Discussion about the Korg PolySix synthesizer

According to Analog.com
http://www.analog.com/library/analogDialogue/Anniversary/21.html, you should
be using any of the "poly" (polystyrene, polypropylene, Teflon) types for a
sample and hold circuit, since a ceramic cap has considerable dielectric
absorption which can cause a type of charge memory that can cause errors in
hold level. Some polystyrene caps can be rather tall, so you would have to
choose carefully. The old mylars look like they are about 10mm high. The
caps I'm using on the clone boards are about 8mm, so there is not much
difference. How much clearance do you need for the new keybed? If the old
caps weren't soldered so close to the board, you could just bend them over
so they would lie flatter.

 

Don B.

 

  _____  

From: PolySix@yahoogroups.com [mailto:PolySix@yahoogroups.com] On Behalf Of
chipaudette
Sent: Friday, May 03, 2013 12:05 PM
To: PolySix@yahoogroups.com
Subject: [PolySix] Mylar caps on the sample-hold circuits on KLM-367

 

  

Hi Folks,

Some of you may know that I've replaced the keybed on my Polysix. The new
keybed has a long metal cross-bar that sits a little lower than the one on
the stock keybed. The new keybed is running into the tall 0.047uF Mylar caps
that are standing tall from the KLM-366. Specifically, I'm talking about
C31-C36 that are the caps that hold up the sample-and-hold output from IC29.


Being too tall, I'm thinking about replacing them. They're listed as 50V
Mylar caps. Would it be OK to replace them with 50V ceramics instead? The
ceramics are WAY smaller and would allow my new keybed to fit easily.

The signals being held by these caps is only used for the keyboard tracking
of the VCF, so it's not like I need a cap with ultimate fidelity. I think
that I need a cap that holds its DC value very well (which is the point of
the S-H).

Would a ceramic be OK here?

Chip





[Non-text portions of this message have been removed]