MOTM

I think this calibration could be done with a voltmeter. John Blacet,
correct me if I say something stupid.

I have not tried this yet, but I will.  The frequency of the HF oscillator
is determined by the DC voltage at pin2 of Q1.  This is an easy access point
to measure because it is also the top side of R7 (closest to LM324 chip)
that rides on top of Q1. So, I  believe that certain voltages could be
associated with these two frequencies at that point and used as calibration
points.

My modification in this part of the circuit involves limiting the negative
voltage at this point to prevent the HF oscillator from going to high it
locks up when excessive negative CV is applied.  Voltage at this point goes
more negative for higher frequencies (opposite of the actual CV) due to
inverting summing amp U1d.

That's my take on it.  I'll fire mine up tonight and see what voltages I
have at that point for the appropriate frequencies.
Larry


----- Original Message -----
From: Eric Frampton <eric@...>
To: MOTM <motm@yahoogroups.com>
Sent: Tuesday, March 26, 2002 1:20 PM
Subject: [motm] Calibrating Time Machine?


Just finished my Blacet Time Machine with MOTM mods (thanks Stooge Larry for
the great additional directions). Works great, sounds right, way cool. Only
thing I can't figure out is this: I don't have a frequency counter that'll
go up to the high end that one is supposed to cal for the sampling rate on
that device - my Fluke drops out way before that. Has anybody figured out a
way to calibrate that trimmer without a frequency counter? I'm not sure it
matters terribly, as my unit seems to be working fine with the trimmer
centered. But it'd still be nice to properly calibrate everything.

e





Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/