Bazz Fuss - first pedal design project!

[rob.reido]

Hi guys,

I've been working of a version of the pretty ubiquitous Bazz Fuss circuit, in order to get the knack for pedal design and prototyping, and I thought I'd post my journey on here as I go along, as a helping hand for some other beginners, and to get a little help myself!

I started out with this variant from Tonefiend's DIY Club:



I didn't really like the variable input HP tone control, so I changed it to a post-clipping Big Muff-style LP/HP panner, with the two filters arranged to give a mid hump, rather than a mid cut. I also found the original had WAY too much bass at the input, particularly on humbuckers, so I dropped the input cap value. This gave me this schematic:



I really like the tight low end, and the tone control has a great midrange growl that I'm not used to from a fuzz.
My only complaint now is that, with the volume maxed, the output sounds about as loud as (if not slightly quieter than) when the circuit is bypassed, which makes the volume pot pretty redundant. I've got a few 2n5088s spare, and I'd like to add a simple common emitter amp with a fixed gain of about 2 or 3 (ie. 6-10dB) after the tone control, to beef up the output and make the volume pot useful, but I can't seem to get one working.

If any more experienced builders be able to draw me up a quick schematic for one, that would be greatly appreciated.

I'll be posting more updates as I get past the breadboarding stage, and start laying out for stripboard (and eventually assembling!). I've been really enjoying the project so far, and I can't recommend it enough for anyone looking to get their teeth into circuit design (or just looking for a cool fuzz!)

[niektb]

I think the problem you're having is a passive tone pot driving a passive volume pot. If you insert a unity gain buffer (Google emitter follower) in-between, I suspect your issue will be solved

[duck_arse]

copy directly the last transistor make-up stage of the big muff pi. or the fender blender. or any of many other circuits making up post tone.

[antonis]

Q1 100k output impedance is awfully high for driving tonestack..

That said, you have two choices:
1. Lower Collector resistor value down to 10k & Emitter pot down to 1k..
(actually turning it into Deluxe Bazz Fuss..)
2. Use a BJT, wired it as buffer (Emitter follower), between Q1 output and tonestack..

P.S.1
Try duck_arse suggestion for output recovery stage only after one of the above choices implementation..
(in the mean of it's a bit "silly" to recover an unnecessary and avoidable loading loss.. - you can see that tonestack impedance is effectivelly set in parallel with 100k Collector resistor, severely dominating equivalent Collector load, hence Q1 Gain..)

P.S.2
I presume P.S.1 will result into no cider on the compliments of Stephen for a week or so..

[duck_arse]

futher to antonis's suggestions, you'd get better results if you changed the 2n5088 to a 2n5089 or similar, or a darlington.

[rob.reido]

Q1 100k output impedance is awfully high for driving tonestack..

I don't know loads about input/output impedances, but I'm assuming this is to do with needing to have a low output impedance coming out of the common emitter clipping stage, and a high impedance going into the filter stage?

[antonis]

Quite right but not exactly.. 

Without messing with any configuration gain formula (which is depended on particular CE amp topology) Collector load is a standard parameter in gain numerator fraction (in the mean of the higher the Collector value the higher the gain - period ('cause it's a very brute approximation and I already see many guys comming with bad intentions..) )

Collector impedance should be considered any impedance seen when looking back to the Collector..
For elementary analysis purpose, the above is Collector resistor in parallel with any following configuration input impedance..
(e.g. a CE amp with Collector resistor of 10k & Emitter resdistor of 1k driving a following stage of 10k input impedance exhibits an overal gain of 5..)
It's exactly the same as considering an unloaded stage gain and then implement Out-In impedances voltage dividing effect..

Here, particular tonestack items values are calculated for tonestack to be driven from a source of significantly lower impedance than tonestack's one AND following impedance driven by tonestack been significantly higher..
(if the later isn't utilized, implementation of duck-arse suggestion shall settle things down..)

[anotherjim]

You can play with that tonestack here...
https://www.guitarscience.net/tsc/bigmuff.htm
You can see what happens with different source impedance (RIN) and output load (RL).
Or if you run Windows, download a program...
http://www.duncanamps.com/tsc/download.html