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loss1234
Joined: Jul 24, 2007 Posts: 1536 Location: nyc
Audio files: 41
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Posted: Thu Jan 17, 2008 6:02 pm Post subject:
renee/ken stone VCA (vca3) problems with bleedthrough |
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I got a new ken stone/Renee schmitz vca finished this week. works good EXCEPT for a tiny (but infuriating) amount of signal bleedthrough (or whatever the term is).
when i connect say a vco to the input, connect a CV in to the cv in and connect the out to my amp or computer, even with NO cv (from envelope or whatever) i hear a tiny amount of the vco bleeding through. Its driving me nuts. Now i tried moving all the offset trimmers and the cv trimmer does what it is supposed to as far as making sure the envelope turns a note on and off. but wayyy in the background i can hear a tiny bit of the constant vco tone
advice?? is this a common vca problem? could it be that the vco output is TOO hot for the vca so some of it bleeds through?
thanks _________________ -------------------------------------------- check out various dan music at: http://www.myspace.com/lossnyc
http://www.myspace.com/snazelle
http://www.soundclick.com/lossnyc.htm http://www.indie911.com/dan-snazelle |
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blue hell
Site Admin
Joined: Apr 03, 2004 Posts: 24075 Location: The Netherlands, Enschede
Audio files: 277
G2 patch files: 320
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Posted: Thu Jan 17, 2008 6:11 pm Post subject:
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Some bleed is normal for analog VCAs, but too much aint ...
Ideally you should quantify this by measuring the output for the VCA fully opened and fully closed ... you could do that by recording the VCA output for those two situations and then look in the wave editor how many dB's of difference there is in the signals, that number would tell if it's good or bad _________________ Jan
also .. could someone please turn down the thermostat a bit.
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loss1234
Joined: Jul 24, 2007 Posts: 1536 Location: nyc
Audio files: 41
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blue hell
Site Admin
Joined: Apr 03, 2004 Posts: 24075 Location: The Netherlands, Enschede
Audio files: 277
G2 patch files: 320
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Posted: Thu Jan 17, 2008 6:36 pm Post subject:
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loss1234 wrote: | this is common? |
That it drives you nuts yes that's good, it brings enlightenment
From how you describe it many dB's might be over 50, assuming you can hear some street noise as well .. that'd not be really bad ... just not too good ... _________________ Jan
also .. could someone please turn down the thermostat a bit.
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frijitz
Joined: May 04, 2007 Posts: 1734 Location: NM USA
Audio files: 54
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Posted: Thu Jan 17, 2008 7:47 pm Post subject:
Re: renee/ken stone VCA (vca3) problems with bleedthrough |
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loss1234 wrote: | I got a new ken stone/Renee schmitz vca finished this week. works good EXCEPT for a tiny (but infuriating) amount of signal bleedthrough (or whatever the term is). |
That design may not totally turn the control current off. I usually design so that there is enough leeway to provide a hard turnoff. You could try connecting a large resistor from where the three bases are connected together to the (-) supply. Something like 1M or so should help.
Also make sure your audio input signal wires are well separated from the rest of the circuit, as pickup can also be a problem.
Remember to let us know if this works.
Ian |
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loss1234
Joined: Jul 24, 2007 Posts: 1536 Location: nyc
Audio files: 41
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Rykhaard
Joined: Sep 02, 2007 Posts: 1290 Location: Canada
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Posted: Thu Jan 17, 2008 10:40 pm Post subject:
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Loss - what are you using in the transistors section? Discrete transistors? A chip? (Can't remember the board layout at the moment and it's all downstairs.)
In my last 2 that I completed, I hand matched the trannies to 3 decimal points on my Fluke 83 and I have no bleed through at all. (That I can tell with my 25+ years of damaged ears. ) I'm far more'n happy with mine in that regard and wont use the chips for them any more.
Curious. |
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Coriolis
Joined: Apr 11, 2005 Posts: 616 Location: Stilling, Denmark
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Posted: Fri Jan 18, 2008 5:17 am Post subject:
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Hi Rykhaard, what do you match for? Hfe?
C |
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loss1234
Joined: Jul 24, 2007 Posts: 1536 Location: nyc
Audio files: 41
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Posted: Fri Jan 18, 2008 5:22 am Post subject:
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i am using the lm394 chip...
and for the regular transistors, 2n3904's and 293906's
here is the instructions for setup. i dont get what the offset does, but it does not seem to effect this. the CV init is the trimmer which does get rid of bleed through during CV but not when there is NO CV.
thanks
"Setting up involves adjusting three trimmers.
Offset is used to set the DC offset of the output to zero. CV Reject is used to null out the effect of the control voltage on the output.
