Discussion about the Korg PolySix synthesizer

I am hopefully getting to the end of fixing up this Polysix, having installed the Kiwisix upgrade kit and power supply board, and have recently completed the various fine tuning and trim adjustments.

But one thing that I cant seem to figure out is why the headphone output is so high.

If I use the main audio output jack and set output switch to High, and Volume knob to 10, I then set my monitor amp/mixer to a comfortable listening level, and the output from the Polysix sounds fine and there is no noise, or it is below audible level of the .

However if I plug in my headphones to the headphone output jack, I have to make sure the volume knob is way down to about 1 or 2, as any louder and listening through the phones is way too loud. If I am careful not to play a note I can turn up the Volume knob to 10 and then I can clearly hear the noise floor on the headphone output, but I am wondering if anyone could explain why the volume level for the main audio output is fine at Volume knob setting of 10 but way too loud for the headphone output.

I tried searching for any info on this but the only threads seem to be related to noisy outputs which is not really the case here but rather a too high headphone amp output. I followed the instructions for adjusting the trim pots in the service manual and the headphone amp offset is at 0mV and level is 0.3V peak to peak and those are set correctly

Once again thanks in advance for any help with this. Cheers. 

Hey t_tangent,

Thank you Yash, I will have a look at those and post back if I find anything. Thanks again.

Hi, see the electronic diagram, the headphones amplifier is connect befor switch attenuator for the output line.
And this is the cause that all polysix have and hight level at the headphones, you can change the input of the amplifier for HP, and connect after this attenuator.
Regards

Very cool info, Roberflas, thanks.

You might want to swap resistors KLM369/R4 and R8 (1k) by 3k3.

On 2017-05-15, 02:24 josh.nursing@gmail.com [PolySix] wrote:
>
>
> Very cool info, Roberflas, thanks.
>
>
> ---In PolySix@yahoogroups.com, <roberflas@...> wrote :
>
> Hi, see the electronic diagram, the headphones amplifier is connect
> befor switch attenuator for the output line.
> And this is the cause that all polysix have and hight level at the
> headphones, you can change the input of the amplifier for HP, and
> connect after this attenuator.
> Regards
>
>
>

Hi roberflas,

Hi Johannes,

Hi t_tangent2003,

Yes, the higher the value the less the headphone amplification.
Be aware that headphones do have different sensitivity. It might be
good for one unit and too loud or too low for another.
For finding the right value for you you might put in a trimpot (for
test) and adjust it to your taste. Then measure the value and mount a
resistor accordingly.

All the best, Johannes

On 2017-05-17, 20:33 t_tangent2003@yahoo.co.uk [PolySix] wrote:
>
>
> Hi Johannes,
>
> Thank you for the suggestion to swap resistor R4 and R8 from 1K to 3.3K.
> I have just done this as it was easy to try out and this stops the
> headphone out level from being deafeningly loud and killing the
> headphones. When the Volume knob is at 10 this works fine so long as
> only 1 voice is playing but if I play more than 1 voice I do get
> distortion on the headphone output. If I turn the volume down to about 5
> then I can play more than 1 voice without distortion. So would this mean
> that if I swapped the 3.3k resistors on R4 & R8 for higher value
> resistor, the headphone output will be reduced further, for example
> using 10k resistors, or is that too high a value for those resistors. I
> could try it but thought I would ask first before removing the pcb again.
>
> Anyway thanks again, and all the best. :)
>
>
>

On 16.05.17 06:57 , Johannes Hausensteiner johannes@eclipso.at [PolySix] wrote:

 

You might want to swap resistors KLM369/R4 and R8 (1k) by 3k3.

Why this? Why not increase simply R3 or add an 25k Trimmer in series to R3 to make it adjustable?

Florian

Thanks to both Johannes and Florian.