K5synth

Hello
(Please excuse my poor english.)

The (since 2004) practiced output-modification prefer to the Kawai K5 (K5m) is not correct.

Reasons:

Point 1:
The ORIGINAL upper-cutoff-frequency (at the modification area of the circuit) is 28kHz.
((R26, R27, R28, R29): 56kOhm parallel to 100pF)
But if you replace the original 56kOhm-Resistors by 150kOhm, the resulting upper-cutoff-frequency is only 10kHz!!!
(150kOhm parallel to 100pF)
And so the sound of the modificated Synthesizer is muffled (not brilliant), because the upper-cutoff-frequency is now much to low.
Note:
To keep the original upper-cutoff-frequency, you must replace C16, C18, C29, C20 (100pF) by 33pF capacitors!

Point 2:
If you replace R19 (56kOhm) by 150kOhm, the gain of the Single-Mode AND the gain of the Mix-Out is much to high.
Reason:
The Mix-Out bases on an ADDITIONAL OP-Amp (gainresistor: R19) and at the input of this additional OP-Amp the four outs of the Output-

Amplifiers (gainresistors: R26, R27, R28, R29) are
summarized by (four) 100kOhm resistors.
And:
If the Synthesizer is in Single-Mode, the output of the additional OP-Amp (=Mix-Out!!!) is switched (by the Relais RY3 and Ry5) DIRECTLY TO ALL output-sockets (Mix, 1, 2, 3 and 4).
And so it is NOT useful, to change R19 from 56kOhm to 150kOhm, because in this case there are TWO amplifications SERIAL.

Summarizing:

The CORRECTED modification:
Replace R26, R27, R28, R29 (56kOhm) by 150kOhm resistors.
Replace C16, C18, C29, C20 (100pF) by 33pF capacitors.
R19 must be 56kOhm (56kOhm is original)

By the way:
I have designed another (much easier and (prefer to noise-gain) better) output-modification. You can see the details under following link (german):
http://www.sequencer.de/synthesizer/viewtopic.php?f=3&t=108837

But here is the shortform for you:

INSTEAD of the old modification:
Solder eight 22kOhm-Resistors at THE UNDERSIDE of the print parallel to the following (39kOhm) resistors:
R33, R34, R35, R36, R37, R38, R39, R40.

(Or: Replace R33, R34, R35, R36, R37, R38, R39, R40 by 15kOhm-resistors.)

Best regards
Böckle Christian

PS.: A special thank to Narfman96

Hi,

thanks for the effort on this!

I am planning to perform this output modification on my K5, by replacing 
R33 through R40.
On the sequencer.de forum post I noticed you advise using 12kOhm 
resistors, while in the below message you mention 15kOhm.
What value would you advise?

Best regards,
Jeroen Oldenhof


Op 17-12-2015 om 7:09 schreef woerz.herbert@... [k5synth]:

>
> Hello
> (Please excuse my poor english.)
>
>
> The (since 2004) practiced output-modification prefer to the Kawai K5 
> (K5m) is not correct.
>
> Reasons:
>
>
> Point 1:
> The ORIGINAL upper-cutoff-frequency (at the modification area of the 
> circuit) is 28kHz.
> ((R26, R27, R28, R29): 56kOhm parallel to 100pF)
> But if you replace the original 56kOhm-Resistors by 150kOhm, the 
> resulting upper-cutoff-frequency is only 10kHz!!!
> (150kOhm parallel to 100pF)
> And so the sound of the modificated Synthesizer is muffled (not 
> brilliant), because the upper-cutoff-frequency is now much to low.
> Note:
> To keep the original upper-cutoff-frequency, you must replace C16, 
> C18, C29, C20 (100pF) by 33pF capacitors!
>
>
> Point 2:
> If you replace R19 (56kOhm) by 150kOhm, the gain of the Single-Mode 
> AND the gain of the Mix-Out is much to high.
> Reason:
> The Mix-Out bases on an ADDITIONAL OP-Amp (gainresistor: R19) and at 
> the input of this additional OP-Amp the four outs of the Output-
>
> Amplifiers (gainresistors: R26, R27, R28, R29) are
> summarized by (four) 100kOhm resistors.
> And:
> If the Synthesizer is in Single-Mode, the output of the additional 
> OP-Amp (=Mix-Out!!!) is switched (by the Relais RY3 and Ry5) DIRECTLY 
> TO ALL output-sockets (Mix, 1, 2, 3 and 4).
> And so it is NOT useful, to change R19 from 56kOhm to 150kOhm, because 
> in this case there are TWO amplifications SERIAL.
>
>
> Summarizing:
>
> The CORRECTED modification:
> Replace R26, R27, R28, R29 (56kOhm) by 150kOhm resistors.
> Replace C16, C18, C29, C20 (100pF) by 33pF capacitors.
> R19 must be 56kOhm (56kOhm is original)
>
>
> By the way:
> I have designed another (much easier and (prefer to noise-gain) 
> better) output-modification. You can see the details under following 
> link (german):
> http://www.sequencer.de/synthesizer/viewtopic.php?f=3&t=108837
>
>
> But here is the shortform for you:
>
>
> INSTEAD of the old modification:
> Solder eight 22kOhm-Resistors at THE UNDERSIDE of the print parallel 
> to the following (39kOhm) resistors:
> R33, R34, R35, R36, R37, R38, R39, R40.
>
> (Or: Replace R33, R34, R35, R36, R37, R38, R39, R40 by 15kOhm-resistors.)
>
>
> Best regards
> B�ckle Christian
>
> PS.: A special thank to Narfman96
>
>

Hello Jeroen

Here I repeat for you the NEW (correct) modification once again:

The SIMPLEST way to modifiy the output-section of an original K5:

Do NOT replace the original resistors!
But:
Solder eight 22kOhm-Resistors at THE UNDERSIDE of the print PARALLEL to the following original (39kOhm) resistors:
R33, R34, R35, R36, R37, R38, R39, R40.
That`s all.

Best regards
Christian Böckle

Hi Christian,

In your original 'much easier and (prefer to noise-gain) better' 
modification from the previous post you also state:

"(Or: Replace R33, R34, R35, R36, R37, R38, R39, R40 by 15kOhm-resistors.)"

But now you advise against this? Why is that?
I believe replacing is a more elegant solution than adding additional 
resistors, of course this induces a certain risk of damaging the device, 
but this is something one needs to evaluate for themselves.

Anway, 22kOhm parallel to 39kOhm gives an equivalent resistance of 
14kOhm.. so my question is answered.
Thanks again!

Best regards,
Jeroen Oldenhof


Op 25-2-2016 om 14:04 schreef woerz.herbert@... [k5synth]:

>
> Hello Jeroen
>
>
> Here I repeat for you the NEW (correct) modification once again:
>
>
> The SIMPLEST way to modifiy the output-section of an original K5:
>
>
> Do NOT replace the original resistors!
> But:
> Solder eight 22kOhm-Resistors at THE UNDERSIDE of the print PARALLEL 
> to the following original (39kOhm) resistors:
> R33, R34, R35, R36, R37, R38, R39, R40.
> That`s all.
>
>
> Best regards
> Christian B�ckle
>
>

Hello Jeroen

Yes, the replacing of the resistors is naturally a more elegant solution, but if you are not a qualified technician the risk to damage the (double sided) printed circuit board is high (and you definitely need 1/8W-Resistors (3,3mm x 1,7mm)).

That`s the reason, why i prefer the simple parallel-soldering-method (Here you can also use conventional 1/4W-resistors.).

Best regards
Christian Böckle