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

[Tim Stinchcombe]

Hi Sam,

> 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.

So it sounds like it _is_ possible, only tricky due to the use of 0603 SMT -
that is the main size we work with in my day job, so I'm not expecting the
Monotron to give me too much trouble.

> 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.

Excellent info, thanks for posting that! Some I had managed to deduce for
myself, but it all helps to build up an overall picture, and a sense of
expectation whilst I wait for them to go on sale here in the UK!

Tim
__________________________________________________________
Tim Stinchcombe 

Cheltenham, Glos, UK
email: tim102 at tstinchcombe.freeserve.co.uk
www.timstinchcombe.co.uk