MBFX
Well-known member
I really like analog octave up, and I have been messing around with one on my breadboard today. I used the Tentacle schematic to start, with 2N5089 and 2N3096 transistors, and 1N4148 diodes. This works well, and sounds pretty good. I have a bunch of transistors and diodes to choose from, though, so I played around with different values. Here are my impressions:
For the PNP transistor, a 2N5087 gives a clearer signal with less noise and a little more boost. It's also dirtier. Germanium transistors are wasted here unless you make a Darlington, and, I mean... why do that?
For the NPN transistors, you can change the tone and behavior of the pedal significantly by changing them around. Try to find a pair with similar beta for best results. 2N5088s are almost identical but noisier. BC548s are darker. BC109Cs, one of my favorites, are dark, fuzzy, and work great with bass/low tunings. MPSA18s give a very strong octave and are very loud and bright. Anything lower gain than around 500 doesn't work well, compared to these.
For the diodes, I couldn't find anything that sounded better than a matched pair of 1N60s. 1N34As were a close second. For silicon, the called-for 1N4148s are the best.
I also tried mismatched transistor/diode pairs that had matching beta/Ir and Uf. This has unpredictable results regarding the tone, but the octave up is pretty solid as long as things match on paper.
For the PNP transistor, a 2N5087 gives a clearer signal with less noise and a little more boost. It's also dirtier. Germanium transistors are wasted here unless you make a Darlington, and, I mean... why do that?
For the NPN transistors, you can change the tone and behavior of the pedal significantly by changing them around. Try to find a pair with similar beta for best results. 2N5088s are almost identical but noisier. BC548s are darker. BC109Cs, one of my favorites, are dark, fuzzy, and work great with bass/low tunings. MPSA18s give a very strong octave and are very loud and bright. Anything lower gain than around 500 doesn't work well, compared to these.
For the diodes, I couldn't find anything that sounded better than a matched pair of 1N60s. 1N34As were a close second. For silicon, the called-for 1N4148s are the best.
I also tried mismatched transistor/diode pairs that had matching beta/Ir and Uf. This has unpredictable results regarding the tone, but the octave up is pretty solid as long as things match on paper.
