[sdiy] VCO that goes SHARP in highest octaves??

[Ian Fritz]

Ah, glad that got it!  I agree with Phil on including the series Iabc resistor.  It can also ensure that the max current won’t be exceded, and someone once suggested it could help with inaccuracies caused by the Early effect.

Ian

> On Jul 13, 2022, at 11:06 PM, Neil Harper <metadata at gmx.com> wrote:
> 
> On 6/17/22 14:04, Ian Fritz wrote:
>> Something else you might try: reduce the values of the integrating cap and the reference current by a factor of two or so. This could possibly reveal any self-heating in the expo transistors.
>> 
>> Ian
> 
> We have a winner!
> 
> Reducing the integrator cap and reference voltage by a factor of 2 as
> Ian suggested now has the VCO working as expected.
> 
> (cents)    C4    C5    C6    C7    C8
> BEFORE    0    0    0    +5    +13
> AFTER    0    0    -1    -2    -4
> 
> 
> The flat higher octaves were easily trimmed out with a very small amount
> of added HF-Trim exactly as expected.
> 
> 
> I haven't tried Phil Macphail's suggestion yet though of adding a
> resistor between the expo pair and the 13700's Iabc pin. Is there an
> advantage to either solution?
> 
> 
> --
> /// Neil Harper
> /// Every Wave is New Until it Breaks