[sdiy] panning vca

Mattias Rickardsson mr at analogue.org
Tue Mar 8 11:25:44 CET 2016


Sorry for the potentially most boring question, but why not build it out of
two OTAs instead? Giving a more trustworthy construction, identical
behaviour for the two channels, proper offness by design, a choice of
better pan laws than the linear one, and much much lower noise if using
LM13700/NE5517?

Might even be done quicker than getting the old circuit working properly.
O:-)

/mr
Den 8 mars 2016 3:28 fm skrev "Joe" <joe.frey at radioles.com>:

> Hello all, I hope I am not becoming tedious with this project. I have
> built a panning vca using a single ota and I am having problems with
> noise. The circuit does what it is supposed to do.
>
> http://www.sdiy.org/richardc64/mmvca/index.html
>
> The power supply I am using is here
>
> http://www.generalguitargadgets.com/wp-content/uploads/ggg_bipolar_ps.pdf
>
> I did as Tom suggested here:
>
> 10u to 220u between V+ and 0V and between 0V and V- where power comes in
> (filter caps) - watch polarity, of course.
> 100n between V+ and 0V and between 0V and V- as close to the power pins
> of each IC.
>
> So I unclipped the test leads I used to to put these caps in my circuit.
> So theses caps are not in my circuit any longer.
>
> I heard no appreciable change in the noise so I unclipped the test leads
> I used to to put these caps in my circuit.
> And, then I created a little custom socket and replaced the CA3080 with
> a LM13600 and heard no real change. I went back to the CA3080. Now I
> have it all boxed up and I am getting a HUGE amount of radio in the
> circuit. I tried to Google rf filter for audio circuits but have found
> nothing applicable, just lots of dissertations.
>  Do that caps that Tom suggested above stop RF? Thanks in advance.JoeF.
>
>
>
>
>
>
>
>  On Mon, 2016-02-29 at 23:08 +0000, Tom Bugs wrote:
> > 10u to 220u between V+ and 0V and between 0V and V- where power comes in
> > (filter caps) - watch polarity, of course.
> > 100n between V+ and 0V and between 0V and V- as close to the power pins
> > of each IC.
> >
> > On 29/02/2016 22:03, Joe wrote:
> > > Tom, No. As I stated I am strictly monkey see, monkey do. Trying to
> > > change that. I am going to get a book, now.  Ray Wilson's "Make: Analog
> > > Synthesizers" was recommended.
> > >   Can you tell me what to add where? Thanks.
> > > Joe.
> > >
> > >
> > >
> > >
> > >
> > > On Mon, 2016-02-29 at 21:34 +0000, Tom Bugs wrote:
> > >> Question - do you have filter & bypass caps on the circuits? They're
> not
> > >> shown in the original schematic.
> > >>
> > >>
> > >> On 29/02/2016 17:06, Joe wrote:
> > >>> Hello and thanks. My power supply is the bipolar power supply circuit
> > >>> provided by General Guitar Gadgets found here
> > >>>
> http://www.generalguitargadgets.com/wp-content/uploads/ggg_bipolar_ps.pdf
> > >>> I have used it before but for other circuits that generate cv. There
> > >>> never seemed to be noticeable downstream noise in the audio in those
> > >>> circuits. Those circuits were the EFM pv-1 and an envelope circuit
> Harry
> > >>> Bissell sent me, also EFM I bet. I used 3080s in those, too. I find
> the
> > >>> same noise where the ground is connected from the bipolar power
> supply
> > >>> board to the panning vca board, by the way.
> > >>>    My audio probe is a 0.1uf cap on the tip of an audio cable with
> the
> > >>> audio cable shield connected to ground.
> > >>>    So, before I try to use a LM13700, is there some procedure I can
> use to
> > >>> determine the noise source. Removing ICs and powering up or something
> > >>> like that?
> > >>>
> > >>>
> > >>>
> > >>>
> > >>>
> > >>>
> > >>>
> > >>>
> > >>> On Mon, 2016-02-29 at 15:06 +0100, Rutger Vlek wrote:
> > >>>> The CA3080 is known to be a bit noisy, but if you find it
> everywhere (even in the ground) I'd do a more fundamental check on your
> power supply and measurement setup.
> > >>>>
> > >>>> How do you supply the board with power? How do you do the audio
> trace exactly? Just to be sure that the noise is actually in the board, not
> in the measurement method :).
> > >>>>
> > >>>> Rutger
> > >>>>
> > >>>>
> > >>>>
> > >>>> On 29 feb 2016, at 03:46, Joe wrote:
> > >>>>
> > >>>>> Hello there, I built this panning VCA and I am happy with how it
> sounds
> > >>>>> except there is a lot of background noise. I tried to audio trace
> the
> > >>>>> noise but I find it everywhere, even in the ground plane. Is there
> some
> > >>>>> advice that someone can give me about how to isolate it. Thanks.
> > >>>>>
> > >>>>> On Sat, 2016-01-23 at 12:58 -0500, Joe wrote:
> > >>>>>> Thanks to all! You guys are the awsomest ever! Joe.
> > >>>>>>
> > >>>>>>
> > >>>>>>
> > >>>>>>
> > >>>>>> On Fri, 2016-01-22 at 16:13 -0500, Joe wrote:
> > >>>>>>> I am planning on building this single as a panning VCA by Richard
> > >>>>>>> Curcio.
> > >>>>>>>
> > >>>>>>> http://www.sdiy.org/richardc64/mmvca/index.html
> > >>>>>>>
> > >>>>>>> I can source a CA3080 and since I am only building one I am not
> worried
> > >>>>>>> about expense. Here's the thing, I don't know what pot values to
> use for
> > >>>>>>> the trimmers and I am definitely thrown by the current
> controlling DC
> > >>>>>>> trimmer, though I understand how to wire it. Can anyone take a
> minute(or
> > >>>>>>> few) to help me figure them out? Thanks, Joe.
> > >>>>>>>
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