2 questions about the .vca

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lilakmonoke
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2 questions about the .vca

Post by lilakmonoke » Sat Jun 23, 2012 8:23 am

just got a .vca and its a great sounding vca. as there is nada manual i have 2 questions:

- the ac/dc switch refers to input signal or cv? i can hear no difference either way. what does it do?

- the vca doesnt close at zero voltage all the way. does that need to be adjusted or is it supposed to close at neg. voltage?

ps: i did an audio test of the .vca, oakley classic vca and cwejman 4mx in the next .vca thread. very interesting!

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tIB
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Post by tIB » Sat Jun 23, 2012 9:07 am

^ mine closed- what envelope are you using?

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lilakmonoke
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Post by lilakmonoke » Sat Jun 23, 2012 12:12 pm

the envs are programmed in pd, so i know exactly they are 0 to 5 volts! probably have to adjust it, but which trimmer? stg needs to cough up basic manuals i think.

what about the acdc switch you have any clou?

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Post by lilakmonoke » Sat Jun 23, 2012 4:41 pm

nobody knows what that switch does or is it just a dumb question? all you .vca users never wondered?

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Post by tIB » Sat Jun 23, 2012 4:47 pm

^ I just thought it changed between AC and DC coupled- so you can use the .VCA on CV or audio.

As for trimmers Ive no idea, sure suit will chime in and guide you through it though when he sees this...

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Post by mojopin » Sat Jun 23, 2012 4:53 pm

viewtopic.php?t=31529

someone else had your issue with bleed. mine doesn't have that problem. interesting that you like this better than the cwejman as i have both. i haven't done comparisons but maybe i should stop just using the .vca for processing cv.

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Post by lilakmonoke » Sat Jun 23, 2012 4:57 pm

tIB wrote:^ I just thought it changed between AC and DC coupled- so you can use the .VCA on CV or audio.

As for trimmers Ive no idea, sure suit will chime in and guide you through it though when he sees this...
i thought so too but it doesnt seem to make a difference on either. the way the layout is i thought it refers to the control voltage not the input signal.
interesting that you like this better than the cwejman as i have both. i haven't done comparisons but maybe i should stop just using the .vca for processing cv.
im in the middle of a major berlin school sequencing project and that vca works magic on fast tg type sequences. definitely a waste of talent on cv only.

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Post by lilakmonoke » Sat Jun 23, 2012 5:08 pm

ok so here is the answer to the mystery switch, thanks!
In DC mode, output_signal = input_signal * control_signal, which is the regular behaviour of linear VCAs.
The AC mode adds DC filtering: constant values (or DC offsets) are suppressed at the output. This mode is usually not recommended for attenuating control signals with the VCA.
that means i should leave it on dc all the time for both audio and cv? because why should there be offsets in an audio signal?

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Post by mojopin » Sat Jun 23, 2012 5:11 pm

it depends on the audio. with a bunch of modulation you can get offsets introduced. also, some oscillator waveforms are offset such as a pulse wave.

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Post by suitandtieguy » Sun Jun 24, 2012 2:34 am

sorry, i've been away from the computer all day.

if your .VCA won't close all of the way you have an offset issue on your control source. the Doepfer EG mentioned in the previously linked thread and the Circuit Abbey ADSR both have output offset issues.

you can blame my module if you want, but if you unplug the control source you'll see that it does indeed close all of the way.

the EGs i use in my live rig are Synthesizers.com and Music From Outer Space ADSRs. i don't have any issue with them.

i opted to put the AC/DC switch on there because i find sometimes you have DC offsets with lots of audio processing that will make the VCA "thump" a bit, this prevents that.
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lilakmonoke
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Post by lilakmonoke » Sun Jun 24, 2012 4:15 am

thanks, im not blaming anyone or anything in particular ;-) i program my own envelopes in pure data via es-3 so im pretty shure about the voltages being from 0-5. is there a trim pot for adjusting?

thanks for the clarification about the switches, its a phantastic sounding vca. ill post some sound examples of my current production soon ... and i keep bugging schneider about ordering more stuff from you so no hard feelings!

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Post by Mitchk1989 » Mon Jun 25, 2012 1:50 pm

Just see if it closes with no jack in the cv input at all. If it takes a plug to stay open, you either have an es3 issue or a general system grounding issue. If it leaks with no plug, it's the .vca or a general system grounding issue.

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Post by felix le chat » Mon Jun 25, 2012 5:27 pm

lilakmonoke wrote:i program my own envelopes in pure data via es-3 so im pretty shure about the voltages being from 0-5. is there a trim pot for adjusting?
Did you check if the ES-3 really outputs 0.00 Volt when sending digital value "0" (digital silence) with Pure Data? :hide:

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Post by lilakmonoke » Tue Jun 26, 2012 1:24 pm

you guys seem to be right. if i unplug the cv (without any envelope) the vca closes all the way. if i add the cv lead it opens up to about a -47 db signal as opposed to -100. there is no signal from the soundcard going to the es-3 because i can see that in my mixer. its still a mystery to me as ive tested 4 vcas that way and the .vca is the only one who has that problem ... and i dont see how the es-3 could output a voltage if there is nothing coming from the soundcard. its just a d/a converter.

i still want to know if there is a trim pot to adjust the initial gain ... yes/no/which one?

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lilakmonoke
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Post by lilakmonoke » Tue Jun 26, 2012 2:00 pm

so i just checked with a multimeter. the es-3 outputs about 60 millivolts by itself without any signal going in. thats whats opening the vca? 60 mv is basically nothing.

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Post by det3 » Tue Jun 26, 2012 2:58 pm

Not at all. When you're dealing with 1V/Oct signals, 83.3mV is one half step on a piano keyboard. When I designed the quantizer on Archangel, the ideal was to have an offset of less than 1mV.
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Post by suitandtieguy » Tue Jun 26, 2012 3:31 pm

i'm sorry, there is no offset trimmer on the .VCA, the circuit doesn't need one.

you should offset your virtual EG in PD, it shouldn't be too hard. the ES-3 outputs swing both ways.
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Post by felix le chat » Wed Jun 27, 2012 1:39 am

lilakmonoke wrote:there is no signal from the soundcard going to the es-3 because i can see that in my mixer.
This never means the output voltage is zero. You have to calibrate it in Pure Data, and the calibration is likely to be different for each ES-3 channel.

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Post by lilakmonoke » Wed Jun 27, 2012 3:22 am

right! thanks to everyone for solving the tech riddle. now its back to making music ...

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