Help with this noises on Tone Bender MK1 please!

[Rnk]

But...

It's a Fuzz, isn't it..??

yeahh but it's too much "over compressed" practically unusable but lowering the guitar's volume the tone bender sound appears so something's wrong!

[Rob Strand]

Here are the voltages:

Q1:

C: -9,12
B: -0,17
E: -0,20

Q2:

C: -5,90
B: -0,16
E:  0

Q3:

C: -5,35
B: -0,08
E:  0

Other transistor combination that I have makes less blocking distortion and the voltages are basically the same except for Q2C which reads -2,34.

Maybe that says something?

I dont know how to check the polarity of the 25uf cap more than putting it in the correct direction according to the layou

Well to me the Q1 emitter voltage looks far to low.   I'd expect at least 1V, perhaps 1V to 2V (can't remember the exact voltage off the top of my head).  It's exactly the type of thing that would cause what you are experiencing.

The reason it is low is probably because Q1 has low leakage.   One way around it would be to add a large valued resistor from the collector of  Q1 (the negative rail) and the base of Q1.   Perhaps 4.7M to 10M.

I'd fix the Q1 bias voltages first.

The Q2 collector voltage seems OK but it does depend on the Attack pot.  At one extreme it should go upto 8V or so.

The Q3 collector voltage should be quite a bit higher to be set-up like a true MK1.   At the end of the day you can play with that voltage to suit your taste.

[matopotato]

Hi guys, here I am back in trouble again...
I've been trying a lot of combinations of transistors with Ac128, russians... and I always get the same result:

When I use the pedal with my guitar volume from 0-8 it sounds good (or at least I think so...) but when guitar volume is on 10 it sounds crap, completely compressed. (I use log guitar pots).

Also when I pick lightly on 10 it sounds good but if I pick hard, same thing.

It's worse with humbuckers than with single pickups.

Check it out:

https://youtube.com/shorts/M4VX0zsGeC8?si=LmxWimir1r-yMGNa

Any help much apreciated

Thank you very much

This is pretty much how mine works. Tone Vendor MKI from pedalpcb.
Could be how the design itself reacts to strong input. That is why turning up and humbuckers max it out and it gets more gated or compressed.
I seldom push over 3 o'clock on either pot.
Some even like this sputtery effect.
In a fuzz face it is more control from the volume of the guitar but my MKI not as much.
Probably a contributing factor why they made MK2, MK1.5 MK3s and other.

[GibsonGM]

Mine does this if driven hard, tho it is the silicon version and I have installed a bias pot.  So, when it happens, I can dial the bias around to make it do what I want.  A little synthy is ok for something, IMO, but I like to dial back the Atari sounds.

[matopotato]

.

[JustinFun]

Mine does this if driven hard, tho it is the silicon version and I have installed a bias pot.  So, when it happens, I can dial the bias around to make it do what I want.  A little synthy is ok for something, IMO, but I like to dial back the Atari sounds.

Hi GibsonGM, do you have a schematic? I've tried and failed several time to get a silicon mki to work properly.

[GibsonGM]

It's not a mk1, it's mkII. Haven't seen anyone put Si's in a Ge design without needing to really mess w/the bias resistors; this is pretty much the outcome of that so here is where to start IMO.

I breadboarded mine first, used a lower gain transistor in Q2, I believe...MPSA42 IIRC.  Then 3904's.  I played w/lots of Q's on the breadboard, putting them in different locations, so you might wish to do the same - I can't be sure WHERE I put the '42, for example! I should've kept better notes. This isn't a 'make it this way' build, you have to tune it to your pref's.   

For a bias trim, I replaced the 47k on Q2 with a 4.7kR followed by a 20k trimmer. On MY build, that gave a good range for Q2 adjustment; when all set - after testing pot on Q3 - I replaced with fixed value R. Then I made Q3's 5.6k a 10k bias POT.   Test it on your own ckt before assembly; there will be a small range of good bias, you want to be sure you can get into that. You have to get Q2 going, then see if the 10k pot does the job well.  I'd like to 'revisit' that, and dial in the range of control better (maybe 5k pot with 2.7k R's on each side), but it does fine for what I do (crackle OK).   Experiment with it!

I never did get REALLY close to the posted ideal voltages, but near enough for real tonebender sounds, I think!

**********Edit: looking at build notes now (scrawl).  Might have to play with the pot value at Q3 collector, I seem to have ended up with (gasp) 27k in that position! 3.3k and 25k pot.    Q2 total Rc came out to 47k, gave 4.5v.   Might be totally whacked, but it sounds good    
I used a 2N3904, MPSA42 and 5088 for Q's.    Probably easier to build stock, then adjust as I did, trying to get a good bias - these notes I'm looking at can't be trusted, may have been "in the middle" at the time.   

[Rnk]

Here are the voltages:

Q1:

C: -9,12
B: -0,17
E: -0,20

Q2:

C: -5,90
B: -0,16
E:  0

Q3:

C: -5,35
B: -0,08
E:  0

Other transistor combination that I have makes less blocking distortion and the voltages are basically the same except for Q2C which reads -2,34.

