Hi folks, noob here
I'm trying to build an audio-filterbox based around the ssm2044 filter IC from the 80s and an Arduino Due. This site:
which shows example circuits involving said IC, shows that you need 15V (and -15V?) to operate it. My first research revealed that I'd need a voltage regulator like a 7805 to get it. To what do I connect these? do I need another PSU? (I have USB and a 12V 2A PSU).
Also I found some information on a similar project, which said I could control the resonance and filtercutoff via digital potentiometers. What would be a good choice here if the stepping of the digi-poti should be at least 256 steps?
To drive those chips you do indeed need 15V and -15V. Stepping up 5V or 12V to 15V isn't that hard. But making it negative is a bit (or at least modules that do so aren't that easy to get.) Easiest way then is to get another 15V supply (isolated from all the other) and connect the positive end of that to GND. (Remember, isolation is key here).
But remember, you don't connect those signals directly to an arduino. Due can only handle voltages between 0V and 3,3V, NOT between -15V and 15V.
Digi-pots are fun to but most of then also only can handle voltages between 0v and Vcc (which is in most cases 5V).
ok, so I use the 3.3V from Arduino, step it up to 15V and connect it to +15V. Then I take a separate 15V PSU and connect positive to GND (somehow creating the -15V because the reference point was changed?). What do I connect to the -15V? Sorry I'm a bit confused about whats going on there
The Arduino will only be in charge of changing the CVs for freq and resonance. The datasheet says they should be in the range of -90mV < Vfc < 90 mV. Can I somehow make that happen with a digital potentiometer? again.. negative Voltages..
You do not need +/-15volt to supply those chips.
The range, according to the datasheet, is +/-5volt to +/-18volt.
What you need depends on the audio level you want to pass through them.
+/-9volt with two 9volt batteries is perfect for testing.
No need for digital pots. The chip has voltage control.
e.g. the full range of the frequency control input is -120mV to +180mV.
Not too hard to make that with PWM, a lowpass filter, and an opamp.
Leo..
Cool, so does that mean I can just use the diagrams shown above, replace the 15v wih my 9v and if it's strong enough it will work? What's is a good voltage for audio signals (already amplified ones, from synths mainly)?
Regarding the PWM control of freq and res: I thought about using the PWM, but wont it oscillate a little bit, even LP-filtered? I thought I would probably hear that when the resonance is all up.
Frodl:
Cool, so does that mean I can just use the diagrams shown above, replace the 15v wih my 9v and if it's strong enough it will work? What's is a good voltage for audio signals (already amplified ones, from synths mainly)?
Regarding the PWM control of freq and res: I thought about using the PWM, but wont it oscillate a little bit, even LP-filtered? I thought I would probably hear that when the resonance is all up.
Depends on the peak to peak output voltage of your synth. The higher voltage is for "headroom".
Bit silly to use a 30volt supply if your synth only outputs 1volt p/p.
15/-15 is used in professional gear where you don't always know what you have to amplify.
The remaining ripple from smoothing the PWM signal depends in how much you filter.
It's a trade-off between ripple and lag. Are these controls only used to adjusting something?
A higher PWM frequency can be used if lag is a problem.
Leo..
