why won't ac187s work in bazz fuss?

[CoolJohnny]

cannot seem to get any usable sound out of the time-tested circuit. ive done si/ge hybrids before but this paid of ac187s doesn't seem to want to work. ive tried moving the collector resistor in all kind of directions to new avail. the only thing that has worked has been a 2n222 in q2 with one of the 187s in the q1...just barely inserted into the breadboard, but backwards. various silicon combinations work fine in same sockets. what gives?

[23]

just a little heads up but some trannies have ummm.... strange pinouts.... has far as why they wont work in both Q1 and Q2 dont know... I had similar issues with a Germ fuzz wouldnt work right with both ge's but with a silicon npn in q2 worked great??? go figure.... hope this helps some

[mac]

The problem is leakage. If q1 is leaky then it will be multiplied by q2 gain.
I solved this problem by adding a resistor to ground between q1 emiter and q2 base in a home made darlington version. This resistor shunts some leakage to ground, but the value depends on gain, leakage and temperature, so a pot is needed.

This is my working Ge version:
http://www.diystompboxes.com/smfforum/index.php?topic=60531.0

mac

[CoolJohnny]

i never thought about the leakage issue. that ge bazzfuss layout you referred me to is the very one im using. it works quite well with the AC128s i have. crunchy with a great midrange snarl and some decent bottom end. with the same setup using the AC187s i do get some sound but it is very faint, well below unity. perhaps some combination of the two will work. ive had great success in the past with hybrid versions using 182s abd twice using some nameless old rca transistors i took out of a waterlogged old heathkit; no biasing needed. bur for some reason i cannot let go of the desire for a 187 version. will try to test leakage somehow. thanks for the tip...

[Dragonfly]

i never thought about the leakage issue. that ge bazzfuss layout you referred me to is the very one im using. it works quite well with the AC128s i have. crunchy with a great midrange snarl and some decent bottom end. with the same setup using the AC187s i do get some sound but it is very faint, well below unity. perhaps some combination of the two will work. ive had great success in the past with hybrid versions using 182s abd twice using some nameless old rca transistors i took out of a waterlogged old heathkit; no biasing needed. bur for some reason i cannot let go of the desire for a 187 version. will try to test leakage somehow. thanks for the tip...

Are you trying to use the AC187's in the same build that had the AC128's working ?

AC187 = NPN
AC128 = PNP

[mac]

Are you trying to use the AC187's in the same build that had the AC128's working ?

AC187 = NPN
AC128 = PNP

I posted this some ago, a NPN-PNP version of the Bazz Fuss.



I guess it could be adapted for Ge transistors by using the same trick, a resistor from q1 emiter to gnd.

mac

[CoolJohnny]

well perhaps they are not AC128s after all.  i bought them a couple years ago from smallbear. they have medium length cylindrical bodies with no writing on them, not all that shiny, no little lip or tag thing on the bottom; only a single blue dot on one side near the bottom of the cylinder that i think denotes the emitter.

i've used them in many breadboard projects in this fashion with positive 9V power supply and no problems. the 187s are the ones acting like they are PNP and i simply don't have the polarity right. what the hell am i missing here...?

thanks for posting that hybrid bazzfuss by the way. i'll have to try it.

[rnfr]

i just made a vero layout for mac's ge bazz fuss.  haven't had a chance to verify it yet tho.  it's in my gallery, link is in my sig.
   
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[mac]

i just made a vero layout for mac's ge bazz fuss.  haven't had a chance to verify it yet tho.  it's in my gallery, link is in my sig.

Please add this legends to the layout: "breadboard it first as Ge are tricky to bias", "bias changes with temperature", and "the value of pot R3 and R1 depends on leakage". A very low leakage Ge might need a 100k or higher. I guess that R1 should be marked as a trimmer. And you can omit D3.
The problem with this project is that as I said above q1 leakage is multiplied by q2, so if you are using leaky Ge and do not know much about bias and Ge inconsistencies, you will find it hard to bias.
R3 is there to shunt some leakage to ground: as leakage increases R3 decreases.
May look simple but it is not.

mac

[CoolJohnny]

i actually got quite a good sound using mac's ge bazz fuss layout above using AC128s. they were pretty easy to dial in a good sound and do not appear all that susceptible to temp (i left them in the windowsill and tried again, they were only a little bit off. other results:

1. with this configuration, i was also able to use a diode pair on the output, ommitting the one on the first transistor. although this might not always work, but using a 33k in R1 position ive had very little trouble with the circuit. used various pairs of germanium, silicon, LED, and zener diodes. all good, cannot decide which is best. i see a rotary diode selector in the future of this ohe....

2. it does not like the gain pot i tried to put onto it, but on a strat and les paul junior both with treble bleed networks it good chimy and clean with a little volume rolloff.

3. input caps that sound best are poly films, .01uf and .022 uf. anything bigger and we get into muff territory. on the outpur, .001 is nice and raspy, .01 is nice but a little nasaly. best has been a little yellow 10pF. some low value elctros would work as well for a bigger, fatter sound. i used a .33uf electro that sounded absalutely sick. too sick for me in fact.

thanks for all the help so far from everyone who has responded. i think the 187s i bought will end up in a treble booster or something.