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

Tue Jul 6 17:38:23 CEST 2010

without looking, a diode would not fix this. You'd need to have a current
source that limits to a safe value.

If you can really kill it this way, that's really bad !   I wanted to
get one my kid (@3yrs) but I'm sure he'd stuble across the hidden
weenine soon...

What is the range of the ribbon ? It looks like a little over one octave
which might be of questionable value imho...

can anyone say "PAiA GNOME" ???

H^) harry

----- Original Message -----
From: cheater cheater <cheater00 at gmail.com>
To: Naoki Iwakami <naoki.iwakami at gmail.com>
Cc: synth-diy at dropmix.xs4all.nl
Sent: Tue, 06 Jul 2010 11:18:32 -0400 (EDT)
Subject: Re: [sdiy] Korg Monotron... Korg 35 chip?

Hi Naoki!
Welcome to the list :) good to see more japanese people on the list,
we'll finally get some trends from over there hopefully :) Hoshuyama
is already putting in his good share of novelties with the expo etc :)

> And I've broken my ribbon by pressing low and high ends at the same time
> while the power is on.  It shorts V+ and GND through the ribbon
> without any protection.

oww, not even a diode? now that's a mod that must be in if i saw one...

> Not through holes but they have test pads on the bottom side of the
> PCB as seen in the picture below.
> http://beatnic.jp/monotron/img/back-side.jpg
>
> Are you mentioning something like these?

yes, those pads are on the conceptual level similar to what i mean,
but not exactly: 1. they should be in the circuit lead. The whole idea
is that you might want to cut a lead, and solder wires to both sides
of the cut. So you just have two holes next to eachother on the lead.
So for example if you want to insert an OTA drive stage between the
VCO and the VCF, there's a lead connecting them that carries the raw
VCO signal. If that lead had two holes in it, you could cut between
the holes, and insert your drive stage by using the two holes provided
for soldering. Makes circuit hacking *SO* much easier. As you said
adding is not difficult with pads, but modifying still is difficult.
Well, this fixes the problem.

and 2. they should be holes :)))) no idea why they didn't make them
holes, it's really perplexing! it makes mods so much easier and more
durable ......

Cheers,
D.

On Tue, Jul 6, 2010 at 08:36, Naoki Iwakami <naoki.iwakami at gmail.com> wrote:
> Hello cheater cheater, all
>
> Not through holes but they have test pads on the bottom side of the
> PCB as seen in the picture below.
> http://beatnic.jp/monotron/img/back-side.jpg
>
> Are you mentioning something like these?
>
> BTW I have also modified my Monotron to add another VCO in it.
> http://gaje.jp/projects/synth_effect/monotron/
> The VCO circuit is based on the monotron's (conceptually identical),
> and the exponential amplifier is the same except tempco resistor (they
> are not using it).
>
> As Sam mentioned, adding to this tiny box is not so hard but modifying is.
> Replacing the LED was harder for me than adding a VCO :-)
> And I've broken my ribbon by pressing low and high ends at the same time
> while the power is on.  It shorts V+ and GND through the ribbon
> without any protection.
>
> -- Naoki
>
> On Tue, Jul 6, 2010 at 9:26 AM, cheater cheater <cheater00 at gmail.com> wrote:
>> 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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>>>
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-- 
Harry Bissell & Nora Abdullah 4eva