[sdiy] Max Filter Cutoff

[David G Dixon]

I gave up on OTAs.  Once I discovered the 2164, I never looked back.  The
only issue with them is that they must terminate at virtual ground, and this
limits their uses a bit.  However, for most filters this isn't really a
limitation, especially for cascaded-stage filters.


  _____  

From: Jacob Watters [mailto:jacobwatters at gmail.com] 
Sent: Sunday, October 23, 2016 11:37 AM
To: David G Dixon
Cc: Tim Ressel; synth-diy at dropmix.xs4all.nl
Subject: Re: Max Filter Cutoff


Ok thanks for the info. I think I need to adjust my circuit a bit. I am
maxing out at 15k using LM13700 and 50pF caps. I get a better range with
just a pot as a viltage divider and no expo conversion, so i am guessing my
error is in the convertor. I am reading TH's book on the 3080 right now. I
will redisgn the expo conversion based on what I am learning. 

Thanks!


-Jacob Watters

On Sunday, 23 October 2016, David G Dixon <dixon at mail.ubc.ca> wrote:



...yeah, but if the filter doesn't go high enough, then it doesn't allow all
the higher overtones when its fully open.  In other words, it doesn't fully
open.  This can change the sound of waveforms even if it is above your
hearing range by subtle modulation.  I only hear up to a little less than
13kHz myself.  Too much loud rock music.
 
In any case, I would recommend 220pF as a good size for filter caps.  It's
always worked well for me.  Of course, all my designs also use the 2164 quad
VCA chip for expo-controlled variable resistors, with the standard 30k input
resistor.  This fixes the "baseline" frequency of my filters at something
like 21kHz.


  _____  

From: Synth-diy [mailto:synth-diy-bounces@
<javascript:_e(%7B%7D,'cvml','synth-diy-bounces at dropmix.xs4all.nl');>
dropmix.xs4all.nl] On Behalf Of Tim Ressel
Sent: Sunday, October 23, 2016 10:48 AM
To: synth-diy at dropmix.xs4all.nl
<javascript:_e(%7B%7D,'cvml','synth-diy at dropmix.xs4all.nl');> 
Subject: Re: [sdiy] Max Filter Cutoff



Since most ears stop at 16KHz I'd say its safe to stop there.

--Tim (can't hear above 10K) Ressel



On 10/23/2016 9:47 AM, Jacob Watters wrote:


I am working on a filter and I was trying to get the maximum cutoff up to
20kHz. I found that I needed much smaller caps than what is usually used in
most filters. 

Then I noticed that on the Arp 2600 the max filter cutoff is labelled as
10kHz.

What is the normal max cutoff for a 4-pole -24dB analog filter?

 

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-- 

--Tim Ressel

Circuit Abbey

timr at circuitabbey.com
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