Nirokesan

SeqV4/AOUT_NG calibration procedure

6 posts in this topic

Can we agree on a procedure and update the WIKI page?  I did a preliminary calibration of my board last night. I assume I did it correctly, but maybe there's something I've overlooked or misunderstood. 

 

Basically did this:

1. Connect DMM to output header pins. 

2. Select 1V, adjust scale trimmer so DMM reads 1V, repeat up to 8V.  (Of course, now my 1V is off my an average of +10mV and 2V is off by +4mV)

3. Switch to bipolar modes. 

4. Select "middle", adjust bipolar trimmer so that DMM reads 0V

 

Is this correct?  Usually when adjusting something for v/oct, there is a scale and an offset trimmer, right?  That way the scale is correct across the full range.   Perhaps I need to first monitor the outputs at "min", then add that value to each test level?  Or do I just have to trim back the 8V result to 7.997V or so to get 1V result back closer to 1.000V?

thanks!

Share this post


Link to post
Share on other sites

The offset trimmer is only used in "bipolar" mode. Only the scale pot is used for unipolar. If you've tried calibrating from low and high ends of the scale (e.g. C2/C4) and the result is still not linear, then this is how your DAC behaves; there is nothing else to do. My channel 1 CV (AOUT_NG) is very non-linear and as such I can only use the gate.

Share this post


Link to post
Share on other sites

Thanks, 

yes I know in this case the offset is only for the bipolar null adjustment, I meant that other devices have an offset and scale (VCO, VCF, etc)

It might have been a good idea to make the AOUT_NG accept a through-hole socket so the SMD DAC could be soldered to an adapter board and easily swapped out to find a good one.  Although, this isn't like swapping out a transistor. $$$

Can you share with me the values for your channels (what you've decided is usable and unusable)?

  I haven't tried an "ear test" yet, still waiting for my new output boards to arrive. Maybe I won't even notice the non-linearity, it amounts to 1cent between 0-1V, half a cent from 1-2V, but not too bad above that.  Perhaps I can just use from 2V and above and pitch my VCOs down, I'd still have a decent 6 Octave range.  

Share this post


Link to post
Share on other sites

If the inaccuracy is only 1 cent, I'd say that's pretty good. From memory my channel 1 had some linear portions but others were off by a couple hundred millivolts.

It just comes down to the DAC; e.g. MAX525 is simply a better (and much more expensive) chip.

Share this post


Link to post
Share on other sites

Hello

8 hours ago, latigid on said:

My channel 1 CV (AOUT_NG) is very non-linear

 

4 hours ago, latigid on said:

From memory my channel 1 had some linear portions but others were off by a couple hundred millivolts

You may have an issue or faulty channel because it's seem out of the DA spec ?!?

Best

Zam

Share this post


Link to post
Share on other sites

Hi Zam,

Yes, maybe I even overheated the pin whilst soldering or I just got a bad one.

Best,
Andy

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now