The TrotskyDrive

axeman010 · May 16, 2007, 05:22:51 AM

Hi Dano

Please accept this as a question and not a criticism but is that way of biasing a transistor a little unstable? (Susceptible to variations in temperature and supply voltage)

I am trying to get in to designing with various transistor types at the moment and understanding biasing etc. I think I'm right in saying that this is a Collector Feedback Bias Circuit. I'm a little curious why you choose this method over the voltage divider bias or auto biasing method which seems to be more widely used for pre-amps, boosters etc.

Any insight that you could give in to how the resistor values were calculated would also be much appreciated.

Clive.

DWBH · May 16, 2007, 11:45:04 AM

Instead of those 1N914 and 1N34A, can I use any other diodes?

I was thinking of a 1N4148 to substitute the 1N914 and 1N60 for the 1N34A, I don't know....

[noob mode on]What are these diodes there anyway? Clipping? [noob mode off]

dano12 · May 16, 2007, 11:57:21 AM

Quote from: axeman010 on May 16, 2007, 05:22:51 AM
Hi Dano

Please accept this as a question and not a criticism but is that way of biasing a transistor a little unstable? (Susceptible to variations in temperature and supply voltage)

I am trying to get in to designing with various transistor types at the moment and understanding biasing etc. I think I'm right in saying that this is a Collector Feedback Bias Circuit. I'm a little curious why you choose this method over the voltage divider bias or auto biasing method which seems to be more widely used for pre-amps, boosters etc.

Any insight that you could give in to how the resistor values were calculated would also be much appreciated.

Clive.

Hey Clive, no worries on the questions. The Trotsky drive started out on the breadboard with fixed value resistors to adjust gain.

I tried the traditional bias route, which is usually the better approach, and then for fun, stuck the bias pot up top instead. To my ears, the pot rotation with the second approach was more interesting both from a design approach and sound-wise. The key drawbacks in my approach are pot noise (DC crackle) and more difficulty in finding the sweetspot.

The values for resistors were breadboard trial and error: select a range of fixed values that gave me the gain window I wanted and then choosing the pot value to cover that range.

dano12 · May 16, 2007, 12:14:11 PM

Quote from: DWBH on May 16, 2007, 11:45:04 AM
Instead of those 1N914 and 1N34A, can I use any other diodes?

I was thinking of a 1N4148 to substitute the 1N914 and 1N60 for the 1N34A, I don't know....

[noob mode on]What are these diodes there anyway? Clipping? [noob mode off]

You can use just about any type of diodes for clipping: silicon, germaniums, LEDs, MOSFETs, et. al.

I chose germaniums because they clip at a lower forward voltage and the Trotsky, with its single low-gain tranny, doesn't push a huge amount of signal through the diodes.

Minion · May 16, 2007, 02:30:59 PM

I built a Trotsky last night and I used an Old 2SC968 Germanium Metal Can (T0-52) and ran it off of a 15v Supply and it sounds Pretty Good....I used one 4148 diode and some Mystery Germanium Diode for the Clipping ....I am very happy with it , It isn"t over the Top but Gives a Nice AC/DC type overdrive, good for R&R and Blues type music.......

ambulancevoice · June 04, 2007, 06:47:55 PM

Quote from: DWBH on May 16, 2007, 11:45:04 AM
Instead of those 1N914 and 1N34A, can I use any other diodes?

I was thinking of a 1N4148 to substitute the 1N914 and 1N60 for the 1N34A, I don't know....

[noob mode on]What are these diodes there anyway? Clipping? [noob mode off]

1n4148 is pretty much the same as 1n914
1n60 is the same with 1n34a

frequencycentral · October 03, 2008, 10:27:06 AM

OMG! I just breadboarded this but using positive earth with a Ge PNP SFT353 and two germanium diodes - I can't believe it sounds so good - there's next to no components!

Amazing!

Deserves a bump for n00bs!

bamera · October 03, 2008, 11:49:10 AM

I built the trotskey a few months ago and I love it. Dano´s classy and very organized project pdf made me want to build it...

cheeb · October 03, 2008, 12:08:01 PM

I built a lightly modified one for a friend and he plays gigs with it regularly. He is in love with it and now there are four people in line that want one, and he's having me make another with a clean blend. It's a hit around here.

ayayay! · October 03, 2008, 01:19:00 PM

Yeah, if people would just get past the crackle (which is hardly noticeable on mine,) they would see that it's really a great pedal. I removed my TS5 on my board in favor of this, for boosting my overdrives & distortions. Not that there's anything wrong with the TS5, but the Trotsky Drive just works better for me when boosting.

kurtlives · October 03, 2008, 03:07:55 PM

I like mine...

Badass little box.

morpha2 · October 03, 2008, 03:34:28 PM

Same here. Mine has earned a spot on the chain for sure.

The Iron Chef · October 03, 2008, 08:15:08 PM

The Trotsky Drive was the first pedal that I built to completion.

QuoteDano´s classy and very organized project pdf made me want to build it

.

I built it to spec except for the transistor. no old soviet stuff here so i I first used a 2n2222 then changed to a 2n3904 for a little more gain. sounds fine, nothing over the top, as advertised. Thanks for sharing. My Trotsky, below.

ayayay! · October 04, 2008, 09:21:29 AM

Ahh, another "built into the lid" pedal. Don't see those often but I like the looks of them. Nice "Russian" text as well! Thanks for sharing!

FisTheGoon · October 04, 2008, 12:57:34 PM

Seem a lot have build this pedal.Anyone can upload some sample from TrotskyDrive?Would love to heard some of it.

danielzink · October 04, 2008, 03:01:01 PM

Quote from: FisTheGoon on October 04, 2008, 12:57:34 PM
Seem a lot have build this pedal.Anyone can upload some sample from TrotskyDrive?Would love to heard some of it.

Videos and sound samples here:

http://www.myspace.com/nmgeffects

ehofherr · October 05, 2008, 07:41:10 AM

Quote from: danielzink on October 04, 2008, 03:01:01 PM
Videos and sound samples here:

http://www.myspace.com/nmgeffects

Excellent demo. The sound is very nice...think I might have to give it a try myself!

ConanB · October 05, 2008, 09:30:04 AM

I've had this FX together for a little while now but I need to get off my arse and finish off it's box >.<
Great sound.

DWBH · November 05, 2008, 03:59:29 PM

Just boxed this baby.
I have TONS of output. I put it in a A box, so I had to ditch the volume knob.
The thing is, the gain knob doesn't work. I hear the crackle, but there's no difference in gain level.
It gives me a rather clean boost, a big one, that's for sure, but when using it with dirt boxes it fattens them up, into an creamy almost-fuzz

Oh, and I used LEDs instead of the 'normal' diodes.

frequencycentral · November 05, 2008, 05:52:06 PM

Quote from: DWBH on November 05, 2008, 03:59:29 PM
Just boxed this baby.
I have TONS of output. I put it in a A box, so I had to ditch the volume knob.
The thing is, the gain knob doesn't work. I hear the crackle, but there's no difference in gain level.
It gives me a rather clean boost, a big one, that's for sure, but when using it with dirt boxes it fattens them up, into an creamy almost-fuzz
Oh, and I used LEDs instead of the 'normal' diodes.

You need to use normal diodes for this circuit to clip, as the LEDs clip at too high a voltage. Try a few different ones. The gain control should also then start to function.

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The TrotskyDrive