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

[dan snazelle]

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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