To: Analogue@hyperreal.org, Machines@hyperreal.org,
From: "Plutonique9 :" Plutonique9@symbiocom.com,
cc: 
Subject: [AH] Tr-707 & Tr-727 Modifications
Date: Mon, 28 Jan 2002 08:48:22 +1100


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Hey there, 
thinkin' the only way to modify the 707 and 727 is circuit bending?
This isn't the case, as simple analogue VCA's and RC envelopes are 
used to shape 3 instruments on both machines. Especially useful 
for the Tr-707 is the smooth fact that you can independently 
control the decay times for the Open-Hat and Closed Hat. On the Tr-
727, these sounds are instead the Long/Short whistle. Also useful 
is to add external audio inputs into these VCA's, essentially 
giving you programable audio gates :)

Three mods i'll cover in this is;

-Open-hat/Closed-hat decay's (Long/Short whistle)
-Ext. Audio Input for Hihats (Whistle)

You will need (aside from you standard electronics tools) a;

- 10k Potentiometer
- 1meg Potetiometer
- 1/8 inch normally-closed phono female socket
- 2.2k resistor (see note)
- 10k resistor (see note)
- Patience :)

Luckily for us hackers, there is plenty of space to mount Pots & 
sockets in these machines (unlike the 606, for example), but try 
and get the smallest ones possible.
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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.
-------------------------------------------------------------------

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.
------------------------------------------------------------------

Ok, thats it from me 4 now. Take care in modifying your machines. 
Never work on them when they are turned on or plugged in, and you 
should of course be comfortable with working on electronics. If 
anyone finds any inaccuracies, point them out 2 me 
(Plutonique9@hotmail.com). Hack at yo' own risk n' stuff and la la 
la.

I'll write up another doc soon on how to similiarly modify the 
Ride (Star Chime) & Crash (Guiro) instruments, for decay times & 
ext. audio inputs.

Seeya

Plutoniq