Maybe that says something?

I dont know how to check the polarity of the 25uf cap more than putting it in the correct direction according to the layou

Well to me the Q1 emitter voltage looks far to low.   I'd expect at least 1V, perhaps 1V to 2V (can't remember the exact voltage off the top of my head).  It's exactly the type of thing that would cause what you are experiencing.

The reason it is low is probably because Q1 has low leakage.   One way around it would be to add a large valued resistor from the collector of  Q1 (the negative rail) and the base of Q1.   Perhaps 4.7M to 10M.

I'd fix the Q1 bias voltages first.

The Q2 collector voltage seems OK but it does depend on the Attack pot.  At one extreme it should go upto 8V or so.

The Q3 collector voltage should be quite a bit higher to be set-up like a true MK1.   At the end of the day you can play with that voltage to suit your taste.

I have tried adding the resistor between Q1 collectors and base and it didn't solved it.
It raised the voltage a bit but still happens the same thing

Wow this thing is driving me crazy....
Maybe keep on searching for more leaky transistors for Q1?

[mozz]

You may need to lower that, try 1 meg, even 470k.

[Rnk]

Here are the voltages:

Q1:

C: -9,12
B: -0,17
E: -0,20

Q2:

C: -5,90
B: -0,16
E:  0

Q3:

C: -5,35
B: -0,08
E:  0

Other transistor combination that I have makes less blocking distortion and the voltages are basically the same except for Q2C which reads -2,34.

Maybe that says something?

I dont know how to check the polarity of the 25uf cap more than putting it in the correct direction according to the layou

Well to me the Q1 emitter voltage looks far to low.  I'd expect at least 1V, perhaps 1V to 2V (can't remember the exact voltage off the top of my head).  It's exactly the type of thing that would cause what you are experiencing.

The reason it is low is probably because Q1 has low leakage.  One way around it would be to add a large valued resistor from the collector of  Q1 (the negative rail) and the base of Q1.  Perhaps 4.7M to 10M.

I'd fix the Q1 bias voltages first.

The Q2 collector voltage seems OK but it does depend on the Attack pot.  At one extreme it should go upto 8V or so.

The Q3 collector voltage should be quite a bit higher to be set-up like a true MK1.  At the end of the day you can play with that voltage to suit your taste.

OKAY.. what I've got so far:

On Q3C I have achieved a right voltage (-8,60V) with a lower leakege transistor.

With a 2M resistor from Collector to Base of Q1 I'm getting right voltages on Emitter (-1,30V)

And in combination with a different transistor on Q2 I GOT RID of the Blocking distortion and It's sounding pretty decent right now.

The thing is, the only transistor that got rid of the blocking distortion is a 1600uA leakeage one... that gives me -2,85/-5,65V on Q2C.
If I put a lower leakage one (150uA) I get a desire (-6/-8,5V) BUT the Blocking distortion comes back....

(The 5nF cap from Input to Ground filters all the crazy high freq noises probably caused by all that leakage...)

Any suggestions?

BTW, I got no words to describe how thankfully I am to all of you for taking time on helping me.
Specially you Rob!!!!

[Rnk]

PROBLEM SOLVED!!!    
 3nF capacitor from the input terminal to ground on the PCB was the solution!!
I started with 1nF and then 2nf but it wasn't enough and then... solved!

Before that I also tried the electrolitic capacitor and some caps across the base and collectors but it didn't seemed to change anything.

Sounding pretty good althought it seems sometimes the mids get scooped and then come back in like a rotary effect... any ideas on this?

Thank you very much man!!

Cool.  3n is a large value.  If I saw that I'd be thinking something is wrong!

Not sure why it has a mid scoop sound.   You should be able to set the tone with the Attack pot.

EDIT: 3pF not nf...   

[Rnk]

PROBLEM SOLVED!!!    
 3nF capacitor from the input terminal to ground on the PCB was the solution!!
I started with 1nF and then 2nf but it wasn't enough and then... solved!

Before that I also tried the electrolitic capacitor and some caps across the base and collectors but it didn't seemed to change anything.

Sounding pretty good althought it seems sometimes the mids get scooped and then come back in like a rotary effect... any ideas on this?

Thank you very much man!!

Cool.  3n is a large value.  If I saw that I'd be thinking something is wrong!

Not sure why it has a mid scoop sound.   You should be able to set the tone with the Attack pot.

EDIT: 3pF not nf...   

SORRY, It's nf yes... facepalm...

[andy-h-h]

Welcome to the world of trying to tune a MK1 Tone Bender - which can often be both slightly frustrating and very satisfying at the same time.  I normally breadboard them first, as you can spend a lot of time tweaking to get good results. 

Apart from testing a few different transistors.  Try reducing the 470k bias resistor on the base of Q2 - anywhere from 180k to 470k can get things working right (or at least sounding different).

It's not unusual for some settings on the attack pot to not sound great.  Occasionally I'll drop down from a B50k to a A25k for this reason (noting the bias resistor value mentioned above).   Some versions of the MK1 have a 33k resistor across the 50k pot for the same reason.

Good luck!