Preamp Output Voltage - how much is too much??

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mac

Well-known member
Joined
Jun 5, 2009
Messages
663
Location
Sunshine Coast, Australia
I am finalising my AD rack strips (four in a box), and am trying to use them without the output transfomers.

I am assuming the circuit was designed to have a dc gapped transformer after the output amp stage. I have about 11V DC after the output amp stage which is freaking me out.

How much DC is too much before I risk damaging the inputs on equipment downstream in the chain (compressor, interface etc).


Schematic and previous thread here
http://www.groupdiy.com/index.php?topic=34150.40

Mac
 
Are you seeing the 11V *after* a proper cap? As seen here?

index.php


Put 4.7K resistor across the output. The cap needs a drain to pull it toward zero. Your meter may not drain it in an hour.
 
Are outputs summed together...if so check them individually because the 100K after the cap  should provide enough of a drain. Me thinks one the electrolytic ain't no good as they don't make good blockers in my experience with them thingys.
 
Thanks for the replies guys.

yes all four channel strips have 11v prior to the output cap. Three channels are about 10.8v after the cap and one channel is 7v.

I have experimented with brand new 100uf / 35v cap which pulls it down to only 10.8v, so I presumed that the 7v channel actually means the cap is failing on that one.

So that i understand the circuit, are the resistors that I highlighted in red doing the job of pulling the output closer to ground, for the previous gain stage?

I assume the orange highlight looks ok, 470k after the output cap, this is what you mean PRR?
Mac
 

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