Sola Sound - Tone Bender Mark I (1965)  [schematic]

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
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Rolbista
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Post by Rolbista »

hey guys, could those of you who have some sort of mk i clone on your hands and are happy with it post control voltages, types of transistors, their gains and preferably leakages in one place to compare? i slapped up a mark i and i think i'm getting there in terms of sound, but overall gain is too low. Reason i'm asking this is that i have quite a few germaniums, but none of them are the popular "fuzz types". I have some TG50 (kinda like 2n404 i think), a lot of asy34s (Polish high end transistors, supposedly high gain and low leakage), OC76, ac163, some white dot sft (low gain, round 40) and some 4 leggers with such crazy gains as 400!

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Post by beedotman »

Rolbista wrote:hey guys, could those of you who have some sort of mk i clone on your hands and are happy with it post control voltages, types of transistors, their gains and preferably leakages in one place to compare? i slapped up a mark i and i think i'm getting there in terms of sound, but overall gain is too low. Reason i'm asking this is that i have quite a few germaniums, but none of them are the popular "fuzz types". I have some TG50 (kinda like 2n404 i think), a lot of asy34s (Polish high end transistors, supposedly high gain and low leakage), OC76, ac163, some white dot sft (low gain, round 40) and some 4 leggers with such crazy gains as 400!
In case of MKI you cannot depend on numbers. It's bitch to bias it properly... and usually with trannies in correct gain/leakage bucket it sounds like shit... only swaping transistors till it sounds good could help here IMO.

Anyway... here are tips from other builders that I have collected (mainly from DAM forum):
I kept Q1 on the low side (around 60 w a bit of leakage), Q2 added about 20 with lower leakage and added another 20 with more leakage for Q3. Then I just sound tested over and over again.
Q1= 60-80Hfe/100-200uA
Q2= 60-80Hfe/100-150uA
Q3= 60-70Hfe/<100uA
Q2 is the one worth really playing with to get the best out of the circuit and Q3 seems to be the part most responsible for the high frequency content. If the gain is too high or the part has too much leakage you'll get a truck load of sizzle as the notes decay.
For Q1 I used an OC75 with Hfe about 65 and leakage around 250uA. I too found lower gain was best here, but no TOO low. 30 for example was two low and didn't give good sustain or saturation.

Q2 is an OC71, Hfe about 95 and leakage somewhere around 200uA. I liked higher gain that Q1 here, but I didn't find that it mattered too much if it was a lot higher. I tried a couple of high gain 2N404a's (~120 and 140) I had and it didn't make a significant difference to the sound to me, maybe just where the sweet spot on the attack pot was.

Q3 is a CV7003 (mil spec OC44) with Hfe around 90 and leakage aroun 75uA. I found the gain to not be too critical but the lower the leakage the lower the noise.

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Post by phibes »

The 2nd quote gains look the best. Read RG Keens pdf on the Zonk Machine. The MKI isn't as friendly to build as a fuzz face but it's not as bad as people make it out to be. What gains did you use?
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Post by Seiche »

so it's advisable to have a "testbed" with sockets or on a breadboard for finding the right trannies before committing to a pretty build?

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Post by beedotman »

Seiche wrote:so it's advisable to have a "testbed" with sockets or on a breadboard for finding the right trannies before committing to a pretty build?
If You're using NOS components good idea is to breadboard everything before building or use sockets in assembled circuit before soldering trannies due to components tolerance.

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Post by phibes »

I'd just breadboard, no need for a test bed. Tone Benders are pretty low are the part count so it should only take 5 minutes to put the circuit together. With Germaniums, it's a MUST to test run them before soldering them to a board. Having say 15 good transistors to try is better than just going with the 3 and crossing your fingers.
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Post by beedotman »

BTW... I think that is easier to find good sounding trio for Zonk than straight MKI circuit, at least I have more luck with ZOnks that with MKI :)

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Post by Rolbista »

today I'll set up the RG Keen's tester on a breadboard to measure all my trannies, so i wanted to see some numbers to shoot at. I socketed the trannies and replaced 8k2 resisstors with trimpots, went along the Sola Sound DAM schematic.

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Post by The Rotagilla »

Okay, I've read this thread three times today and maybe I'm just not getting it so thanks in advance for your patience. I've seen several posts (with several answers) regarding trimpots and biasing but didn't see one post with any sort of definitive answer so...

