[sdiy] Re: [AH] Odyssey 2800 CV Mod

[Jim Johnson]

If you don't understand the details of doing this mod, you should probably
hire a competent tech to do it, rather than risk trashing your instrument.

Seriously.

Jim Johnson 
Metaphoric Software
-------------------
Makers of Techno Toys
Software for Electronic Music
http://www.technotoys.com
info at technotoys.com



*********** REPLY SEPARATOR  ***********

On 4/16/02 at 6:50 PM Sawtooth wrote:

>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