[sdiy] as3340 PW/tuning issue

[Mattias Rickardsson]

On Fri, 3 Jan 2020 at 02:48, ColinMuirDorward <colindorward at gmail.com>
wrote:

> Ooops, it's just an artifact of setting my scope to ac coupled input.
> Sorry folks.
> Colin
>
> On Thu, Jan 2, 2020 at 4:48 PM ColinMuirDorward <colindorward at gmail.com>
> wrote:
>
>> Is it a shortcoming of all my 3340 designs, or is PWM supposed to do a DC
>> offset, as well?
>> So at the smallest duty cycle, I get 0 to +10v, and at the other end, I
>> get 0 to -10v.
>> At 50% duty is -5v to +5v.
>>
>
AC coupling the scope (or audio device input) removes the DC offset that is
an actual part of a non-50/50 % pulse wave. I guess we all regularly
mistake it for moving the signal up and down. :-)

Keeping the pulse wave tops & bottoms at constant voltages (i.e., keeping
the PWM DC offset) is often desired for several reasons such as further
signal treatment/modulation or just keeping the control of the signal
peaks. But it could have some drawbacks as well: The DC offset created in
the pulse wave essentially equals the PWM CV. Modulate the PWM quickly, and
the modulation is potentially heard as well.

I have removed the DC-offset (actually by subtracting the PWM CV, not by
AC-coupling - caps are big and expensive) of pulse waves in oscillator
designs in order to avoid audible thumps or tones when quickly changing the
PW setting by changing presets or modulating it heavily. When doing this
it's important that the CV is not noisy, because it is heard in the
resulting signal.

Happy new 20/20 pulse waves!

/mr
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20200103/e8d83f8e/attachment.htm>