Abusing the SSM2044

etaoin · Joined: Jun 30, 2005 Posts: 761 Location: Utrecht, NL

Has anyone ever seen the SSM2044 being (ab)used for anything other than an LPF? I have two spare but have no need for further low pass filters. Can it go low enough to act as a phase shifter for example?

Maybe I should just try a few things on breadboard.

Dave Kendall · Posted: Fri Aug 03, 2007 7:11 am Post subject:

This from mutronics' website refers to the mutator (rack VCF), but should apply to the SSM 2044 or any LPF I guess....

Dan Lavin · Posted: Fri Aug 03, 2007 7:51 am Post subject:

Dave,

That's actually an excellent suggestion. Using Fonik's SSM2044 board and a little hand-wired expansion board, a HPF can be created and mixed with the low pass to create a notch filter. Then he would have a nice LP/HP/notch filter. On my Oberheim SEM, I rarely use straight LP or HP...it's usually a combination of the 2.

StephenGiles · Joined: Apr 17, 2006 Posts: 507 Location: England

Didin't Tom Henry design a Phaser for Polyphony using a 2044?

softfin · Posted: Sat Aug 04, 2007 4:59 pm Post subject:

Interesting topic!
Would be very interesting to hear if you come up with ideas how to get specifically the SSM2044 to act as highpass filter.
The SSM2044 is such a great filter that adding a little more versatily like hipass and notch modes, it could be one of the best filters around, IMO.

StephenGiles · Joined: Apr 17, 2006 Posts: 507 Location: England

I can't get into our attic at the moment as it's too hot up there, but I'm sure there was a 2044 phaser.

guitarfool · Posted: Sun Aug 05, 2007 8:55 am Post subject:

StephenGiles · Joined: Apr 17, 2006 Posts: 507 Location: England

Ah yes of course, the 2040 - well, nearly got the number right!!

Peake · Posted: Sun Aug 05, 2007 10:45 am Post subject:

I have a Castle 3 phaser, and it uses the SSM 2044.

Here's a post from AH regarding filter chips in phase shifters, and an interesting note on imperfection:

On 10/13/02 11:42 AM, "p. hendricks" <ph> wrote:

> On 10/13/02 10:47 AM, "Mike Peake" <peake> wrote:
>
>> Other phasers utilizing filter chips for
>> their core:
>> Castle III: SSM 2044
>> Roland Digital Rhodes: IR3109 (excellent)
>
> what about the symetrix phase filter?
>
> http://www.modezero.com/phase-filter.htm.htm

>
> uses SSM 2040's YUM! sure looks nice.
> -phil
>
>
>
I replied to Mike then saw this post. They are *VERY* nice. We originally
designed them with three SSM2040's but the effect was too much! The units
bent notes and were just wild. All the units had the PCBs laid out for three
chips though, just not stuffed with them. The main factor to their sound was
that the two SSM chips didn't have their CV control matched. The same LFO
would move one filter farther at each of the ends of the sweeps and this
made them sound very unique. That and the fact that they had 2 LFOs and CV
in. They are a little noisy compared to the units today, but that adds a
bunch to the character of the sound. They show up now and then but we never
made a whole lot of them.

-James

--
James Husted
The ErsatZ Planet Graphics & Sound
James@ersatzplanet.com

Dave Kendall

Hi guys.
Well, I had a go at following the Mutator manual's HPF tip, using a mutator (because I haven't got a SSM2044 filter yet....)
The phase reverse trick works, but splitting the signal and running it into a Yamaha 03D didn't get anywhere near total phase cancellation. Balancing the normal and inverted phase signals is very critical, to the point that I could hear what sounds like discrete "steps" when fine adjusting the 03D faders - (quantized fader resolution maybe?) and never got total cancellation.

The mutator has VCAs and other things in its signal path too, which probably make matters worse.

Another problem was the non-linearity of the resonance response. One twitch of the resonance knob, and the phase shifted enough that the partial cancellation became hardly any cancellation. The relative balance of the 2 channels needed quite a bit of adjustment - around 6dB or more, according to the fader markings.
Perhaps a constant volume(gain?) circuit in the resonance path is needed to deal with this. I don't know how the SSM2044 behaves in this regard, but I suspect the resonance response of the mutator is frequency dependent - at low freq, the RES is less pronounced, which does however give it a nice warm bass end. It sort of reminds me of the EFM VCF6C diode ladder filter.....

Interestingly, with feedback at medium to high levels, phase cancellation was greater than with no RES - the residual signal was much lower.

I guess phase linearity in the inverting and non-inverting part of the circuit needs to be very stable across a wide frequency range, and accurate (drift free) level trimming will be important, and that's before the resonance issue is addressed....

All for now....

cheers,

Dave