may be too big to fit in some amp cases. The use of IC regulators is also a good compromise for performance/complexity ratio.
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Old 22nd October 2005, 06:41 AM   #19
lopan is offline lopan  United States
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Briefly looking at the schematics for a DH 500, I believe the removal of D11, D12, D13 and D14 would improve transient response at the expense of over voltage protection but it should make a significant imoprovement.

Also changing the bridge DB401 to soft recovery diodes might soften the amps sound. Not sure but no danger here.

DON'T remove the fan.

Additionally removing the output relay would definitely reduce output impeadance and therefore increase the damping characteristics. But you would need to build some protection in at the power supply and beware that this relay suorts the caps when powered down. Without the relay the caps will drain very slowly.

There is a 100 uf bypass on the board thogh this is electrolytic and therefore could be improved.

Finally the output speaker fuses should be bypassed not high end equipement would dare this in the signal path.

Changes should be made one at a time. So that problems can be more easily resolved.

Let me know what you think

Take care
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