[sdiy] ASM-1 VCO questions--it works!!!!

[synth at charlielamm.com]

It works!  It works!  It works!!!!!!

I have it hooked up to a PAIA 9700 Midi
to CV and the 2 together keep tune over the entire range of my A-80
controller!

Magnus you RRROCK!!!  If you are in the States (CA Bay Area)
there are drinks on me!!!!!  Thanks for all the help...I would have gone
around and around on this one for WEEKS if not for your help w/ the
calibartion procedure.

I have to do a bit more checking of some revisions I made this morning,
but I think my single-sided, single ASM-1 VCO PCB layout is good to go.
I will post the PCB on my web site along with "what I learned" and get a
few more fab'd up.

Thanks again!!!

On Mon, 17 Mar 2003, Magnus Danielson wrote:

> From: charlie lamm <charlie at charlielamm.com>
> Subject: Re: [sdiy] ASM-1 VCO questions--please help
> Date: Sun, 16 Mar 2003 15:02:11 -0800 (PST)
>
> Hi Charlie,
>
> Now live from Provance...
>
> > Thanks for the help so far...
> >
> > I guess I am still not that clear on this. Sorry for all the questions....
> >
> > a) OK, I can set the system to 0V at the summing op amp and then trim the
> > 10K trimmer in series with the 150K (let's call this "P3") to hit 8870.
> >
> > I can do this now after correcting a few things on the circuit.
>
> Great!
>
> Your oscillator core works as expected then.
>
> > b) From your directions, sounds like I want to add 1V more to hit twice
> > this frequency (up one octave) or about 17.740K  I should tweak P2 (that's
> > the "Scale" trimmer) to make this happen.  I shouldn't need to adjust
> > anything else to make this happen.  BTW, for me, this works.
>
> Good. Yes, you should apply some suitable multiple of 1V (say -2V) on one of
> the 1V/Oct inputs and trim P2 to hit the octave transposed variant of C#9.
> By this you trim the scale. Better use a note several octaves away since then
> more of the scale error shows up.
>
> > What next?  This is where I get confused.  I can't add another volt, that
> > would take things way outside of my hearing range.  Should I try -1V, -2V,
> > -3V etc?
>
> Negative voltages work equally well. Try -3V or -4V.
>
> > Assuming this is correct, should I only use P2 to make sure each of these
> > voltages makes the pitch go down by 1/2?
>
> Yes, for this phase you ONLY trim P2.
>
> > c) It sounds like once I am ALL DONE, the final step is to adjust P1 for
> > whatever pitch range I want using P1.  P1 should not at this point change
> > my calibration.
> >
> > Is this correct?
>
> You've got it! This is why I recommend the extra trimmer, it makes the trimming
> a straight-forward process and no looping over the trimmers.
>
> > I have another question also.  Thanks to what you said below, I checked
> > the voltage at the 20K/10K voltage divider.  It wasn't 5V.
>
> Bingo! ;O)
>
> > I corrected a power supply issue.  Now it's 4.98V.  Is this adequate?  Or do
> > I have to have exactly 5V for the oscillator to scale?
>
> No, this last part you trim with the new "P3". 4.98 is as good as it needs to
> be. Actually, if you would run this Vref from a precission source, you would
> ruin a natural balance and get more dependent on the powersupply, not less.
> The secret is that V+ for this divider and V+ for the R15 reference current
> divide out, and only the 1/3 ratio of the resistors stay in, as does the
> trimming of R15+P3.
>
> So, you're very close it seems.
>
> > Thanks again.  I will get this working someday!!!
>
> Please report back when you have all the waveforms up and running and it can
> pass as a modular synth in most neighborhoods.
>
> Cheers,
> Magnus
>