THAT2180 confusion

oolfur · Joined: Oct 08, 2015 Posts: 12 Location: NY

hey board,

I am trying to scale 10v CV to work with some THAT2180B chips I have - and the datasheet is a bit confusing to say the least...

here is the sheet ; http://www.thatcorp.com/datashts/THAT_2180-Series_Datasheet.pdf

according to page 4, using the positive control port I need to scale my 10v CV down to 720mV, and offset it by negative 540mV. am I right?

now here is my main problem...

I am so bad at math! let alone applying it to electronics

but i'm trying to learn albino

I plan to buffer the output of the VCA with a 5532 (as recommended by THAT in one of the design notes) and am hoping I can use the second unused opamp to do the scaling/offset.

How can I effectively scale and offset my CV to be compatible with my VCA?

many thanks for your help!
-oolfur

LFLab · Posted: Wed Dec 09, 2015 8:44 am Post subject:

There are a couple of projects with published schematics which use the 2180, those might be a better starting point than the datasheet (although they are usually pretty good at THAT).

ACXsynth VCA
GMSN Pure VCA

piedwagtail · Posted: Thu Dec 17, 2015 8:16 am Post subject:

I did kick my ACX version into touch for awhile, but these recent posts encouraged me to re-examine the situation.

I used a 10k trimmer with a 1k to -15V.
CV opamp mixing was all 47k in and 1k5 for the feedback resistor.
Trimming with a 0-5V envelope/gate gave a good area of linear operation and clipped into a square.
I am using a signal mixer to attenuate and mix the signal.

It works fine but does need attenuation control for both signal and CV. Having a 'scope for assessment is....a very good idea.

R

LFLab · Posted: Fri Dec 18, 2015 4:43 am Post subject:

That's interesting, my own build of the ACXsynth VCa also needs attenuation, but I figured this was just because of the need to adjust it, maybe it needs different resistors, will need to look into it, because they are pretty nice VCA's.