Percolator Transistor Question

[matmosphere]

What is the hfe of the 2n404a? I've been playing around with the percolator and jerkulator circuits a bit, but I don't have a 2n404 so I thought I'd see what I have that's close.

[claytushaywood]

Im not sure the hfe on original percolators is definitively measured.  I know smallbear sells 404's between 50 and 200hfe.  I've mostly seen numbers between 100 and 200hfe.  I've had great results with 175hfe.

I believe the 2n404 is kind of important to this circuit.  Maybe not though.  let me know you're results!

[matmosphere]

Thanks, that's somewhere to start. I've got a few things in that range to experiment with.

[Bret608]

The one I got from Smallbear was 57 hfe. I think you can get away with pretty low gains in this circuit for the germanium.

[matmosphere]

Also good to know. I have a few low hfe ac128's that I'll try out.

[cajone5]

I built one that sounds killer with transistors around 50hfe

[midwayfair]

It actually doesn't matter that much because of the way the circuit works. The bias is going to be set by the resistance of Q2+ R4 on the emitter of Q1, which varies based on the signal (which runs into the base of Q2 and changes the resistance between its emitter and collector). R1 is also a TON of negative feedback at such a small value. There probably aren't many germanium transistors you can plug into Q1 that will end up with a voltage very far different from 4-5V on the collector.

Plus the original units are both unicorn tears and inconsistently built, so the answer is "whatever sounds good to you." There is no "right" in this case like there is with some fuzzes.

[matmosphere]

Thanks guys, I'm trying to make an octave fuzz based of the percolator. I keep going back to the Escobedo Jerkulator over the interfax for some reason.

When I hook up the transformer Octavia style, I get a huge volume drop and everything starts sounding thin. Do the diodes after the transformer need to be germs or should I try something else.

[midwayfair]

When I hook up the transformer Octavia style, I get a huge volume drop and everything starts sounding thin. Do the diodes after the transformer need to be germs or should I try something else.

The transformer gives you two identical out-of-phase signals. You then rectify those signals with diodes. The diodes have to have low forward voltage because otherwise they'll gate your signal, but the low forward voltage does mean that they clip your signal at a lower level.

So you have two things going on here:

1. A bunch of your signal gets lost when you mix out of phase signals. This is actually why you get an octave effect, so curing this defeats the purpose.
2. Your signal is clamped to a lower voltage by the rectifying diodes. Curing this doesn't help because you want the Fv to be low to pass sound properly.

They don't have to be germanium. Schotky diodes will also be fine. But generic silicon won't work.

If you've included the diodes from the perc BEFORE the transformer, though, REMOVE THOSE. That might help, but I'm not sure how much.

Finally, remember you can always add a make-up gain stage.

[matmosphere]

When I hook up the transformer Octavia style, I get a huge volume drop and everything starts sounding thin. Do the diodes after the transformer need to be germs or should I try something else.

The transformer gives you two identical out-of-phase signals. You then rectify those signals with diodes. The diodes have to have low forward voltage because otherwise they'll gate your signal, but the low forward voltage does mean that they clip your signal at a lower level.

So you have two things going on here:

1. A bunch of your signal gets lost when you mix out of phase signals. This is actually why you get an octave effect, so curing this defeats the purpose.
2. Your signal is clamped to a lower voltage by the rectifying diodes. Curing this doesn't help because you want the Fv to be low to pass sound properly.

They don't have to be germanium. Schotky diodes will also be fine. But generic silicon won't work.

If you've included the diodes from the perc BEFORE the transformer, though, REMOVE THOSE. That might help, but I'm not sure how much.

Finally, remember you can always add a make-up gain stage.

Thanks, Jon. I guess I will experiment with a gain stage after the transformer, that's a little more fun than just a clean boost at the end.