Voltage Controlled Signal Amplitude

[CutRock]

Hi all -

First, as a preface, I have a very limited EE background. So, if possible, a simple solution would be much preferred. Along those same lines, as I'm not familiar with much of the terminology surrounding audio electronics, this may be a very straightforward question - so my apologies if this is something I could have looked up quite easily if I knew of the right keywords.

For background, I've struck an interest in analog synthesis and have started researching schematics for the different components I'll eventually build. To keep my oscillators as versatile as possible, I'd like to be capable of selecting which waveform to output from a rotary switch, but also be able to run that selection into other VCO's. To accomplish this, I believe the easiest mechanism would be to control the signal using a voltage which can be run to each VCO to mirror the selection.

Essentially, this is the functionality I'm looking for:


The effect can be discrete - either having the signal unaltered or completely off, and doesn't need to be able to output the signal at continuous levels of attenuation.

Thanks all.

[sawreyrw]

If you really want what the picture shows, you could easily implement this with an analog switch. 15 volts may be a little high for newer devices, but you could use a lower voltage signal at the input and then amplify it at the output.

[Mooly]

Your picture does show just a simple switching arrangement whereby the output is shut off as the control voltage changes its logic level.

As sawreyrw mentions, an analogue switch IC would do this. Many types available. If you could put up with lower levels you could use the common CMOS 4016/4066 IC's to experiment with.

JFET's are another option and can work well if applied correctly.

One thing though when switching any "audio" type waveform. If the switching occurs part way through a cycle (not at the zero cross point), then you will get a click/pop/thump in the output as you are effectively switching when the waveform is at some "equivalent" DC value. I'm not sure if there are specialist switching IC's available to cater for that.

[Dirk95100]

Originally Posted by CutRock

For background, I've struck an interest in analog synthesis and have started researching schematics for the different components I'll eventually build. To keep my oscillators as versatile as possible, I'd like to be capable of selecting which waveform to output from a rotary switch, but also be able to run that selection into other VCO's. To accomplish this, I believe the easiest mechanism would be to control the signal using a voltage which can be run to each VCO to mirror the selection.

Essentially, this is the functionality I'm looking for:


The effect can be discrete - either having the signal unaltered or completely off, and doesn't need to be able to output the signal at continuous levels of attenuation.

Thanks all.

What you need is a VCA (Voltage Controled Amplifier)
Loads of diy stuff out there. Start http://www.musicfromouterspace.com/a...DLLVCA001.html

[HighTec]

You can also look at how Ecler has implemented the VCA THAT1280 in their PAM4100 and PAM6100 amplifiers.

THAT1280 Datasheet --> http://www.thatcorp.com/datashts/THA..._Datasheet.pdf

Ecler PAM4100 service manual --> Ecler Diagrams, Schematics and Service Manuals for FREE

[HighTec]

Ooops, made a mistake. It's THAT2180 not 1280 like I wrote. Btw, why can't I edit my post? Mods, an edit button would be a nice feature, don't you think!?

[Mooly]

Originally Posted by HighTec

Ooops, made a mistake. It's THAT2180 not 1280 like I wrote. Btw, why can't I edit my post? Mods, an edit button would be a nice feature, don't you think!?

You can... but only for around 30 minutes after posting.

[HighTec]

Originally Posted by Mooly

You can... but only for around 30 minutes after posting.

Yeah, enough time to edit.

[Nico Ras]

How about a relay???

[CutRock]

Thanks all,

Originally Posted by sawreyrw

If you really want what the picture shows, you could easily implement this with an analog switch. 15 volts may be a little high for newer devices, but you could use a lower voltage signal at the input and then amplify it at the output.

sawreyrw - This looks like a very straightforward and cheap solution. If possible, I'd prefer not to have to adjust the amplitude of the waves before and after, but if I can't get anything else working as is, this is probably the route I'll take.

Originally Posted by Mooly

JFET's are another option and can work well if applied correctly.

Thanks Mooly - would you mind providing a reference, resource or search term that I can look into for how to accomplish this? Also, what do I have to consider to get this option to be 'applied correctly?'

Originally Posted by Dirk95100

What you need is a VCA (Voltage Controled Amplifier)

Originally Posted by HighTec

You can also look at how Ecler has implemented the VCA THAT1280 in their PAM4100 and PAM6100 amplifiers.

Thanks Dirk & HighTec - Although I'm sure VCA's would accomplish what I'm looking for, the VCA IC's (THAT2180) seem a little expensive for what I need to accomplish and a diy VCA would probably be quite a bit more than what I need for only a discrete on/off switch. Nevertheless, I appreciate your suggestions.