MOTM

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

I would advise just setting the one turn trimmer to mid span and adjust
the 20T for 2KHz. This is hardly critical to the TM operation or sound.

The delay CV is exponential mostly for ease of adjustment.

I had a chance to try out the J, Larry Hendry negative voltage clamp and
it works fine. A good solution; but where to add it on the board next
rev???? Very tight.

http://www.wiseguysynth.com/larry/tm2050/all_mods.htm

Regards,
___________________
John Blacet
Blacet Research
http://www.blacet.com

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





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----- Original Message -----

From: Eric Frampton <eric@...>
I don't have a frequency counter that'll go up to
the high end that one is supposed to cal .....
Has anybody figured out a way to calibrate that
trimmer without a frequency counter?

----- Original Message -----
From: John Blacet <blacet@...>
I would advise just setting the one turn trimmer to
mid span and adjust the 20T for 2KHz. This is
hardly critical to the TM operation or sound.

--LH--
Both of my Time Machine modules are calibrated to the frequency specified by
John in the instructions. I measured the voltage at the bottom of R7 (I
think I said top before).  With no external connections (well there is that
power supply thing), here are my measurements:

Delay pot set to zero:
TM # 1 = 0.022
TM # 2 = 0.021

Delay pot set to ten:
TM # 1 = -0.118
TM # 2 = -0.119

But, as John said, the top end is not critical.  When I first fired mine up
(trimmer in the middle I think), my max frequency was about 250KHz instead
of the 400KHz.  The short end of the delay seemed short enough even at that
lower frequency.  I my way of thinking this is a good way to calibrate
without a frequency meter.

Larry H