altec 1591A output hum hiss

[moons]

Hello Again,When I set the mix output for the microphone at 7 on the dial I have minimal noise almost dead quiet at the output, But If I move the dial to lower the setting I get a low hum and If I go above 7 I am getting a hiss Which I guess is because of to high of a setting.I can run it at seven but If the singer is really pouring on the dynamics the signal overdrives at the recorder,The signal is best with the mix set to about the 4 mark for my setup but its more noisy (low pitch hum),This problem happens regardless of the compressors other settings.Any sugesstions.Thanks

[moons]

Ok what I have done now is cut the chain to bare bones,It goes as this Dynamic mic (tried several different types)The 1591a,and recording divice and I still have that low frequency hum at say 3 on up to 7 then after 7 it turns into the hiss,Kinda like a blind date gone wrong!! I did try an eq between the 1591 and the recorder and if I cut some lows off the hum subsides a bit.But I lose the lows of coarse in the track by doing this,The unit is still usable but I was confused by the dead quite at 7 and low hum as it goes down,Hope this may help.Thanks Again.

[bfish]

Sounds like your gain structure is a little whacked, as evidenced by a low signal to noise ratio. The hissing (might) indicate you have something too "hot" in the front end of the chain. I'd suggest studying the requirements for optimum gain structure setup (for a recording app), then applying that knowledge to your setup by measuring I/O levels at each stage (both quiescant and driven), and optimizing each device settings to maximize the S/N ratio and dynamic range ability. THEN compress as needed.

That process in itself is fairly complicated when you're dealing with gear you can safely presume to be operating at spec. Throw in some vintage components that may or may not be up to par, and the job can drive you to drink...

[bfish]

You can check the 1591 for hum by listening, or measuring for ACmv (at the output) by unhooking all the inputs, and (individually) shorting them. It's fairly uncommon, but occasionally you'll find a hummimg plugin mic pre (1588, etc). Check for that too, either by substitution or removal.

If the 1591 hasn't been serviced for years, it's very likely to have a few leaky electrolytic caps buzzing away, just waiting for an opportunity to create a little smoke, and a little smoke from a 1591 can be a really bad thing.