Nurse Quacky Transistor Selection

[RDV]

There was another "my quacky ain't quackin'" thread recently, and I thought since I ain't done crap lately, I'd try to address the problem. I've got an MC1458 in it just like it's supposed to have, yet it still doesn't quack worth crap. I read that the transistor seems to have a bit of influence over how well the envelope works, and boy is that the truth!

Grab-bag RS type: not too bad

2N3904: bad, distorts and doesn't let go of the envelope worth crap

2N2222: ding ding ding ding, we have a winner, quacks and adjusts wonderfully!!

Socket the tranny and try your crappy-ist possible trannys and ye shall quack!!

RDV

[smccusker]

I used a 2n3904 in mine, sometimes I get this sortof swooshing effect as the envelope closes. Its not coming from the guitar, it sounds like theres a bit of noise or something going through. any ideas?

[amz-fx]

Low hfe transistors work best in the Dr. Quack, as I posted in a message thread last week...  a crappy transistor is often better than a new high priced one!

regards, Jack

[RDV]

Socket it and try trannies till you get one that gives you the response you want. You'll know when you hear it.

Here's a sample of mine with the tranny I liked:
Quacky

RDV

[smccusker]

Socket it and try trannies till you get one that gives you the response you want. You'll know when you hear it.

Here's a sample of mine with the tranny I liked:
Quacky

RDV

Mine sounds alot like that with a 2n3904 in it, if I roll back the pots alittle.
I still dont know where the noise is coming from. Is it possible it could be coming from a bad solder joint or something?

[Mark Hammer]

Getting lucky once or twice, I can understand.  Getting lucky half a dozen times, though, well that's another thing.

I've built a half dozen of these puppies, including a Baseballs which is simply a dual version of the filter section with some bells and whistles, and I have never selected for the tranny.  I know I've used 2N5088's for the Baseballs (as per the factory schem - clearly NOT a tranny with hfe <100), but I couldn't even tell you what I put in the others, and they have all worked.

Am I really THAT lucky, or is hfe more important in some contexts than others?   I'm perplexed.

[amz-fx]

It's not that it doesn't work with the 2n5088 but I believe there is better response & control with a low hfe transistor.

-Jack

[Mark Hammer]

Fair enough.  Is it the sort of thing that depends on, or alters, the trimpot setting?  Alternatively, is it the sort of thing that can be offset by the trimpot setting, or by a different series resistor between trimpot and tranny base (stock is 22k)?

In other words, is the selection critical if you simply want to stick a transistor on the board and not be bothered with farting around, or can a poor choice introduce problems that are NOT easily addressable by a tweak here and larger/smaller value there?

[Albert Kreuzer]

Just built my first of these last week with a BC547 (hfe around 360) and it works quite well. I replaced the .005 and .010 filter caps with .010 and .022 for bass and I'm very pleased with the sound.

.02, ymmv, etc.

Cheers,
Albert