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

[cheater cheater]

Hi Sam,
we'd been talking about your hpf mod with Richard, and we deduced that
the main problem is that there's no easy place to hack into the ground
terminal of the sallen key topology -- is that right? If so, have you
thought about suggesting to korg that they add a 'hack terminal' in
there? What I mean by 'hack terminal' is a trace with two through-hole
terminals added for anyone to use, separated by about 2-5 mm of trace
that can be cut through. I guess this would make your life much
easier. Out of curiosity, in what other places are you missing such
'hack terminals' in and have to resort to SMD desoldering?

I'm hoping Korg will get to know of this 'deficiency' and will think
about making a nice revision. :-)

I am completely mesmerized by the monotron. First of all - correct me
if I'm wrong - it's the first fully analog synth from a major
manufacturer in a quarter century; but that is nothing compared to the
fact that it was made hackable, and even more so, that the company
*encourages it*. I can see some golden days for analog coming up. I
hope Korg will listen to feedback from hackers like you and will make
it even nicer :^) and I hope other companies will find out that Korg
have made some really solid money on it and will follow the trend :)

BTW, thanks for the writeup earlier in the thread. Very informative,
please come back with more as soon as you can :)

Cheers,
D.

On Mon, Jul 5, 2010 at 21:01, Tim Stinchcombe
<tim102 at tstinchcombe.freeserve.co.uk> wrote:
> 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
>
>
>
>
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