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

[HOSHUYAMA]

Hello Dan,

Here is the schematic:

http://beatnic.jp/monotron/img/lfo-schem.gif

Takeda-san says that the inverters are 74AHC14.

Sam HOSHUYAMA
Saitama, JAPAN

HOSHUYAMA wrote:
> Hello Dan,
> 
> 74HC14 (maybe AHC) is used just as a schmidt trigger or an inverter
> to reset an integrator.  The integrator and reset switch is like 
> Moog VCO with a JFET buffer followed by 2 HC14 inverters.
> 
> Sam HOSHUYAMA
> Saitama, JAPAN
> 
> dan snazelle wrote:
> > any ideas on how they are implementing the  74HC14 as a vclfo?
> > thanks so much for this info
> > 
> > 
> > 
> > 
> > On Jul 4, 2010, at 11:34 AM, HOSHUYAMA wrote:
> > 
> > > 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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> > >> 
> > >> 
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> > 
> >  
> 
>