Green ringer: replace the PNP with a Mosfet

[Elijah-Baley]

Hello guys!
I'm building a Green Ringer clone, the Earthquaker Devices Tentacle from http://tagboardeffects.blogspot.it/2016/11/earthquaker-devices-tentacle.html

I read a weird mod about the original Green Ringer: http://tonepad.com/buildReports.asp?projectID=46
The first commet says: «[...] Also tried to change PNP transistor, I've found REALLY GOOD MOD that improve octave effect - try to replace 2N3906 with 2N5088 (sounds gooood) or BS170 (MOSFET) which is the best, best, best,...it really improves the sound.»

From PNP to Mosfet... what about the pinout orientation?

Thanks!

[antonis]

<try to replace 2N3906 with 2N5088 (sounds gooood)..>

Q2(p-n-p) Base is biased at about 5V resulting in about 3.3V at Collector and 5.7V at Emitter..
(not ideal bias for a phase splitter but quite satisfactory..)

Replacing Q2 with 5088 (n-p-n) results in 4.3V at Emitter and 4.7V at Collector..
(very small margin for signal swing - about 200mV_pp with a minimum V_CE of about 200mV )

Taking into account Q1 voltage gain (slightly less than 3), any signal with voltage higher than 70mV_pp should be distorted before the FW rectification of the octave circuit..

I'm not sure if that "sounds gooood"... 

[Elijah-Baley]

Thanks a lot.

I just tested the circuit of the Tentacle. I have to say it already sounds good! Enough octavish, not too much fuzzish.
I could use the BS170 for something else, like a booster.



I am studying, more than anything else, how control the octave effect. My old notes says to act on the R7 10k. Low value = Less octave up. A linear 10k pot (or maybe 20k) could be cool. Or a simple DPDT two or three way. I am undecided beacuse this wanted to be a simple pedal, and now I have just a On/On DPDT e none good pot. I'll think about it.

I advise this circuit to who had problems with the original Green Ringer. Sounded good immediately.

Thanks and bye!

[antonis]

My old notes says to act on the R7 10k.

Your new notes should also include R6...
(or else, Q2 should behave as an unequal gain phase splitter..)

[Elijah-Baley]

Indeed I wasn't so sure about my notes.
Thanks again!

[PRR]

> also include R6...

Or not.

Changing both R6 and R7, still equal, will do little.

IF the intent is "less octave", then UN-balancing the phase splitter is one way to do it.

[rankot]

I have buit this in simulator and it is obvious that only one of the resistors - R6 or R7 - shall be replaced with a potentiometer. But actually, both of them can be replaced with potentiometers and usefull range for R6 is from 820 ohm to 10k, while for R7 it is from 100 ohm to 35k. At least with those values signal gets changed on oscilloscope. And R7 range is connected to R6 value - greater the R6 value, more usable range for R7.

Interesting results can be achieved changing value of C3 from 1n to 47n.

[Elijah-Baley]

I'm gonna keep this pedal simple.

Anyway, these are precious information for the next time.

[antonis]

IF the intent is "less octave", then UN-balancing the phase splitter is one way to do it.

It depends on exactly what "less octave" means..

If it deals with waveform amplitude (and NOT frequency), I totally agree..
(which also can be obtained by keeping R7 = R6 and using different forward voltage drop diodes for D1 & D2..)