Discussion about the Korg PolySix synthesizer

Hello everyone;

since I wanted to get to the bottom of the capacitance problem with some
KLM367A clones I got me a dedicated capacitance meter and did some
measurements on various old and new boards. All measurements were done on
populated boards with the processor removed. I measured:

pin2 of IC22 socket to TP3 (that's essentially the capacitance across C22
to ground)
pin3 of IC22 socket to TP3 (that's essentially the capacitance across C23
to ground)
pin2 to pin3

I realize the absolute values probably don't mean too much; however it
should still be possible to compare the overall behaviour. The picture is
quite clear IMO.
All measurements in pF. The percent value is the difference between the
first and second column.


board		pin2	pin3	pin2<->pin3	percent

old1		40.7	46.7	92		14.7

old2		32.2	36.1	89		18.3

new1		23.1	28.7	81.3		24,2

new2		24	33.5	56.6		39.6

new2 (mod1)	19.0	18.4	53.0		-3.2

new2 (mod2)	26.0	40.5	58.5		55.7


board "new2 (mod1)" has two 10p caps installed, "new2 (mod2)" has two 33p caps.

A couple of weeks my guess was that the difference between the two "clock
legs" becomes too great for some boards to properly function. The above
measurements seem to point into this direction as well. I have some more
half-finished clones on which I will do additionla measurements once they I
finished them.

I have no idea why the overall capacitance for board "new2" was
significantly lower than for board "new1"; I also don't know if this may
affect operation.

Ideas? Comments?

Hi Malte,

Since there were no circuit modifications other than C23 being lowered to
10pF then we will have to suspect the layout, density and shape of the
copper on the new board (or even the properties of the new ceramic
resonator, if you didn¹t do a transplant!). From a practical point of view I
have constructed well over ten of these now and I only issue I have
encountered has been the clock instability, which, as we know, was rectified
by changing the above. Apart from that the board seems to offer a very
credible replacement to the original. As interesting as circuit analysis is
I think there is a risk of getting to bogged down in theory and looking for
problems where there are none. This might, if viewed by a non-technical
reader, also imply that the board isn¹t fit for purpose in some way and put
them off restoring their classic! (Which was the whole point in the first
place).

One thing I do hear from the people who have had a board constructed for
them is that there is something a little different about the tonal quality
of the clone board. Weird this as it does not actually sit anywhere directly
in the signal path. What they perceive as Œdifferent¹ might just be cleaner
waveforms and control voltages acting on those components which do. Whether
this is a result of you observations or just what the instrument should have
sounded like when it was new remains to be seen.

If you want to pursue this line of enquiry then I guess the next stage is
cutting tracks and rewiring them taking different routes.

Just a thought!

Andy


On 12/11/2010 09:49, "Malte Rogacki" <gacki@gacki.sax.de> wrote:
> 
> Hello everyone;
> 
> since I wanted to get to the bottom of the capacitance problem with some
> KLM367A clones I got me a dedicated capacitance meter and did some
> measurements on various old and new boards. All measurements were done on
> populated boards with the processor removed. I measured:
> 
> pin2 of IC22 socket to TP3 (that's essentially the capacitance across C22
> to ground)
> pin3 of IC22 socket to TP3 (that's essentially the capacitance across C23
> to ground)
> pin2 to pin3
> 
> I realize the absolute values probably don't mean too much; however it
> should still be possible to compare the overall behaviour. The picture is
> quite clear IMO.
> All measurements in pF. The percent value is the difference between the
> first and second column.
> 
> board pin2 pin3 pin2<->pin3 percent
> 
> old1 40.7 46.7 92 14.7
> 
> old2 32.2 36.1 89 18.3
> 
> new1 23.1 28.7 81.3 24,2
> 
> new2 24 33.5 56.6 39.6
> 
> new2 (mod1) 19.0 18.4 53.0 -3.2
> 
> new2 (mod2) 26.0 40.5 58.5 55.7
> 
> board "new2 (mod1)" has two 10p caps installed, "new2 (mod2)" has two 33p
> caps.
> 
> A couple of weeks my guess was that the difference between the two "clock
> legs" becomes too great for some boards to properly function. The above
> measurements seem to point into this direction as well. I have some more
> half-finished clones on which I will do additionla measurements once they I
> finished them.
> 
> I have no idea why the overall capacitance for board "new2" was
> significantly lower than for board "new1"; I also don't know if this may
> affect operation.
> 
> Ideas? Comments?
> 



