Tonebender mk1

[JebemMajke]

Hello

Some time ago i accidentally stumbled upon a small box filled with black glass Mullard Philips transistors and Valvo transistors.

oc44-oc75, and some others included ( many different AC141/142/188 ....,, tfk's oc602-oc614 ).

oc45 rangemaster is very very nice and very very dark <3.

So, I was wondering what would a tonebender mk1 sound like with different transistors.

oc75/oc72's, for example and so on.

Can anyone give me any advice on the target voltages, and which resistors are used for biasing?



I see that attack pot is biasing q2, but which resistor is biasing q3? 8,2k or 15k?

[PRR]

By conventional design thinking, Q and Q3 have NO active bias, and will not amplify well.

However in Germanium, device leakage gives an (unpredictable) bias.

You have to try it. Be prepared to select transistors.

[JebemMajke]

Well, I guess I could just put trimmers almost everywhere.

Can you suggest some target voltages?

q1 c=9v, obviously.

q2c = 5-8v(8.5)

but q3 ... I can not even imagine .... 7v, like some sort of a Rangemaster? But that would be silly I think because q2 is a Rangemaster.

Also, what is the point of 1M resistor before q1? I could replace 8.2k with a trimmer to help the output bias of it.

[Rob Strand]

Try these,
VE1 =    1.3V to 3.4V reported range  ; more than 2V best.
VC2 =   3.5V to 8.8V ; maybe 5.5 to 8.6 more usable
VC3 =    6.8V low  8V typ.

[Electric Warrior]

OC75s worked well for me, especially with a 470k on Q2b (but you should probably tweak that depening on the transistor/hfe/leakage and the range that you would like to have on the attack pot - vintage units used a range of different values here). No surprise, some early units had three black glass transistors which are usually assumed to be OC75s - now way to tell for sure, though. Lots of parts numbers and values were scraped off..

Auditioning transistors is very important, indeed. Lots of tone shaping potential here. Give your OC75s a try and report back with voltages. You'll probably find that you won't need much tweaking if any at all..

but q3 ... I can not even imagine .... 7v, like some sort of a Rangemaster? But that would be silly I think because q2 is a Rangemaster.

Just because it uses the same topology as a rangemaster does not mean it was biased to the same voltages 
I measured a little over 8V on Q3c in my clone. Sounds alright to me: https://picosong.com/8r8G/

[chriscustom]

Hello everyone
Has anyone managed to achieve this MK1 sound? Pay attention to the breaks in the sound of pauses.
https://youtu.be/7KrVOmZaH6I

[willienillie]

It's called "gating."  I've never messed with the Mk 1 circuit, but I can get a nearly identical sound with my Fuzz Factory clone.  (And could that dude not find any shirts that fit?)

[chriscustom]

It's called "gating."  I've never messed with the Mk 1 circuit, but I can get a nearly identical sound with my Fuzz Factory clone.  (And could that dude not find any shirts that fit?)

Thanks for the answer.
I know what this Gating effect is called. But I can't get it on MK1. Set the voltage on the transistors. I picked them up based on their gain and leakage....
Got good results. But I can't achieve the Gating effect in any way.
Now my MK1 sounds something like this: https://youtu.be/VVYP7-ub_tk
As you can see, there is no strobing, but it doesn't sound bad.

[bmsiddall]

I recently built a Ge NPN Mki which was nearly stock, no trimmers (i used 470k//470K on Q2 base to change the sweep of the attack knob).  I ended up using a 2N1306 for Q3 as it gave me about 8.5V on the collector.- gives a lovely bacon sizzle to the attack.

Q1: HFe 70, leakage of 400 µA+ to get emitter voltage to 2 V. 
Q2: HFe 127 and moderate leakage of about 250 µA
Q3: low leakage appears to be the key on this transistor to get collector voltage to about 8.5 V.  Ended up with HFe 101 and 50 µA leakage.  Gains up to 135+ don't seem to matter much.

[Steben]

It's called "gating."  I've never messed with the Mk 1 circuit, but I can get a nearly identical sound with my Fuzz Factory clone.  (And could that dude not find any shirts that fit?)

Thanks for the answer.
I know what this Gating effect is called. But I can't get it on MK1. Set the voltage on the transistors. I picked them up based on their gain and leakage....
Got good results. But I can't achieve the Gating effect in any way.
Now my MK1 sounds something like this: https://youtu.be/VVYP7-ub_tk
As you can see, there is no strobing, but it doesn't sound bad.

Not bad? That's overbritishing the situation here. It is gorgeous.
Old school circuit, prone to different transistors. Every pedal has its character.

[chriscustom]

Not bad? That's overbritishing the situation here. It is gorgeous.
Old school circuit, prone to different transistors. Every pedal has its character.

Thanks. You're absolutely right.
I tried different transistors and get different sounds. And they all sound different, which is very good!
Now there is a gate. Q1 - MP40A, Q2 - AC128, Q3 - MP41A. The sound is very good. So the same great results with Q3 - P416B.

[bmsiddall]

Chris, can you post voltages and hfe/leakage if possible?  For the record 

[chriscustom]

Yes, of course.
Now I built it like this:
Q1 AC218 88/298, Q2 AC128 95/399, Q3 MP41A 100/106
Voltage: Q1 Ue - 1.89v, Q2 Uc - 2.8v (max attack) - 9.07v (min attack), Q3 Uc - 9,24v; Ub - 0.012v
Battery voltage: 9,37v
Very interesting results can be achieved if you install a 10K pot with a 100/150 Ohm serial resistor in the Q2 collector. By changing the bias within a small range, you can compensate for the temperature dependence of germanium transistors. Well, and get additional sounds. Base Q2 I installed 220 kOhm
Good luck and interesting events for everyone!

[Steben]

I find it striking some mk1 and mk2 can be cleaned up with guitar volume and some not. Is that simply because of very large leakage? It means you can choose your character by leakage. It becomes a quality.

[chriscustom]

My MK1 is not clearing. But MK2 and MK3 are very well cleaned.

[Steben]

My MK1 is not clearing. But MK2 and MK3 are very well cleaned.

I think this applies to most mk1 vs mk2 and mk3s. However, some 1s clean up and some 2s less. I guess it is about leakage.