Ideas for building a discrete distortion pedal out of BJT's

[bobbysatya]

Hi everyone, I've been wondering lately if it's possible to build a "generic"  sounding distortion pedal that is in the same ballpark as a Boss DS-1 (neither fuzz nor muffs) with only BJT's. When I look around the web, most of the dirt pedal designs that exclusively use BJT's are fuzzes with only one or two distortion circuits. Discrete distortion designs around the net are mostly utilizing either FETs or op-amp chips. To be honest, I HATE FETS! They are hardly available at your local electronic store, each stage must be properly biased manually, and the easier way to get them is either by driving 100 miles away from your hometown or by ordering online. I never find them friendly for beginner or even intermediate DIY builders. Can someone point me to some decent discrete BJT distortion designs? Any share of thought about designing one is also highly appreciated.

[PRR]

> same ballpark as a Boss DS-1
> I HATE FETS!

DS-1 is op-amp and BJTs. There are JFETs in the production unit but they are just bypass switching; you can replace all that with a mechanical switch.

> driving 100 miles away from your hometown or by ordering online.

Welcome to the 21st century. I don't think I could buy a JFET without driving 300 miles, maybe more.

Where I used to live, there might be a JFET within 50 miles but it would be in a bad (low-low rent) neighborhood and no parking.

UPS/FedEx brings me all that stuff, faster than I would get off my @ss and drive far away.

[GibsonGM]

I do recommend you mail order some FETs, bobby...they are not that hard to understand if you build a Fetzer Valve circuit (Runoffgroove.com) and try to understand how it works.  Small Bear has a nice tutorial on this, as well....you can use a pot on the drain and dial in your correct operating range, really not bad once you get the hang of it.

But to your original question...YES, of course you can make a decent distortion with BJT's!  Any amplifying device can do the job.   
Guidelines?   Amplify your guitar...run it thru some clipping diodes...do whatever filtering you like (maybe send some highs to ground...).  You may choose to use 2 stages of amplification to make the amp'ing part clean, and hitting the diodes with a clean signal, letting them do the clipping rather than the BJTs.  All that's needed is an output signal from the (1 or 2) gain stage(s) that's over a couple of volts, depending on your diodes.

Look at opamp based distortions - you can do just about the same thing with BJTs.  I just found one on Youtube..."one transistor distortion".

It won't sound fuzzy if you don't use the TRANSISTORS in a distorting mode...if you use them just to cleanly amplify, and hit some LEDs or 914's, what have you, you will remain in distortion territory      Overdriven transistors DO sound just like fuzz, you're right....so do most opamps, IMO. 

[idy]

Look up Electra Distortion. Oh so simple, who needs more? Spawned many a boutique distortion with fancy name and promo copy.

[Gus]

Search this forum there have been a few BJT circuits over the years

[teemuk]

Peavey's "TransTube" preamp circuitry is principally based on generic BJTs.

[aion]

You could also check out something like this:
http://www.diystompboxes.com/smfforum/index.php?board=16.0

Should be able to sub this out for a gain op-amp in any pedal, including a DS-1. It's not going to provide many benefits for other applications like tone controls, but will definitely provide a different flavor than your standard op amp, and you don't really have to design something new around it.

Boss uses similar "discrete op amps" (actually differential amplifiers) in the BD-2, OD-3 and part of the DS-2, but theirs are all FET-based.

[bobbysatya]

Happy new year everyone! I apologize for taking so long to reply. I had an internet connection problem since christmas. Back to the topic. So, I need your opinions on this since I don't really have an idea of what I'm going to do. I was fiddlin around with bazz fuss circuit not too long time ago and I found that the tone was pleasing. I lower the input cap down to 0.047uF and managed to get a distortion-y tone out of it especially when I boost the circuit with LPB-1 or tube screamer style circuit. The only problem is that I can't get rid of the gated decay. I have an idea of employing a simple constant current source circuit to feed the bazz fuss to keep it from having a gated decay as seen in Joe Davisson's CCS Drive. Do you think this would work?

[duck_arse]

what transistor are you using in the bazz? a darlington (or discrete darlington) often cures the gating.

[bobbysatya]

I have built two bazz fusses. Both used high gain BC549 and MPSA18. Haven't built a darlington version but definitely will. The gating of my  bazz fusses are hardly noticeable, but when I lower the volume knob on my guitar It becomes a low gain fart. I was once putting a 1Meg resistor from collector to base hoping it would cure the gating, it worked but the gain dropped considerably. This circuit doesn't clean up as good as a well biased Fuzz Face does. Does the darlington version completely cure the gate in your opinion?

[duck_arse]

I dunno. I built it with mpsa13 because people said single bjts sputtered.

I've only recently fixxed the vol control on my guitar, I suppose I could give it a listen in the daylight hours.

[bobbysatya]

I will try to build a darlington version tomorrow before taking a further step in modifying the circuit. If it really does cure the gate, then my quest is over. My goal is to design a discrete distortion pedal with natural decay (a.k.a not gated) out of BJTs. Being able to clean up with guitar's volume control is not really necessary as long as the circuit decays naturally. Wish me luck!

[duck_arse]

good or bad?

[bobbysatya]

Well I'm not a native English speaker but the word "luck" by itself has a positive meaning until you put the adjective "bad" in front of it. So regular "luck" will be equal "good luck". Let me know if I'm mistaken.

[bobbysatya]

Hey everyone! Wanna make some report here. So, I breadboarded a darlington version of the bazz fuss few minutes ago and I must say I'm very happy with the result. The darlington configuration kills the gate and the fuzz decays more naturally than its single transistor counterpart. I believe if I put a single stage booster with correct filtering I'll be getting closer to what I'm trying to achieve!

[deadastronaut]

try the 'X-ROCK'

nice simple distortion, cleans up really well too...

breadboard it..

http://www.diystompboxes.com/smfforum/index.php?topic=106498.msg978782#msg978782

[bobbysatya]

It seems that your design is promising. In fact I have drawn the pcb layout for the X-Fuzz but I haven't built it because I'm focusing on building a distortion pedal. What do I need to transform the x-fuzz to x-rock?

[deadastronaut]

build the x rock seperately, 

a couple of guys built both xfuzz/xrock into 1...

i think theres a vero for both on there..IIRC..