Sansamp classic

[lowell]

Was getting no signal and no power led. Checked all battery connections, new battery etc.. Found one open resistor - 4.7k across two of the lead/norm/gain switch pins. Now I get something, but very low volume and very distorted. Still get no power LED. If I short the LED negative to ground it lights up, but this doesn't affect the signal issue.

Is the little transistor in here that has K117 on it an 2sk117? Also, anyone know if it is a buffer or voltage amplifier? When I look at the 2sk117 datasheet and compare to the circuit it looks as though the Drain has a resistor to ground and the Source has 9v on it. Seems wrong. Any info appreciated. Seems as though Tech21 protects their schematics quite well.

[dai h.]

some anonymous Japanese guy rev. engineered it (along with an Aussie guy (R.Strand?)) years ago, so the schematic should be on the web. (This one: )

http://www.diystompboxes.com/pedals/...ssic_Rev11.gif

http://www.diystompboxes.com/pedals/...ssic_Rev12.gif

(Yes), the FET is a 2SK117(might be different gain ranks found in different units, but I'm assuming it doesn't matter(?)) used as a buffer.

FWIW, the later "SansAmp Classic" uses a surface mount part there (I don't know which). I tried some goofy experimentation (basically swapping parts including the FET) some years back to try to get the same sound (as I remembered) from the Classic as an original (without the added 'Classic' moniker) I used to own, and as far as I could tell (just by ear), the input cap seemed to be the difference (an axial ceramic with poor tolerance and presumably way more distortion used in the original vs. a bog standard green mylar in the Classic).

[lowell]

Thanks for that! Nice to see how it works. I replaced the K117 with a J201. Yes I made sure the GDS were in the correct positions as it was not a direct sub. My voltages are:

D: 8.3v
G: 4.3v
S: 7.7v

Source voltage seems doesn't it? The odd thing is that when I measure G to S I get ~0v. ??

The LED didn't seem to be grounded per the schematic so I clipped it to ground. The pedal began to work a bit, but only on initially inserting the input plug. After about 7 seconds the signal farts out and dies completely. I'm lost.