This Week on the Breadboard: The Spunk-O-Matic

[Chuck D. Bones]

This circuit was inspired by T1redHands' contest entry. Loosely based on the Karma Suture, which in turn is based on the Harmonic Percolator. The main thing I did to be different was use a MOSFET for Q2. This could be built on a PedalPCB Antithesis board (omit R7). Mind the pinouts on the transistors.




Knobs (L-R): OUTPUT - DIODES - DENSITY - INPUT



HAPPY 420 Day!

 

[cooder]

Ooooh Spunky!

 

[t1redhands]

In all of my experimentation with the HP circuit I have never thought to try a MOSFET for Q2. BRB gonna breadboard this...

 

[Chuck D. Bones]

It was just a crazy thing I tried and it worked!
The DC voltage on the 47uF cap is much more stable with a MOSFET for Q2.

 

[cooder]

 

[szukalski]

Giving this one a whirl (with opinionated knob placement).
Dave - I put a 500k trim pot in series with R2 for adjusting Q1. I'm thinking 750k resistor with a 500k, thoughts?

 

[Chuck D. Bones]

I have no clue how big R2 might need to be. That trimpot should be at least 1Meg.

Note to Cooder & Szukalski: The tranny I used for Q1 (1T308) has the collector pin in the middle. A dual footprint is highly recommended.

 

[szukalski]

I verified my layout yesterday with a higher gain 2N1309 and OA9 diode. Sounded pretty good. I may try a few different components but am happy with what's coming out already!

 

[Chuck D. Bones]

Check the Vce on the 2N1309. HFE has a strong effect on biasing.

 

[szukalski]

I’ll check it this evening. It was spot on 2V at the collector with the 2N1309 (170 HFE) and sounds primo. Boosted with the Texel and it is a rock beast. I tried with a lower gain Russian transistor and it was not half as fun..

 

[Chuck D. Bones]

ping

 

[cooder]

ping

Ping... would you remember what hfe your 1T308 had @Chuck D. Bones ?

 

[Chuck D. Bones]

Measuring it right now...

HFE = 73
Ic = 0.75mA
Vbe = 228mV
Iceo = 14μA

 

[cooder]

Awesome.... cheers.
I got a box full of them so should be finding something similar. Would higher hfe be better as szukalski said?

 

[Chuck D. Bones]

I don't know, I did not try high HFE. Try different ones and see what sounds good to you.
It's about dialing-in the bias. Most important is low leakage. Next most important (to me, anyway) is low-medium HFE. Adjust the resistors as req'd to get the bias in range.

 

[cooder]

Awesome, thanks!

 

[spi]

does it still sound like a karma sutra?

 

[music6000]

View attachment 73933
Giving this one a whirl (with opinionated knob placement).
Dave - I put a 500k trim pot in series with R2 for adjusting Q1. I'm thinking 750k resistor with a 500k, thoughts?

Something like this:

 

[Nostradoomus]

Yeah I dunno about the switch placement on that one.