Recapping ala Jim Williams

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paulrichards7

Well-known member
Joined
Jun 10, 2008
Messages
68
So I came across these words of wisdom for Jim Williams:

Another problem with leaving in older caps is for one they are usually too small in value. Designers typically use the smallest and cheapest parts they can so low end roll off are set to 20 hz or so. That will create phase shift beginning at 200 hz.
To remove it, roll-offs must be set to 2 hz so the phase shift begins at 20 hz or lower = not audible. Soundcrafts and others have that problem as they use 47 uf/25v caps everywhere, the use of 220uf caps does wonders. Those are still quite cheap, a 1000 piece bag of Panasonic FM 220 uf 25 v caps costs only $80. That's 8 cents each. There is no reason to buy lesser caps when these are so cheap.

and wondered how they might apply to the caps on the audio path of my mixer channel
http://i390.photobucket.com/albums/oo345/paulrichards7/audio-path-caps.jpg

They have different capacitance and voltages and wondered if this is specific to that design or due to Studiomaster pricing
Thanks
Paul
 
The rolloff is set by values of both parts. it's called an RC filter and you can use it for power supplies etc. too. 
It's an EQ
I just did something to a fuzz pedal that could serve to demonstrate.
The thing was great sounding, super tough tone, but it had a really uninteresting 60hz HUM when I plugged in a wall wart.
SO
I Added an RC filter on the dc supply.  a 220uf capacitor and a resistor.
At first my filter was high with a corner frequency to roll off below 300 hz  but this made the effect sound weak, I believe I was stealing too much energy with the resistor. 
I adjusted part values and put my corner at 62 hz and hum was still coming through, but pretty far reduced.  The energy was back.
I changed the resistor value and moved the filter up to about 75hz and this did the trick... still had energy, but no more hum.
this I suppose demonstrates the knee or slope of the filter and how the resistor plays into the equation.

I haven't looked at the schematic but you want to keep your values somewhat "reasonable". Caps have to fit their locations etc.

 
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