Cicada build Report

[jmusser]

http://members.optusnet.com.au/~jethro.dog/mypic158.jpg. I finally got around to building this last night, and it made a real nice OD, or Fuzz, but I never did get any up octave out of it now matter how I adjusted the outboard pots, or the trimmers. I noticed on the schematic, Brett had referenced a 1meg trimmer, so I traded that out with the 100K, but to no avail. I then found the original post, and it said that the 1meg was a misprint, so the 100k was correct. I adjusted it as he indicated, with the "Octave" pot adjusted to max, and searched all over the trimmer for a setting that brought in the octave, but no dice. On this same post, I have found where he said "add a 4.7uf cap to the 2.2K at the source of the J201 for more gain and sustain, but I don't think this would help the octave problem. I did initially add a 10uf to pins 1 and 8 of the LM386 to give more output (from another post), and thought that that mod may have something to do with the octave, but in or out it makes no difference with the octave. The addition of the 10uf makes a huge difference in the volume of this thing. The only thing I'm getting which gives an indication of the up octave being present, is a "Bronx Cheer" sizzle right before the note decays while you're set on heavy fuzz. This whole thing is sort of reminiscent of my battle I lost with Tim's Octup circuit, so I'm wondering if it could be tied to my Strat's single coil at the neck? As far as I know, pick up style and manufacturer should only cause problems with volume or responce, and not an up octave, but I sure could be wrong on that. Anyway, if you have a suggestion, I'm all ears.

[brett]

Hi
First thing I'd suggest is to use an audio probe to check that pins 2 and 3 of the 386 are both getting some signal.  An audio probe or sensitive DMM will tell you.  If either pin misses out, you'll only get a fuzz-like fundamental that has a "blatty" finish.  (Sounds like your symptoms). 

The blatty finish is due to signal losses due to the diode forward voltage.  To minimise the effect I added the JFET booster and suggested germanium or Schottky diodes, which have much lower forward voltage (0.3V) than regular silicon diodes (Vf=0.6V).
cheers
   

[jmusser]

Thanks Brett for getting back to me. I will check out everything tomorrow sometime when I get off work. I did use the Schottkeys you recommended, because I bought a batch to use with Tim's effects. I actually have sort of a "warmth" to the fuzz, sort of like I get with the Titan Boost's octave option, but there's no identifiable separate octave. What type of voltages would I be looking for on pin's 2 & 3? Also, if end up with too low of a voltage on either pin what do I need to change to make it sufficient? It sounds like I may not even have enough voltage going past the diode. I'm interested, because I really feel that what ever is going on here with your effect's octave, is also the problem with the Octup. Would this have anything to do with my pick ups not driving the booster hard enough to create the voltage the circuit needs? I'd ask more question's but I believe I've just about approached my quota! I just think it's odd that in both of the circuits, I'm using the same values that Tim and you have had good luck with, and I'm not able to coax an up octave out of it. I almost have the feeling that these circuits are going to be specific to a certain type of pick up, and they'll either have to have some sort of preamp, or their frequency responce is is just not at a level that could ever produce an up octave with these two circuits. I'm just sort of free associating here, and trying to come up with some sort of scenario.

[trevize]

try to match your diodes first, i've used germanium diodes on my ramblers. if you match them you don't need the trimpot.
And turn down the tone pot of your guitar!