Trotsky Drive Help and Mod Ideas

[Kearns892]

Hey all! Just got back from a summer away from home and the electronics, and naturally one of the first things I wanted to do was get back to making guitar pedals. Today I rigged up a trotsky drive on the breadboard, and it sounds pretty nice, but one thing. I understand this is supposed to be a light overdrive, but even with gain pot maxed (and yes I tried both ways) I get just a little warmth and some buzz (buzz id say is from breadboard being next to computer). I was wondering if this is normal because there is hardly anything there at all. I'm using the 2n2222 transistor.

If this is normal I would like your suggestions as to what I could do to squeeze a little more gain out of this. Also looking for other mod suggestions. Right now I am not using the bright switch, and I may add a diode switch and tone control, but not sure which type would be best suited for this pedal.

Thanks a lot for the help. 

[petemoore]

  Specifically starting with a schematic allows us to convey relevant info.
  Secondly I would do a basic debug on it, just to see if the circuit looks like it should work/is biased.
  Mods...I'd make certain it should be working right before applying mods, voltage measurements, do the knobs seem to work according to logic.
  Schematic please.

[Kearns892]

Sorry, I meant to post the schematic up, but it will be a bit before I can sit down long enough and get voltages.

It's straight from Beavis Audio (thanks a lot for the schematic) only revision is lack of bright switch. I did not use the breadboard layout, just the schematic.
http://www.beavisaudio.com/bboard/projects/bbp_Trotsky.pdf

Also forgot to mention my 9 volt reads about 8.2 volts :/ need to find another one.

[12milluz]

I built this too- never got it working. But its a fine schematic. Anyways, the 8.2 of the battery...that should still work fine.

[WhenBoredomPeaks]

My favourite circuit ever.

The 2n2222s have different pinouts so try it both ways.

But id rather throw away the 2n2222 and put a 2n3904 instead of it there.

Now i share my favourite mods with you.

- I omitted the bright switch entirely because i gonna use GE clipping diodes and they are quite dark.
- I swapped the 2n2222 to a 2n3904 because we gonna need higher output because of the GE diodes.
- I used GE clipping diodes. (they are some random ones, i never heard about them)
- If it is too harsh, try put in a little cap parallel to the diodes like this:



- That cap gonna filter the highs, the bigger the cap the less the highs. Start with 3nf or something like that.
- The input cap gonna filter the lows, i left the stock value in.
- I liked symmetrical clipping more than the others.
- LEDs, 1n914s ,1n4148s gonna have WAY higher output but much less clipping.
-The bigger the resistance of the Gain pot, the bigger the gain. However there are no changes in gain above 50K if i remember well.

This is a pretty easy circuit, the only source of problems could be the transistor orientation imo.

I have pictures of my working breadboard Trotsky, if you still can't make it work, i can post the pic for you.

[Kearns892]

Thanks for the replies, I think I will try a different transistors to up the gain (and I'll take your recommendation on the 2n3904) and a variety of diode combinations to see what I like, but only after I am sure I have the circuit right.
I also flipped the transistor just to be sure, when i did that I got a very low signal and the gain knob didn't really do anything, so I think what I had before was correct.

Now voltages
Battery: 8.5v
Q1 (with gain pot at max)
C: 6.90 v
B: 0.0 v
E: 7.45

[jacobyjd]

The Trotsky is one of my favorite circuits as a boosting utility for gain recovery, etc. I usually use a fixed resistor (33k) instead of the 50k gain control for that purpose...but anyway--I use 2n5088 transistors for this circuit almost invariably (5089 would work well too), and from my experience, if you use silicon diodes, you're not going to get much crunch out of it. Use 1n34a's and you'll get a really nice little distortion.

