debugging maestro fz-1a

[brett]

Hi again
good idea about tweeking the base resistance Lucifer. R5 seems ripe for increase (maybe to 10k) - though it will tend to lower the gain of the negative part of the signal. However, because less of the positive part of the signal is 'lost' when Q2 is better biased (base around -0.1V to -0.15V), it should give better sustain, and may wind up giving MORE gain overall.
After that you might increase Q3's base resistor and/or add some collector-base resistance.
cheers
ps I'm assuming that you measured the bias on Q2 with the fuzz pot on 'minimum' If not, it would be handy to know what the range of voltages are for c/b/e on Q2 at max and min fuzz.

[Harry]

measurements were taken with both pots at max. ill get you the bias at minimum when i get home.

thanks for the suggestions guys i will try them out tonight.

[Harry]

ok q2c at minimum is -1.55 at max it is -1.06

[LucifersTrip]

ok q2c at minimum is -1.55 at max it is -1.06

that's not terrible. min should be close to your supply and as I wrote earlier, max should be .8V and lower. just disconnect one side of R7 and see what range that gives you. It should give you .8 and under. Measure the pot when you hear max fuzz, then use a different R7 to give that measurement.

[Harry]

alright now. r9 was raised to 15k (ill probably swap with 22k). q3c measures -1.25. r5 was raised to 10k. q2 measures -.69 now.

q1's emitter is still higher than it's base...

as far as the sound goes, it does the Satisfaction riff convincingly. with bridge pickup selected, tone control open and amp's tone control open (tweed amp) the high strings sound pretty harsh and grainy but can smoothen out a bit when you back off on the tone controls. there's not much sustain to speak of (which i like). no gating. having never played an original unit, should there be any gating? it sounds ok with chords, not bluesy sounding more brash but not unusable. does this sound way off or am i close?

[Harry]

*double post

[brett]

Hi Harry
Because Q1 is an emitter-follower, the value of the emitter resistor doesn't matter too much, as long as it isn't too high. In this case, the value is quite high (10k) causing a fairly severe mis-bias of Q1 (moreso if the leakage is low). I think it'll work better if you change the 10k to 4.7k (or you could parallel a 10k with the existing 10k). That should approximately halve the voltage at the emitter, making things better. Potentially, you could go as low as 1k, but this might bias Q1 almost right and some of the brash sound could disappear. Tune it in until you like it.
cheers

[Harry]

brett, ill try that next time i have a chance.

q2c is now reading -.73 and q3c is -.93.

it sounds great now! i really would like to thank you two once more. i have wanted a fuzz tone forever. my first post on this forum was 8 years ago and i was looking for help getting one of these working. if i remember correctly i was trying to use 2n2222 transistors . yall taught me a few things and i really do appreciate it.

[LucifersTrip]

as far as the sound goes, it does the Satisfaction riff convincingly. with bridge pickup selected, tone control open and amp's tone control open (tweed amp) the high strings sound pretty harsh and grainy but can smoothen out a bit when you back off on the tone controls. there's not much sustain to speak of (which i like). no gating. having never played an original unit, should there be any gating?

That sounds about right...and there's no gating in any of my three originals (60's knockoffs). If I don't feel like the harsh highs on the high strings, I go the complete opposite direction and use neck pickup with treble completely rolled off. It's very cool there, too...

q2c is now reading -.73 and q3c is -.93.

it sounds great now! i really would like to thank you two once more. i have wanted a fuzz tone forever. my first post on this forum was 8 years ago and i was looking for help getting one of these working. if i remember correctly i was trying to use 2n2222 transistors . yall taught me a few things and i really do appreciate it.

killer!   those voltages are right around where it should sound good. play it loud & celebrate!

[brett]

Play it regularly and smile