Fet circuit

[pazzo63]

HI,does anybody have a correct schematic of the FET circuit fora 90's Dumble ODS?THANKS IN ADVANCE for the help d

[heisthl]

I don't know if this is 90's or not but it works well as drawn.

https://tubeamparchive.com/download/file.php?id=1771

[toneman]

Can't take credit for this but it works

[Funkalicousgroove]

That's the one I've been using, sounds good!

[fp2000]

I believe both schematics are different. The first one shows the B+ voltage applied to S, and the second one shows the B+ voltage applied to D. Which one is correct?

[Funkalicousgroove]

B+ is applied to the drain, there is also a Case that isn't on any of the schematics, it should be grounded.

[heisthl]

I believe both schematics are different. The first one shows the B+ voltage applied to S, and the second one shows the B+ voltage applied to D. Which one is correct?

ARRRRG! That was an error on the schematic, thanks for catching it - I went back and corrected the file on the original post.

Just out of curiousity, do you anticipate a need for the FET input? I read somewhere the intent was for acoustic instruments.

[Funkalicousgroove]

I use a 5.1K to bias the FET and make it quite a bit hotter, the "Real article" sounds kind of anemic, but with the 5.1K , and the trimmer turned up, it makes a real nice boost-especially with an HRM.

[heisthl]

Pretty close to the 4k7 I chose, ideally you would have a front panel control and the option to switch it in and out. Most "pedal board" setups have at least 1 clean boost that could be eliminated with the use of the FET if you could select it via footswitch.

[ayan]

Pretty close to the 4k7 I chose, ideally you would have a front panel control and the option to switch it in and out. Most "pedal board" setups have at least 1 clean boost that could be eliminated with the use of the FET if you could select it via footswitch.

I've always used 6.8K myself, stock value sounded bad to me since Amp #1.

Gil

[Funkalicousgroove]

You could put it on a relay, or change that 150K dropping resistor and run it off a pair of 9v batteries in a pedal. It would probably run fine off of a 9v alone, but in my experience Jfet's seem to have more headroom at higher voltages.

[heisthl]

Wonder why he went discreet instead of IC? One of my favorite pedals in years past was the MXR micro amp which uses a TL0 61 (JFET).

[Funkalicousgroove]

they used to look like this: