Grounded collector operation

Started by mth5044, December 09, 2013, 03:47:34 PM

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mth5044

I'm working backwards on a fuzz and have found the orientation of the first stage, Q1/2N5088, as having a grounded collector as well as an input cap to ground. I've never seen this before, is that actually operational or was something lost in translation?  That 1M resistor between the base and the emitter is strange as well, not to mention that the 4046 isn't grounded.

If anyone could shed some light on what is going on around Q1, I would be very grateful. Thanks!


R.G.

Quote from: mth5044 on December 09, 2013, 03:47:34 PM
I'm working backwards on a fuzz and have found the orientation of the first stage, Q1/2N5088, as having a grounded collector as well as an input cap to ground. I've never seen this before, is that actually operational or was something lost in translation? ...
If anyone could shed some light on what is going on around Q1, I would be very grateful. Thanks!
It may have worked. I'd have to do more than glance at the schemo to tell, but maybe.

Bipolar transistors work in inverted mode, with the emitter taking the place of the collector and vice versa. The base-emitter withstanding votlage is low, generally about 7V for most modern devices, so it won't work with big voltages, but then 9V isn't that big, and if it biases with the colletor (that is, the datasheet emitter) down a few volts from 9, it may be OK. Ish.

The gain in inverted mode is much, much lower than in normal mode. That may have been the point. Or maybe they were looking for some breakdown as part of the sound.
R.G.

In response to the questions in the forum - PCB Layout for Musical Effects is available from The Book Patch. Search "PCB Layout" and it ought to appear.

mth5044

Very interesting! Transistors seem to get stranger and stranger as more things are mentioned. Thank you for the info. The fuzz is pretty degraded so perhaps the 'breakdown as part of the sound' was intended with this setup.

amptramp

The base-emitter breakdown voltage is sometimes used as a noise generator with the junction acting like a noisy zener diode.  For silicon transistors, the breakdown voltage is usually in the 5 - 7 volt range.  But R.G. is right, this seems to be an effort to get a low gain out of a normal transistor, because there is no biasing resistor from the base to ground.  The 0.1 µF to ground from the input is a mystery, unless this was intended to be driven by a power amplifier.