MidiboxCV calibration

[t_xen]

Hi all.  :)

I have constructed a MidiboxCV and need some help.

Here's what I have for the power. I have the core powered by a 12v powersupply and is being ran through a 5v regulator into the Core Module. I have the CV firmware uploaded into the core and its operating normally. Since I was not able to obtain an AOUT_LC, I went ahead and etched my own board.  ;D

The R-2R section comes within .5% tolerance.

Instead of the rated 12v bipolar supply on the AOUT_LC, I have 2 batteries rigged to give a supply of +9v/-9v and ground to power it.

I seem to have a problem with calibrating the thing to drive a linear VCO. could the batteries be an issue, possibly under powering the AOUT_LC?  ???

[t_xen]

Oh duh.  :P

RTFM.

I changed the line  "#define DEFAULT_AOUT_INTERFACE 1" to "#define DEFAULT_AOUT_INTERFACE 2".

Recompiled and uploaded.

Now it's behaving properly. I only get about 7.5 volts for the maximum output (prolly cuz I'm using 9v batteries), but that is fine since the linear VCO's I'm driving have an accuracy of only 5-6 octaves.

Anyway it's getting late here in the Pacific NW, so I'm going to try it out on my synth tomorrow and see how it does.

I'll post a pic here of the end result.

thnx and good night.  ;)

[t_xen]

Here are the results.

After attempts at calibrating, here's what I've got.

I set the calibration minimum to 0v. then I set the maximum to 7v (9v battery powered).

then when I select the 1v setting and set the output, I switch to 2v and I get 1.996v. I adjust to 2v and then switch to 4v. the multimeter reads 3.996v.

Looks like it's falling flat, folks.  :-\

Apparently (I think I read this somewhere before) that the AOUT_LC isn't suitable for driving Linear VCOs because of the lack of accuracy, but should be fine for driving anything else that's analog.  ::)

I requested some samples from Maxim-IC for 2 MAX525's to attempt an AOUT, but I'm not gonna hold my breath.

No images yet, I want this working before I post it.  :)

Here the image of the AOUT_LC I constructed.

I don't have a drill to make the holes for the pins, so I just put the circuit on top and surface mounted all the parts. I used clippings from the resistors to make bridges that go over the traces. This took very steady hands.  ;)

I'll post an image of the AOUT in this thread after it's constructed.

l8r  8)

[t_xen]

Side note...........

Since the AOUT_LC I constructed isn't accurate enough for diving linear VCOs, I'm going to use it in the MidiboxSID I constructed. I have a filter board I've constructed. CEM filters seem to be a little expensive and hard to come by, but the filter I created is directly  off the filter from the Soundlab Mini-synth section (the analog synth I'm attempting to drive with the MBHP_CV).

I'll post a PIC of the filter in the SID forum.

;D

[TK.]

Are the OP amps directly supplied by the batteries - so, isn't there a voltage regulation? In such a case it's very unlikely to get stable results.

Best Regards, Thorsten.

[t_xen]

yea, I was directly supplying the opamp with the batteries. Oh well, the board is no longer in the case I've created for the Midibox_CV. It's now in my 4xSID, controlling a filter board from RJW Soft. I've just etched an AOUT module since I was able to aquire 2 MAX525s and a MAX6007B shunt as free samples from Maxim IC. This would be better anyhow since I have an analog synth with 2 VCOs, 2 VCO modules, and 3 VCFs. Should be the best route since I have the beginnings of a modular synth.  :)

Thanks for the info, TK.  :D