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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
Psycho LFO
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synthesist



Joined: Feb 17, 2011
Posts: 79
Location: austria
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PostPosted: Wed Jun 22, 2011 7:34 am    Post subject: Psycho LFO
Subject description: gets picked up by white noise source...
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hey!

I've build a mfos soundlab including the white noise source. Also I build a reduced version of the psycho LFO. My problem is, that even if I dont plug the psycho lfo in any input of the soundlab, the white noise source picks up the clock signals. It actually "receives" the clock like a radio would do it.

It's not only the psycho lfo. Also other clock signals from CMOS chips bleed through.

So my question is: could it be a shielding problem, since I use kind of wood for my frontpanels. Most people would use aluminum with a connection to ground.

I am using two 9 volt batteries for a bipolar powering, but I am sure this cant be the main problem, cause I got the same problems when I build CMOS synths and power them with only 1 battery.
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andrewF



Joined: Dec 29, 2006
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PostPosted: Wed Jun 22, 2011 7:50 am    Post subject: Reply with quote  Mark this post and the followings unread

certainly could be a ground connection problem/poor shielding.

Though quite possibly there are not enough decoupling capacitors and the signal from the psychoLFO is getting onto the power rail.
These are not always shown on schematics but every module should have a 10uF cap and a 100nF cap on each power rail for decoupling, as close as possible to where the power connection is.

Another cause of this is when the power supply is being overworked, tho maybe not relevant with batteries.
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synthesist



Joined: Feb 17, 2011
Posts: 79
Location: austria
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PostPosted: Thu Jun 23, 2011 3:17 am    Post subject: Reply with quote  Mark this post and the followings unread

just soldered the decoupling resistors. Only the 100uF ones cause there is no space left for the 100nF ones. But it didnt help of course, because I just figured out that also the oscillators from the soundlab interact with the white noise.
By the way - the oscillators really control the white noise like transmission!
maybe someone smart could use this as a new synthesizer control without cables Wink

thanks for the help. You are the inventor of this modular-puppet-synth? Thats a great device!
I saw it on youtube and I wondered how you "shield" this thing?
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andrewF



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PostPosted: Thu Jun 23, 2011 4:34 am    Post subject: Reply with quote  Mark this post and the followings unread

synthesist wrote:

I saw it on youtube and I wondered how you "shield" this thing?


the Paia tube pre-amp has shielded cables up to the tubes on the side of the head. Otherwise there is no shielding and never had a problem with crosstalk. When I built it I was pretty clue-less about electronics, just lucky I guess dunno
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kkissinger



Joined: Mar 28, 2006
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Location: Kansas City, Mo USA
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PostPosted: Thu Jun 23, 2011 10:17 am    Post subject: Reply with quote  Mark this post and the followings unread

You may want to try larger (2 to 4 times the ohms) resistor values for the LED current-limiting resistors.

When I built the Super-psycho modulation source (similar to the psycho modulation source) I discovered that when the oscillators were tuned close to each other that they would eventually couple. Furthermore, there was some bleed from the module to some other modules. After I replaced the LED current-limiting resistors with higher values, the coupling and bleedthru stopped.

_________________
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http://kevinkissinger.com
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