Thought I'd go ahead and share this. I use this circuit to noise test NPN transistors. Works a lot better than my previous method of using sockets for Q1 in a Big Muff circuit.
The way it works is you hook it up to your amp and listen as you swap transistors. Use a known quiet transistor to compare. It's still all about ears and therefore subjective, but it's easy to get into the groove and get very high confidence levels. Yeah, the smart folks would be using a scope or something, but ears work okay for me at the moment.
Notice there's no "input." You could play your guitar through this, and it's just a yucky sounding fuzz. Also notice there's a 3.3nf cap to ground at the base of the unit being tested. This is a compromise. No cap at all would make every transistor seem rather noisy, but too big a cap might let a noisy transistor sound reasonably quiet (but a really loud static-producer would still obviously be loud even with a big cap).
I have included sockets for a CBE and BCE arrangement transistor, just use the appropriate socket, and a switch to choose between NPN or PNP devices. I'd recommend only using the NPN/PNP switch when power isn't applied to the circuit. If one of the contacts makes marginally before the other breaks then you could create a short across the supply.
Would using an on/off/on switch maybe solve the problem of a potential short? As there shouldn't be a chance of both sides being able to make at the same time.
ReplyDeleteYes good idea mate, that would be preferable
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