MojoTone High Voltage FX Loop

[loudthud]

Although the LND150 has an Idss rating of 1 to 3 mA, it can conduct more current when Vgs goes positive. Up to 5.5mA if you look at the curves, and it doesn't really stop there. What you have to account for is the +/- 20V breakdown of the Gate. In the marketing hype section of the data sheet it claims the device has ESD protection. No data elsewhere on how robust the protection is. The schematic shows no Gate protection other than a series resistor on the Return side. That may be sufficient, but you'll never know from the data sheet.

[GainFreak]

You're right about the ESD protection. Adding two back to back 12V zeners from gate to source or to ground will be a good idea!

[Jazz P Bass]

O/k.
This is what I ended up with.

Thhe Send Trim is now a 470K resistor.
The Return Trim is now a 220K resistor.
The Cathode resistor of the Return mosfet was reduced to 310 ohms & the bypass cap was removed.

The Bass is still a little off but all in all it is darn close.

Unfortunately for the customer, the Fat Boost colors the sound.

NOTE: it is not shown on the schematic but the Send input has a permanent (non switched) 470 ohm resistor to ground.

[Jazz P Bass]

BTW, all problems can be solved by plugging in the effect in front of the preamp and not installing the loop circuit . Have you considered such a solution?

Mark

Yeah, I tried the Fat Boost in the front end.

Because the Marshall has the Gain knob maxed, there is nothing left that the pedal can do.
The circuit is already peaked.