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KORG 700S (Mini-Korg K-2)
MODS - External Audio Input and Other Outputs

| Synth Index | Korg 700S | 700S Mods1 | 700S Mods2 | E-Lab Japan CV/Gate Mod |

 | Audio In to VCF | Audio In to Ring Mod | Other Outputs | To Do's |

External Audio Input to VCF
The 700S came with 2 Audio Output, one labelled Low and One High. Normally only one would be used and I don't think I'd find use for the High Output, since its level is very low. 
So i just de-solder the High Output, wrapped up the bare resistor/cap, and use it as an Audio Input,

On the 800DV, audio input could be tapped to the waveform selector. I tried this on the 700S and it didn't quite work... but there's another point to cut the audio in between the VCO and VCF...
The VCO Output / Traveler VCF Input is actually Pad 7

Korg 700 Schematics - Audio In to VCF Location:

Click to Enlarge!

VCF Board (SB-018) Pad 7 Location:

Click to Enlarge!

So basically disconnect the dark purple wire on Pad 7 on the SB-018 Filter Board, then wire an SPDT switch, centre going to Pad 7, one end goes back to the dark purple wire, the other going to the Audio In socket. This would switch the Audio In signal in place of the VCO output, into the VCF Traveler.
There's another way of doing this on the 700S. The dark purple wire at Pad 7, actually goes to the Effect On/Off Switch at the Korg 700S left hand side panel.

Korg 700S Schematics - Audio In to VCF Location:

Click to Enlarge!

Back side of Effect Switch:

Click to Enlarge!

So basically again, disconnect the dark purple wire on the centre (right, facing from back) of the Effect Switch, then wire an SPDT switch, centre going back to the switch (see light blue wire in picture on the right above), one side to the dark purple wire, the other side gong to the Audio Input Socket. 
Whichever way to do it, it's still the same:
I did the 2nd method, tapping it off the Effect Switch, as I planned to mount the switch on the left panel.



External Audio Input to Ring Modulator
This is not as simple as I thought. On the 700S Additional Schematics, Pad 113 is labelled MODUL.IN which i take it as meaning Modulator Input. Feeding an Audio Input to this Pad does something to the ring modulator, but it's not "ring modulating", the VCO audio is still passing thru.... (but being modulated by the audio in)....
So in fact Pad 113 is the "Modulated by" input or whatever - i just thought there must be another input that i had to tapped the audio to, so the ring mod has 2 inputs to ring modulate!!
I tried the other pads and found Pad 112 works.... So basically we need a DPDT switch, switching whatever going to Pads 112/113 to the audio input signal:

This again can be done on the 700S Ring Mod PCB (SB-027) board. Looking from the front, Pads 112/113 are the red and orange wires located on the 2nd row from the left:


Or again, the switching wire points could be at the left panel.



Audio to MODUL.IN
I actually did one more thing while i was at it.  i also did one that routes the AUDIO IN to Pad 113 (MODUL.IN) only. This will ring-mod the 700S VCO with whatever you feed in the Audio Input (eg drumloop), could be interesting... (this is actually a by-product of the mod above... se below)
Instead of having many switches selecting to the Audio Input, I actually used a 3-pole 4-way Rotary Switch instead! So that I have:



2 Ext Audio to VCF Traveler
3 Ext Audio to Ring Modulator
4 Ext Audio to MODUL.IN

The wiring is not too difficult, but i can't be bother to draw it here.....

i mounted it on the Left Panel, where i have removed the name plate and put the External CV Switch. But this time I have to drill thru the inner metal casing, and the a hole on the thin metal cover.




Other Additional "Modular" Outputs
Well, on the Analogue Solution website, you could buy a socket kit, that gives you the CV/Gate In, Aux CV to VCF In, External Audio In, External Audio to Ring Mod and also some "Modular" outputs. There's a table on their site stating what in/out sockets you'd get.
i didn't purchase the Analogue Solution sockets this time, since I already have enough info on the 700S and I felt that it's time to experiment myself to find these.
While looking for the Ring Mod pads, i was actually tapping on each pads to see what gives what. For example, there are White Noise (Pad 110) and Pink Noise (Pad 109).

However, unlike the 800DV, these outputs are not triggered or ADSR-ed outputs, ie they're continuous endless audio signal - eg the White Noise (Pad 110) just gives you a constant endless white noise out, the waveform out gives you the wave VCO, pressing any keys on the keyboard will affect the pitch, but releasing the key will NOT stop it, it will ole on that note...

So all these are actually NOT TRIGGERED/GATED. I started to understand the term "Modular Outputs" on A.S. site - they're by no means separate outputs, but outputs from say VCOs etc as in Modular Synths, before any ADSR or gating/triggering...

There are actually outputs like these on the Korg MS-20, were you patch them to other modular inputs to build up synth patches. Well, since  already have the holes drilled on the rear panel of my 700S, i thought i might as well tap these to the sockets - never know, maybe i'll use them in other modulars one day!
Looking at the 700S Additional Schematics it's not difficult to find these pads. Here's a table of the pads that i have tapped out to the sockets:
Pad Number What is What Notes
105 Ring Mod Out If using Ext Audio In to Ring Mod,
since internal Synth is disconnected,
this will act as a "Ring Mod FX Only" individual out.
Waveform Selector Out VCO Out Or it could be Pad 113 (MODUL.IN)
110 White Noise Out Beware: Loud!
109 Pink Noise Out Beware: Loud!

Da Sockets....



Future Plans (To Do List...)
Well, this is what I've done so far on my 1st Korg 700S, as of 22nd December, 2003.
Future plans include:
- Adding MIDI
I don't want to add a Synhouse Midi-Jack II, because it doesn't support Pitchbend or Portamento, the Hz/V has limited key range, and also it doesn't support extra AUX CV's. Putting a Kenton Pro-Solo inside is gonna be a waste, so it's gotta be something smaller, cheaper and has enough controls, maybe a Paia Midi2CV8 with Hz/V option. Or maybe i'll build an antilog amp (V/Oct-to-Hz/V Convertor...)

- Sorting out the VCF CV Voltage
Needs 0-20V on the External VCF CV, maybe build a gain circuit...

- Rackmount 700S
Well, i have the boards, just need to add a transformer, some pots and wire it up and drill the 19" rack panels... i'll get to it one day!
- 2nd 700S
I should still have another 700S coming.... I dunno what I'll do to it yet.....
UPDATE: The 2nd 700S arrived, then stayed as is for a long while, until July 2005, it's been CV/Gate modded.
Details on the Korg 700S #2 Page here.




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