Doepfer

Hi Stu,

There are no simple answers to your questions I fear. The realm of 
active filters is huge, as any quick Google search will tell you 
(I've been learning avidly about them for around the 6 years I've 
been into synths, and am easily made to look like an amateur in the 
right company). And on top of that if you ask your question of 10 
different people, you'll probably get 10 different answers.

This sort of question is certainly asked from time-to-time on the 
Synth-DIY list, so you could try searching its archives, and you will 
probably find many suggestions (albeit mostly voltage-controlled):

http://dropmix.xs4all.nl/synth-diy/

(Synth-DIY main page: http://search.retrosynth.com/synth-diy/)

I don't know much about the many A-188 modules, but you will need to 
know the frequency of the clock that you want to get rid of, and also 
those that you definitely *don't* want to get rid of (as already 
pointed out). If you want to stick with a fixed-frequency filter, 
then you could try looking at one of the many 'cookbook'-type books 
which exist on the subject, wherein you just feed in your cut-off 
frequency and out pop the component values that you use in the 
particular circuit in question - Don Lancaster's 'Active Filter 
Cookbook' is one of the better-known ones, but there are lots of 
others. I will add that if you *really* want to learn about filters 
you will need to check out a decent book: I find Schaumann & 
Valkenburg's 'Design of Analog Filters' pretty good, but you will 
have to be prepared to get your head down for some serious studying!

Probably the quickest route is to find someone who has already done 
something very similar, so it is a shame no such person has responded!

Tim


--- In Doepfer_a100@yahoogroups.com, "Stu Grimshaw" <grimshaw@...> 
wrote:
>
> Hi group,
> 
> working with the a188 bbd, i'm kind of hand-tied by the fact that i
> need a filter (of which i only have two) to remove the clock signal
> from the echoes produced. 
> 
> so i need to buy another one, or do i ? is there an easy way to 
build
> a fixed freq lpf ? it's easy enough on the guitar, i.e. a passive
> circuit, but what's the score with all this active circuitry ?
> 
> any help or advice greatly appreciated.
> 
> stu
>