[sdiy] panning vca

Jeff Brown guitaricon at verizon.net
Tue Mar 8 05:00:46 CET 2016


I take it that by "noise", you mean "hum" from the AC power mains?
I think it most likely to be a "ground loop", or a floating ground.  I
assume you ran 3 wires from you panning VCA board to the power supply: +V,
-V and ground.  Does the ground on your power supply go to earth ground, or
does it just float?  If you have 3-conductor AC power cable for the power
supply, one of the wires should be an earth ground and you can tie into
that, but make sure it's the correct one!.  Otherwise, your ground is just
floating and will pick up just about everything floating around the ether.
The hum/noise will tend to get noticeably better (or worse) when you touch
the ground on your panning VCA board.  You will be providing a slight path
to ground with your body, or else an attenna.

If you are grounding the power supply through the AC power cord ground, THAT
ground might not be good.  Try a different outlet.

The possibility of a ground-loop would be indicated if you have more than
one path to ground, like if you power supply ground is tied to earth ground,
but your panning VCA ground is also tied to earth ground by a different
path.  Its usually best to have only ONE ground path to earth ground (like
at the power supply) and everything else go through that (known as a "star"
ground).

I hope this is of some help.

-----Original Message-----
From: Synth-diy [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of
Joe
Sent: Monday, March 07, 2016 9:29 PM
To: Tom Bugs
Cc: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] panning vca

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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> >>>>>>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
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> >
> >
> 


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