Resistor/capacitor combo at +9V

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fishfude
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Post by fishfude »

Hey folks,

I think this should be a simple one, but I was wondering what the 2.2k resistor and 100uF cap combo at the +9v input on this Tim Escobedo, 'Calavera', circuit snippet was for? Is it simply a filter (low pass?)? Also, are the other 0.1uF caps just for DC filtering?

Image

Thanks!

ff

teleK
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Post by teleK »

the resistor and capacitor make sure there is only DC coming into the circuit, the other capacitors make sure only AC enter and leave the circuit

fishfude
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Post by fishfude »

That's what I thought, but why would you have to worry about AC coming from a battery?

Thanks,

ff

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Nocentelli
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Post by Nocentelli »

It tells you on the schematic: "The RC network on the power supply is neccessary to keep oscillations down and power consumption reasonable".

The resistor from +9v to large electro cap to ground is common to many pedals: It is a low pass filter with an extremely low cut-off frequency, designed to send pretty much any AC present in the power supply (from a poor quality AC-DC adaptor, from another electrical device sharing the same power outlet, or perhaps induced by nearby audio signals in wires, or induced within the circuit itself) to ground. Some oscillating fuzz "designs" will not work properly if this power filtering is present. The resistor will drop the supply voltage somewhat, and resistors around 47ohm or 100ohm are usually used to minimise the voltage drop whilst still forming a suitable RC filter. Here, the higher-than-average resistor value also serves to reduce the power consuption of the circuit. Many of Escobedo's circuit snippets use low power consumption as a selling point, which is only really valid if you use batteries.
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fishfude
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Post by fishfude »

Ah yeah, sorry, so it does! Thanks for the other info though!

ff

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