The Amp Garage

Is this anything like what you did?

Here is a spec sheet for the OT that didit found:

If the guitar cable from the Send jack to the Recv jack results in performance similar to having an effects device in the loop, then I was thinking of plugging a guitar straight into the Recv jack and see what happens.

I get a gain of 49.15 to 61.4 for Q2 using .001 S to .002 S for the forward transconductance. I get 0.7692 for the voltage divider after C5.

I did but unfortunately the loop just passes the thin, low-volume audio when the level trimpot is around the center of its range but when I turn it all the way clockwise or counter-clockwise the audio just drops out all the way. Still can’t hear any effects in the loop. The bypass switch works, cor...

The cutoff voltage is important in this case because it sets a hard limit on how low the source resistor's voltage can go. I stared at this one for a couple of minutes. Taken literally, it makes no sense. If you mean it sets a limit on how low the the Gate-to-Source voltage can go, it doesn't matte...

In this setup, if the power supply is suddenly connected, the gate goes to the mid-power-supply voltage. Current flows in the channel and the source voltage rises until it gets to a point where it starts cutting back on the ability of the channel to conduct by backing down the Vgs. We know that if ...

...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...

Q2 is a little harder, more guesswork. The gate is held at ground by resistors, so current rises until the 1.5K source resistor is from 1 to 3v above ground and this starts shutting off the transistor. The current in this device will be between 1V/1500 and 3V/1500. That's between 666uA and 2ma. if ...

The channel of Q1 will let current through to the source and this current through the 47K resistor will raise the source voltage until it gets into the range of 1 to 3 V higher than the gate. So the 47K source resistor will have something like half the power supply voltage across it. The current th...

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 source will be -1V minimum, -3V maximum. Since the gate ca...

Yoda wrote: ↑Sun Jul 26, 2026 12:40 am I have 119v across that 10k resistor.

That's way too much. As R.G. and sluckey deduced, there is something wrong with this board.

Yoda wrote: ↑Sat Jul 25, 2026 9:52 pm I am also only getting about 40v on the side of the 10k 2w resistor closest to the 10uF capacitor where the instruction say to check for <400v.

What is the voltage drop across that 10k resistor when this happens?

Then there's this one below. People report getting a full range from the pot. My question can I omit one of the .022uf caps or are they both needed, can and the 470k grid stopper resistor go? Seems like the 1M pot would be taming the harshness on its own? You cannot omit one of the .022uF capacitor...

The Quadratus wrote: ↑Mon Jun 29, 2026 8:55 am Would you happen to know where I could find a BOM for this?

I've never seen one and I don't have one.