[ppatchmods]

i have built about 3 trotsky's now and it is a great circuit! As far as the cap next to the diodes, that's pretty much what the switch, just makes it switchable.  On 2 of my builds(one on perf and one on pcb) I've had to do something weird to the circuit! I've had to tie the unconnected ends of r4 and r3 together to get it to work right. One of my pcb circuits worked fine, the other had to me moddified for whatever reason.  I like a 1n34a's in parallel and i put a switch to change to 1n914. It gives it more sparkle and about twice the volume. I use the 2n2222a metal can tranny.

[Kearns892]

So would you all say my voltages and and very light warmth are normal from silicon sym. diodes and a 2n2222?

Petemoore also mentioned biasing, how would I go about that on this type of circuit? I checked the FAQ but the link is broken.

[Kearns892]

I think I have it right, while I would still like for someone to confirm my voltages and would still like to have a little more gain out of it, after switching to the 2n3904 it sounds a lot better. I really like the dark sound you get with the C3, but unless I can squeeze a little more gain I don't know if I will have enough to justify the cost of housing this. Still though, I really like the sound. Still have to try different diodes, thanks for the tips guys.

[ayayay!]

IIRC, I settled on a 2n2222 and 1n4001 + Ge/1n4001 for clipping.  I also got zero crackle using the 2n2222, which was a nice benefit.  Not saying that will work for everyone. 

[ppatchmods]

I got a little crakle but just with ge diodes. on the silicon side it was pretty quiet.
http://www.youtube.com/watch?v=YY_DR4VvJZ4

[Kearns892]

Thanks for that video that obviously demonstrated I have some sort of problem with mine, almost no drive comparatively, and I have used 2222s, 5088s, and 3904s. If someone could please give me the correct voltages that may give me a place to start looking, for now im gonna keep looking this over.

[ppatchmods]

I can't get you the values right now, but I would check all your solder joints and try temporarily connecting the open ends of r4&r3 together. See if that makes a difference.

[ppatchmods]

these may help: http://www.diystompboxes.com/smfforum/index.php?topic=69198.0
http://www.diystompboxes.com/smfforum/index.php?topic=69790.0

[Kearns892]

I'm on a breadboard, went through and checked continuity though at each connection, and the schematic I am working from lists no r4.

Ive been tweaking the parts more, and the gain pot only changes the voltage from 8.1v - 8.45v the base measures 2.61v and emitter is 7.98v which further confuses me. Gain pot doesnt seem to do much, but volume control works.  I think I will try replacing the gain pot with a fixed resistor next, ppatchmods, what schematic did you use?

[Kearns892]

these may help: http://www.diystompboxes.com/smfforum/index.php?topic=69198.0
http://www.diystompboxes.com/smfforum/index.php?topic=69790.0

I already looked through one of these and it doesnt look like I made the same mistake ayayay! made I have my input cap going to base and from base a 2.2 Meg res going to Collector. The other one never saw the issue resolved.

Tried replacing the 50k gain pot with a 33k resistor as jacobyjd did and that didint change anythign, I guess the gain pot wasnt the problem. Changing diodes next...

[jacobyjd]

these may help: http://www.diystompboxes.com/smfforum/index.php?topic=69198.0
http://www.diystompboxes.com/smfforum/index.php?topic=69790.0

I already looked through one of these and it doesnt look like I made the same mistake ayayay! made I have my input cap going to base and from base a 2.2 Meg res going to Collector. The other one never saw the issue resolved.

Tried replacing the 50k gain pot with a 33k resistor as jacobyjd did and that didint change anythign, I guess the gain pot wasnt the problem. Changing diodes next...

Yeah--the 33k trick won't really fix any problems--it's just a way to get it down to 1 knob as more of a dirty boost than a distortion. Good luck! Way to stick with it.

[Kearns892]

I understand that, thought i would swap it out instead of the pot though, just because the mechanical side of pots are less reliable, hoping i maybe just ran into a bad pot, but that wasnt the case.

Switched from 1N60 Germanium diodes to 1N914s maybe placebo affect but they sound even weaker. Really stuck, could use some more places to try to find the problem.

Thanks for your support and I apologize for my neediness.

[jacobyjd]

Could you take a clear picture of the front and back of your board?