[sdiy] [AH] KORG 700S CV Hz/V / gate retrofit

[Tony Kalomiris]

I'm currently working on a MiniKorg that's in for repair and I've also been looking at some mods for it.
The keyboard is an exponentially weighted design like in the MS20, but unlike the MS I don't think there is an exponential converter in the 700.
I'll need to have another look at the schematic, if there is one you can feed in a 1 V/OCT input properly scaled and tuned - you can do this to the MS if you fine tune the scaling at the CV input summer - add a trimmer of 100 ohms in parallel with expo base IIRC to go from 21 mV/oct to the required 18 mV/oct for a 1 v input change.

Of course I'm only working with one sheet from the service manual. Does anybody have the manual or a link to one...I should buy these darn things to have in stock already !

Btw, I'm tempted to pop open those Keio (epoxied ?) modules, and see what's lurking in there..;-)

Tony

On 2010-07-25, at 4:58 PM, cheater cheater wrote:

> On Sun, Jul 25, 2010 at 21:15, David Bulog <d2ba at xtra.co.nz> wrote:
>> Korg 700S was used entirely for this classic track
>> http://www.youtube.com/watch?v=S5QErPDNcj4
> 
> This demo... is not especially encouraging the purchase of a Korg 700S.
> 
>> Hi there has anyone done CV Hz/V / gate retrofit to e Korg 700S
>> I have two ways to go--Kenton which would ensure a good match for any of
>> there midi -cv interfaces
>> http://www.kentonuk.com/products/items/sockets/korg/700s.shtml
>> 
>> or DIY
>> full mod diag
>> http://www.cykong.com/Synths/Korg%20700S/Images/Korg700-CVGateInModFull-Schmo.gif
> 
> What you're looking for is an exponential converter. Those can be had
> in many forms and most VCOs with linear FM input have an exponential
> converter. You might want to look at a 2164 based one, they're
> extremely stable. I think David Dixon had some boards for his VCO, but
> not sure. You'd take the VCO and stuff just the exponential converter,
> basically, and maybe or maybe not you'd need to add a current->voltage
> converter with gain but that's not a big thing if it's needed at all.
> 
> The DIY one you have posted doesn't seem to have any temperature
> compensation and does not use precision voltage references, so it'll
> be quite crap I think. That doesn't mean the Kenton's much better,
> it's probably just as bad. SSM 2164 based exponential converters are
> currently the best ones you can get, and the chips aren't expensive at
> all.
> 
> Cheers,
> D.
> 
> 
>> part 1
>> http://www.cykong.com/Synths/Korg%20700S/Korg700S-Mods1..htm#Proper%20External%20CV/Gate%20In
>> part 2
>> http://www.cykong.com/Synths/Korg%20700S/ElabJapan/ElabKorg700CVGateMod.htm
>> 
>> thanks in advance
>> David
>> To: analogue at hyperreal.org,
>> From: Zane Whitaker zanewh2000 at yahoo.com,
>> cc:
>> Subject: [AH] MiniKorg Mod Woes
>> Date: Tue, 2 Dec 2008 17:38:38 -0800 (PST)
>> 
>> ________________________________
>> Hello AH'ers.
>> 
>> Long time archives lurker here. I have posted once or twice since around
>> 2002, usually when one of my synths breaks, and this is no exception.
>> 
>> A little background first:
>> This site:
>> "http://www.cykong.com/Synths/Korg%20700S/Korg700S.htm"rg700S.htm" is the
>> most common source of information for Minikorg mods. I previously did the
>> 'basic' CV/Gate and Audio Filter-In mods with no problems. By basic, I mean
>> I didn't need to build the buffer/tuner circuit, as you get everything but
>> the repeat function without it, and you don't even need to hold down a key
>> to use the external Gate, at least not on mine.
>> is the most common source of information for Minikorg mods. I previously did
>> the 'basic' CV/Gate and Audio Filter-In mods with no problems. By basic, I
>> mean I didn't need to build the buffer/tuner circuit, as you get everything
>> but the repeat function without it, and you don't even need to hold down a
>> key to use the external Gate, at least not on mine.
>> 
>> 
>> BTW
>> 
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>