[sdiy] Odyssey 2800 CV Mod

[Sawtooth]

Hello,

is anyone here who modded his 2800 Ody with CV/Gate In/Outs? On the
www.overacker.com ARP recource site is a description on the mod as I'd like
to do it, but unfortunately I'm still a newbie in DIY engineering, so I'd
need some further assistance. Since my Frostwave Quad Midi to CV converter
is on it's way from Australia now, I want to do it as quickly as possible to
be able to use the Ody in my productions and I'd appreciate your help if you
did that kind of thing and got some minutes to write me a mail.

In that text by a Gene he wrote: "Break connection between Keyboard sample
hold buffer (A1b) and the CV pin on the backplane connector. Add a dual
op-amp (1458 etc.) configured as two series inverters so that you can use
the first one to sum the org. keyboard sample/hold buffer output with a
signal from the CV Input Jack (added on rear panel)"

As I said I'm a noob, so what does he mean? I know what a op-amp is but have
no clue how I can configure one as two series inverters and for what reason
and actually wouldn't care as long as there would be a manual with pictures
=). Now it's gets even harder for me to understand:

"The result will be upside-down so use the other inverter to right it again.
Use closely matched 1% or 0.1% resistors so you don't have to add trimpots
to make the gain exactly +1. u can use a DVM to match them. However adding a
trimpot to the ext. input is a good idea, especially if you epoxy it to the
inside of the rear panel sticking out through a hole..."

I have a DVM but don't know how to match resistors =( The rest of the text
sounds like greek to me:

 "CV output:   Op-amp buffer on the above CV sum to an output jack.

Gate input:

The Odyssey's internal gate is created by a keyboard bus that goes to +15
whenever any key is pressed. This gets cut down to about +10 by a resistor
divider, after an isolating diode. To add an external gate, add an input
jack to a diode to the juction of the resistor divider (diode black line
towards divider). This provides a "wire-or" function. I'm not sure what the
minimum gate requirement is but this works for the MPU-101.

Trigger:

The ARP envelope needs a trigger to set the attack flip-flop. It is derived
from the rising edge of the external gate as follows: External gate input
jack to a 0.01uf cap, to an op-amp inverter with 10K input resistor and 220K
feedback resistor, to another inverter with 100K input and 100k feedback, to
a 0.01 cap, to a diode, to the keyboard trigger bus (diode black line
towards trigger bus). You can add an external trigger here too just by
adding another 0.01uf/10K input to the first inverter."


"Input jack to a diode..." Doesn't say which kind of diode. May be obvious
for engineers but I'm really pretty clueless how to do anything described
there. I can handle a soldering iron and I'm willing to learn but I'd need
someone who's got some spare time to explain in to me in a language I
understand...a list of necessary parts and maybe the copies of the
appropriate boards in the service manual with indicated spots where I have
to put which part. I find the description above pretty confusing. =(

You can read the full text at:
http://machines.hyperreal.org/manufacturers/ARP/Odyssey/mods/arp.odyssey.cv.
in.mod

Your help is highly appreciated.

Best wishes,
Roland Brehm