Inverted transistor amplifier

[soggybag]

I ran across an interesting article over at Jack Orman's site. Has any one read this and tried the ideas here?

http://www.muzique.com/lab/reverse.htm
http://www.muzique.com/lab/fuzzface.htm

[brett]

Hi
I tried this with modern Si transistors a couple of years ago.  Probably after mis-orienting a 2N3904 or PN100. 

As single and dual BJT boosters, I couldn't find anything exciting when using modern transistors "backwards".  Gain was about 7 in a common emitter circuit, so it should have been 50 or thereabouts with two in a row.  Maybe I should have used three in a row to make them clip ?  They seemed noisey, but maybe that's mojo for you  .
cheers

[R.G.]

Using a bipolar transistor backwards (i.e. swapping c for e) is an old, old trick. What it does is force the collector-base junction to act like a base-emitter junction.

The first transistors in common manufacture were symmetrical - that is, the collector and emitter junctions were fabricated the same way, by putting indium pads on each side of a germanium "base" - yep, that's where the word comes from. Once it was understood that the two junctions did different jobs and once it became possible to make transistors with different kinds of junctions on each side of the base, they were made different to do the normal job better.

Still, inverted mode was used for somethings, notably using bipolars as solid state analog switches, for a long time.

Today's devices have base-emitters heavily optimized for high, linear gain in the normal mode. This leads to a reverse breakdown of about 5-8V and a high gain. When you use the collector junction for a "base-emitter", you get a very unoptimized one for gain, so the side effects sometimes turn out to be useful when they're abused in effects.

Sometimes. With only a 5-8V breakdown, some modern base-emitters are operating near breakdown voltage on 9V.

The gain is very low, they're not optimized for noise as brett notes. It's an interesting bywater to play in, but I've never seen a commercial pedal or DIY project using one.

[mac]

After reversing the polarity, what happens to the transistor when used in normal conditions? Does it become noisy?

mac

[caress]

i think the soundwave breakdown by death by audio uses 2n5306 darlingtons (7,000-70,000 hfe!) in a reversed junction setup.