Author Topic: Reverse Polarity PNP Range Master  (Read 1274 times)

guysmiley

Reverse Polarity PNP Range Master
« on: November 29, 2018, 05:30:24 PM »
So I have an odd question, not a troubleshooting one.  I breadboarded, tested, and wired up this range master circuit with negative ground.  A circuit flipped, so it can run off a standard power supply.  I got the idea from tonefiend"s website here:http://www.seymourduncan.com/tonefiend/wp-content/uploads/DIY%20Club%20Project%204%20v01.pdf On his circuit and all others I've found doing similar things to fuzz faces the collector on the transistor is going to the gain pot then to ground.  However, every test I've done, this won't work.  I have to flip my transistor around.  I have a nice pedal up and running.  It sounds great.  I know some people warning against doing this and my voltages on the transistor are a bit off.  But the stock values seem to sound good. 

My question is, why is my pedal working?  It can't be everyone else online has a wrong schematic.  I'm using a Ac128 with the pinout very clearly marked.  The nub is the emitter.  Ive double checked and tested all of them.   Just curious really.   Here's my build and edited schematic.   
Thanks, for any explanation! 

KR Audio

Re: Reverse Polarity PNP Range Master
« Reply #1 on: May 26, 2020, 07:45:14 PM »
Good question, the pnp transistor you have in that circuit is not running in its normal state. Though it would if you had a negative supply voltage. You have the transistor runnings as an impromptu square wave oscillator. Which for the purpose of a hard distortion or fuzz is exactly what you want which is why it sounds good to you. Though it's not conducting in the normal fashion a transistor would. In fact if you put a negative supply on there you would have an emitter follower which is near unity gain. i.e. no distortion.

tonyharker

Re: Reverse Polarity PNP Range Master
« Reply #2 on: May 27, 2020, 07:08:17 AM »
The rangemaster is not supposed to be a fuzz.  Its a treble booster.

KR Audio

Re: Reverse Polarity PNP Range Master
« Reply #3 on: May 27, 2020, 12:43:57 PM »
Ah, ok that makes even more sense. Frequency boost and attenuation are achieved by Low Pass and High Pass Filters.  Even though the transistor isn't conducting normally, your guitar signal is still going through the circuit and the high pass filters that have been constructed into the pedal at the input and the output.  Remember, in this circuit, the transistor only acts as a buffer which is done to have a more suitable impedance at the input and output. The Rangemaster is what we'd call an "active" tone control. Though the term can be misleading, as the active part of the circuit ( the transistor or op-amp) usually isn't placed there to affect the signal but to manage impedance. The circuit is working because the signal is still going through the high pass filters which in this case is all you're trying to get out of it. with regard to my first post, if you kept the circuit the same and the same positive voltage but turned the transistor up-side-down, that would give you a square wave (Fuzz/distortion).  Germanium transistors also suffer from leakage at the base and emitter junction so that could also contribute to why the signal is passing in an atypical topology. 
« Last Edit: May 27, 2020, 05:36:29 PM by KR Audio »

davent

Re: Reverse Polarity PNP Range Master
« Reply #4 on: May 27, 2020, 01:25:32 PM »
An aside, the 'blend' control from the Joe Gagan's Easy Face Fuzz works very well in a Rangemaster instead of switching between fixed caps.

http://www.generalguitargadgets.com/pdf/ggg_ff5_sc_easy.pdf

dave
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