u/Mascavidrio

Finally got my hands on this one! I've been spam refreshing Reverb until one showed up. It's definitely a Brassmaster variant (but we already knew that). The fuzz and clean work the same way as bass and sensitivity on the Brassmaster but the squish seems to be a crazy combination of both harmonic and brass switches as well as the brass control all at the same time. At low gain and barely any squish there is a crazy bump in mids but then everything gets crazy as the fuzz and squish increase. Definitely an interesting pedal. It's going to take me forever to trace since it's all SMD and I can't see shit.

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So, this is happening!

They take forever to get here but so worth it.

I'm invoking the collective knowledge of y'all on this one as I'm stumped. I'm working on a Traynor TS 50B preamp from the original Traynor schematic as well as the AionFX TS-50 Bass Preamp build docs. I'm trying to add an XLR output I found in a GK 800 RB preamp schematic. It's also the same one in the Growling Krizzly schematic. It's just a TL072 using both op-amps to output to the XLR jack. I figured since the Traynor already uses a TL071 that I would combine them and use a TL074 and both the Traynor and the Growling Krizzly run on +15V/-15V.

I was careful not to leave the unused op-amp inputs floating. Everything sounds great, however, if I unplug the input jack, I get a high-pitched squeal that changes pitch and intensity with the gain pot. I noticed the AionFX schematic has a 47pF cap across the gain pot but this didn't help. I had to go up to 220pF as 100pF didn't help either.

I traced the circuit using an audio probe and the squeal is coming from the first op-amp in the TL074 and of course, carries all the way through the circuit. The noise is not present on pin 3, but it is present on pins 1 and 2. I added decoupling capacitors to the +15V/-15V pins of the op-amp as close as I could but still doesn't help.

With a longer instrument cable plugged into the 1/4" jack but not plugged in to the instrument, I don't get the squeal, but if I use a shorter cable like a patch cable, the squeal is back.

I tried reverting to the TL071 and removing the XLR section and the noise disappears. I tried a different TL074 but the noise is back.

If I short the input path to ground the squeal stops.

I'm sure it's something stupid I'm missing, or maybe I need to use the LF353 as in the Growling Krizzly or just use a separate TL072 but it seems to me like using the TL074 should work.

Halp.