Pepper Spray Transistor gains/biasing

[Gristlepig]

Hey y'all,

Anyone have any sage wisdom regarding ideal gains for the GE/SI pair in the Pepper Spray?

I built mine up about a year ago and shelved it. It just sounded like a fuzzy, muddy overdrive. I just dusted it off last night and decided to go to town swapping trannies in and out.

I had originally had it set up with a 2N404A with a gain of about 70 and a 2n3565 gain 140. After swapping in and out the 5 2N404A's I've got here and a gazillion different SI's, I've got an improvement with a GE at 190 gain and a 2N2222A at 114 gain.

But it still sounds rather lifeless. Not nearly as raunchy and noisy as many of the youtube videos I've seen. It's definitely lacking that crispness and raunch... Though the diode lift setting sounds plenty sweet and shimmery with the volume backed off on my Jazzmaster...

I suspect the transistors might need a little help in the biasing dept, but I'm unsure as to what I should be looking for in regard to voltage readings. From what I gather, it's not as straightforward as shooting for 4.5v on the collector of Q2...

I appreciate any help you folks might be able to offer.

[nieradka]

i think the ideal gains for the harmonic percolator are lower than that. Ive built several, they sound like the videos online (certainly not just a muddy overdrive,)  with the ge with a hfe vaguely around 50. I used mp16b russian transistors, but really it doesnt seem that picky. 7 out of 10 transistors out of the bag sound right. I used the pn3565 out of the bag without measuring. Hopefully someone can give you better advice.

Are you using the albini specs? And a tantalum for the 47uf (I forget why, but Ive heard its actually important)?   

[Bret608]

I'd be curious to know as well if you're using the Albini or "stock" specs. I haven't tried the stock yet (although I will soon), but my understanding is the Albini might have a bit less gain.

Once I figured out that I had the 2n3565 in backward (for way longer than I'd care to admit!), I liked it a lot. It sounds a lot like on the Albini clips (despite my setup being way different than his). It is the darkest drive I've ever played, and I've heard the stock specs are kind of the same deal. I actually don't like the diode lift; however, the silicon option I have in there (1n914s) is quite good. It turns it into a mean overdrive.

For what it's worth, my 2n404 is 57 hfe; the 2n3565 is 228.

[midwayfair]

This isn't a situation like a fuzz face where you're doing a balancing act on the biasing. It's basically whatever sounds good without oscillating at max gain.

Remember that the gains are multiplicative like in a Darlington arrangement. So using a lower-gain in Q2 is like lowering the gain in Q1. It's just easier to use a trash transistor in Q1. Medium leakage is also fine (and possibly better) there. My Q1 was ~40. I also lowered the gain on both transistors in the Albini specs. For the diodes, I vastly prefer something that clips like silicon.

[Bret608]

One thing that may help also--and you may be miles ahead of where I was when I first built this--would be to double check the orientation of Q2. To my brain, the silkscreen image on the PCB basically said "orient this 180 degrees opposite of where it should be!" 

So with the 2n3565, I had the flat side that indicates the emitter facing "southeast" relative to the top of the PCB ("north"). Turns out it should go "northwest." The same is basically true for the emitter tab on metal-can transistors.

Good luck! I hope this helps.

[Gristlepig]

Thanks for the info guys!

I built it to the Albini specs. How could I not? I've got huge respect for his work on both sides of the recording desk.

So, it looks like I'm barking up the wrong tree with a 190hfe Q1... Perhaps I'll pick up some low gain GE's from Small Bear and see what happens. I tried it against my buddy's Chuck Collins HP a few days ago, not even close. The violence and raunch just isn't there.

I used BAT41 as clippers. I did socket them, so perhaps playing around with some different SI diodes might help.

As for tranny orientation, I've got them right. I even tried reversing them both and individually.

Tantalums? I got 'em in there. I followed the BOM to a T... even even the metal/carbon film specific resistor placement (I can't imagine that would make much of a difference tho..)

I've got another PCB around here. I'll try building one up to stock specs and see what happens.
I've got a friend who wants me to build him one into one of those cool Pedal Enclosure Pro Prism wedges, but that ain't happenin' until I can get mine sounding right.

Looks like i'll be placing a SB order this afternoon...

[das234]

Yet ANOTHER project on my prospects list. 

I see the doc for this has very specific recommendations for which parts to use (and links to small bear to get them).  Has anyone tried using plain old Tayda parts in the Pepper Spray?   

[nieradka]

Ive built with tayda greenie film caps for c2,c4,c7 and a tayda tantalum for c4. Ive heard its important (i forget why) to use a tantalum for the 47uf, Tayda doesnt carry that value, so i got some off ebay. I used some other generic 100pf silver mica from somewhere. I used generic 5% resistors.

I used a ebay russian mp16b for the 404a and a tayda pn3565. For the diodes, any germanium diode should work for the first pair (of course, theres some variation), the second pair I liked a set off oa126s.

I built several and they sound pretty much exactly like the ones in the albini videos.