Combining 2 CV signals

[radiance]

Here a link to an online simulation I made https://tinyurl.com/y92dxtbm

What I need is a CV signal (roughly) between +8V and +15V.
This is achieved by either a potentiometer or an external input, or both. The external input gets a signal between 0V and +13,5V (Buchla 208).
On the right side you can change the potentiometer and the voltage from the external input.
The way it works now in the simulation would be perfect...(I hope the real world agrees)

Question: I added two schottky diodes to "kinda" isolate these two sources (the potentiometer and the external input). Is this an OK method for this? I tried opamp summing, extra buffers etc.etc. but somehow this works best and is simple.

 

[radiance]

Just to clarify a bit more...I don't want to sum the two signals, I want to "combine" them.

 

[user 37518]

Just to clarify a bit more...I don't want to sum the two signals, I want to "combine" them.

Can you explain what you want to achieve, I don't understand.

Summing and combining are the same thing

 

[radiance]

I want to be able to use both CV signals at the same time without them affecting each other.
The way it behaves in the simulation is what I want. I achieved this by adding the Schottky diode's and I'm wondering if this is a "correct" way of doing things...

 

[user 37518]

I want to be able to use both CV signals at the same time without them affecting each other.
The way it behaves in the simulation is what I want. I achieved this by adding the Schottky diode's and I'm wondering if this is a "correct" way of doing things...

Ok, some questions:

- Do you want an either/or CV, for instance when one CV signal is present the other CV signal should be automatically bypassed or do you want the output of the opamp to be CV1 and CV2 both at the same time?

If what you are looking for is the latter, a simple inverting summing amp will be able to do this, since you are summing currents. Due to the effect of the virtual ground, none of the inputs will interact with the other inputs. This is not the case when you use voltage summing, for instance passive summing.

 

[radiance]

I want both CV signals (opamp and CV potentiometer) to be present at the same time but not summed.
Before I used a switch to switch between the two CV signals but due to a lack of space I want to get rid of the switch.
I tried virtual earth summing but since both CV signals are between (roughly) +8V and +15V the results are not what I want. The simplest way was with the two schottky diodes.

If you play around with the "CV voltage" and "voltage" sliders in the simulation and watch the scope you'll see what I'm trying to achieve here.

 

[radiance]

Someone @ Modwiggler suggested this method...

https://tinyurl.com/y85w7oqg
I kinda like this better than my idea...