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#7361
after many hours tweaking my truebypassed vox 847 my preferred settings are...

input resister - 100k
frequency cap - .009uf mojo cap
q resister - 40k
midrange resister - 1k
gain resister - 1.2ohms !
inductor - fasel yellow.
transistors - bc550

the gain resister (actually a trimpot) is way low but it needs to be to compensate for the higher input resister.
Last edited by mildew at Aug 5, 2015,
#7362
current wah mod state is this.


input resister 220k

bass resister 1k

q resister 68k

gain resister back to 470ohms

pitch cap .009uf mojocap

added a stripboard SHO booster on output side.
Last edited by mildew at Sep 7, 2015,
#7363
Can anyone explain the difference between the vocal mod, and the 535q's q pot?
The vocal mod involves varying the size of the resistor in parallel with the inductor, the q control adds a 1.8k [?] pot in series with the inductor, leaving the resistor in parallel at the stock 33k.

Does the q control thus do the opposite of the popular vocal mod, which would involve shifting the 33k resistor to a higher value such as 68k or even 100k?

Thus, would the vocal mod not be even better in conjunction with the q control?
RIP Gooze

cats
Last edited by mulefish at Apr 9, 2017,
#7364
Quote by mulefish
Can anyone explain the difference between the vocal mod, and the 535q's q pot?
The vocal mod involves varying the size of the resistor in parallel with the inductor, the q control adds a 1.8k [?] pot in series with the inductor, leaving the resistor in parallel at the stock 33k.

Does the q control thus do the opposite of the popular vocal mod, which would involve shifting the 33k resistor to a higher value such as 68k or even 100k?

Thus, would the vocal mod not be even better in conjunction with the q control?

Both are essentially the same thing. You are referring to the vocal mod as a fixed value while the potentiometer gives you a variable value. The higher the resistance, the more vocal quality/Q you get. You can replace that 33K with a potentiometer or put the 33K in series with a potentiometer so it doesn't go down to 0Ω and you don't get any wah effect.
Last edited by Griffin Effects at Apr 10, 2017,
#7365
Griffin Effects But the thing is that in the 535q  the variable resistor is not in series with the 33k resistor, but is instead parallel with it. It is, however, in series with the inductor. Thus my thinking is that the pot has an inverse effect, essentially shunting more signal through the 33k resistor rather than through the inductor, which would have a similar effect to lowering the 33k resistors value.

Is this correct?
RIP Gooze

cats
#7366
mulefish You need to take into account that the inductor has a resistance (probably around 30ohm). Both the 33K in parallel and the small value variable potentiometer have an affect on this. So a variable pot in series with the inductor will increase the overall series resistance (pot 1.8K + 30ohm = 1.83K) at max rotation. 
So at max rotation we would have a total of ~1.73K (1.8K + inductor 30ohm and 33K in parallel ) and at minimum rotation we would have ~29.97ohm (33K in parallel with inductor 30ohm).
Hope that makes it a little clearer and hope my math was right. It's early and pre-coffee.
Sorry. Had to edit this. All my ohm signs turned into winky smile faces! 
Last edited by Griffin Effects at Apr 11, 2017,