[sdiy] Question for MOTM300 UltraVCO owners...

[David Ingebretsen]

Mouser:

http://www.mouser.com/ProductDetail/Xicon/270-30M-RC/?qs=sGAEpiMZZMu61qfTUdN
hG1VZapgQ2mzwZWL3boU4wbs%3d

They have 2.8M, 3M, 3.01M, 3.1M available in 1%, 50 ppm

David

David M. Ingebretsen, M.S., M.E.
Collision Forensics & Engineering, Inc.
2469 East Ft. Union Blvd., STE 114
Salt Lake City, UT
84121

dingebre at CFandE.com

Work: 801 733-5458
Cell: 801 842-5451



>> -----Original Message-----
>> From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-
>> bounces at dropmix.xs4all.nl] On Behalf Of Jean-Pierre Desrochers
>> Sent: Tuesday, March 13, 2012 9:45 AM
>> To: synth-diy at dropmix.xs4all.nl
>> Subject: [sdiy] Question for MOTM300 UltraVCO owners...
>> 
>> 
>> Hi,
>> 
>> I read some web pages about the MOTM300
>> UltraVCO assembly & HF tracking modification.
>> I have a MOTM300 vco's to fine tune myself.
>> After a couple of hours of tweaking trimpots (1v/oct, HF tracking
resistor
>> values swapping) I ended up with the HF tracking resistor R50=3.3M, a bit
>> high for a resistor to me but the vco was tracking around 8 octaves very
>> nicely ! I was very happy about that.
>> I used a very accurate Korg tuner and a 5.5 digits HP voltmeter for all
the
>> tweakings.
>> Some days later measured back the overall tracking and found the top
>> octaves were flat and getting worse in the higher freq..
>> I found that 'blowing' on the R50 resistor was changing the HF tracking
>> accuracy.
>> This is not suprising since 5% carbon resistors like this are
1000-1500ppm /
>> degC sensitive !
>> And the resistor is series with a 1N4148 so..
>> 
>> So here is my question to MOTM300 owners:
>> Did your VCO's stay stable days after your HF tracking tuning ?
>> Mine went flat at high frequencies..
>> I'm considering to use metal film type resistors but again, in the
megohms
>> spectrum they tend to have high ppm/degC deviation.. (around 1000-
>> 1500ppm) compared to lower resistance values, but I found some 50-
>> 100ppm parts at Digikey for values from 1meg to 2.2meg.
>> Your precious advices are welcomed.
>> Thanks
>> J-Pierre
>> 
>> 
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