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