Hiss on 8ch preamp

[sonolink]

So I built this 8 channels preamp like 7 years ago for a guy. It's based on Rochey's Edens together with a mic frontend for pad and phantom. The amp is fed with an Uber PSU (again Rochey's). It's got -15v, +15v, and 48v. A separate 12v PSU regulated to 5v feeds the digital switching.

The guy brought me the unit a few days ago. The PSU was half toast probably due to a power surge. So I fixed everything and it's all working now BUT I have lots of hiss and I can't find the reason or the source.

Any ideas?

Cheers
Sono

 

[JohnRoberts]

all channels or just one?

JR

 

[sonolink]

All channels...

 

[JohnRoberts]

look for a common fault, perhaps a PS regulator oscillating?

JR

 

[sonolink]

I replaced all 3 regulators. No go....

 

[pucho812]

does the hiss change level when you adjust any gain pots?

Can you isolate each channel and test them one by one without the others connected?

 

[sonolink]

I can do that disconnecting the audio outputs and the power feeds of all the channels except one.
I'll check what happens and report back.
Thanks a lot for your help guys
Cheers
Sono

 

[NOON]

Probe the circuit and see where the hiss is being introduced. Is it on the power supply rails, is it coming from the front end or is it coming from the preamp boards? Common denominator is the psu but if there was a nasty surge it could have damaged components on the other boards.

 

[sonolink]

Hi guys,

I replaced most components on the PSU and the hiss is gone!! So most probably the surge damaged it and it was feeding into everywhere.

Thanks a lot for your help!!
Cheers
Sono