[sdiy] Max Filter Cutoff

[Tom Wiltshire]

Olivier Gillet has several nice 2164 filter examples on the Mutable Instruments site. Ask me if you can't find them.

Tom

On 24 Oct 2016, at 15:50, Quincas <quincas at gmail.com> wrote:

> Dave, I have a spare 2164... Do you have any filter schematics you'd be willing to share with us diyers? I can make OTA filters just fine, but I'm not terribly familiar with the 2164 yet :)
> 
> Cheers!
> Q
> 
> Quincas Moreira
> 
> On 23/10/2016, at 3:12 p.m., David G Dixon <dixon at mail.ubc.ca> wrote:
> 
>> 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 at dropmix.xs4all.nl] On Behalf Of Tim Ressel
>> Sent: Sunday, October 23, 2016 10:48 AM
>> To: 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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