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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
noise cornucopia picking up signals
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roborobert



Joined: Jan 15, 2013
Posts: 24
Location: austria

PostPosted: Sun Oct 13, 2013 1:14 pm    Post subject: noise cornucopia picking up signals
Subject description: oscillators (and others) show up in noise output
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hey there,

as far as i searched this subforum i couldn't find much helpful information on this subject.
my noise cornucopia module is picking up the signals of other vcos, lfos and envelopes.
it does it so intense that the module becomes useless. e.g. random gates not random at all anymore...

is it likely that my noise transistor is just not noisy enough?
i tried many (3904, bc550, 2n2222s, 2sc945), but even with the best scratch (...whatever) metal can 2n2222, i still had to crank up the trimmer quite a bit to get the desired aproximated +/- 5V.
is it likely that all my transistors are supersilent?
i clipped off the collector lead.

i already added ferrite beads on the power rails at the module.
also (as suggested in an older thread) i tried to add capacitance on my power bus and on the module itself ( i ended up with two 1000uF Caps showing no sign of improvement).

i do know that i have quite some party going on on my power rails, envelopes, vcos and lfos are visible there when i check the power bus on my scope in ac mode (they are also audible on the vcos themselves). if i can read my scope right the intensity is about 5-10mV for the negative rail and a bit more for the positive.
i would love to get rid of this uninvited lot but ferrite beads on each and every module as well as shielded cables all over did not do the job.

i hope someone can help,
best, rob
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rumblin_cynth_rampo



Joined: Nov 15, 2012
Posts: 33
Location: Cardiff, Caerdydd, UK

PostPosted: Fri Oct 18, 2013 7:32 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Rob

I have only bread boarded this module.

I found that 2n3904 were OK for the noise level I went through about 20 of them and about 5 were good. Ray recommends the 2n5172 and I tried a couple of those and they were all good with little twiddling of the pots to get a nice level. Didnt have much luck with 2n2222s


Have you tired to power the module of a separate power supply (bench supply) to see if it still picking up junk.

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wackelpeter



Joined: May 05, 2013
Posts: 208
Location: germany
Audio files: 8

PostPosted: Thu Feb 11, 2016 1:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

hm... finished my noise cornucopia yesterday and it's picking up signals too...

I have 100nf decoupling caps for all IC's, ferrite Beads and 10uF on the power rails... and shielded cable on all 5 noise Outputs with grounded shiel on one side...

tried switching between boths PSU on the "Signal" PSU it's picking up my 4046 VCO (the VCO is clean and not picking up noise)
whereas on the "Divider, Sequencer" PSU it's picking up the signals from the gates etc. the faster my main clock runs the faster the Background signals are...

also my random gates are affected by this as those signals modulate the Amplitude of the White noise...

My White noise was calibrated to circa +/-5V...

Some thoughts what to do?
Any help will be much appreciated.

Maybe something i had to add:
I have cut off the collector of the trannie to avoid acting as antenna...
and in the Feedback path of the first amplifying op amp i have a 150 or 180K resistor with a 50k trimmer in series... so it's somwhere between 150k and 230k... so the noise Level from the 3904 shouldn't be too low i guess...
what i mean when the Level is to low and i'm picking up any signals i must amplify both to get the noise Level to +/-5V and when the noise is louder there's less amplification needed and therefore those signals where also less amplified...
but a i write this i believe it's nonsene... the AM Modulation on my noise is perhaps before the op amp and no matter how much i amplify my noise, both factors will be amplified... have to pull my board otu tommorrow again to have a look for this...

i'm running mine on +/-15V...

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wackelpeter



Joined: May 05, 2013
Posts: 208
Location: germany
Audio files: 8

PostPosted: Sat Feb 13, 2016 12:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

got this fixed...

seemed like it was very sensitive to noise over the power rails... as the same symptoms on both PSU'S appeared... tried to increase the Input caps to 22uF and adding more decoupling caps over the board... but no luck...

then decided to simply add 2 Input Regulators 2x10R and 78L12 & 79L12 and afterwards 2x100nf before my original beads and caps and voila it worked...
maybe a bit unusual and luckily easy to convert on stripboard when you have enough space left...

so now only my noise volume must be raised a bit and a resistor increased and hopefully my random gates will work from start...

edit: works well with a 150k and 50k trimmer in series... just had to pull the trimmer a bit... maybe a log pot seems to be more usefull for gate control as it changes very quick from fast gates to slow randon gates at about 1/4 or 1/3 of pot turn...

maybe something i'm not sure about... my control for ticks on grainy noise seems to have no effect... when i look on my scope both grainy noise Outputs seem to have a constant 5V Peak to Peak value... Looks a bit like it was cut to that peaks... there's neither a visible nor an audible effect...

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