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MOSFET weirdness [Cosmopolitan content]

Started by midwayfair, September 21, 2012, 03:22:50 AM

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midwayfair

I did up a Cosmo tonight and what should have been a simple build turned into a six-hour puzzle.

1. Cosmopolitan
2. The MOSFET does not work at all in proper orientation, work very poorly in an incorrect orientation.

3. I tried every mosfet I had, BS170s and 2N7000s, about 10 of them from both Tayda and Smallbear, and nothing works, so I know it's not a bad MOSFET. I also know that the circuit and layout is fine because every bipolar silicon I tried works properly (but it's loud and has a little more noise) as do FETs (when oriented correctly). I've also verified that the MOSFETs work in another pedal (but not another screwdriver, since I don't have an unsoldered socket).

Here's my voltages:

D 4.6
G 8.5
S 4.6

Which is just plain weird because there's definitely only 2.7K resistance to the drain.

I've triple checked the datasheets, and the Tayda ones have the normal DGS pinout (and SGD for 2n7000). So if they were going to work, they'd work

But here's where it gets weirder: If I swap the gate and the source, I get some sound, but it's gated. My voltages also look slightly more normal (9.4, 8.8, 0v), but they're still waaayyy wrong according to my other build (which reads ~9, 2.5, and .5v, which is exactly what I'd expect to see).

4. No subs in this build (yet).

Any one have any ideas? I haven't changed the bias resistors yet.

I guess if I can't get a MOSFET to bias in there, I could just change C1 and R2 to reduce the volume to tolerable levels.