[sdiy] RE: [AH] Parametric EQ

[Tom Wiltshire]

Hi Scott,

What did you do about the resonance response of the SSM2164? I found  
that getting a reasonably constant resonance out of it w.r.t cutoff  
was quite difficult. Did you bother with any compensation? In the  
end, I think I decided I didn't care that much (it sounded so *fat*  
and *good* anyway...yuummmm!) and I've just got a couple of back-to- 
back 4V7 zeners on the LPF output amp. This isn't shown on this  
earlier circuit diagram, but they're on IC2.2, in parallel with C4.

http://www.electricdruid.com/VCResonator.jpg

T.

On 21 Feb 2010, at 01:31, Scott Juskiw wrote:

> I'm using the SSM2164 too. Nice chip, easy to work with for filter  
> and amp. It's the programmability and morphing part that is the  
> real challenge.
>
> On 2010-02-20, at 6:22 PM, Tom Wiltshire wrote:
>
>> Yeah, I've had a crack at this problem too. My version uses the  
>> SSM2164 as a voltage controlled SVF, two amps for the filter  
>> stages, one for the resonance, one for the amount. You can rack up  
>> as many of these bands as you like, with three CVs for each band  
>> (Cutoff, resonance, amount). My prototype has three filter boards.
>> Morphing sounds like a great addition - nice work.
>>
>> T.
>>
>> On 20 Feb 2010, at 23:26, Scott Juskiw wrote:
>>
>>> I am working on something similar to this. My version is a single  
>>> module with 5 (possibly 6) channels of bandpass filters.  
>>> Frequency, resonance, and gain are fully programmable, plus it  
>>> has the ability to morph between presets. I was really hoping to  
>>> get it finished by next spring but that seems doubtful at the  
>>> moment. Maybe by next fall. If you can wait for it, I'll let you  
>>> know when I'm finished. I'll have PCBs for sale, same as my other  
>>> projects.
>>>
>>>> I've suggested this before (maybe on other lists): It would be  
>>>> swell if
>>>> someone designed a single-channel parametric EQ PCB that allowed  
>>>> full
>>>> control over frequency, bandwidth, gain, and whatever else could  
>>>> be thrown
>>>> in for good measure. Then, the DIY crowd could adapt it to  
>>>> whatever format
>>>> they wanted. Did I mention CV control of the parameters? One  
>>>> could then
>>>> decide how many channels they want (3, 4, 16???) to build out a  
>>>> super EQ of
>>>> their own size. I know I'd be interested in doing this in MOTM  
>>>> format.
>>>
>