Hi Everyone,
What was the original value for C7 (PB2019) on the original op amp Big Muff, does anyone know? On the PB2015 it was 1uf. On the PB2019 it's 10nf. I've searched the net and have seen all sorts of values for this component; the most common being 150nf. Does anyone know what the original value was?
Thanks in advance...
Daniel
That capacitor is part of the filter in the tone bypass mode. I'm not sure why it would be 10n. The series resistor arrangement also seems a little odd to me (hopefully someone else can add to this). I'm not sure what the
correct value should be, but here are the calculations.
This RC network forms a first-order high-pass filter with a pass band above and decrease of 6dB/octave below Fc.
HPF calculation:
Fc = 1/(2πRC)
Fc = 1/(2π * (47k+47k) * C)The frequency corners for the different HPFs are:
- 10n = 169.4Hz
- 150n = 11.3Hz
- 1uF = 1.7Hz
It varied but it was never 1uF or 10nF, the usual set up was 220nF with 2 x 47k resistors.
The series resistors are a divider to try and keep the level a bit more even when switching from the lossy tone stack to bypassing it.
Quote from: Scruffie on June 09, 2020, 02:52:00 PM
It varied but it was never 1uF or 10nF, the usual set up was 220nF with 2 x 47k resistors.
The series resistors are a divider to try and keep the level a bit more even when switching from the lossy tone stack to bypassing it.
Ah, the divider makes sense. Thanks for the input there.
For the sake of completeness, the Fc for 220n is 7.7Hz.
There will be little practical difference between 220n and 150n.
Thanks everyone for your input.
So what do you all recommend to use for C7?
I've got this chematic. Maybe will help...