Anyone know how to wire a din filter pedal for a MaxiKorg?

mm-pro · Post by **mm-pro** » Sun Jun 02, 2013 12:23 am

Trying to convert a Yamaha FC7 into a din filter pedal for a MaxiKorg.

Anyone done this?

Regards,

MM

WaterDrum · Post by **WaterDrum** » Fri Jun 07, 2013 8:53 pm

First I had to google , what a MaxiKorg is .
So obviously I dont have one ,

but I did modify a FC7 and a FC9

both use a potentiometer that ranges
from 50 k Ohm (heel position) down to zero Ohm (toe position) ..
Linear resistance curve (not audio taper) .

dont wanna write a (useless) explanation , so

Questions :
what pedal could be used originally ?
does the MaxiKorg expect an ohmic resistance or CV ?

if CV , I cannot help you (somebody else can ? ),
maybe EHX (not really vintage):
http://www.ehx.com/products/expression-pedal

do you want to modify the pedal especially for the MikroKorg
or try to keep it for "universal" use ? ( + extra switch )

first steps :
if Ohmic resistance :
check the Cable pinout with this (or start soldering)
http://www.thomann.de/gb/pro_snake_tpy_2003_bpp.htm

if NOT CV control ,
connect a potentiometer to the MicroK and check the range
from zero to full effect
= effect starts , now disconnect pot
and get value with multimeter

mm-pro · Post by **mm-pro** » Fri Jun 07, 2013 9:20 pm

The Korg supplies 20 volts DC. I want to use the FC7 to attenuate that CV.

Thanks!

WaterDrum · Post by **WaterDrum** » Sat Jun 08, 2013 6:43 am

first : I am not responsible for any damage to your "Dinosaur"
(there IS danger of damaging it )

do you know of a pedal that did work in the past ?
how many cables are connected to the DIN inside MaxiK , 2 or 3 ?
do you have a repair manual ?

now I understand this :
20 Volts (!) out from the DIN jack ( so vintage )
attenuated by FC7
and back into the same DIN
so in theory you would want to connect the FC 7 in serial at first
(or as a voltage divider with 3 cables at the DIN inside the MK)

at least 1 thing to consider:
there might be a limitation of current inside the MaxiKorg
then maybe (!) you may go as low as zero Ohm , *DANGER* )
if not :
when the FC7 is at a position that gives you lets say 10 Ohm
you would have a current of
20 volts/10 Ohm = 2 Ampere

that gives you 20 volt x 2 A ---> 40 Watt !!
(thats more than enough to fry something )

2 millimeters further it is 100 Ohm:
20/100 x 20 = 4 Watt

I am not shure if the FC7 can eat that ...
+if your synth would like this (close to shortcut) situation *DANGER*

so probably an extra resistor for safety in series is necessary
depending on the combined resistance (pre-resistor + pot )
= a resistor with an appropriate high Watt value

first steps :
to check the pinout of the DIN jack :
how many wires connected inside MK ? (wants to be opened)

1."quick n easy check"
cut off one plug of a MIDI cable
evtl the standard MIDI cable is too thin for high Ampere values ?
I am not really shure
(you could use it to connect to FC7 cable , - later if possible at all)

2.better solder solid cables to a single MIDI jack
access wires
check out the Voltage pins with multimeter (or your tongue , NOT )

experiment with a potentiometer to find the the values of
the working range and use a pot with high enough power rating
(start 1 Meg Ohm ? )
use a second pot as a safety resistor
start with high ohmic values (1000 Ohm ---> 0.4 Watt)
be very cautious with low ohmic values

if you are not shure what you are doing , leave it ...
and consult a vintage specialist or an electronic guy (recommended)

post for more questions , or post your result , I am interested ..
btw: just checking your website ....
dont You know a good tech ? could be an easy solution for him

mm-pro · Post by **mm-pro** » Sat Jun 08, 2013 1:06 pm

Thanks for your help.

I do know a tech....though his hourly rate is higher than mine, I guess in this case it would be worth it. I could easily solder the jack, but I need someone to evaluate the resistance and not fry the synth.

Also, I read that the filter input does take 20volts, but I am not sure I trust that. The other thing which complictes this is that the Maxi has two din pedal inputs and I want one pedal to go to both.

I will take it my tech.

