Need help with a Trotsky Overdrive.

[ayayay!]

Gotta admit I feel silly asking, but I'm missing something obvious here.  I'm using this schem, but not the layout.   



The problem is it won't even come close to unity gain.  It works, but doesn't work well.  I've used N3904s and even 5133s, which should knock that thing out of the park!  They all test out fine on my meter (between 170 and 230.)  I've built it twice now and get the same result. 

I'm wondering if I have the gain pot wired incorrectly.  That seemed to be a question that came up a lot in other Trotsky Drive threads, but I've tried it a couple different ways now and don't know if it's right.  Can someone please describe to me how you would wire up that gain pot? 

The only changes I made were that I used a 100k pot on the gain and 250K pot on the volume.  Feel free to bash me if that's what my problem is.  Just make it a detailed bashing so I can fix this thing.   

[slacker]

To wire the gain pot the way it's shown connect one of the outside lugs to the R1 and connect the other 2 lugs together and to the collector.

[ayayay!]

Done.  That's how I had it the first time, Slacker.  Thanks for verifying.  So now that that is out of the way, here's the volatges. 

Using an N3904:
When gain knob is maxxed, I get 8.81 volts across the collector.  Minimum is 8.1   
When gain is minimized, I get 8.18 across the Base.  Minimum is .56

And should I be OK on those pot values?  I'd think they would be fine. 

[ayayay!]

Would someone mind taking voltage measurements on theirs and posting for me?   

[kurtlives]

Best of luck with it man...

I had troubles with mine a while a go and posted a thread. Once I finish two more amps and a few pedals Ill get back to it.

I remeber a friend of mine saying it would be pretty low gain with that 50K pot. I think he suggest using 25K maybe he suggested 100K...I forget

[DryRoasted]

When i built mine I had exactly the same issues you describe, then I turned the tranny round and hey presto!  I'm sure you didnt make the same stupid mistake i did, but might be worth a go.

[ayayay!]

Socketed.  Flipped several times.  All trannies test out good. 

Hmmm, I'm looking at this schem and I'm starting to think I may know the answer.  I don't have the pedal in front of me, but I'm thinking I may have wired it with the Input cap going to the 2.2m resistor, then the collector.  It should be going to the 2.2m resistor, then the base.

If that's what it is, then I have the input and the 9V going to the collector, and only the 2.2m going to the base.  I'm starting to think that's it.

I'll let you know (late) tonight.   If that doesn't do it, then I'll load up the layout software and post how I did it so you can all examine it.

Thanks guys! 

[ayayay!]

I'm thinking I may have wired it with the Input cap going to the 2.2m resistor, then the collector.  It should be going to the 2.2m resistor, then the base.

  Yep!  That was it.   

So now that I've had some time to play it it's pretty cool.  Only the last 1/3 of the gain is useable.  Everything before that is crackle, but that could be because I'm using a 100k pot and the schem calls for a 50K.  Plus I'm using a n3904.  Anyone recommend another tranny to try? 

Also the .022uf cap is wayyyy too big.  Muffles everything.  I'll try a .0033 or something akin instead. 

Tonewise I gotta say it was better than I expected with my Tele.  Pretty cool Robin Trower type vibe when I kicked in the phaser.  This pedal could easily be happy with a buffer in it.  It played really nicely with my pedals, even my wah.  Not a good preamp/booster though, which I was hoping for.  That's okay.  It surprising solid gain and worked well with me fiddling around with the knobs and pickups.

I would recommend building one, but again I advise building a buffer in or having another pedal with one.

Oh yeah and it sounded really good with my Dyna Comp.  It could pass for a real pedal and I'd definitely use it in a gig if I could figure out the crackle thing a little more. 

I almost forgot, I used a 1n4001 and a Ge in the clipping.  Yum. 

[gutsofgold]

Any chance of a sound clip?  I built a Unidrive (booster with volume and gain controls) and wondered if the Trotsky is the same idea/sound.

[~arph]

Only the last 1/3 of the gain is useable.  Everything before that is crackle, but that could be because I'm using a 100k pot and the schem calls for a 50K.

Definately

[ayayay!]

Hmm, so would a 25K be OK.  I usually don't like to go down in value with a pot, but I don't think I have a 50k handy...

Just a thought.  Thanks guys.

And I'll try to record a clip by the weekend gutsofgold. 

[kurtlives]

Socketed.  Flipped several times.  All trannies test out good. 

Hmmm, I'm looking at this schem and I'm starting to think I may know the answer.  I don't have the pedal in front of me, but I'm thinking I may have wired it with the Input cap going to the 2.2m resistor, then the collector.  It should be going to the 2.2m resistor, then the base.

If that's what it is, then I have the input and the 9V going to the collector, and only the 2.2m going to the base.  I'm starting to think that's it.

I'll let you know (late) tonight.   If that doesn't do it, then I'll load up the layout software and post how I did it so you can all examine it.

Thanks guys! 

I dont exactly follow what your saying...

http://www.aronnelson.com/gallery/main.php/v/DRAGONFLY-LAYOUTS_0/album17/trotsky+pcb.gif.html

Is that layout correct for what your talking about?

[ayayay!]

Well, remember I didn't use a layout.    I just built it on perfboard from the schem.  The layout you posted looks correct as well.  I don't like using layouts.  They're great, but I learn soooo much more when I build directly from a schem.  I breaboard sometimes too, but for most stuff I just go straight for the perf. 

What I did wrong was I had the input cap (which is C3 on your layout) going to the left side of R2.  Imagine C3 vertically connected to the 2.2M R2.  Like that, it was going into the Collector of Q1, instead of the Base. 

Hey wait a minute!  Looking at the layout you posted kurtlives, there's a 1M resistor going to ground from the input (R4)  The beavis drawing below doesn't have that.

[kurtlives]

The 1M is just a pull down resistor to prevent popping. I notice Andy always uses them...

[ayayay!]

Yeah I thought about that after I posted.  I thought maybe it was for input impedence but realized it's probably for popping.  Mine doesn't pop so I'm not going to bother with it. 

[~arph]

Hmm, so would a 25K be OK.  I usually don't like to go down in value with a pot, but I don't think I have a 50k handy...

Yes, but you will have less gain. The gain is determined by the ratio between the pot (and res in front of it) and the 680R emitter resistor.

[ConanB]

I recently threw together a trotsky using a 2N2222 because I didn't have any of the others handy and it sounds ace. Definetely recommend it to others.

Now to find a few other overdrives to try out. Peppermil next I think.

Anyways, I guess the schem of the trotsky could get confusing with the transistor placement because the close-up of the tranny socket is rotated slightly from what the schem says, regarding the BCE.

[ayayay!]

Just for kicks I threw in a 10k resistor in place of the 3.3k on the 9v feed, and a 25K Linear Gain pot.  Worked great!  Almost no crackle whatsoever, but of course it didn't really "clean up" much on the lower settings.  Still it was better than the 100k pot I was using and it suits my needs.  Definitely sounds be with the Tele though.  I might try a cap w/ lift switch on the diodes to tighten up the flabbyness on the humbucker equipped guitars.