[sdiy] pt2399/rebote2.5 delay question

Derek Holzer derek at umatic.nl
Wed Sep 12 19:00:57 CEST 2007

Hi all,

I'm working on a project with the Tonepad Rebote2.5 delay, based on the 
PT2399 chip. The idea is to do a complex delay network where the signal 
gets bounced around between different delay lines. But now that I've 
listened to it a bit more, I realized that the low pass filter is too 
aggressive. I'm losing too much signal on each pass of the delay.

I'm guessing the main place to look is in the caps bridging pins 13/14 
and 15/16. These are the bridges from the output of the LPF op amps back 
to the negative inputs of those same op amps in the delay chip itself. I 
might try throwing some different values in there, but of course this is 
also tied to the resistor values.

Is there a standard formula for computing the LPF cutoff frequency in 
this situation? The configuration appears to be an inverting op amp, and 
the spec sheet gives no info about setting cutoff frequencies.

Here is the spec:


and here is the plan of the Rebote2.5:


Thanks much!

derek holzer ::: http://www.umatic.nl ::: http://blog.myspace.com/macumbista
---Oblique Strategy # 186:
"Work at a different speed"

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