Digital FX Board C16 Alternative

I know I keep asking questions like this, which I’m sure is very irritating, but…
I find myself short of a 470pF ceramic capacitor. Would a 680pF one work at C16, maybe, or do I have to make another Rapid order?


Look at the schematics

No part under the “8 poles Chebyshev” and “4 poles Chebyshev” sections should be changed. They are antialiasing filters, and the values are selected to minimize filter ripple. I battled a lot to get this section to work with only “standard” values. Any other value here could either: 1/ move down the cutoff frequency of the circuit and muffle/darken the sound badly. 2/ move up the cutoff frequency and cause the sound to be awfully aliased, always. 3/ add more ripple and give a “resonant” sound at a random frequency. Unless you want one of those…

Thanks for the rapid reply pichenettes.

So that section of the board filters the audio input to eliminate frequencies from the audio that would cause aliasing, before it gets to the ADC.

I’ll put in an order on Monday, get it on Tuesday, hopefully. Now, I wonder what else I forgot to buy. This is all because I didn’t want to pay Farnell’s £16 US delivery charge, so decided to try and source all those US stock items from other local suppliers. I’ve ended up paying more in UK delivery charges on multiple orders though. Should have ordered the lot from Farnell in the first place :frowning:


should i send you one? (or more, haven’t looked at the schem)

@rosch thanks for the kind offer. I’ll order one tomorrow from Rapid , though, so don’t worry. They seem pretty good for those ceramic and Wima film caps Farnell only have as US-stock (note to UK Shruthi constructors).


Sorry, another silly question:

Would the 470pF version of this cap from Maplin work?
Note the 470pF seems to have a different temperature coefficient (X7R) than the lower-value ones, and a different one from the recommended Farnell component from the BOM (C0G/NPO). Not sure how significant this is.

Also realised while looking at the circuit diagram that the filter also works on the Osc input from the Control board. Silly me for not noticing this before.


Part looks good.

And works!