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Compressor Noise


I've noticed that our compressors, dbx 266xs, add noise to the signals we're running through them. Even when there is no compression added, it creates a soft hiss, like a speaker turned up too high without anything coming through it. When I bypass the compressor via the front panel's bypass, the noise disappears. I set the input gain from 6db to -4db with the back panel button, and that lessened but did not eliminate the noise. We have the signals run into the compressors from the snake. Mics to snake, instruments to DI to snake, snake to compressors and out into the mixer. The 266xs have output gain, so it's not that we're running the mixer trims to hot. Where's the problem in the signal path? Any help is appreciated.
June 18, 2013 @04:37am

If I'm reading your signal flow correctly, that's the 266XS circuit's inherent self-noise being amplified by the mic preamp on the mixer.
You said your signal flow is:
Mics/instruments/DI -> snake -> compressors -> mixer
Which is not ideal. The 266XS is designed to take line-level signals, not mic-levels, so when you're boosting the makeup (output) gain on the compressor and then preamp gain on the mixer, you're amplifying more noise than you should have to.
The ideal signal flow is:
Mic-level (e.g. mic, D.I.) -> snake -> mixer -> [Insert send] -> compressor -> [Insert return] -> mixer
This allows the mic preamps on your mixer to (cleanly) amplify the weak mic-level signal to line-level, then sends it to the compressor without needing to overly amplify the signal with the (noisier) compressor circuit.
June 18, 2013 @06:53pm

You didn't read the manual did you? ;-)
June 19, 2013 @04:24am

I figured that was the case. I know most effects are made for line-level, and assumed that was the case with these also, especially when lowering the input gain reduced some noise. What you said was what I was thinking, but I wanted to be certain. Thanks much.
Unfortunately, with our current configuration we aren't able to use our mixer inserts, although I've been trying to move us towards reconfiguring to allow it.
About using inserts, I have another question. Our mixer has an effect insert, TRS send/return. However from what I read in the manual-- ;) must have missed the part about line-level --the 266xl's only have inserts for adding outboard effects into the compressor itself, such as eq for frequency compressing. Would these work for putting the compressor into the mixer's TRS insert, functioning as an input/output for the mixer's send and return insert signal? I hope that makes sense.
June 23, 2013 @06:04pm

No, that's not necessary. You just need a TRS -> dual mono cable (often called an insert cable) like this one: http://www.sweetwater.com/store/detail/STP201
The TRS plugs into the mixer's insert point and the left (send) goes into the compressor input and right (return) goes to the compressor output.
June 23, 2013 @07:46pm

Great, thank you. That simplifies things. I appreciate the help.
June 26, 2013 @03:02am