Connect a varying waveform of low frequency (triangle wave from an LFO is ideal) into the CV input of the VCA, and connect the output of the VCA to a control voltage input of a VCO. Monitor the output of the VCO. You should now be able to adjust these trimmers so that there is no modulation present on the output, and the output is at zero volts. Note that these trimmers interact to some extent, so you will need to alternately adjust them until the best result is obtained. On the prototype, CV bleed through was totally eliminated.
CV Init is used to set the VCA to zero gain at 0 volts CV input. Feed an audio signal into an input, and monitor the output. With no CV at any of the inputs, and the optional external Initial Gain pot, if used, set to its zero position, adjust this until no signal is heard. " _________________ -------------------------------------------- check out various dan music at: http://www.myspace.com/lossnyc
http://www.myspace.com/snazelle
http://www.soundclick.com/lossnyc.htm http://www.indie911.com/dan-snazelle |
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Dego
Joined: Apr 22, 2008 Posts: 139 Location: Sweden
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Posted: Thu Aug 07, 2008 11:38 pm Post subject:
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Is it still bleeding? Did you manage to fix it? |
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loss1234
Joined: Jul 24, 2007 Posts: 1536 Location: nyc
Audio files: 41
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jean-louise
Joined: Apr 27, 2009 Posts: 73 Location: berlin
Audio files: 2
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Posted: Sun Aug 30, 2009 11:01 am Post subject:
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i have a similar problem with a VCA-2 wich i think is the predecessor. it uses a NE5543.
i have powered everything (VCO, VCF, ADSR, VCA) from a dual battey setup (+/-9V).
the VCA is very quiet and there's massive bleedthrough.
when i power only the VCA from two different batteries with only ground tied together, it is still quiet, but there's no audible bleed at all.
my conclusion would be:
the bleedthrogh creeps through the power lines.
probably something's wrong with a part of the VCA, maybe a transistor or the NE5534, i can't imagine that it's supposed to be so quiet. especially compared to the dr-110 single transistor VCA
hm |
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jbaken
Joined: Feb 07, 2012 Posts: 7 Location: brooklyn
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Posted: Wed Apr 11, 2012 7:57 pm Post subject:
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Sorry to dig up an old thread but im having a similar problem. I get a bit high passed sounding bleed when I plug my vco into my cgs vca. I'm using matched transistors and separate plugs for the two modules. |
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eXisteNz
Joined: Jun 08, 2010 Posts: 48 Location: Italy
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Posted: Fri Mar 08, 2013 4:35 am Post subject:
No solutionS |
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I've built the vca but i have the same problem....do you still have that bleed? |
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wackelpeter
Joined: May 05, 2013 Posts: 461 Location: germany
Audio files: 10
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Posted: Sat Jul 19, 2014 8:22 am Post subject:
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i just finished this VCA from Bergfotron:
http://hem.bredband.net/bersyn/VCA/lm13600%20vca%201.htm
whilst adjusting it i noticed that it's different from it's Outputs as my VCA3+ i've built...
the one VCA has about 50% of the Input signal silenced while my VCA3+ cuts nearly 100%
altough the 50% seem to be normal for that LM13700 VCA but what makes me wonder is that this Output is centered via 0V/GND while the VCA3 always put's a steady positive voltage out...
The Output of my VCA3+ is centered around +7V... is this normal? have i made a mistake?
I mean audiowise it makes not much difference but when i want to modulate a CV theres is always a positive signal of at least +7V left varying from 5,5V to 8,5V when VCA is open...
when remving the wiper of trimpot for CV rejection from +15V it is nearly 0V when closed ...
whilst the VCA is open the Amplitude swings between those ca.0V to nearly 4V or 0V to 8V depending how the Manual control pot is turned...
when i remove the wiper pot of that trimmer from +15V also the signals are a bit distorted and folded not as symetrical as with the wiper connected...
maybe important instead of a dual Transistor i used 2x BC550C i guess can't check that at the Moment as they're glued together and i had to desolder them...
is that the correct an normal behaviour of the VCA3+? Are there any mods possible to Center the Output around GND not losing the Performance in silencing the Audio signals? _________________ https://soundcloud.com/bastian-j |
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wackelpeter
Joined: May 05, 2013 Posts: 461 Location: germany
Audio files: 10
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wackelpeter
Joined: May 05, 2013 Posts: 461 Location: germany
Audio files: 10
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Posted: Sun Mar 01, 2015 10:17 am Post subject:
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Not a real bleedthrough issue with the Signal but some clicks when i have an envelope with short times or a fast running lfo connected to my VCA...
tried to reduce this with a Little Lowpass including an 330R resistor in series and a 330nF cap to gnd at the CV Input...
This reduces the clicks a lot and make things a bit smoother...
Are there any other good or better ways to solve this? I can remember reading something about a similar Problem here in the Forum but can't remember or find the thread right now.
Any advice is of course welcome...
cheers Bastian _________________ https://soundcloud.com/bastian-j |
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