[sdiy] Ratio switching!

[John Loffink]

For that level of accuracy, use 1% metal film resistors for the divider and
add a 15-25 turn trim pot about 1/10th to 1/20th of the total resistance for
tuning to the exact value.

If you try to select from 1% resistors you will pay more for a batch of
resistors to select from (100-500) than you will for the trim pot, not to
mention the time it takes to get the exact match.

If you try to use 0.01% resistors, you will pay more for them than the trim
pot.

You also need to buffer with a highly DC accurate op amp, such as an LT1013.

The Stooge Industries 831 Voltage Interval Switch (no longer available)
provides a good reference point.

John Loffink
The Microtonal Synthesis Web Site
http://www.microtonal-synthesis.com
The Wavemakers Synthesizer Web Site
http://www.wavemakers-synth.com


> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-
> bounces at dropmix.xs4all.nl] On Behalf Of karl dalen
> Sent: Wednesday, May 23, 2007 7:17 PM
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] Ratio switching!
> 
> Is it silly to assume one to build a accurate frequency ratio
> switcher with simple resistor dividers? (i.e no pot's).
> 
> For example a desired 2416.33mV would require (E24) 16.000k ohm and
> a 5.100k ohm which gives at best a voltage of 2417.06mV error of 0.01661%
> 
> Not to bad!
> 
> Perhaps just use a quality pot to trim only for the very lowest of ratios?
> 
> If i only could easily get hold of a supplier for the complete E196
> series! :-(
> 
> Suggest a supplier please!
> 
> Reg
> KD
>