New idea? introducing the transistor SRPP

[slacker]

As you probably know there's a few classic DIY designs like the Mini Booster and BSIAB2 that are based on jfet SRPPs/mu amps. I've often wondered if you could make an SRPP using transistors but never tried it. MartyMart's recent Mr Mostorto got me thinking about it again so I thought I'd give it a go.
A quick google came up with this http://www.tubecad.com/2004/blog0016.htm which I basically copied with some component changes, to give this.



For the transistors I used BC109s, but any medium to high gain NPN should work. I used 1N4001 diodes just because they were at the top of my box of bits
As it is the circuit makes quite a nice dirty booster/overdrive, but it's really more of a building block than a finished design.
Here's a quick sound clip of the booster driving my Fender Twin. I haven't got a mic at home so the output is from the preamp out through a condor speaker sim. The clip captures the sound but it's a bit fizzy, it's sounds a lot better in reality.

http://www.eskimo.plus.com/fxstuff/transistor_srpp.mp3

The first couple of bars are clean then the booster kicks in. It's only giving the amp a slight boost so most of the sound is the SRPP rather than the amp being overdriven.

If you've got a spare 10 minutes give it a go you might like it 

[DDD]

Great circuit, черт побери!
The advantage of the present circuit is that there is no capacitor from the base of the upper tranny to the collector terminal of the lower one. The said capacitor usually is a reason of poor functioning with high signal attack levels.

[MartyMart]

Nice slacker, I imagine three of those with some gain control and tone tweaks inbetween
could sound great !

MM ...... hmmm ..... 

[markm]

Yeah, Gain control could be ideal!
How 'bout it? 

[stm]

Looks interesting and promising.
Perhaps an 820R resistor at the emitter of the lower transistor might help stabilizing the bias, increase input impedance and improve linearity around the operating point.

[slacker]

Cheers for the comments. This thing really is in the very early stages of development and can probably be improved quite a bit.
Marty I like the idea of multiple stages, I was thinking maybe 2 in series BSIAB style. It's got loads of volume on tap so adding tonestacks shouldn't be a problem.
If you want to vary the gain I tried a fuzzface style gain control using a 10k pot between Q2s emittor and ground with a 22uF cap to ground off the wiper. A negative feedback gain control using a 1M pot wired as a variable resistor from after the output cap back to the base of Q2 also works.

[MartyMart]

Looks interesting and promising.
Perhaps an 820R resistor at the emitter of the lower transistor might help stabilizing the bias, increase input impedance and improve linearity around the operating point.

I did the same thing on the Mr Mostorto circuit, using a 680 ohm and a 4u7, though I'm not certain it was
doing that job, perhaps just providing even more gain from the Mu pair ?

MM.