I'm in the process of building an MOTM-101, and I'm confused about a
few things.
First, is the Random output mod. On page 16 it says "The amplitude
of this signal can be adjusted by lowering R11 (bigger output). With
the value shown it will swing 1.5Volts."
That makes sense, but why was it designed to have a such a low output
in the first place when all of the other AC outputs are 10Vpp?? Is
there a reason why I shouldn't change it??
If you view U2A as an inverting amplifier:
Vout = Vin (Rin + Rf)/Rin
So if Vout is 1.5V, and R11 (Vin) is 100K, and R12 (Vf) is 150K, then
the gain of the amp is 2.5 and Vin is .6V.
http://www.tellun.com/motm/mods/motm101/motm101.html"Changed R11 from 100K to 27K to get 10 Vpp on Random output. Random
output level is now similar to Pink output level."
So if Vin is .6V then:
Vout = .6 (27 + 150)/27
Vout = .6 (6.6)
Vout = 4V
Which works, since the Pink output is 8Vpp. What I don't understand
is how can the output of U2A be only .6V in the first place?? There
is only a 1K resistor going from the output of U2A to the jack.
Secondly, has anyone tapped the INTCLK signal to add an internal
clock output?? I'm thinking of connecting the switched lug on the
EXT CLOCK jack to a new jack with a 1K resistor, but I'm wondering if
there will be enough current.
The MOTM-101 internal clock uses a 555 as an astable multivibrator, a
proven circuit that is over 30 years old. However, I noticed that
Paul added a diode in parallel with the timing resistor. Why did he
do that?? I'm guessing it's to keep knob twisting from glitching the
clock.
Anyway, the circuit uses a TLC555, a more practical low-power version
that can source only 10ma at output. A regular 555 can source 200ma.
It's a flamethrower that can literally ring doorbells and drive
speakers. Since they are pin for pin replacements, I'm thinking of
replacing the TLC555 with a regular 555 to drive the extra output.
Any ideas?? Should I increase the value of C19 (a .1uF bypass cap)
to handle the larger transient??
Other people have mentioned that there are two unused op-amp halves
(and I have no idea why) that can be hacked as output buffers, but
I'd rather not do that.
Speaking of low output impedance, if your system uses 5V for 500/600
power, there is a new op-amp for cooking bratwurst and driving blue
LED's (to keep planes from flying into your modular) :
http://focus.ti.com/docs/prod/productfolder.jhtml?genericPartNumber=OPA569Finally, what is the difference between the MOTM-100 and MOTM-101??
Based on the "Electrical Theory of Operation" I'm guessing that a
jumper for vibrato input was replaced with a panel switch. Will the
MOTM-102 have a clock output?? ;)
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"For ye may all prophesy one by one, that all may learn"
-- 1 Corinthians 14:31