Preamp boost sounds weak after FET put on a footswitch

[Garveyte01]

Hi, everyone I have been playing my #124 for about a year now, I decided the FET boost on a Footswitch is ideal for me. Following Martin Mannings ODs eyelet board files (he did a great layout) I took my time and I feel like I followed everything exactly, but my preamp boost sounds thin and weak after wiring up….whether it’s switched from pedal or from the rear panel switch it sounds very weak. The FET and the OD works great. Any ideas where to start diagnosing something like this?

[martin manning]

Are you saying the FET boost sounds fine when in OD but weak in Clean? How is the FET bias? What are voltages to ground at the top and bottom of the FET's 10k drain resistor?

[erwin_ve]

Are you saying the FET boost sounds fine when in OD but weak in Clean? How is the FET bias? What are voltages to ground at the top and bottom of the FET's 10k drain resistor?

I think he is referring to PAB.

[martin manning]

Ah, ok. Most likely some wiring error or bad solder in the PAB switching circuit?

[Garveyte01]

Yes I am talking about the PAB, it sounds weak no matter what is on or off. I did notice I get a slight volume increase when adjusting the bass pot. When PAB is engaged the volume goes down, tone gets thin and the circuit gets some “white noise”. The The FET works really good I set the bias via the two 9volt battery method. I went through this thing for 2 days now checked all my solder joints all connections and I am missing something, all wiring seems to be correct. Also the PAB worked before I modded it so obviously I’m to blame I was just asking on here in case I missed anything. Maybe I’ll start changing the switches in the PAB…could the inside of the switch be bad?

[martin manning]

I don't think it's likely that a switch is bad, but PAB increases gain and that might be enough to start an oscillation. Does the Clean volume have any effect on the thin tone?

[Garveyte01]

Clean volume doesn’t have any effect on the “thin tone”. I also wanted to state that the rock/jazz switch works great, but if I try to engage the PAB via the Footswitch or the manual switch in the rear it has that lower volume thing tone.

[martin manning]

I also wanted to state that the rock/jazz switch works great, but if I try to engage the PAB via the Footswitch or the manual switch in the rear it has that lower volume thing tone.

Are you saying you can get a good PAB manually with the R/J in middle (off) position or just that the R/J works well in Rock and Jazz positions?

[Garveyte01]

Hi, the rock jazz switch works well in both positions. But I can’t get a good PAB. Also you had mentioned the middle position of the rock jazz switch switch? I only have a on-on at the rock jazz switch, could this be the problem.

Update I’m poking around and noticed my PAB relay isn’t switching (I’m not hearing the audible click) the FET and the OD click sound normal. Could a bad relay be doing this?

[martin manning]

Using an on-off-on switch for the R/J gets you PAB in the middle position. That is how #124 works, and that's why it does not have any connections on one side of the manual PAB switch. I don't know how the PAB relay not switching could result in a thin sounding PAB. You could try disconnecting the bottom of the treble pot (CCW lug) and the bass pot wiper and see if that results in a loud and clear PAB.