Discussion about the Korg PolySix synthesizer

I play a lot of bass-heavy music.  It would be super easy to add a
switch for this mod.  I look forward to trying this on my big
subwoofers!

On Tue, Aug 20, 2013 at 9:53 AM, chipaudette <chipaudette@yahoo.com> wrote:
> I finally followed-up on Tony's suggestion that C61 on KLM-368 appears to have no purpose and that it could be removed.
>
> When I look at C61, I also see no purpose.  I see that it could possible attenuate the lowest bass frequencies.  I was curious to see the effect of removing this component.  Not wanting (yet) to permanently remove C61, I simply bypassed it with a single clippy jumper wire.  Easy!
>
> The result appears to be ~6 dB more of the deepest bass frequencies (down in the 33 Hz neighborhood).  That's deep.
>
> If you're interested in the mod, you can check out the details at:
>
> http://synthhacker.blogspot.com/2013/08/polysix-deeper-bass-bypass-c61.html
>
> If you've got good headphones or really good speakers, there's also an audio comparison.
>
> My conclusion is that maybe the Polysix doesn't need these super-deep frequencies.  It is a fun change, but I'm not sure it's how I want it to sound all the time.  I'll have to live with it for a while before I make my decision.
>
> Thoughts?
>
> Chip
>
> --- In PolySix@yahoogroups.com, Oakley Sound <oakleylist@...> wrote:
>>
>> I've been following Chip's progress with interest. And his recent post
>> on the dynamic noise reduction filter on the effects board spurred me
>> onto to investigate further. I too have noticed that the P6 is somewhat
>> duller than other synths and I had always assumed that with the ensemble
>> mode off the output was as bright as it could be.
>>
>> Chip's findings that all four ensemble modes pass through the DNR filter
>> was something I hadn't really thought about before.
>>
>> http://synthhacker.blogspot.co.uk/2013/02/mystery-circuit-polysix-post-effects.html
>>
>> In summary: the P6 has a 12dB/octave low pass filter that is set to
>> around 600Hz (the actual value depends on whether the BBDs are engaged)
>> when no notes are playing. This filter opens up when it detects audio
>> from the voice card. As Chip noticed it takes a finite time for the
>> filter to open and the filter doesn't always open fully in all cases. I
>> measured the filter took up to 100mS to open fully. That's a significant
>> loss of high frequency sound at the start of each note.
>>
>> Yesterday I went a stage further than Chip. Chip's mod basically forces
>> the filter open. I decided to remove the filter from the circuit
>> altogether. This has the advantage of no dynamic filtering (which is of
>> dubious amenity) and reduces the circuit pathway that the audio has to
>> go through. The LM13600 isn't a hi-fi part and removing it improves the
>> signal quality.
>>
>> The mod:
>>
>> Remove links J28 and J29. Remove R115 and R109 (which disables the
>> envelope follower). Remove C73 and C61.
>>
>> Link out, with a piece of solid core wire, the two left hand holes of
>> J28 and J29. Now connect with a piece of insulated wire the lower of
>> these now filled solder pads to the lower pad of C73. The filter is now
>> bypassed.
>>
>> Link out, with a piece of solid core wire, the two holes of C61. This
>> capacitor serves no useful job that I can see.
>>
>> Result: the P6 can be as bright as any synth. Percussive sounds ring out
>> where they didn't before. String sounds are really very majestic - you
>> can really pull off sounding like a string machine now. The slight
>> increase in background hiss is not a problem for me.
>>
>> Tony
>>
>> http://takla-makan.bandcamp.com/
>> http://www.oakleysound.com
>>
>
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