Reverse Power Booster

[amz-fx]

Breaking the rules.

Thinking outside the box.

Reverse Power Booster

regards, Jack

[KerryF]

Very cool.  I may have to try this with one of my AC128s 

[JimRayden]

Fascinating.

---------
Jimbo

[petemoore]

  *Thank You very much for sharing this concept Jack !!!
  I haven't tried it yet of course...but probably will..
  *I thought I'd tried most everything as far as clippers/boosters...

[MartyMart]

Good stuff Jack, this explains ( partially ) why some of my "reversed" Ge builds IE: getting the pinout wrong
can often sound quite good !!

MM.

[Dirk_Hendrik]

Well Jack,
as it isn't the first of april and this comes from you those are the only two reasons for not having to feel like being bullshitted. However, I feel an extreme urge to heat up that soldering Iron and put this to the test straight away.

[tcobretti]

I wouldn't believe it either if it wasn't from Jack.  I'm gonna have to breadboard it later.

[Gilles C]

Well it seems we always have something knew to learn and discover about old things.

After getting some Ge transistors from Aron last week, I started to checked what he said about these Ge transistors that could be be used both ways with a different hfe on each side, and now I learn that we can do the same with Si transistors.

Add that to having found last week that some transistors could oscillate when reversed biased whith the base left open.

I don't see any reason to stop using transistors... 

Thanks for the article.

Gilles

[Meanderthal]

 I can believe it... ever get your tranny orientation wrong? Sometimes it works anyway! And in a good way too! Also, I've heard that OC140 in particular will work either way...
I'm glad someone is exploring this!

[amz-fx]

     Keep in mind that this has limited application...  I would not use the Si version as a booster since it will have limited frequency response (but still good enough for guitar) and low gain.

As I state in the article, the interesting thing about it is how it clips...  different from a normal transistor booster with lots of even harmonics and other wild stuff!  Put a normal booster in front and the reverse booster in series behind it for some new tones...

regards, Jack

[Harry]

I can only guess what this is gonna spawn...

[tcobretti]

Ok, I just breadboarded this guy and ran various pedals that I had into it.  I wired mine as PNP so I could try Ge, but I also had some 2N5087s that I figured I'd plug in and try.  I wired a 1k pot from the collector to +9v, and found that usually it sounded fuzziest at 0 ohms resistance, and got less fuzzy as you cranked it up.  It's a pretty interesting circuit.  First and foremost it gated the signal.  If fact it gated so much that just running guitar thru it with no boost didn't work well at all.  When I ran a booster into it I got a fairly full sounding fuzz.  When I ran my Boss SD-1 into it, it got kinda fuzzy, which was interesting.  Si FF into it really didn't do much except gate the noise from the FF.  When I tried different transistors in it, the Ge sounded, well, like a Ge, while the 5087 at times introduced a knarly distortion to the high end that sounded pretty cool.  With my limited experimentation and knowledge, I'd say that the Si is promising for a Dirty Sanchez kinda noise fuzz.  I'd also say that if somebody smarter could figure out how to control the gating a little better, it would be a good add on the end of a noisy fuzz.  Poor man's noise gate!

I'm definitely curious to see what some of the more experienced designers do when they get their hands on this.  Tim Escobedo, you out there?

[amz-fx]

Things to consider:

a) Transistors with lower B-E capacitance have less emitter doping and work better in reverse mode.

b) Lower doping levels contribute to lower beta specs, and  these devices are better for reverse operation.

What makes one bipolar transistor different from another?  The actual size of the P-N layers has an impact on the transistor's basic operating properties. There are also different N and P dopant materials: Examples of N-type are phosporus, antimony, arsenic, bismuth.  Examples of P-type: aluminum, indium, gallium, thallium.  The amount of dopant, and the relative amounts in each layer also determine the characteristics of the transistor. 

Furthermore, the base layer may be doped at different levels in the area contacting the collector than next to the emitter, or even have different dopants near the respective opposite layers.  Mix and match these ideas (and others) and you can make a lot of different transistors!

regards, Jack

[JHS]

Good inspiration Jack, I think I must do some more experiments with this kind of circuit.

I built a Ge-reverse RM accident a few month ago on a breadboard and got it to work after rebiasing, but never thought about it again.
I remember that the overtone spectrum shifted a bit when the trannie was reverse wired, not much but some Ge-trannies (AC128 f. ex.) sounded ritcher and way more organic.

It's no magic, most old Ge-trannies w low hfe are sym. and nearly identical beween E and B and B and C, that's the reason while they work reversed too.

JHS

[Gus]

http://www.diystompboxes.com/smfforum/index.php?topic=39466.0

First transistor

And from one of the first effect sites
Jamie Heilman's Angry Beard III

The output transistor is a Ge pnp inverted

http://www.harpamps.com/schematics/angrybd3.pdf

[amz-fx]

And from one of the first effect sites
Jamie Heilman's Angry Beard III

The output transistor is a Ge pnp inverted

http://www.harpamps.com/schematics/angrybd3.pdf

The output on that circuit is taken from the collector, not the emitter.  Not the same effect...  I'm not sure what he's trying to achieve there...

-Jack

[markm]

This is quite interesting indeed Jack. Gotta mess around with this idea a little bit real soon!
Thanks alot for the tidbit of info! 

[Gilles C]

To complement this idea, here is an interesting article

http://www.edn.com/index.asp?layout=article&articleid=CA47314&1=1

where they compare a reversed 2N3904 to a 1N34 diode.

Gilles