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Old 1st December 2006, 03:09 PM   #1
deiksac is offline deiksac  Czech Republic
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Default Power Supply - need to reduce voltage - any hint?

Hi,
I have one Alesis Matica 500 with one dead channel at home. I decided to replace the dead channel with a chipamp (for biamping a small PA) but Maticas supply rails are running quite high - +-63V. Once I saw a PS design using discrete transistors to reduce voltage - could anyone point me to something like that? I wasn't able to find such a thing using either google or local search :-(
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Old 1st December 2006, 03:20 PM   #2
Spev is offline Spev  United Kingdom
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what output voltage are you after?

LM317/LM337 may just do the job
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Old 1st December 2006, 05:55 PM   #3
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LM317 is a bit weak. LM338 is better.
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Old 1st December 2006, 06:19 PM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
a chipamp with a regulator from +-63Vdc. That is one heck of a regulator dissipation!

Buy a discrete amp that works off +-63Vdc.
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Old 1st December 2006, 06:24 PM   #5
paulb is offline paulb  Canada
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Or just use the + side of the supply, and use a chipamp configured for a single-ended power supply. If you're biamping, use this for the tweeter as you probably want a capacitor in series with the tweeter anyway.
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Old 1st December 2006, 08:57 PM   #6
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Not the easiest solution, but maybe a switching step down regulator?
Low losses, high regulation...
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Old 2nd December 2006, 12:13 AM   #7
Minion is offline Minion  Canada
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You could also try takeing a few turns off of the Transformers secondary windings to lower the voltages ???


Just a thought!!!
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Old 2nd December 2006, 12:21 AM   #8
Zen Mod is offline Zen Mod  Serbia
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Default Re: Power Supply - need to reduce voltage - any hint?

Quote:
Originally posted by deiksac
................. Once I saw a PS design using discrete transistors to reduce voltage ......................

that approach means lots of heat;

you must try other ways,one of them is already mentioned-can you unwound some turns from xformer?
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Old 2nd December 2006, 12:25 AM   #9
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I feel it would be easier fixing the broken channel than building a stable running high current regulator from scratch. What's wrong with it anyway?
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Old 2nd December 2006, 07:19 PM   #10
deiksac is offline deiksac  Czech Republic
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unwinding turns from the transformer would make no sense as the healthy channel would have too low rails

re repairing the dead one - seems like there was some liquid in the amp, the pcb in the input part is burnt badly and eight transistors in the power part are gone, one repair guy (who is usually able o repair anything) returned the unit to me saying it is rather risky to repair it as the transistors are expensive and the amp quite complicated - lot of money could be spent for parts with no results. Maybe I should try another repair guy. The stupid thing is that alesis do not diclose amps schematics.

using monolithic regulators (such as LM338k) - dunno if they can take such big input voltage, afaik these are supposed to accept Vin about 40V, maybe I am wrong however thats why i asked for some discrete design, there is enoough cooling capacity in the amp. But it is not that elegant solution.

using chipamp designed to work with unbalanced rails does not sound that bad, just one of the rails will suffer heavier load so it may drop a bit in voltage which seems rather unwelcome to me
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