First attempt at drawing a schematic...made it louder (Sound Clips Added)

[patrick398]

Greetings Comrades.
My last post was concerning a modded Os Mutantes Fuzz i was working on. I had a go a putting a vero layout together which, much to my surprise, worked. It has blendable input caps, an extra gain stage, and a pot for biasing Q2 and Q3 (I also changed a few resistor and capacitor values). It sounds great but it just lacks a little volume. I drew this schematic on schematic.com and as far as i can see it is all correct. Would be nice to have a few pointers regarding certain conventions it's good to follow though. Am i right in thinking the 22k resistors after Q2 and Q3 are limited volume? Or is it a combination of those and the 100k pot at output?
Thanks!

[patrick398]

Forgot about one of the caps. Also trannies are BC108 not BS108!

[Ben Lyman]

Hi Patrick, nice job for your first schematic drawing!
I noticed you have a 1k5 parallel to your volume pot at output.
This is going to turn the total value to somewhere less than 1k5 and send most of your signal to ground.
Pull the 1k5 and see what happens

[patrick398]

Thanks for the reply
Yeah that makes sense! The 1k5 in parallel with the output pot is on the original schematic which i was working from:
http://turretboard.knucklehead.dk/wp-content/uploads/2012/04/os_mutantes_schematic.jpg
Could i be getting less volume because i've added an extra set of clipping diodes or is it because there's also a 1k5 resistor going to ground after Q2?

[swever]

What is the switch you added in the second version "around" the transisotrs supposed to do?

[patrick398]

It brings in a 50pf cap between base of Q1 and Collector of Q2 which introduces lots of fizzy noise. Not to everyone's tastes but it reacts well with the tone and bias pot which i like

[GibsonGM]

Try bypassing the 2nd set of clipping diodes - that should give you a lot more level.

[swever]

Or maybe use leds instead of the secont pair of 914's.

[GibsonGM]

You could also double them up...2 diodes or LEDs in each direction, to raise the level at which clipping occurs...

[patrick398]

Will bypassing the second set of clipping diodes or doubling them up result in less fuzz? Just done a little reading on diode clipping but i'm still unsure of exactly how it works

[swever]

Yes, I think adding diodes in series will raise the clipping threshold.

[patrick398]

Whipped out the 1K5 resistor and that's done the trick. Holy Moley it's loud now haha.
Thanks for your help again people! Off to read about diodes until my head hurts 

[duck_arse]

too loud? try a 10k vol pot instead of 100k. the 22k before it will set the loudest out level, along with the pot value.

and - I think you need a resistor in series with Q2 collector and the pot, to prevent putting the full supply across it. maybe 1k will do.

[patrick398]

Thanks man, i think the volume is perfect now. Too loud is a good place to start, then just go up from there.
Do you think that 1k between Q2 and the pot is essential? I just screwed the back onto the enclosure and undoing all four screws seems like an awful lot of effort right now. Am i at risk of frying that transistor? 

[Ben Lyman]

Whipped out the 1K5 resistor and that's done the trick...

Great idea! Who thought of that? 

[duck_arse]

Thanks man, i think the volume is perfect now. Too loud is a good place to start, then just go up from there.
Do you think that 1k between Q2 and the pot is essential? I just screwed the back onto the enclosure and undoing all four screws seems like an awful lot of effort right now. Am i at risk of frying that transistor? 

frying - possibly yes. if you've had the nob twisted to both extremes on that pot, and the transistor is still alive, then maybe no, instead, and leave it alone.

[patrick398]

Yeah i've had to at both extremes and have been playing around with it like this for a couple of days now so i guess it's fine? Sounds great at one extreme and don't get anything at the other extreme

[duck_arse]

..... and don't get anything at the other extreme

stay away from this extreme. that's one use of the extra resistor, as a stopper or limit. for your next build, for sure.

[patrick398]

Ok thanks a lot for the heads up
Just out of interest (if it's not too complicated or time consuming to explain) what exactly is happening at this extreme?

[patrick398]

For anyone that's interested, here are a couple of sound clips from this pedal. Definitely not everyone's cup of tea but personally i love nasty, spluttery, weirdness. The cap on the switch is certainly going to seperate the men from the boys too
First clip is 4.7u input cap, second clip is 6.8n input cap and third clip is with the cap between Q1 and Q2 switched in

http://www.filedropper.com/osmutantesmodbuild-170820172035

(Didn't know where to host them so it's this crappy download file unfortunately)

Peas x