Introducing the slackface

[slacker]

I've been playing round with this for a while and I think it's worth sharing. I admit it's not exactly ground breaking but it's got quite a smooth overdrive/fuzz tone and it cleans up nicely if you back off the guitar's volume. I used BC109s with HFEs of about 350 but other mid gain trannies sound good as well.
I'll post some sound clips when I get time.
Cheers for looking
Revised schematic below

[Joecool85]

Interesting looking circuit there.  I can't wait for sound clips for it!

[petemoore]

   INteresting 100k/22uf arrangement.
  Have you tried a bypass cap on the 2k2...maybe make the 2k2 smaller/adjustabel...
  What DOES that 100k pot sound like there, and would you assumilate it would be good/ as a panel mount pot?
  Then there's the 330k between collectors...
  What is the bias at Q2c with these fixed resistor arrangements?

[Paul Marossy]

Man, I gotta quit coming to this forum. I always see yet another interesting distortion circuit to take for a test ride... 

[slacker]

   INteresting 100k/22uf arrangement.
  Have you tried a bypass cap on the 2k2...maybe make the 2k2 smaller/adjustabel...
  What DOES that 100k pot sound like there, and would you assumilate it would be good/ as a panel mount pot?
 

The 100k pot is basically a gain control, when it's turned all the way towards the 2k2 resistor the 22uF cap acts as a bypass cap for the 2k2 and you get maximum gain. Turning the pot the other way rolls off the gain and some of the high frequencies, I think it must load down the input a bit.
I was originally going to have a fuzzface type gain control but I didn't have any pots of the right value so I came up with the 100k pot idea. The pot's worth having as a panel mount, but like a lot of fuzzes you can just leave it on max and use the guitar's volume control.

Then there's the 330k between collectors...
  What is the bias at Q2c with these fixed resistor arrangements?

The 330k is only there because I originally had a decoupling cap between the 2 trannies and it was part of the biasing for Q2. While I was experimenting I removed the cap and the lower bias resistor off Q2 and left the 330k in there. I think it looks stranger than it really is because of the way I drew the schematic, if you think about it connecting Q2s collector and base it makes a bit more sense. It doesn't do a lot to the overall gain of the circuit but it reduces the noise, I don't really understand what it's doing, hopefully someone can explain it. Q2s collector biases to about 4.25 volts.

[petemoore]

  I would think the 330k influences biasing, but also would act as a 'damper' being between the two collectors, ie as one is going up the other is going down swing...there would be a voltage difference there...how much... ? ... would be interesting to switch or pot that position to see what different resistances 'do' with the position the 330k is in. Kind of a 'new' one on me.
  As long as it sounds cool...that's what matters.
 

[Paul Marossy]

I built it today, and it really frustrated the heck out of me. All I can get is an occassional splatty sound out of it. The collectors are measuring only 1.2V or so with a 9V battery putting that is putting out 8.3V, and I can't see where I made a mistake (using BC109s). 

I guess I'll just start over... 

[slacker]

Cheers for having a go, shame you're having trouble with it. I don't know if this will help but I've redrawn the schematic which makes the 330k resistor connections a bit more obvious.



Here are my voltages, battery 9 volts
Q1
C 1.64
B 0.64
E 0

Q2
C 4.80
B 1.64
E 1.01

I did find that with some trannies I got a splatty sound or none at all, you might need to adjust Q1's collector resistor to get it to bias properly. The only other thing I can think of is the gain control might be wired wrong, so that Q1's base isn't getting any voltage. I think the schematic is drawn correctly but just in case it should be like this. One outer lug to Q2's emittor, the other outer lug to the 1K resistor, the middle lug to the 22uF cap to ground.

Here's a quick sound clip of mine, the gain's on max and the first half of the clip is with the guitar volume at about 7 then the second half's flat out. The guitar's a Tokia Silver Star > slackface > condor > sound card.
http://www.eskimo.plus.com/fxstuff/slack.mp3

Hope this helps

[Paul Marossy]

Hmm... that's the way I have it wired up. It must be my transistors then. I'll try foolin' with that Q1 collector resistor as that seems to be the problem. Right now, I basically get no sound with passive pickups and real splatty sounds when using a guitar with a hot preamp in it. Nice and nasty sound, BTW. 

[slacker]

just a cheeky bump really, but did you have any luck with this?