Search found 1446 matches

by Mooger5
Fri Jun 21, 2019 12:36 pm
Forum: HELP!
Topic: Korg Poly-800 Chorus mod
Replies: 22
Views: 4558

Re: Korg Poly-800 Chorus mod

Weird but anyway last resource RC network at pins 5 and 6 of MN3102. On page 3 of datasheet look for the table example (1) where values for R and C for fastest clock rate are displayed. Connect both to pin 7 with a resistance 1k to mix with incoming modulated signal from output of comparator. If thi...
by Mooger5
Sun Jun 09, 2019 9:20 am
Forum: HELP!
Topic: Korg Poly-800 Chorus mod
Replies: 22
Views: 4558

Re: Korg Poly-800 Chorus mod

Yep the saw wave's amplitude varies from about -4.5 to a positive value. R69 100k limits the flow of the positive current. So, a value less than 100k will make the ramp rise earlier, shortening the wave period which means of course increasing the frequency.
by Mooger5
Fri Jun 07, 2019 12:14 am
Forum: HELP!
Topic: Korg Poly-800 Chorus mod
Replies: 22
Views: 4558

Re: Korg Poly-800 Chorus mod

And I got it all wrong hahaha. See IC8a, the final comparator: the reference voltage set by the divider at pin 2 is -4.5V! There's no way "my" saw wave reached that low, it was +4.5 to zero. So my calcs were nonsense LOL. If the ref voltage is -4.5 at pin 2, the signal voltage at pin 3 must at one t...
by Mooger5
Thu Jun 06, 2019 5:47 pm
Forum: HELP!
Topic: Korg Poly-800 Chorus mod
Replies: 22
Views: 4558

Re: Korg Poly-800 Chorus mod

To shift the master delay time down to flanger range, the MN3102 datasheet shows the minimum and maximum values of resistance 'allowed' which could be adjusted with a potentiometer. A capacitor of a suitable value is also added. Pin 7 though, is tricky... anyway, this involves soldering to the pins ...
by Mooger5
Thu Jun 06, 2019 5:29 pm
Forum: HELP!
Topic: Korg Poly-800 Chorus mod
Replies: 22
Views: 4558

Re: Korg Poly-800 Chorus mod

It's just that the LFO time and the 'nominal' delay time are two separate things. No matter how much the LFO is tweaked, the chorus effect will never sound like a flanger unless the nominal delay time is adjusted to the adequate value. The one in the Poly800 chorus is fixed and is not in the flanger...
by Mooger5
Wed Jun 05, 2019 3:18 pm
Forum: HELP!
Topic: Korg Poly-800 Chorus mod
Replies: 22
Views: 4558

Re: Korg Poly-800 Chorus mod

Your questions are pertinent. Would like to know the source of those mods. Q8 is a constant current source. D6 is there for thermal compensation. Removing it from the circuit would make the current fluctuate, affecting the saw wave. I *think* I got it (someone please correct me otherwise): bbd.jpg Q...
by Mooger5
Wed Jun 05, 2019 3:16 pm
Forum: HELP!
Topic: Korg Poly-800 Chorus mod
Replies: 22
Views: 4558

Re: Korg Poly-800 Chorus mod

Your questions are pertinent. Would like to know the source of those mods. Q8 is a constant current source. D6 is there for thermal compensation. Removing it from the circuit would make the current fluctuate, affecting the saw wave. I *think* I got it (someone please correct me otherwise): Q9 is alw...
by Mooger5
Tue Jun 04, 2019 11:18 pm
Forum: Gear Services & Other Goods
Topic: looking for sliding potentiometers for Casio RZ-1
Replies: 8
Views: 3465

Re: looking for sliding potentiometers for Casio RZ-1

They do look like generic mono pots though the scale next to them makes the travel lengths appear confusing.
The sliders are the things for which there are no standards. So try to find the equivalent pots and carefully replace the new sliders with the old ones.
by Mooger5
Tue Jun 04, 2019 11:04 pm
Forum: HELP!
Topic: Korg Poly-800 Chorus mod
Replies: 22
Views: 4558

Re: Korg Poly-800 Chorus mod

Eager to see them. The saw core resembles a lot the relaxation oscillator of the Polysix VCO, so making R69 adjustable could probably vary the delay time. My last bet is adding a resistor and capacitor to pins 5 and 6 of the 3102 to offset the time, as per the datasheet. Damned complicated stuff. I ...
by Mooger5
Tue Jun 04, 2019 3:49 pm
Forum: HELP!
Topic: Korg Poly-800 Chorus mod
Replies: 22
Views: 4558

Re: Korg Poly-800 Chorus mod

It is possible, it is just korgs own way that i m not used to and its a bit frustrating.
Try r69.
by Mooger5
Fri May 31, 2019 11:55 am
Forum: HELP!
Topic: Dx7 strange problem, help me!
Replies: 6
Views: 2430

Re: Dx7 strange problem, help me!

Rasputin adds another score! If the ghost note was b3 then it was thr diode d36 failed open that caused it right? Any idea why? The op played only octaves and maj7 intervals though it would seem other notes in the same octave would also be affected. I cant think of a better explaination other than m...
by Mooger5
Fri May 31, 2019 11:09 am
Forum: HELP!
Topic: Korg Poly-800 Chorus mod
Replies: 22
Views: 4558

Re: Korg Poly-800 Chorus mod

No problem. Please replace c43. Must be missing something here. The darasheet clearly ststes pins 5 6 and 7 determine the clock speed by mrans of rc network. If pins 5 and 6 arent usef then pin 7 alone makes the 3202 run under external time control. There must be still something that sets the minimu...
by Mooger5
Mon May 27, 2019 11:08 pm
Forum: HELP!
Topic: Korg M1 - one key not working
Replies: 2
Views: 1658

Re: Korg M1 - one key not working

Never owned an M1, but I know it uses the same keyboard as the DX7. Maybe the following is of some help viewtopic.php?f=5&t=110938&p=815864#p815864
by Mooger5
Mon May 27, 2019 11:02 pm
Forum: HELP!
Topic: Dx7 strange problem, help me!
Replies: 6
Views: 2430

Re: Dx7 strange problem, help me!

The FS keyboards don´t use rubber contacts, but three stacked laminated springs per key instead. Their state is always being scanned by a microprocessor. When a key is off, the movable middle spring is in contact with the top one and when the key is pressed it pushes the middle spring down, making c...
by Mooger5
Mon May 27, 2019 10:26 pm
Forum: HELP!
Topic: Korg Poly-800 Chorus mod
Replies: 22
Views: 4558

Re: Korg Poly-800 Chorus mod

Feedback in a delay line works much like resonance in a filter. Although it can be either positive or negative. When the delay time is long enough, feedback determines the number of audible repetitions. Same as echo. Because the effected signal gets processed over and over. If the delay is too short...