Saturated transistor full-wave rectifier

[earthtonesaudio]

An interesting full wave rectifier uses only one transistor, albeit in a rather funky way.

Anyone tried it?  Looks fun.

[Derringer]

do it mang

totally trying this out

[JKowalski]

I believe that the "gain reversal" effect is commonly found in wild fuzz type effects and accounts for most of the octave parts of said circuits. I know I have seen it crop up on a couple things I have analyzed.

[jasperoosthoek]

Cool idea, thanks for sharing!

[Derringer]

tried this out on my scope

using these values I almost got an octave ... slightly more than half wave rectification, not symmetrical
RB1 = 10K
RB2 = 12K
RL = RE = 3.3K
Rx= 1M pot


but then I substituted a 50K pot for RB2 and by dialing in Rx and RB2 I was able to get very close to a symmetrical FWR output
you would definitely need a booster though

[Earthscum]

How's it respond to a larger signal, or distorted signals?

[Derringer]

I ran a 2V signal through it ... don't know otherwise

it attenuated the signal so much I don't even know if it's worth it ... i.e. you're not going to save on parts because you're going to need a big ass booster too

[Earthscum]

An idea: try running smaller signals, maybe 1V, and maybe a higher one... I don't know if you can. I'm interested in whether it acts differently with different signals. Really wish I had a scope.

[Rob Strand]

I built that in pspice back in the 90's when the article came out.  It does work.

It reminded me of the single opamp rectifier in the CA3130 datasheet.
See fig 11 of,

http://www.intersil.com/data/fn/fn817.pdf

[Earthscum]

I actually came across this today while doing a google search for oscillators:

http://www.tompolk.com/inventions/455_KHz_Oscillator/455_KHz_Oscillator.html

Should be operating in the same realm, no? I'm wondering if you couldn't convert this circuit to R-C timing and use it in some stompbox circuits. Use one as a negative current source for the other. I don't really know what I'm talking about...  I'm running on coffee only and kinda loopy and it sounds like an idea to me, but that's about it, lol.

[Derringer]

An idea: try running smaller signals, maybe 1V, and maybe a higher one... I don't know if you can. I'm interested in whether it acts differently with different signals. Really wish I had a scope.

with my scope and signal gen (and keep in mind I'm no expert with this equipment) this circuit does not seem to respond much to lower signals, the output is very very low.

However, on the other side of things, with larger voltages, as long as RB2 and Rx are adjusted, you still get an octave along with some other octave-like shapes

it's difficult for me to say exactly what voltages I'm inputing. I have a 0 - 2vp-p range and then a 0 - 20 voltp-p range, both controlled by a pot.
If that pot is linear then I'd say on the high side of things I pushed it up to around 10 v p-p.

[brett]

Interesting....

[R.G.]

It does work - if the source impedance driving it is low enough to drive the loading when the transistor saturates.

It's kind of a half-circuit.

[DDD]

I've tried this circuit and have to saythe following:
1. The circuit is simple, but it requires some additional signal conditioning stages. So, the total complexity is the same or more than of the other octave-up circuits
2. The resulting sound is not impressive at all.

[Earthscum]

Too late to try, but would something like an MPF102 buffer be low enough with a source resistor of a couple k or so? That would only add in a few more parts to the circuit, compared to a transistor stage... unless there's some kind of kewl trick you could do with another tranny playing twister in there.

DDD - more complex than the Octup! or Push-me Pull-you? Those are pretty simple... the Octup works great if you use a 10k source pot with the cap connected to the wiper. At bottom is under unity, but not unusable by any means. Nice and smooth, almost perfect. At top is dirty and loud.