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Old 1st April 2009, 01:06 PM   #1
diyAudio Member
Join Date: Feb 2005
Location: Tokyo Japan
Unhappy DC Power supply questions, advice appreciated!

I've recently purchased a Preamplifier ( the manufacturer is no longer in business, I can't consult them or get as schematic or service manual ) + the DC power supply is *missing*

There is a 5-Pin connector, not unlike an audio XLR with a couple of extra pins, that connects the ( non -existant ) DC power supply to the PreAmp with a cable

On the Preamp is a label written:

"10 Watts"

"Pin # 1:@18V DC Unregulated
Pin #2: Zero volts
Pin #3: 12V DC +
Pin# 4: Zero volts
Pin #5: 12V DC - "

Starting from scratch; is it possible to reverse engineer a DC power supply with this information alone? Or are there other parameters that would need measuring ?

"18V DC Unregulated" could this be an AC/DC transformer ( non-switching ) type ( ? ) Would this need to be a certain rating : 10 watts /@ 0.6 Amps for example ( ? )

"Zero volts" are simply blank pins that aren't used ( ? )

12V + and 12V- could be either an AC/DC transformer, or ( eg: lead-acid ) battery supply ( ? )

Sorry, I know I'm such a dummy....

Amp is solid-state BTW

Any advice appreciated !

Electric Gypsies
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Old 1st April 2009, 08:48 PM   #2
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Jason Hubbard's Avatar
Join Date: Apr 2001
Location: Poole, England
Default power supply for preamp

You will need a transformer - 2 x 15v with a center tap will do nicely.

Feed this into a pair of regulators - if you google for LM317 or LM337 dual rail power supplies you will see kits that you can buy. They have just about everything on the PCB and can be set to give you the 12v split rail outputs you need, and there will also be a 0v connection too (and yes, this must be connected).

To get the 18v output you can tap off just before the LM317 regulator - you could put a pair of diodes in series (each will drop 0.6 volts) to get as close to the 18v as you can.

Hope that helps.
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Old 1st April 2009, 11:39 PM   #3
diyAudio Member
Join Date: Feb 2005
Location: Tokyo Japan
Default Thanks for your posting!

Very informative + most helpful!

Electric Gypsies
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