[sdiy] PWM noise in analog ground in Optigan-like system

[cheater cheater]

Sorry, missed the link :-) Shielding of PWM stuff always helps..

That's just speculation, I have little experience on that field, but
if I were you I would just have the PWM controller and the motor in
the same box physically; put a small shield can around the PWM
controller itself, those arduinos are quite small, and finally connect
the can to the motor. Make sure none of that ground/shielding touches
the 'other side' of the arduino which communicates with the rest of
the synth; might even want to use a shielded cable for that, with the
shield connected on the synth side but not on the pwm side.

HTH
D.

On Mon, Mar 29, 2010 at 14:38, Derek Holzer <derek at umatic.nl> wrote:
> Thanks for the quick reply.... as I mentioned, schemos and layouts are here:
> http://www.umatic.nl/tonewheels_technical.html
>
> Except that in place of the PWM circuit listed there, I'm using an Arduino
> with PWM output to a TIP122. Layout of analog side remains the same.
>
> I found some tips on shielding here:
> http://www.edn.com/article/CA6288042.html
>
> which seemed to work, namely the following:
>
> Keep motor cables as short as possible.
> Use a motor cable with a high-quality shield.
> At the motor end of the cable, make a low-impedance connection between the
> shield and the motor frame.
> At the amplifier end of the cable, make a low-impedance
> connection between the shield and the chassis ground.
>
> Best!
> Derek
>
>
> On 3/29/10 2:30 PM, cheater cheater wrote:
>>
>> Hi Derek,
>> It might be easier to say what's up if we can get some schematics
>> and/or board layouts. Here are some ideas that might or might not help
>> you:
>>
>> - more decoupling
>> - maybe you're not decoupling the right thing
>> - EMI issues? Try shielding the bugger away.
>> - use separate ground for the PWM; make sure it doesn't touch anywhere
>> - if all else fails, two-wire signaling in the analog path: normally
>> synths use single-wire signaling, which means that the audio is an AC
>> signal, the value of which is referenced to ground. But the question
>> is, 'what is ground'. In difficult situations the ground will be
>> different from point to point, or contain noise, which - when
>> referencing the audio to the ground - makes it appear as if there's
>> noise in the audio signal. Instead of referencing your audio to random
>> places in the ground plane, you can carry the ground your previous
>> 'part' (op amp, transistor, ...) was referenced to, from the place
>> where it gains the reference, parallel to the signal trace; then you
>> reference the next 'part' from that ground trace, and go on like that.
>> That's one practice used in big mixers where there's a lot of noise
>> attacking your audio no matter what you do.
>> - kill it with fire
>>
>> HTH
>> D.
>>
>> On Mon, Mar 29, 2010 at 13:27, Derek Holzer<derek at umatic.nl>  wrote:
>>>
>>> Hi folks,
>>>
>>> the system I am building uses a PWM motor controller (Arduino+TIP120) as
>>> well as an op-amp buffer for a phototransistor. Think of it a bit like an
>>> Optigan... technical details here:
>>> http://www.umatic.nl/tonewheels_technical.html
>>>
>>> I've been running the PWM controller and the op-amp buffer from separate
>>> wall-warts for some time now, but this week I wanted to combine
>>> everything
>>> into one box with one power supply. And, of course, I can hear the PWM
>>> coming through the + and ground lines to the op-amp.
>>>
>>> I tried using a separate LM7809 voltage regulator with decoupling caps
>>> (100
>>> uF between supply and ground, 100nF between regulated and ground) for the
>>> audio portion, but enough noise still comes through the ground alone to
>>> be
>>> heard (noise can be heard with + disconnected). And it still fails to
>>> remove
>>> the noise from the + side as well!
>>>
>>> I also tried small ferrite beads on the + and ground lines. No noticeable
>>> difference.
>>>
>>> Short of plugging two different wall warts into the same box, one for the
>>> PWM and one for the audio, what can I do to remove this noise?
>>>
>>> How far back in the power path do I need to separate the powers and
>>> grounds
>>> of the two systems? For example, at the AC/DC conversion stage?
>>>
>>> Thx+best!
>>> Derek
>>> --
>>> ::: derek holzer ::: http://macumbista.net :::
>>> ---Oblique Strategy # 8:
>>> "Accretion"
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>
> --
> ::: derek holzer ::: http://macumbista.net :::
> ---Oblique Strategy # 90:
> "In total darkness, or in a very large room, very quietly"
>