--- In tr-707@yahoogroups.com , "memology2003" <memology2003@y...> wrote:

>
> Hi,
> I would like to add a few more trigger outs to my 707 and 727 to
> trigger percussion synths I have built. Can anyone give detailed
> instructions for doing this eg schematic plus connection points.
> Thanks,
> Steve

Hi Steve,

I will give very general, rather than specific, trigger info - just because I have thought
about doing this. I have made quite a few trigger circuits, just not in the 707 as of yet.

Trigger circuits tend to just be a dual op-amp. First amp is an amplifier to make certain
that the input signal will be of an appropriate level. Second amp is a comparator, if a
signal goes above a certain level, consider it a trigger source and output a pulse. On the
output side of things, you can select parts which define how long the resulting pulse is.
If you look up on synth-diy pages, you will find many variations on the trigger generating
theme.

The only trick to doing this in a 707 is finding places where the drum outputs are. I'd say
try the transistors which act as sort-of VCAs for each sound, towards the middle of the
second schematic page (which is not in front of me now). When a drum hit happens, one
of those transistors for each voice is going to surge a bit.

To makes testing this out completely easy, one can breadboard a trigger circuit. I have one
on my bench permanently which I modified from Thomas Henry's Electronic Percussion
Cookbook. For the trigger out, install an LED with a current limiting resistor. If you plug a
drum machine output or some other source, you should see the LED blink when a hit
sounds. Program a 707 pattern with a single drum sound. Then you can connect the
trigger circuit to the +V and ground inside the 707, such as off of one of the IC pins. Then
you can poke around the VCA circuitry near your sounding voice with the trigger input
wire. You get a good, clearly-defined blink- then you can just install the circuit in case as
it is. And/ or do the same for the next voice!

It was hard for me to fit the mods I wanted inside my 707, so triggers had to wait. When I
get my next 707 and do these mods, I will post detailed info, but this might not be until
summer 2005. I have an aluminum box which I am going to install the top of the 707 case
onto. Case is going to have its own power supply, switchable SRAMs/EPROMs, better
clocks with range trimmers and voltage-control. More decay controls, and full trigger I/O.
Now if I can just tweak the write mode …!
CJ