user52120: I created the circuit in this schematic on protoboard,

and the code,
https://github.com/elkayem/midi2cv
I use a dual opamp and a single dac, because i only need note and velocity.
The opto i use is, H11L1
It works but has a strange issue that i can not figure out.
The author says the code supports midi notes from 21 to 108.
When I send midi notes to test the device, 
(Arduino powered with +12, TL082 Opamp powered with +15 to GND )
The notes <= 36 gives +15V in the output of the opamp.
The note 37 gives +3.43V 
The note 38 gives +1.7V 
.
.
.then it increments as expected until note 108 which gives +7.52 V
Also to add I have +1.5V DC offset on the both outputs of the opamp.
(This, i can live with but i would love it not to happen. ) 
I would be very happy if you help me on this, thank you.

user52120: I changed the opamp to LM358 and all problems solved it works perfectly!
If you have enough motivation and time please explain me why, but i will research and learn anyway. 

52120: <p>I created the circuit in this schematic on protoboard,
<a href="https://i.stack.imgur.com/bOLG2.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bOLG2.jpg" alt="schamatic"></a></p>

<p>and the code,
<a href="https://github.com/elkayem/midi2cv" rel="nofollow noreferrer">https://github.com/elkayem/midi2cv</a></p>

<p>I use a dual opamp and a single dac, because i only need note and velocity.
The opto i use is, H11L1</p>

<p>It works but has a strange issue that i can not figure out.</p>

<p>The author says the code supports midi notes from 21 to 108.</p>

<p>When I send midi notes to test the device, </p>

<p>(Arduino powered with +12, TL082 Opamp powered with +15 to GND )</p>

<p>The notes &lt;= 36 gives +15V in the output of the opamp.
The note 37 gives +3.43V 
The note 38 gives +1.7V 
.
.
.then it increments as expected until note 108 which gives +7.52 V</p>

<p>Also to add I have +1.5V DC offset on the both outputs of the opamp.
(This, i can live with but i would love it not to happen. ) </p>

<p>I would be very happy if you help me on this, thank you.</p>
 52120: <p>I changed the opamp to LM358 and all problems solved it works perfectly!</p>

<p>If you have enough motivation and time please explain me why, but i will research and learn anyway. </p>