Q1 - The base to ground 1M, trimpot...yes or no?
The collector to ground 8k2, trimpot...yes or no?

Q2 - No trimpots at all...yes on no?

Q3 - The base to ground 8k2, trimpot...yes or no?
The -9v to emitter 15k, trimpot...yes or no?

Thanks guy, really appreciate the help.
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Post by skumberg »

As I see it q2 bias is already variable with the attack knob. I tried several oc75 in q1 and they all seemed to work. There might be some small sonic differences though. oc75 have a bit of leakage 350ua is not unusual. When it comes to q3 you could keep the 8k2 and adjust the bias like this: Attach a 470k resistor to base of q3, the other end goes to a voltage divider(wiper on trimpot, 100k perhaps) between -9 and ground. This way you keep the eq response. Set the bias of q3 where you like it best. In one end it will gate provided your q3 has low enough leakage to gate, in the other end you'll have a ton of gain and noise. With the original set up you'll need a bit of leakage in q3 to reduce the gating. I bought some TI 2g381 years ago and out of the 13 I received the gains were 40-100. The highest was 100 gain with 320ua leakage. The lowest 40 gain with maybe 60ua leakage. I ended up using 90hfe 160ua in q2 and 65hfe 160ua in q3(with adjustable bias). It sounds very good.

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Post by sickman82 »

skumberg wrote:Attach a 470k resistor to base of q3, the other end goes to a voltage divider(wiper on trimpot, 100k perhaps) between -9 and ground.
Could someone be kind enough to draw this up in a schematic? I'm having difficulty visualising it. It seems like a good option. Another way you can bias the MKI, is to tag a 5k pot to the emitter of Q3 going to ground, around 2-3k is where it biased up nicely with my build. It is quite gated, but not bad enough for me to be concerned by it. It certainly sounds like a MKI. Q3 is the main offender with biasing problems and noise.
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Post by skumberg »

I got the idea from this page 8) http://www.guitar-pedals-effects.com/Page1.gif

Just look at how q3 is biased. You could for example ignore the 470k going to q2 and keep the stock mkI attack(bias) for q2. There is a 33k as well in the schematic and one should add another resistor between the pot and 9V- to limit the maximum bias current.

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Post by sickman82 »

Thanks for the tips, Skumberg. I'll try them out at some stage. :thumbsup
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Post by beedotman »

Bam! D*A*M strikes again with sexy stuff!
Mullard OC82DM powered Tone Bender MKI! :shock:
Circuit looks almost stock - 2M2 lowered to 1M for volume boost and bias resistor on Q2 base is propably changed (but I can't read value...). NOS russian caps looks cool :)
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Post by beedotman »

Oh... and forgot about small (3300pF) cap on pedal input to ground (mounted on switch) :slap:

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Post by Electric Warrior »

beedotman wrote:Circuit looks almost stock - 2M2 lowered to 1M for volume boost and bias resistor on Q2 base is propably changed (but I can't read value...). NOS russian caps looks cool :)
180k between Q2's base and 9V. Stock value.

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Post by beedotman »

Electric Warrior wrote:
beedotman wrote:Circuit looks almost stock - 2M2 lowered to 1M for volume boost and bias resistor on Q2 base is propably changed (but I can't read value...). NOS russian caps looks cool :)
180k between Q2's base and 9V. Stock value.
Yup! You have right! Now I see it!
Thanks EW :thumbsup

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Post by agoldoor »

FYI: I have one of these coming my way... I finally will own a DAM! I'll answer any questions if you still are unclear on any values...

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Post by beedotman »

agoldoor wrote:FYI: I have one of these coming my way... I finally will own a DAM! I'll answer any questions if you still are unclear on any values...
Lucky Bastard! :thumbsup
You have other Pigdog MKI to compare, right?

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Post by Taller76 »

beedotman wrote:
agoldoor wrote:FYI: I have one of these coming my way... I finally will own a DAM! I'll answer any questions if you still are unclear on any values...
Lucky Bastard! :thumbsup
You have other Pigdog MKI to compare, right?
Agreed, nice score!
I had a Jerms MKI and a Pigdog Electric Eye....sold them both....HUGE mistake.
Should have at least kept the Jerms MKI....lost track of it though...C'est la vie.
This thread has inspired me to build an MKI...havent built anything in almost 2 years...thanks for all your contributions and thanks for the inspiration guys.

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