Doepfer

Hi,

although this doesn't belongs really to the Doepfer modular system I hope I reach the appropriate people here:

I'm looking for a voltage controlled filter built in a chip like the CEM chips for example for a electronics project of mine. Ideally a 2-pol high and low pass in a chip. Resonance is not necessary.

Is there another manufacturer who is developing and delivering such chips today?

Olli


http://www.gretz-net.de/olli/

Hello

> Is there another manufacturer who is developing and delivering such chips today?
Not really.

THere are a lot of NOS SSM2044 in the market (check ebay).

I know also that there is someone in the UK who does a replacement for 
SSM2040 or 2044 as a small pcb in smd technology (Sorry I don't find the 
URL at the moment). But in fact it is nothing else than four OTAs with 
Buffers (FET or TL07x). So you don't have to pay USD 40, if you can do 
it with separate chips for USD 5.


Florian

Hi,

cool, thanks for your advice!

Olli

--- In Doepfer_a100@yahoogroups.com, Florian Anwander <fanwander@...> wrote:

>
> Hello
> 
> > Is there another manufacturer who is developing and delivering such chips today?
> Not really.
> 
> THere are a lot of NOS SSM2044 in the market (check ebay).
> 
> I know also that there is someone in the UK who does a replacement for 
> SSM2040 or 2044 as a small pcb in smd technology (Sorry I don't find the 
> URL at the moment). But in fact it is nothing else than four OTAs with 
> Buffers (FET or TL07x). So you don't have to pay USD 40, if you can do 
> it with separate chips for USD 5.
> 
> 
> Florian
>

Hi olli

via http://matrixsynth.blogspot.com/2010/12/diy-digital-synth-demo.html 
I stumbled over http://www.national.com/mpf/MF/MF10.html#Overview

Needs a clock instead of CV, but a simple VCO (no extreme linearity is 
required for this kind of VCF) shouldn't be too difficult.

I think it would be also extremely useful as anti aliasing filter for 
the BBD modules.

Florian

> Hi olli
>
> via http://matrixsynth.blogspot.com/2010/12/diy-digital-synth-demo.html
> I stumbled over http://www.national.com/mpf/MF/MF10.html#Overview
>
> Needs a clock instead of CV, but a simple VCO (no extreme linearity is
> required for this kind of VCF) shouldn't be too difficult.
>
> I think it would be also extremely useful as anti aliasing filter for
> the BBD modules.
>
> Florian

The main disadvantage of switched capacitor filters (SCF) is that you still
need an analog anti aliasing filter at the audio input and a tracking filter
(at least 12dB/oct) at the audio output to suppress the clock signal that is
used to control the SCF. This makes the design very complex as one needs a
high speed VCO that controls the clock of the SCF and two analog tracking
filters that have to follow the high speed VCO frequency. This is the reason
why our dual SCF has not yet been released. In this design 4 analog tracking
filters (all LM13700 based in our design) are necessary in addition to the
high speed VCO and the actual SCF. From my point of view it's too costly for
what you get. Ingo has tried out our prototype some time ago and as far as I
remember he agreed (Ingo please correct me if I'm wrong).

Best wishes
Dieter

Hi Florian,

thanks for the links. Very intersting!

I'm planing a harmonizer to adding higher hamonics to a signal with a very special design. (don't know wheather it will sound good). High and low pass filters would be for pre and post filtering the drive signal and the pure added harmonics, where no resonance is needed.

I know those frequency controlled filters. Linear Technology offers some with linear phase behavior and already integrated oscillators, where the frequency can be set with an external resistor. But most don't operate in the audio frequency range ( http://www.linear.com/pc/viewCategory.jsp?navId=H0,C1,C1154,C1008 )
But I haven't checked everyone, because I have very few time working on this project due to my studies at the moment.

Kind regards,
Olli

--- In Doepfer_a100@yahoogroups.com, Florian Anwander <fanwander@...> wrote:

>
> Hi olli
> 
> via http://matrixsynth.blogspot.com/2010/12/diy-digital-synth-demo.html 
> I stumbled over http://www.national.com/mpf/MF/MF10.html#Overview
> 
> Needs a clock instead of CV, but a simple VCO (no extreme linearity is 
> required for this kind of VCF) shouldn't be too difficult.
> 
> I think it would be also extremely useful as anti aliasing filter for 
> the BBD modules.
> 
> Florian
>

<<snip>>
> This makes the design very complex as one needs a
> high speed VCO that controls the clock of the SCF and two analog tracking
> filters that have to follow the high speed VCO frequency.

<<snip>>
> From my point of view it's too costly for
> what you get.

I'll echo Dieter's sentiments on this - yes it can be done, but you have to work very hard to make it happen, so in the end it is much easier to make a voltage-controlled filter using more conventional means, i.e. transconductance amps etc. My efforts with the MF10/LMF100 may give an idea of what's involved (though I did try and push the clocking frequency beyond the normal audio range):

http://www.timstinchcombe.co.uk/synth/mf10/mf10.html

Tim