using a PNP transistor in the "Buzzaround-Alike" project

[mordechai]

On the *other* forum, there's an intriguing project for a Burns Buzzaround-type circuit called the "Buzzaround-Alike".  Instead of two transistors driving a third into saturation, it replaces Q1-Q2 with an op-amp, and the end result really sounds good.   Here's the schematic:


I would like to build this up, but it's an NPN circuit.  Instead of using an NPN germanium, I want to figure out a way to build this up by "flipping" a PNP transistor, sort of like how ZVex flipped the two PNP germaniums in the Fuzz Factory circuit.

Never done this before, and not sure how to make it work.  There's a vero layout ready for the regular NPN circuit, which I'm attaching here:


Anybody have suggestions about what to do with this vero layout to "flip" the relevant components so that it can accommodate a PNP germanium transistor?

[M.A.P]

Hi mordechai,

I'm working on replacing NPN with PNP types in the clipping stages of a BMP circuit atm. I would flip the whole circuit between the negative pole of the 4µ7 cap after the input op-amp and the 100nF cap in front of the output op-amp. Be careful because the poled caps and diodes still have to be built in in the right way.

If I were you I would first redraw the schematic and post it here. I think you have to creat your own vero layout for this.

Greetings from Germany
Marcus

[smallbearelec]

Hi--

If you already have one or more low-gain/low-leakage PNP devices in your spares drawer/junk box, think about combining a low-gain NPN and a low-gain PNP in a Sziklai Darlington pair.

http://diy.smallbearelec.com/HowTos/BreadboardGeDarlingtonRMs/BreadboardGeDarlingtonRMs.htm

You might already have a suitable NPN device for Q1. If you do need to buy, decent low-gain NPN germanium is readily available and cheap (for now).

http://smallbear-electronics.mybigcommerce.com/low-gain-and-high-gain-1/

Regards
SD

[chuckd666]

I have breadboarded a Buzz-Alike and it's incredibly forgiving with different ranges of NPN germanium transistors. I had a bunch of fairly low HFe/leaky-ish AC176s which all sounded great in the circuit! I'd definitely recommend getting a few cheap NPNs from our friend smallbear there and trying a few out.

[mordechai]

Hi mordechai,

I'm working on replacing NPN with PNP types in the clipping stages of a BMP circuit atm. I would flip the whole circuit between the negative pole of the 4µ7 cap after the input op-amp and the 100nF cap in front of the output op-amp. Be careful because the poled caps and diodes still have to be built in in the right way.

If I were you I would first redraw the schematic and post it here. I think you have to creat your own vero layout for this.

Hi  Marcus and thanks for the insights.  I absolutely stink at making vero layouts, but I'll give it a shot.  In any case, I will also redraw the schematic and post it -- I'd be interested in your take on it. 

[mordechai]

I have breadboarded a Buzz-Alike and it's incredibly forgiving with different ranges of NPN germanium transistors. I had a bunch of fairly low HFe/leaky-ish AC176s which all sounded great in the circuit! I'd definitely recommend getting a few cheap NPNs from our friend smallbear there and trying a few out.

Chuck, this is great news...because I also have a whole bunch of leaky AC176's and never knew what to do with them.  I'll give them a try.  Did you have a favorite leakage/gain combination with that transistor in this circuit?