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AR SP-4

rickl

rickl

I'm just a bass player
Subscriber
a friend asked me to look at his Audio Research SP-4. "It doesn't work".

A quick search shows that @ConradH has posted thoughts and even a very nice resto page here. And searches on AK found another post from him.

I brought it home and heard something rattling in it. That can't be good.

Cap lead broken on the negative rail.

those big caps could use some support.

Replaced it and found no negative rail. funny how some preamp manufacturers think 4 diodes for a bridge and caps on each side of a lm78XX/79XX regulator is good enough but ARC has to make it complex. my guess one of the transistors failed but need to dig into it.

I'll try to post updates as I get it working and updates.

A couple pics.

Front.jpg broken-cap-ps.jpg top.jpg
 
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Any room for cap clamps? Without seeing the rest of bow those caps are installed, maybe use radial snap caps or screw terminals with clamps. You would just need to extend the wires on the bottom side to reach.
 
Lavane said:
maybe use radial snap caps... You would just need to extend the wires on the bottom side to reach.
Click to expand...

i replaced both with snaps, extended wires and held in place with zip ties. I might improve it but I want to get it working before I make it pretty. I might hot glue or zip tie the other big caps that are flopping around before they break off too. Or just replace like the other ones. I need to make an order and replacing them won't cost much.
 
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I'm surprised they installed them like that. Even larger radial caps mounted on PCB's are glued by other manufacturers. If zip ties work that's fine. I've used them before.
 
A quick update.
  • PS is now +20/-20 from the rectifiers (replaced the diodes and added fresh ps caps).
  • found many electrolytics that thought they were resistors. replaced them and now it passes a signal.
  • volume pot noisy with repeated DeOxit applications.
  • DeOxit the selector now works.
  • Phono works now
  • both channels are kind of hiss/noisy.
  • 5 second relay delay doesn't work. my guess a bad transistor but the PCB traces are so fragile the vanish with a touch of a soldering iron.
it looks nice but going to return it as is.

I'd like to put in some Hafler DH-101 boards but i'm kind of sick of working on it.
 
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