[sdiy] VCO tuning philosophy re-visited

[Oren Leavitt]

On 2/6/2011 9:44 PM, David wrote:
> I know we have hashed this before, but as I’ve now had some time to actually dig into the Steiner VCO (schematics here: http://www.xmission.com/~dingebre/spvco_main_1.4.pdf) and compare it to my Blacet VCO, JH Living VCO, and MOTM Ultra 300 VCO, I’ve noticed a difference in high frequency tracking. Nyle did not have a high frequency adjustment and I’ve noticed that most who do include them typically say they didn’t adjust them (notably JH) or when I’ve tried to adjust them, they tend to mess up mid frequency tracking or have had very little effect. (Ian, I know your VCO tracks over 15 octaves so don’t rub it in  ).
>
> Where can I learn more about high frequency compensation and how it works?
> Where can I learn more about why high frequencies droop?
>
> Philosophy:
> Do you tune a VCO for mid range tracking, like over one octave around middle C, and then let the low and high ends fall where they may?
> Do you tune a VCO for wide range tracking, like over 5 octaves and let the middle range fall where it may?
> Do you use/adjust/design in to a VCO a high frequency tracking trimmer?
> If so, does it affect the mid frequency tracking?
>
> Finally, where is the best place to compromise, low end, middle, high, and what percent error is OK musically? To me, even when I measure an exact doubling of frequency from 8kHz to 16kHz, the 16kHz still sounds flat. I’ve tuned the Steiner VCO a dozen different ways, and none sound any better to me.
>
> Have I finally gone over the SDIY insanity cliff… What’s that ringing in my ears?  Stop the noise…. PLEASE STOP THE NOISE………….. ok, that’s better. Now where’s my trimmer adjustment tool, oh there it is, stuck in my ear…
>
> David

Hi David,

In the early issues of Electronotes there's a very nice explanation of 
how the various schemes for analog VCO HF tracking compensation work.
Nice to hear you've got the Steiner VCO and other stuff working nicely.

- Oren