CEM3378 + SID Idea

Design Concepts
1

finally my holliday started, so its soldering time again.

next project is the AOUT_LC and my CEM VCF.

I had a nice idea, to build a Box like this:

So there are

2 Audio In

2 CV In          for controlling the CEM with other analog gear

2 CV Out        to controll other analog gear with the midibox

1 Audio Out

further

2 Depth knobs      controlling the depth of the midibox and external CV

2 Filter Knobs        controlling the CEM manually

1 Master Vol

1 Switch              to select between MIDIBOX or external CV

but since im quite a noob in designing my own circuits maybe someone can have a look on this layout I made, if it’ll work.

I tried to limit the CV voltage for the CEM to 5V using a ZENER diode. I hope in this way the ZENER will cut off any voltage above 5V?!

(for example when the manual CutOff pot delivers already 5V and the AOUT delivers also some Volts) don’t know if i made that right.

further i’m not sure about the CV out (red box) is it the right way to go to buffer the output with an OpAmp?

I know it’s a flaky design, but it’s like i said… me <- n00b ;D

so long, Julian

2

Nice one mate, keep it coming :slight_smile:

I’d love to see a multi-channel version!

PS.. .Do I know you from IRC as Monome?

3

another question…

Is it possible to drive the TL072 on the AOUT_LC with +/- 5V isntead of 12V?

since the CEM doesnt need more than 5V CV anyway…

so long,

julian

PS: no, i’m quite seldom on the IRC…

4

Is it possible to drive the TL072 on the AOUT_LC with +/- 5V isntead of 12V?

since the CEM doesnt need more than 5V CV anyway…

No, the TL072 is a OPAMP. The input voltage of such amps must never exceed the supply voltage! The D/A ladder will deliver up to 5V which would be the absolute maximum allowed.

You will at least get heavy distortion on the outputs.

Raphael

5

On the other hand: the full +/-5V range is not required for the CEM3378 anyhow, and I’m also not sure, if a buffer OPAMP is really useful

I remember, that during my experiments some weeks ago I added an additional pot as voltage divider between the AOUT_LC outputs, and the resonance/CutOff input of the filter in order to reduce the control range.

This remembers me, that I wanted to determine the best fitting divider values for my own final board (which will be a quad-filter) - so, i can give you more infos soon

Best Regards, Thorsten.

6

The TL07x family will happily run up to +24v (+- 12v) so you should be fine. It’ll give slightly more headroom than +9-12v as well, good for transients.

That said, i’d probably just use a Mosfet buffer/gain stage as it’ll draw less current and take up less space.

I’m looking forward to seeing how this one turns out :wink:

7

another question…

Is it possible to drive the TL072 on the AOUT_LC with +/- 5V isntead of 12V?

No. It’s unity gain stable, but NOT an rail-to-rail opamp. Better to use bigger margins for opamp supply. (You can find rail-to-rail, unity gain stable opamps but it will cost ya)

(By the way, the circuit is averaging not an adder) It’s hard to hit the rails this way without CV inputs being over the rails. And hitting the rails with opamp isn’t LETHAL :smiley:

Moebius

8

On the other hand: the full +/-5V range is not required for the CEM3378 anyhow, and I’m also not sure, if a buffer OPAMP is really useful

I remember, that during my experiments some weeks ago I added an additional pot as voltage divider between the AOUT_LC outputs, and the resonance/CutOff input of the filter in order to reduce the control range.

This remembers me, that I wanted to determine the best fitting divider values for my own final board (which will be a quad-filter) - so, i can give you more infos soon

Best Regards, Thorsten.

I’m really looking forward to hearing more about your quad-filter! I have 4 CEM3378 here that’s only waiting to be put into good use (that is, connected to the quad SID i’m planning to build)