medigrade
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Closed-hat decay (short whistle)::
Locate on the main board Resistor "R123" (10k). This resistor sets the decay time of the Closed-hat (short whistle). You need to desolder & remove this resistor from the board. Where you removed "R123", replace with a 10k potentiometer & a 2.2k resistor in series.
*note
The 2.2k resistor in series with the 10k pot sets the "minimum" decay time for this instrument. Experiment with slightly shorter resistors to fine tune the minimum decay time (eg. 1.8K), too
small of a value though, and the instrument will not sound.
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Open-Hat decay (Long whistle)::
Locate on the main board Resistor "R126" (1 meg). This resistor sets the decay time of the Open-hat (long whistle). You need to desolder & remove this resistor from the board. Where you
removed "R126", replace with a 1 meg potentiometer & a 10k resistor in series.
*note
The 10k resistor in series with the 1 meg pot sets the "minimum" decay time for this instrument. Experiment with slightly shorter resistors to fine tune the minimum decay time (eg. 5k), too small
of a value though, and the instrument will not sound.
Also, the Open-hat/Closed hat are identical sample wise, the only differnce is the decay times of the VCA. So by turning the decay time of the Open-hat right down (to 10k or so), the Open-hat will
sound the same as the Closed-hat.
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External Audio Input for Open-hat/Closed-hat (Long/Short whistle):
This modification allows you to run external audio signals through
the Hihats (whistles) VCA circuitry (as opposed to the sample
sounds).
Locate on the main board Capacitor "C69" (1uf). This is a
polarized electro capacitor ("-" and "+" polarities). The Audio
input into this VCA enters the "-" side of capacitor (4 reference,
The "+" side of the capacitor is connected to resistor "R125").
You need to cut the circuit trace leading to the "-" side of
Capacitor "C69". Now you need to solder both sides of the "cut
trace", to a normally-closed phono socket. When nothing is plugged
into the socket, the signal going into the VCA will be the
original onboard sample, when you plug in something, it will cut
the sample signal from the VCA input, and insert your external
audio source.
There are three tabs on a normally-closed jack. One is ground, and
should be soldered to a suitable ground point inside the Tr-
707/727. The Second tab will be the tip connection, this should be
soldered to the side of the cut circuit trace which connects to
the "-" side of Capacitor "C69". The Last tab is used to close the
signal connection between the trace to cut, when nothing is
insereted into your phono socket. This tab, of course, is soldered
to the other side of the signal trace you cut.
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"Ride and Crash Decay & stuff"
ride decay:
replace r73 with a pot. the biggest i had was 1m, and the decay
didn't go long enough, so i put another 1uF capacitor in parallel
with c49. i put a 10k resistor in line with the pot to set minimum
decay, but it still almost disappears, which is fine with me. on the
closed hi hat, i didn't actually put a resistor for minimum decay.
that way it is almost silent (except for a quiet snapping) and i can
have the open hi hat hissing along by itself and then slowly bring in
the closed hi hat to get busy.
ride vca input:
is the + side of c34 (NOT the side connected to r60). the easiest
thing to do is cut the trace so the + side of the capacitor is
isolated. plutonique9 suggests using normally closed jacks, which
switch when you insert a plug. i had trouble with my shitty radio
shack jacks so i wired the jack and pin 1 of ra4 (which used to go to
c49) to two sides of a spdt switch, and the middle lug of the switch
to c49.
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crash decay:
the crash has a slightly different decay envelope for some reason,
instead of just replacing a resistor, you wire the pot between ground
and the joint of r58 and c50. again i used a 1m pot (in line with a
10k [color=red](12k??) resistor) and put another 1 uF capacitor in parallel with c50.
crash vca input:
same as ride, cut trace to isolate the + side of c35, wire switch and
jack between c35 and ra3 pin 1.
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