[sdiy] panning vca

Tue Mar 8 21:01:04 CET 2016

I'd start by putting your project inside an earthed (grounded) metal box 
first if you are getting RFI problems

If that doesn't fix it, then start putting little ceramic capacitors across 
the input and output ports.  If you can identify the radio station causing 
the problem, and more importantly it's frequency, then you have some idea of 
how much filtering you need.

Keep ferrite sleeves as your trump card to play if the RFI problem is really 
stubborn... Like if you can see the broadcast tower from where you're 
working! ;-)

-Richie,

-----Original Message----- 
From: Joe
Sent: Tuesday, March 08, 2016 7:02 PM
To: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] panning vca

All, Is this good advice to kill the radio I here from my circuit?

Place 22pF capacitors across the two 100k feedback resistors on the
output amplifiers. This will curtain the excessive bandwidth and may
make the circuit less susceptible to acting as a radio receiver.

http://www.sdiy.org/richardc64/mmvca/index.html

Thanks. JoeF.

On Mon, 2016-03-07 at 21:28 -0500, Joe wrote:
> 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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