Mesa Boogie Studio Caliber DC-2 Recording out noisy, any ideas on how to improve it?

[stoneattic]

My main amp is a Mesa Boogie Studio Caliber DC-2 that has a "Recording out" that's too noisy for pretty much anything. I get much quieter results mic'ing the speaker in live or recording situations. According to the schematic there's not much to the circuit, just a 5532 op amp, a transformer (or choke), a few caps and resistors.

I was hoping one the much more knowledgeable folks here might have an idea for reducing the noise. Maybe a quieter op amp?

I posted the schematics here since Schematic Heaven seems to be down.

TIA!

[Rhodesplyr]

I've just been working on a .50 Caliber that also seemed pretty noisy to me. This amp is from 1988, and I actually called Mesa to ask them what was normal. They told me pretty straightforwardly that it was simply a noisy design and that a raw, high-gain sound was what people wanted back then.

I looked at it more closely, and I think the Achilles' heel of the amp, noise-wise, is the DC supply to the footswitch. It's a half-wave rectified supply with a single filter capacitor, and it runs all over the circuit board with a large loop area. I'm not sure if the PCB layout of your amp shares this, but it might be a good place to look. Specifically, on the .50 caliber, this noisy control voltage gets very close to low-level signals and high-gain stages at the LDRs Mesa uses for channel switching.

Check to see if your amp is noticeably more noisy on one channel than the other. On the .50 Caliber, the Rhythm mode is noisier even though it's lower gain because the control voltage is partially grounded through the footswitch in Lead mode.

You might try increasing the value of the 150uF filter capacitor for the footswitch control voltage, but there's not much that can be done about it due to the PCB layout.

12AX7s that are selected for low-noise may help, too.