MUFF WIGGLER Forum Index
 FAQ & Terms of UseFAQ & Terms Of Use   Wiggler RadioMW Radio   Muff Wiggler TwitterTwitter   Support the site @ PatreonPatreon 
 SearchSearch   RegisterSign up   Log inLog in 
WIGGLING 'LITE' IN GUEST MODE

Variable modulation using a VCA
MUFF WIGGLER Forum Index -> 5U Format Modules  
Author Variable modulation using a VCA
craigyb
I have been considering how you apply modulation using a mod wheel from an external controller or in fact any voltage source.

I'm guessing that a mod wheel will just generate a voltage just like a pitch bend wheel does.

So my idea is this, will it work?

LFO into a VCA and the VCA level controlled by the mod wheel.
Output of the VCA to the FM input of a VCO/s

To me it should work, I was just wondering how other people apply modulation in a performance.
ranix
yep, works just fine. I use the SSL octal linear VCA to do it and other similar things using the Synthesizers.com Q143 and/or foot pedals

the VCA is attenuating the signal. The peak to peak voltage difference is decreased, which decreases the "volume" of the LFO, and changes in the mod wheel or foot pedal or whatever basically are changing the amount of volume decrease
craigyb
Thanks, I'll give it a try when I get 5 mins in the studio
Navs
The mod wheel could be even simpler if it just acting as an attenuator and you can patch directly into its potentiometer. You wouldn't need a VCA if you only want manual control.
craigyb
But that's not really possible if your doing MIDI to CV conversion. I think I would only get a CV for the mod wheel.

If I had a discrete 1V/OCT keyboard then it might be possible to patch that way if it's design allowed or you could mod it so.
gregae
ranix wrote:
yep, works just fine. I use the SSL octal linear VCA to do it and other similar things using the Synthesizers.com Q143 and/or foot pedals

the VCA is attenuating the signal. The peak to peak voltage difference is decreased, which decreases the "volume" of the LFO, and changes in the mod wheel or foot pedal or whatever basically are changing the amount of volume decrease


True, but for a Q108 VCA, the output will swing between 0 and +5 Volts - it can't go negative. If the input to the VCA input is a bipolar signal, only the positive portion of the input signal will appear at the output (attentuated according to the VCA's CV input) This would give the OP only half of what was expected.
Navs
craigyb wrote:
But that's not really possible if your doing MIDI to CV conversion. I think I would only get a CV for the mod wheel.

If I had a discrete 1V/OCT keyboard then it might be possible to patch that way if it's design allowed or you could mod it so.


But of course d'oh! lol Me and my analogue mind ... I was thinking of something like the Analogue Systems wheels that allow for an external input.

(edited for correct module)
jkjelec
Some VCAs are AC coupled....these would be intended only to reduce the level of audio signals (approx. 20 Hz minimum frequency), and would not properly pass though/attenuate a low frequency signal like an LFO or a DC signal. You would need to understand the specs of your VCA, or else just give it a try and see if it works.

The module's circuit designer might choose to AC couple a VCA in order to optimize it's performance for Audio signals. (If their design intent is to provide the best possible VCA for audio.)
jkjelec
gregae wrote:
Quote:
True, but for a Q108 VCA, the output will swing between 0 and +5 Volts - it can't go negative. If the input to the VCA input is a bipolar signal, only the positive portion of the input signal will appear at the output (attentuated according to the VCA's CV input) This would give the OP only half of what was expected.


Wow that is the strangest thing I ever heard! This is heading into Paia Gnome type circuit design world screaming goo yo Just joking! hihi
craigyb
My VCA has AC and DC coupling, but the lower cut off frequencies did concern me. I will have to try it out, see what works
steffengrondahl
gregae wrote:
True, but for a Q108 VCA, the output will swing between 0 and +5 Volts - it can't go negative. If the input to the VCA input is a bipolar signal, only the positive portion of the input signal will appear at the output (attentuated according to the VCA's CV input) This would give the OP only half of what was expected.


This is not correct. The output of a Q108 is bipolar. So the input. The VCA only responds to positive voltages for control inputs (CV) - trying to modulate with a bipolar signal strips off the negative part.
ranix
gregae wrote:
True, but for a Q108 VCA, the output will swing between 0 and +5 Volts - it can't go negative. If the input to the VCA input is a bipolar signal, only the positive portion of the input signal will appear at the output (attentuated according to the VCA's CV input) This would give the OP only half of what was expected.


this does not seem to make sense
gregae
steffengrondahl wrote:
gregae wrote:
True, but for a Q108 VCA, the output will swing between 0 and +5 Volts - it can't go negative. If the input to the VCA input is a bipolar signal, only the positive portion of the input signal will appear at the output (attentuated according to the VCA's CV input) This would give the OP only half of what was expected.


This is not correct. The output of a Q108 is bipolar. So the input. The VCA only responds to positive voltages for control inputs (CV) - trying to modulate with a bipolar signal strips off the negative part.


Well this is certainly embarrassing oops. I totally misunderstood the description in the Q108 spec sheet (the 'Voltage Levels' section).

Sorry guys...
Rex Coil 7
steffengrondahl wrote:
gregae wrote:
True, but for a Q108 VCA, the output will swing between 0 and +5 Volts - it can't go negative. If the input to the VCA input is a bipolar signal, only the positive portion of the input signal will appear at the output (attentuated according to the VCA's CV input) This would give the OP only half of what was expected.


This is not correct. The output of a Q108 is bipolar. So the input. The VCA only responds to positive voltages for control inputs (CV) - trying to modulate with a bipolar signal strips off the negative part.


I think steffengrondahl is actually incorrect. Copied from the Q108 information page at Dot Com's website .....

"Voltage Levels
It's important to understand the voltage levels used to control the amplifier. The Q108 Amplifier responds to control signals that are 0 - 5 volts. Where 0 volts is off and 5 volts is full volume. The Q109 Envelope Generator produces 0 - 5 volt outputs which are perfect for use by the amplifier and can be patched directly. The Q106 Oscillator produces waveforms that are -5 - +5 volts, so if you want Amplitude Modulation (tremolo) you'll need to attenuate the signal by 2 (adjust the Control Level to 5) and shift it up (adjust the Gain control to 5) which will result in an on-off range. This attenuation and shifting (offset) can also be accomplished with a Q125 Signal Processor."


And ......

"AC and DC Signals:
The Q108 Amplifier will work for both AC and DC signals. This means you can control the amplitude of both audio (AC) signals and of slow moving or non-moving control signals (DC)."


This is a slightly different application but the concepts remain consistent with other uses.

Perhaps this helps .... seriously, i just don't get it


thumbs up

EDIT: Ok .. wait ..... I clearly have my head up my ass here ..... I'm totally wrong and have totally contradicted myself here ......but you see ...

I HAVE A SERIOUS MEDICAL CONDITION!!!!!! (see pic below)




Dead Banana

It's ok though, I am on a nationwide waiting list to have a clear bellybutton installed so I may be able to see when I'm walking ....

meh

lol lol lol lol lol
jkjelec
I see the misunderstanding that the Q108 description can cause. In the example being described, the Q106 VCO is being used as the modulator, NOT the signal being modulated. So this bipolar VCO needs to be scaled and offset so that its full swing is 0 to 5V rather than-5V to +5V. The signal being modulated, for example a VCO with an output of -5V to +5V, can be connected directly to the audio signal input of the VCA.
MUFF WIGGLER Forum Index -> 5U Format Modules  
Page 1 of 1
Powered by phpBB © phpBB Group