Build report: Mutantes Fuzz

[Harry]

Oh I was thinking ya'll could see it better my laptop has a monitor about 8". 

EeePC? 

No a very large cell phone. 

[biggy boy]

Hi
I just tried out this circuit, using the mods in the schematic below.
The circuit right now is very noise and picks up radio stations when I disconnect the ground wire that goes to the amp, from the board.
It works I can play though it and hear my guitar, but its very noisy in a bad sense. Sounds like a staticy out of tune radio channel.

I took some measurements and found the Q2 collector to be to high.
So I guess I have to put a larger resistor in there?? until it's 4.5volts Right??

What should the collector voltage be for the the first transistor Q1, should it be around 4.5v also?

Note that I used 2N3904 transistors and sili diodes.
Here the numbers

supply= 9.26v from a battery

Q1
C = 7.7v
B = .662v
E = ov

Q2
C= 9.05v
B= .621v
E= 0

Edit:

Back to the basement!
I'm going to take out the collector resistors and put in trim pots and make some ajustments.
See what happens.






Thanks!
Glen

[JasonG]

I cleaned up the pcb layout from that vintage mutantes article  a while ago. I will post it in the layouts gallery when I figure how to do that again.

[biggy boy]

OH getting close it's starting to sound good
My trim pots wouldn't fit in so I soldered in some sip pins on the board. I have been socketing different resistors taking measurements, almost there.
I'll update the schematic with the right values once I get it biased right.

I'm still interested in knowing what the correct bias voltage for Q1 collector should be.

[biggy boy]

OK
so far I'm getting the best sound with both transistors biased at 3.5v.
To get this I have a 10k on the Q1 collector and a 5K on the Q2 collector The complete opposite of the schematic that was originally posted.

It sounds really fuzzy with this setup
Now I just have to get rid of the hissing noise that is there all the time.
I tried putting a 47pF cap across the input to ground, but that did nothing.
Is there something else I can try to get rid of the hiss.

The board it just sitting on my bench (no box) with jumper running from the board to the guitar and amp cables, I have not added the jacks yet.
it's kind of good it didn't work the first time, It makes you have to figure things out and I'm learning stuff. IE: biasing
Been fiddling and playing with this board for about five hours now.

[Gus]

I am not a fan of the bias used in this effect.
  Temp and Hfe affect it.  If you want to adjust the bias adjust the 3.3meg and 1meg base to 9VDC resistors.
  Measure your transistors and note what the resistor change does to the collector voltage
"The Art Of Electronics" has a writeup why this bias is not the best.

[biggy boy]

I am not a fan of the bias used in this effect.
  Temp and Hfe affect it.  If you want to adjust the bias adjust the 3.3meg and 1meg base to 9VDC resistors.
  Measure your transistors and note what the resistor change does to the collector voltage

Thanks Gus
I'll give that a try.

[Gus]

Good to read you posted the best sound was at 3.5VDC.
  Myself and others have posted over the years not to get stuck thinking 1/2 the supply 4.5VDC for a 9VDC supply is the best.  It depends sometimes 1/3 or 3/4 or 1/2 supply etc sound "better"

[biggy boy]

OK I've taken a cap 47pF and tried putting it in every place I could think of to quite this hissing down no luck.
Does anyone have any pointers to send me in the right direction?

I went over my solder joints again thinking maybe a dry joint. still the same.

Should I try different transistors? Maybe this type of biasing circuit doesn't like 2N3904??


Thanks
Glen

[bluesdevil]

Biggie Boy - Check the polarity of your 10uf caps.

[biggy boy]

Biggie Boy - Check the polarity of your 10uf caps.

Thanks for the advice!
I checked my board and I have them the same direction as in my schematic.
I believe thou that the first one doesn't matter because that is an ac signal?

[bluesdevil]

Yeah, I got mine on the breadboard and it works both ways at the input. . This thing works with every combination of transistors I threw at it without messing with the biasing, so gotta be something in your layout or soldering if the 2nd 10uf is correct

[biggy boy]

Yeah, I got mine on the breadboard and it works both ways at the input. . This thing works with every combination of transistors I threw at it without messing with the biasing, so gotta be something in your layout or soldering if the 2nd 10uf is correct

What are your voltages on the two tranies?

[bluesdevil]

These are transistors I settled with (for now!).
Q1 collector = 8.25
Q2 collector = .625 (while playing) .086 (while not)
Q1 is 2N2222A hfe 150
Q2 is BC184L hfe 460

Those seem like weird readings, but that's what I got. I have a dodgy connection somewhere that I have to wiggle once in a while, so that may account for it.

[biggy boy]

These are transistors I settled with (for now!).
Q1 collector = 8.25
Q2 collector = .625 (while playing) .086 (while not)
Q1 is 2N2222A hfe 150
Q2 is BC184L hfe 460

Those seem like weird readings, but that's what I got. I have a dodgy connection somewhere that I have to wiggle once in a while, so that may account for it.

Thanks for taking the time to take the readings.
Yes it is funny
I tested for hours yesterday and had the collector voltages all over the place and it all sounded ok.
Q1 high Q2 low and visa vera.....
Both high and it was bad. Both at around 3.5 good. One high one low good also.

[bluesdevil]

No problem, Biggy. This circuit has actually driven me nuts because as soon as I get it to sound right to my ears, something changes and I start swapping parts again.... I think Gus is right about the bias configuration not being very stable. I notice now as I was just playing  it can go between a glitchy slightly gated fuzz to a thicker smooth sound.... I need to rip this off the breadboard and get on with something else, haha!

[Uma Floresta]

Well, I finally got some of the original transistors (BC109c) in there. With those and the missing 500pF cap in there, it does sound more like a square wave, as per the intentions of the original designer. The first pair I tried in there gave me major radio station interferance and noise, but another pair I tried had absolutely no noise - in fact, they gate toward the very end of the sustain. It gets some major sag when put in front of one of my OD pedals - very fun.

After all the single transistor OD experiments I did, I decided to just build a copy of the Lovepedal Woodrow (single transistor into clipping diodes to ground) and have both effects in the same enclosure (USA Big Muff enclosures). I should be done with that one soon - it's one of the lowest parts count drives I've ever seen. 

[Gus]

Have you looked at this/
http://www.diystompboxes.com/pedals/mbb.GIF

Buffers and tone control added the Bee Baa distortion section.  Not the textbook bias used with the cap bypassed emitter resistor for max gain.  You can tune the mud with the caps between stages and the tone control is more of tilt control.

You might want to change the 2nd transistor collector resistors to one 10K and connect the tone control input cap to the collector the loss in the stack might be enough.

Have fun, Two cascade stages are fun.

[GREEN FUZ]

OK I've taken a cap 47pF and tried putting it in every place I could think of to quite this hissing down no luck.
Does anyone have any pointers to send me in the right direction?

I went over my solder joints again thinking maybe a dry joint. still the same.

Should I try different transistors? Maybe this type of biasing circuit doesn't like 2N3904??


Thanks
Glen

I`ve just been auditioning different trannies. With 2n2222`s and 2n3904`s I got loads of undesirable noise. Motorboating,static,hiss, radio stations, the lot. 2N5089`s improved matters but changing to BC108`s cleaned it all up nicely.

[Uma Floresta]

Yes, try some different transistors. A couple of the BC109cs give me no noise at all. Others (including another set of the same transistors) gave me tons of noise and interference.