Rev eng of Jen KPS 900 phaser - confusion.

[nelson]

Hi everyone,


I am in the process of reverse engineering a non working Jen KPS 900 phaser. So far, I have a pretty straightforward buffer, two allpass stages and fixed feedback deal.

What is puzzling me is that U2 is a quad opamp yet seems to be used as the variable resistance to ground for the opamp allpass stages and has no V+ or gnd connections on the correct  pins 4 and 11.

I will update this thread with detailed gut shots soon.

The PCB appears unmodified, no attempt at repair.

In the early rev eng stages it appears as if either U2 should be a CMOS buffer affair or a multi transistor/jfet dip package, either that or an opamp application I have never seen before.

Does anyone have a jen KPS 900 and can pop it open to confirm what the two IC's are? I have searched for a schematic to no avail. This effect is pretty rare and I am not holding my breath - but it would be much appreciated.


Preliminary schematic and gut shots to follow.

[soulsonic]

Hey, I just repaired a Bad Stone; sounds like you have a similar circuit there. The Bad Stone I repaired uses a CD4009 hex buffer as the variable resistance. You can check out the Bad Stone schematic here:  http://www.muzique.com/schem/badstone.gif
In this schematic, the device labeled "E" is the CD4009. "F" is an LM324. All the rest are RC4558. The transistor is a 2N5088. Man, there's alot of question marks on that schematic; I should redraw it with the info I've learned from the one I repaired.

I hope this helps!

[snap]

man! you haven`t been to nelsons page in a while!

[soulsonic]

Ha! I'd never seen that corrected schematic before. It should be more widely advertised.
Yeah, I hadn't visited his page in awhile...

[nelson]

I popped in a CD4049UBE in the *14* pin socket and the phaser fired right up.

Strange that a 14 pin socket would be used for a 16 pin chip - 4009.

It phases nicely when biased. Not the best phaser I have ever heard.

I will finish the schematic and post gut shots. Then stick it back up on ebay where I got it.

[nelson]

Here is what I have.....

http://electroconducive.googlepages.com/KPS900.pdf

The pedal is working......

It is not making sense to me.

[alunr]

Hi All,

First post and with it a reigniting of a 12 year old thread!

I was gifted a KPS900 many years ago as "non working".  During this lockdown I've been having a good sort out and Happened across this pedal.  Unfortunately it hasn't magically fixed itself in the interim...

So, is there a circuit diagram for the original pedal around anywhere? Some good photos of the connections from the circuit to the pots and inputs would be useful too as I've got 2 loose wires.

I'm going to go through the board testing the capacitors and resistors etc and then I'll see if I can get anywhere testing the ICs too. 

The ICs are a Motorola MC14007B and a Motorola MC3403P

Thanks for any help!!!

[alunr]

[Scruffie]

Over on the 'other forum' https://www.freestompboxes.org/download/file.php?id=23599

[alunr]

Over on the 'other forum' https://www.....org/download/file.php?id=23599

The link didn't copy properly... 

[duck_arse]

welcome to the forum, alunr. it is compulsory for all first-time posters to read this thread ....

https://www.diystompboxes.com/smfforum/index.php?topic=124168.0

[Scruffie]

Over on the 'other forum' https://www.....org/download/file.php?id=23599

The link didn't copy properly...

It did in its own way (it's censored) .free stomp boxes. (remove the spaces).

[alunr]

Over on the 'other forum' https://www.....org/download/file.php?id=23599

The link didn't copy properly...

It did in its own way (it's censored) .free stomp boxes. (remove the spaces).

Ah, thanks!  I'm new here so didn't know the etiquette regarding external links

Once I've fixed 5is I've got an 80s cry baby to fix then I'm going to start on some projects of my own . Thanks all!