Sola Sound Yellow Hybrid Tone Bender

mdc

Active member
Diode was indeed flipped in the schematic, thanks for the catch.
 

Chuck D. Bones

Well-known member
All of the voltage measurements make sense, just need one more.

Can we get a measurement of the zener voltage (voltage at D2-K)?

Is the TONE control oriented correctly? As drawn, clockwise rotation makes the sound darker.

Ya know... If this was built on a BMP board, we could have a gain recovery stage between the TONE and VOL controls. Just a thought. :unsure:
 
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mdc

Active member
TONE is correct - CCW is bass cut, CW is treble cut.

Voltage on the zener cathode is 4.86.

Also, there's a layout available here:
 

Chuck D. Bones

Well-known member
Cool. We have independent confirmation of the trace. The schematic even has ref des. ;)

Interesting that C5 has different values in different pedals. That would be a good place for a FAT switch.
 

mdc

Active member
I have about 6 or 8 OC140s on hand, when I get a sec this weekend I can get some hfe and leakage numbers from them. My recollection is that they're very consistent gain-wise and very low leakage.
 

MGB

New member
Congrats guys !... That's a superb team effort and great show of talent as I watched this thread unfold.

Now, sorry for the noob question here, but doesn't that GC92H Ge diode fall in the unobtanium bin ?

Is there a known replacement or an equivalent part that would be easy to get ?

Thanks
 

Chuck D. Bones

Well-known member
Congrats guys !... That's a superb team effort and great show of talent as I watched this thread unfold.

Now, sorry for the noob question here, but doesn't that GC92H Ge diode fall in the unobtanium bin ?

Is there a known replacement or an equivalent part that would be easy to get ?

Thanks
Corrected a typo... :rolleyes:

Just do like we do with ALL Germanium devices: install sockets and try various parts. I plan on tweaking the 220K resistor as req'd to get the right bias on Q3 if I can't get there by subbing transistors and diodes. Here's a good starting point: go for low leakage on Q3 and fairly high leakage on D1. If Q3's Vc (collector voltage) is too low, then switch to a transistor with less leakage or a diode with more leakage. Do the opposite if Q3's Vc is too high.
 
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Bobbyd67

Active member
Ahahaha I just noticed this thread xD Good job boys!!! (and gals possibly.... Chances are slim ... The hobby is great but you gotta admit .... It's kinda of sausage fest xD)
 

mdc

Active member
I was digging around the other day to try and find some specs on CG92H and on first pass I could only find this sidebar to a review of the Peak Zen50 diode tester in an old issue of everyday practical electronics:
 

mdc

Active member
OK, so!

I built the circuit on vero with the following parts:
Q1: 2N3440 / hfe 110
Q2: BC549C / hfe 513
Q3: OC140 / hfe 85 / leak. 0.00mA

D1: 1N270
D2: 5.1V zener

Q3 collector biased to 2.6V

Outside of those component choices, the only sub was a B20K for the W20K.

I honestly can't tell any meaningful difference versus the original. Sounds great, overall volume is about the same as stock - unity at ~2 or 3:00, good amount of output past that point. Extremes of the tone control sound about the same, and I can find a spot near the middle that's about identical.

I used the dirtbox effects layout I linked earlier, so consider that verified (fyi, the tone control is wired in the reverse from the original in that layout, but that might also be more intuitive...).

I'm stoked - thanks again for all the help in this!
 

Chuck D. Bones

Well-known member
Cool. I have not gotten around breadboarding this yet. I ran some sims and it did what I expected. No gating. Asymmetric distortion, lotta harmonic content. How does it sound with chords?
 

mdc

Active member
Quite good, I think—it's a pretty saturated-sounding fuzz, but there's a nice raggedness to the high end that makes it seem a bit more articulate than a big muff or something else with similar topography. It's an excellent bass fuzz, even with the 10nF cap in there. I've not played an original supa fuzz but I've built a copy of that circuit and found it too bassy to be usable; this is a much better sounding pedal and sits really nicely between what you might expect from a medium-gain TB circuit and an actual big muff.
 

Julian A

New member
Took voltage measurements of my old build. They're pretty much where they should be. It has BC178C for Q1 & Q2 and a GT402B for Q3. 5.1V zener.
The GE diode is an AN307 (not that it changes much). I haven't made any changes to it, and will likely keep it as is. Would like to build the new NPN one though.

-9.24v input

Q1
C: -4.11
B: -0.645
E: -0.03

Q2
C: -4.37
B: -0.67
E: -0.047

Q3
C: -2.6
B: -0.147
E: 0

Note that Q3s voltage will vary with temperature. Good ol germanium. My room is a pretty cool ~60⁰F. After touching Q3 for 10 seconds, the voltage was around -2.35.
 

music6000

Well-known member
Quite good, I think—it's a pretty saturated-sounding fuzz, but there's a nice raggedness to the high end that makes it seem a bit more articulate than a big muff or something else with similar topography. It's an excellent bass fuzz, even with the 10nF cap in there. I've not played an original supa fuzz but I've built a copy of that circuit and found it too bassy to be usable; this is a much better sounding pedal and sits really nicely between what you might expect from a medium-gain TB circuit and an actual big muff.
So, PedalPCB layout Tone control as per Original cuts Treble clockwise from 12 O'clock & cuts Bass counter clockwise from 12 O'clock.
 
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mdc

Active member
I mean to be fair they also put the input on the left hand side and drive on the wrong side of the road.
 

music6000

Well-known member
OK, so!

I built the circuit on vero with the following parts:
Q1: 2N3440 / hfe 110
Q2: BC549C / hfe 513
Q3: OC140 / hfe 85 / leak. 0.00mA

D1: 1N270
D2: 5.1V zener

Q3 collector biased to 2.6V

Outside of those component choices, the only sub was a B20K for the W20K.

I honestly can't tell any meaningful difference versus the original. Sounds great, overall volume is about the same as stock - unity at ~2 or 3:00, good amount of output past that point. Extremes of the tone control sound about the same, and I can find a spot near the middle that's about identical.

I used the dirtbox effects layout I linked earlier, so consider that verified (fyi, the tone control is wired in the reverse from the original in that layout, but that might also be more intuitive...).

I'm stoked - thanks again for all the help in this!
I agree that the Tone control makes more sense Reversed so Treble is Clockwise from 12 O'clock

On all other Sola Sound Tone Bender's it is labeled as TREBLE..............BASS, not TONE.
 
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