Seppo s magic filter controlled by a pot

[cimo]

Hi

I have just built Seppos filters and since i am too damn broken to get and AOUT i ll be happy to have just a pot to controlcut and resonance.

Now before i explode the styroflex caps in my face, what level of voltage is expecting the cv in?

Can I hook up a single pot to control both channels or do i need a stereo pot?

I also assume the pot has to be wire has in a AIN, + and - on the 2 tips and sending the central pin to the filter s CV in.

Simone

[Imp]

That problem sounds oddly familiar ;)

in the Wiki it says  "The frequency input of the 2044 expects an input of about -100..+100mV" ...maybe a battery wired to the outer pins of the pot would do the trick, it's (-) should be connected to the ground oft the circuit, the wiper of the pot to CV in  ...i haven't tried it yet, so maybe it needs some improvement...

One pot is enough i think...

[seppoman]

in the Wiki it says  "The frequency input of the 2044 expects an input of about -100..+100mV" ...maybe a battery wired to the outer pins of the pot would do the trick, it's (-) should be connected to the ground oft the circuit, the wiper of the pot to CV in  ...i haven't tried it yet, so maybe it needs some improvement...

oh yes it does need some improvement ;) your construction would need a 200mV battery and still wouldn't output a bipolar voltage.

But a battery is the wrong solution anyway. I said "the input of the 2044", not "the input of the module". That's a difference! In conjunction with an AOUT_NG with bipolar mode, that module input gets (expects) around -5V..+5V.

You could try using two 3.something k resistors and a 2.7k Pot inbetween to build a voltage divider between the +-12V rails that outputs around +-5V. But I'm not quite sure if the frequency range would be as expected. Even if it works, using a stereo pot would be a good idea.

The clean solution would be to add an opamp cirquit to transform the input to a V/oct one. I promised a long time ago that I would publish a schematic for that... If you can wait for some more weeks, it's definitely on my agenda. If you're in a hurry: http://www.analog-synth.de/synths/mod2/ssmlowpass/ssm2044.pdf You can see the standard implementation on the right side of the schematic on page 3. That way you get trimpots to adjust range and offset. If you build that cirquit for both SSMs, you can safely use a single pot connected to GND and 12V to control both at the same time and match the response of both filters perfectly.

S

[cimo]

[nILS]

Nice, is that one of the pollin transformers? Kinda looks like one :-) I think I need to build that kinda "AOUT" too to test my SSM boards.

[Sasha]

...I promised a long time ago that I would publish a schematic for that... If you can wait for some more weeks, it's definitely on my agenda.

That would be great Seppo. I don`t believe I could get NG soon.

@ cimo Good, dirty work mate.

[cimo]

...i was expecting ti to be the midibox of the week! ;)

@Nils, no it s not form Pollins, it comes from the local shop, 12+12 300mA

@Sasa, f course it s not a final job, just a test board to be hooked up with a cs-05 and a cs-08, when i ll get an AOUT-NG i ll make a nice case.

I am really looking forward to try out the little bastard

Simone

[Sasha]

@Sasa, f course it s not a final job, just a test board to be hooked up with a cs-05 and a cs-08, when i ll get an AOUT-NG i ll make a nice case.

I am really looking forward to try out the little bastard

Simone

I know it is not a final job, but for a dirty testing environment it is pretty well built. Honestly. I love how you mount everything together. Even for testing it is good idea to put some more effort as you did to avoid braking off some wires and short circuits.