Noisy Channels on Mixing Console

[damonpence]

I have an old analog console I purchased recently and it has a couple of noisy channels.

To clarify, its White Noise that I am hearing, and it's not a scratchy POT that's causing it and to add the channel EQ is not Enable, 48V is off, Phase Invert is not inverted, and the PAD is not enabled. The sound I am hearing is happening both with an input plugged in and without. It sounds like I have added white noise to the input of the channel and adjusting the Gain and Fader will cleanly increase and decrease volume.

I have looked at the capacitors and they look to be in good shape. They are Aluminum Organic Polymer Capacitors. My thought process, it's the OP-AMP causing the static noise. The channel uses INA162UA which is a balanced input Audio OP-AMP.

So, the million-dollar question. Could an OP-AMP cause the white noise I am hearing or could I be chasing the wrong issue? I am asking cause I probably have more channels with the same issue and debating on picking up an Oscilloscope but if this could not be caused by an OP-AMP I need to start over in my thought process.

Any help is appreciated.

Thanks,


The Console is
Crest Audio HP-Eight 56 Channel

Full Schematic:



OP AMP Section:

[Enzo]

Op amp or other semiconductor is most likely.

SChematic? If you have it, post it. If you don't, try customerservice@peavey.com and ask for it.

[The Dude]

Do you have a scope? If so follow the signal path and see where the noise starts. Also check for DC on the output pins of op amps. Often (though not always), noise is accompanied by DC voltage. The nice thing about a mixer is that you have plenty of working channels to compare voltages with the noisy channels.

[nevetslab]

Are these 1NA162UA Balanced Mic Preamps soldered in, or socketed? Are these an Epoxy Block, similar in concept to the API2560 Discrete op amps, or Jensen 990 Discrete op amps? I would swap that mic preamp with other modules where the white noise issue isn't happening, and see if the problem moves. I've never been inside a Crest Audio console like you just picked up. If there are enough channels (channel strips? Block of channels in larger panels? Don't know the mechanics of it either), worst case, you now have 'Spare Channels' with this one issue.

[damonpence]

Do you have a scope?

I don't, I know its probably something I need to have but not sure how much I would use it. lol, but you never know till you have it, right?.

Also check for DC on the output pins of op amps. Often (though not always), noise is accompanied by DC voltage. The nice thing about a mixer is that you have plenty of working channels to compare voltages with the noisy channels.

I will do that. I know right now channel 1 has alot of noise, channel 2 has noise but not as much and channel 3 is pretty clean. I really hope I don't have a massive repair on my hands but if I do then its part of the passion.

Also, adding the link to the OP AMP Datasheet if that helps.

https://www.ti.com/lit/ds/symlink/in...ouser.com%252F

[damonpence]

Are these 1NA162UA Balanced Mic Preamps soldered in, or socketed?

Yeah, they are soldered in and they are SMT/SMD style. so I couldn't even add a socket.

[Enzo]

You are tracking a noise. I'd use my scope, but lacking that, look up "signal tracer" and make one. Essentially you use some other amp you have, and you make a probe on the end of a guitar cord and plug it into that other amp. Now probe the circuit you are fixing. You can now hear what is passing through any spot.