WaterDrum · Post by **WaterDrum** » Sat Jun 08, 2013 1:29 pm

just edited a little bit
so we meet here ...
there is a stereo pot with the same values 2 x 50 KiloOhm avaiable as a sparepart for FC 9 (from Yamaha)....
could solve your prob ...
maybe show my post to the tech , he will know what to do

Also, I read that the filter input does take 20volts

external CV ??? very different situation

mm-pro · Post by **mm-pro** » Sat Jun 08, 2013 1:47 pm

One pin on the din is the voltage return. There is also 9 volts on two of the pins. So...9v/20v/grd/input/9v on 1/4/2/5/3/

Regards,

MM

WaterDrum · Post by **WaterDrum** » Sat Jun 08, 2013 2:24 pm

thats odd ...
you could experiment with pots in the way I pointed
for the 20 volt and for the 9 Volt
but from now on you might better have a service manual .
and/or a plan of the circuit

mm-pro · Post by **mm-pro** » Sat Jun 08, 2013 2:41 pm

I think I am going to wire a cable and try a low external voltage from a Moog cp251 of 5 volts and see how much that affects the filter. If it's enough for my needs, I could use one pedal into the cp251 and feed voltage to both filter inputs quite easily.

WaterDrum · Post by **WaterDrum** » Sat Jun 08, 2013 3:25 pm

so you want to send voltage ontop of an existing voltage ...
not shure if that works .

Main question :
is this a CV signal input (e.g.for a stepsequencer) ???
or kind of an "ohmic insert" ?

you shure have a dedicated knob for the filter function ?
trace the cables that are soldered to the knob (=potentiometer)
is there some kind of connection to the DIN ?
can you read the value of the knob potentiometer ?
the two "9 volt pins" are they connected (=identical)?
9 volts against ground ?

one more Q : "Korg WD1" is that a 1994 Wavedrum ?
oh and here easy to find
http://ebookbrowse.com/korg-maxi-korg-8 ... f-d3441348

the full download seems to be a download prog (*.exe)
so its only online for me ...

mm-pro · Post by **mm-pro** » Sat Jun 08, 2013 4:44 pm

Yes, an original Wavedrum with the programmer.

I have the schematic for the DV800...though, that model doesn't have the Din filter pedal connections. I think only the Univox branded Maxi-Korgs in North America had them...but perhaps in other places too?

Regards,

MM

mm-pro · Post by **mm-pro** » Sat Jun 08, 2013 4:59 pm

I believe the filters are CV controlled from pin 5 on the DIN plug.

I am going to try 5 volts and see how limited the range is...if I need more voltage, I will probably have my tech create a proper connector for it.

WaterDrum · Post by **WaterDrum** » Sat Jun 08, 2013 6:20 pm

Headline of the original user manual
"Know it , dont blow it"

did you look at the schematics I have linked to ?

page 3/11 you find the DINs ...
how much are you into reading schematics ?

<table><tr><td><a href="http://ebookbrowse.com/korg-maxi-korg-8 ... 1348">Korg Maxi Korg 800 DV Schematic pdf</a></td></tr><tr><td><iframe src="http://docs.google.com/gview?url=http%3 ... edded=true" frameborder="0"></iframe></td></tr><tr><td>View more <a href="http://ebookbrowse.com/korg-maxi-korg-8 ... f-d3441348" target="_blank">ebooks</a> on <a href="http://ebookbrowse.com" target="_blank">ebookbrowse.com</a></td></tr></table>
upper din pin 5 connects 1 resistor to both integrated circuits
might be inputs
2nd din has a ground connection to a kind of "jack matrix"
labeled as "accessories" (= insert effects" ??? )
2nd din has no more pins connected (?)
pin 5 points to "for lower" ??

2 possibilities now
1. the IC is waiting for CV , you put voltage in and all is good

2.the IC wants to have an easier connection to ground ,
what you wanna do is not to lower the voltage ,you want to raise it .
this could be fatal

-if you burn a resistor ,well , ok ...
-if you burn an integrated circuit chip (hard to get ....)
you need to understand the circuit , or be *Extremely* cautious
you will know
still curious .

WaterDrum · Post by **WaterDrum** » Thu Jun 13, 2013 1:54 pm

a google search brings the following result :

mm-pro · Post by **mm-pro** » Fri Jun 14, 2013 3:13 am

cool thanks!