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Old 10th February 2004, 03:04 PM   #1
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Question Easiest way to reduce rails.

I am trying to increase my rails from 80 to about 100vdc for my amp so that under load they drop to only 75vdc or so. (and not the current 62 vdc they come down to under full load.)

While I can replace the outputs and drivers with hi-volt types, I do not want to play around with the input stages and leave them at 80vdc or so.

Whats the easiest way to do it? i have considered the following:

1) Zener and resistor combo running off the main rails.
2) Connect 4-6 diodes in series to get the desired voltage drop from the main rails.
3) Dedicated power supply.

1 and 2 would have a smoothing cap at the end for some regulation.

Any thoughts would be appreciated,
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Old 10th February 2004, 03:08 PM   #2
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Have you tried adding some (lots) of uF in the Supply ????
I may be the easiest and best way to solve your problem
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Old 10th February 2004, 03:10 PM   #3
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You can also use a low noise regulator as the lm317/337.
In my view the best solution!
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Old 10th February 2004, 03:17 PM   #4
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Hmmmmm
Max working Voltage for the LM's are 40 Volts
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Old 10th February 2004, 03:20 PM   #5
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Quote:
Originally posted by ACD
Hmmmmm
Max working Voltage for the LM's are 40 Volts

The LM317/337 are floating regulators...40 volts are the maximum input output diferencial voltage...consult the data sheet!
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Old 10th February 2004, 03:20 PM   #6
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your subject line seems to contradict the body of your message. I assume that you are trying to raise voltages on a power amp (that would then rule out those 317 type linear regulators).

if the rail drops from 100vdc to 62vdc under load, you are using too small of a transformer. 10% of regulation is probably max. 40% is unheard of. Mine does about 4% at rated output.

Sounds like you have overloaded your transformer. Using large caps will help but not much under this type of load / capacity imbalance.
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Old 10th February 2004, 03:25 PM   #7
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Hi ACD!

See:
http://www.hw.cz/data_ic/lm317.pdf
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Old 10th February 2004, 03:32 PM   #8
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Thanks Tupe_Dude. Got it
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Old 10th February 2004, 03:32 PM   #9
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Quote:
Originally posted by Tube_Dude
consult the data sheet!
Yes.. Did you see current they can handle as well??
besides regulators in power amps??? I'd take Millwood advice and go for bigger trafo my self..
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Old 10th February 2004, 03:34 PM   #10
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Quote:
Originally posted by Notorious

Yes.. Did you see current they can handle as well??
besides regulators in power amps??? I'd take Millwood advice and go for bigger trafo my self..
But here nobody pay attention!!

The regulators are for the input stage!!

The guy want increase the rails from 80 to 100 volts and maintain 80 volts for the input stages..
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