[sdiy] Korg Monotron... Korg 35 chip?

[HOSHUYAMA]

Hello list,

> > Would that also mean that I could use one Monotron as 
> > highpass, and one as lowpass?
> 
> Good question - so far I have not seen a mod to reconfigure a Monotron for
> the highpass filter (which may mean it is difficult). Can't wait to get my
> hands on one to see how do-able that is! But note that the Monotron isn't
> using the Korg35 per se, just the same arrangement of transistors that are
> in the Korg35 (as far as I can tell from the various photos of it around the
> web).

I already succeeded at adding a high pass input to the monotron filter
in an experiment.  But, it is difficult to change the signal pass on 
the PCB with tiny SMDs.  Actually, I broke a PCB and had tough time 
to recover.  So I did not use high pass configuration in my modification.

Additional info for those who are thinking of modifying a monotron.
Correcting my English is welcome.

 - DC-DC converter is used.  Stable 5V is generated from 3V or less.
 - A bias voltage 1.35V generated by an opamp from 5V is used for virtual grounding.
 - 74HC14 is used for VCO and VCLFO.
 - The left LM324 is for gate generator, VCO CV mixer, and exponential converter.
 - The right LM324 is for VCF CV mixer, VCF signal mixer/attenuator, and VCF buffer.
 - 6-pin chip beside the left 324 is a pair transistor for VCO.
 - Large 3-pin SMDs are N-channel JFETs.
 - Small 3-pin SMDs are bipolar transistors.
 - SMD capacitor values can not be seen.  (tiny brown SMDs)
 - Resistor values are easy to read. (tiny black SMDs)
 - A 3.5mm jack has 4 terminals: chip, 1st ring, 2nd ring, and 3rd ring (ground).
   In the external input jack, 2nd ring is used to turn off the gate signal to VCF.
   In the headphone output jack, 2nd ring is used to control the power amp IC to
   mute the loudspeaker.

Best,

Sam HOSHUYAMA
Saitama, JAPAN

"Tim Stinchcombe" wrote:
> >  Hey all, has anyone else noticed the Korg Monotron?
> 
> Reckon so...
> 
> A couple of recent threads at Muffwiggler:
> 
> <http://www.muffwiggler.com/forum/viewtopic.php?t=14577&postdays=0&postorder
> =asc&start=0>
> 
> <http://www.muffwiggler.com/forum/viewtopic.php?t=18358&start=0&postdays=0&p
> ostorder=asc&highlight=>
> 
> And there are many Japanese blogs/sites with some great-looking
> modifications:
> 
> 
> http://www.korg.co.jp/Product/Dance/monotron/welove/
> 
> 
> http://beatnic.jp/monotron/
> 
> Google translate:
> 
> <http://translate.google.co.uk/translate?u=http%3A%2F%2Fbeatnic.jp%2Fmonotro
> n%2F&sl=ja&tl=en&hl=&ie=UTF-8>
> 
> 
> http://masa921.hp.infoseek.co.jp/monotron_mod.htm
> 
> Google translate:
> 
> <http://translate.google.co.uk/translate?u=http%3A%2F%2Fmasa921.hp.infoseek.
> co.jp%2Fmonotron_mod.htm&sl=ja&tl=en&hl=&ie=UTF-8>
> 
> > In the 
> > adverts it states that it uses the same filter as the MS-10 
> > and the early MS-20. My question is this: The MS-20 has 
> > lowpass and highpass filters. The MS-10 only low pass. Would 
> > this mean that the korg 35 chip is configurable as both?
> 
> The original was, yes, just hook it up slightly differently for highpass...
>  
> > Would that also mean that I could use one Monotron as 
> > highpass, and one as lowpass?
> 
> Good question - so far I have not seen a mod to reconfigure a Monotron for
> the highpass filter (which may mean it is difficult). Can't wait to get my
> hands on one to see how do-able that is! But note that the Monotron isn't
> using the Korg35 per se, just the same arrangement of transistors that are
> in the Korg35 (as far as I can tell from the various photos of it around the
> web).
> 
> Tim (still pissed at Korg for not releasing it worldwide in one go)
> __________________________________________________________
> Tim Stinchcombe 
> 
> Cheltenham, Glos, UK
> email: tim102 at tstinchcombe.freeserve.co.uk
> www.timstinchcombe.co.uk
> 
> 
> 
> 
> 
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