The Amp Garage

The replacement loop arrived from Mojotone today and after installing everything works and sounds great, it was definitely a bad board! Already got my refund from the seller too.
Thanks everyone for the help!

Yes I was referring to the voltages on the source pins, man you guys are good, I had no idea that documentation even existed for the loop! Very nice. Also I moved the B+ supply to the PI power supply node and it bumped up the B+ on the effects loop board to 311v. Much better but still no audio. Yes...

I had a prospective new client say to me over the phone that if he liked my work enough he might even pay me! What nerve!

Yes I was referring to the voltages on the source pins, man you guys are good, I had no idea that documentation even existed for the loop! Very nice. Also I moved the B+ supply to the PI power supply node and it bumped up the B+ on the effects loop board to 311v. Much better but still no audio. Yes ...

Clients are insufferable and some have even made me regret doing this for the public. I have stories but don’t feel like typing them all out right now. But basically people want everything for free.

Well I followed Mojotone instructions and swapped the 1.5K with the 47K resistors on the effects loop board and I am now getting 265v of B+ on the FX loop board itself and 35v of voltage drop across that 10k/2w resistor. This fixed the problems I was having with voltages/power supply but with the l...

Well I followed Mojotone instructions and swapped the 1.5K with the 47K resistors on the effects loop board and I am now getting 265v of B+ on the FX loop board itself and 35v of voltage drop across that 10k/2w resistor. This fixed the problems I was having with voltages/power supply but with the lo...

...and Q2's drain will be 50V to a big fraction of the supply voltage after the 10K, depending on its threshold voltage and transconductance. The Drain current of Q2 is determined almost exclusively by the 1.5k resistance of the Source resistor. The voltage drop across the 150k Drain resistor is ty...

Any idea what those voltages should have been at Q1/Q2? Maybe we can guess. Te LND150 is a depletion mode device, meaning it conducts if the gate to source voltage is not negative. It's a MOS device, so its gate caannot conduct any current. The datasheet says that the cutoff voltage from gate to so...

How good are your soldering skills? For under $5 you could replace Q1, Q2, and C6. Chances are really good that the FX loop would work good as new. Worth the gamble IMO, unless you do a botched soldering job. They’re good enough to give it a shot if I end up stuck with the board, then I have nothin...

Mojotone also sells their own copy of the LND150 effects loop.

Any idea what those voltages should have been at Q1/Q2?

Stevem wrote: ↑Sun Jul 26, 2026 2:57 pm On Q1 and 2 what dc voltages to you read when you prob the side of the transistor with one tab on it?

I get 17.6v on Q1 and 1.15v on Q2.

Double post.

Double post.