Tone Bender MKII - Original Layout - What do you think?

[Chris Brown]

Hi all,

I wanted to share this and get any feedback from the fuzz experts here... This is my attempt at the original layout for the Sola Sound Tone Bender Professional MKII.

I think I hit it spot on.  Please share your thoughts.



When I build I am going to replace 8k2 with a 470 ohm wired to a 20k trimmer jb-welded to the back of a 5K pot... for internal and external bias network, however for now I just want to focus on getting as close to the original layout as possible.

Regards,

Chris Brown

[tatter]

Here are some close-ups of an original stripboard layout, including underneath the board shots that might help. Scroll down near the bottom for the pics.
http://dam.10.forumer.com/viewtopic.php?t=502&start=45

[Chris Brown]

Awesome,  Tonight I'll incorporate the differences that I see and update the layout. Thanks very much for the helpful link...  I googled for a long time trying to find a shot of the solder side... that's exactly what I've been needing to see.

[Chris Brown]

I was able to make some changes based on the link posted by tatter.

The spacing between C5 and C6 seems to be different between the different versions (marshall, roto, etc etc) and some also have an added 100ohm resistor to the right of C6.

Here's what I hope is the final version:

Any input is appreciated. Have fun

[kennsol]

Hi!
R2 was 10K or 12K on originals with OC75 transistors (10K versus 100K makes a lot of difference). R1 sometimes 12K. R3 47K on pedals featuring OC75's.
The values you specify was used on pedals featuring audio drivers (OC81D's) The limiting resistor you mention (100 ohm) was used on some early supa fuzzes...
Layout looks good, though..!
Kenneth

[Electric Warrior]

here's one with more realistic part sizes and different resistors, according to kenneth:

[Electric Warrior]

layout works.

[sharkminusbear]

Just built this, sounds awesome. I used OC75's for Q1 and Q3, and an OC76 for Q2 (it sounded better than the OC75 I had for Q2).



It sounds better than the BYOC I built, there's less noise, and the attack control is very useful (unlike the BYOC). Not to hard for a beginner.

[Electric Warrior]

I bet it was a lot cheaper than the b.y.o.c. as well

[Nitefly182]

Funny I was just finishing up a Bender with this layout and I have one of those huge Mallory 150 .1uf caps on my board too 

I bought some orange drops just for kicks and the .1uf is as big around as my thumb. It would dwarf everything else on the board.

[Electric Warrior]

I used Vishay MKT1813 in mine.. a lighter shade of yellow

[Nitefly182]

[yeeshkul]

nice job 

[Cliff Schecht]

Why not shorten the leads on the transistors? The emitters are especially susceptable to noise if you have no emitter degeneration.

[Nitefly182]

Why not shorten the leads on the transistors? The emitters are especially susceptable to noise if you have no emitter degeneration.

I've never had any problems. However, I just finished this build and using the trim pot I can only adjust the voltage within an extremely narrow range from about 9.22 volts to 9.35 volts. I skipped the bias mod and just used the trim on the board and I dont know whats up. Two lugs of the trim are tied to one strip and the remaining leg is at the other strip. It should be working perfectly but its just not altering the voltage. I dont know whats up but its pissing me off.

[yeeshkul]

9.22 - 9.35 on Q3C?
What value is the C resistor and what value is the trimpot and vhat voltage is on your battery lugs?
What is the Hfe and leakage current of Q2 and Q3?
This happened to me also and i had to use 50k trimpot to balance the voltage - it very depends on the 2nd and 3rd tranny leakage/Hfe..

[Nitefly182]

9.22 - 9.35 on Q3C?
What value is the C resistor and what value is the trimpot and vhat voltage is on your battery lugs?
What is the Hfe and leakage current of Q2 and Q3?
This happened to me also and i had to use 50k trimpot to balance the voltage - it very depends on the 2nd and 3rd tranny leakage/Hfe..

I just tried dropping a 50k pot in place of the bias resistor and was only able to get the bias down to 9v. The transistors are a tonebender set from small bear so the leakage should be reasonable although I dont have leakage measurements. Im using a power supply and a 50k pot for the bias resistor right now.

[yeeshkul]

what resistor did you use in Q2 collector? People refer finding 47k in devices with OC75s. The thing is that the bias voltage of Q3 quite depends on collector voltage of Q2.
Q2 leaks -> there is voltage on RC2 => this make voltage on Q3B (Vcc - VC2) => this makes voltage on Q3E (VQ3B - 0.2V ish).
Then Q3C quite depends on how strong is the divider RQ2C/fuzz pot.

EDIT: RC2 down -> VRC2 down -> VC2 up -> VB3 up -> VE3 up -> VC-E down down => VC3 down

[Nitefly182]

what resistor did you use in Q2 collector? People refer finding 47k in devices with OC75s. The thing is that the bias voltage of Q3 quite depends on collector voltage of Q2.
Q2 leaks -> there is voltage on RC2 => this make voltage on Q3B (Vcc - VC2) => this makes voltage on Q3E (VQ3B - 0.2V ish).
Then Q3C quite depends on how strong is the divider RQ2C/fuzz pot.

I used a 47k resistor for the Q2C and for some reason the voltage at Q2C is only 150mv. Its supposed to be about 1v right?

[yeeshkul]

i've just measured half a volt on mine. i use top quallity matsush*ta trannies. they have very small leakage current so that's why. if your Q2 is leaky the low voltage makes sense.
Q2 leakage curent up -> VRQ2c up -> VQ2C/VQ3B down

EDIT: let me check out some leaky Czech OC75 for Q2. I write back soon.