Bias resistor ratios

[patrick398]

Just going to knock up a hyperion fuzz quickly but annoying i don't have any 2M2 resistors. I've got 1M and 3M3. From what i understand the 2M2s are being used to bias the bases of the trannies and the Intensity pot and 10k resistors are being used to bias the collectors. I'm assuming there is some desirable ratio between the two but i was just wondering if i can adjust the 10k resistors and maintain the same ratio using 1M or 3M3 resistors. I'd hazard a guess that this might change the impedance of the circuit to?

[antonis]

Without schematic my only proposal should be to place a pair of 1M+3M3 in parallel with another one.. 

To be more specific, 2M2 resistor is used as feedback bias for MPSA18 and should pass slightly more than 1μA current for a Collector bias on 4.5V, resulting in a hfe of about 400..

IMHO, due to feedback bias, 3M3 should marginally work well, biasing Collector lower than less 1V from previous bias with same 10k Collector resistor value or near 4.5V with a 12k value..

Circuit impedance is (hfe X re) // (feedback resistor/Voltage gain) so you can calculate new impedance..


P.S.
Feel free to doubt for my, by heart, calculations, Patirck..

[garcho]

Analyzing Devi Ever circuits can be a bit of an exorcise in futility. Just throw it together and see if it works, that's basically how all DE pedals are made anyway, it's more about mangling the guitar and slapping some trendy graphics on the enclosure then about impedance biasing etc. Use the resistors you have and call it something new. That's not a criticism, there's a lot of musical uses for an infinite variety of manglers and such, but there's not any engineering going on worth doing math for. I respect the "let me FSU and see what happens" ethos, as long as it's honest.

[patrick398]

Without schematic my only proposal should be to place a pair of 1M+3M3 in parallel with another one.. 

To be more specific, 2M2 resistor is used as feedback bias for MPSA18 and should pass slightly more than 1μA current for a Collector bias on 4.5V, resulting in a hfe of about 400..

IMHO, due to feedback bias, 3M3 should marginally work well, biasing Collector lower than less 1V from previous bias with same 10k Collector resistor value or near 4.5V with a 12k value..

Circuit impedance is (hfe X re) // (feedback resistor/Voltage gain) so you can calculate new impedance..


P.S.
Feel free to doubt for my, by heart, calculations, Patirck..

Jeez, how did i not think of paralleling the two resistors haha!

Analyzing Devi Ever circuits can be a bit of an exorcise in futility. Just throw it together and see if it works, that's basically how all DE pedals are made anyway, it's more about mangling the guitar and slapping some trendy graphics on the enclosure then about impedance biasing etc. Use the resistors you have and call it something new. That's not a criticism, there's a lot of musical uses for an infinite variety of manglers and such, but there's not any engineering going on worth doing math for. I respect the "let me FSU and see what happens" ethos, as long as it's honest.

Yeah totally take you're point, i'll just throw some shit at it and see what sticks...or maybe what stinks