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

Hi Andrew, let me address a few points:

> Since there were no circuit modifications other than C23 being lowered to
> 10pF then we will have to suspect the layout, density and shape of the
> copper on the new board (or even the properties of the new ceramic
> resonator, if you didn't do a transplant!).

I actually did transplants for the two new boards. It would also be
possible that even the type of chip socket for IC22 plays a role here.
After all, we're talking about very low capacitance values here.
Interestingly both the Polysix and the Poly-61 all use the same values (10p
and 22p) in the clock circuit for their 8048 and 8049 chips.

> As interesting as circuit analysis is
> I think there is a risk of getting to bogged down in theory and looking for
> problems where there are none.

As I see it we have a problem (clock instability on some boards), we have a
solution (lowering C23) which points at the general source of the problem
(capacitance mismatch). I think it is a good idea to pinpoint this as far
as possible. This in turn should give us the chance to simply measure this
part of the circuit on newly constructed boards and see if we are within
certain specs (and then possibly change the values accordingly). It may
also lead to new values for C22 and C23 that fit all boards.

> This might, if viewed by a non-technical
> reader, also imply that the board isn't fit for purpose in some way and put
> them off restoring their classic! (Which was the whole point in the first
> place).

Perhaps, but they would be wrong about this.

I'll work on this a bit more when I have time. A deeper search led to an
Intel Application note (AP-155) that discusses the various oscillator types
from roughly that era (and how to troubleshoot them!). Interesting read, to
say the least.

Hi Malte,

Interesting that you should mention the IC socket. I generally fit those
which have contacts made of Beryllium, but sometimes tin, gold and other
mixtures of the elements. I wonder if the type of metal affects the
capacitance? I guess it must have a certain value if it conducts. Would
explain the reason why some worked and others failed.

Cheers,
Andy


On 12/11/2010 11:53, "Malte Rogacki" <gacki@gacki.sax.de> wrote:

>  
>  
>  
>    
> 
> Hi Andrew, let me address a few points:
> 
>> > Since there were no circuit modifications other than C23 being lowered to
>> > 10pF then we will have to suspect the layout, density and shape of the
>> > copper on the new board (or even the properties of the new ceramic
>> > resonator, if you didn't do a transplant!).
> 
> I actually did transplants for the two new boards. It would also be
> possible that even the type of chip socket for IC22 plays a role here.
> After all, we're talking about very low capacitance values here.
> Interestingly both the Polysix and the Poly-61 all use the same values (10p
> and 22p) in the clock circuit for their 8048 and 8049 chips.
> 
>> > As interesting as circuit analysis is
>> > I think there is a risk of getting to bogged down in theory and looking for
>> > problems where there are none.
> 
> As I see it we have a problem (clock instability on some boards), we have a
> solution (lowering C23) which points at the general source of the problem
> (capacitance mismatch). I think it is a good idea to pinpoint this as far
> as possible. This in turn should give us the chance to simply measure this
> part of the circuit on newly constructed boards and see if we are within
> certain specs (and then possibly change the values accordingly). It may
> also lead to new values for C22 and C23 that fit all boards.
> 
>> > This might, if viewed by a non-technical
>> > reader, also imply that the board isn't fit for purpose in some way and put
>> > them off restoring their classic! (Which was the whole point in the first
>> > place).
> 
> Perhaps, but they would be wrong about this.
> 
> I'll work on this a bit more when I have time. A deeper search led to an
> Intel Application note (AP-155) that discusses the various oscillator types
> from roughly that era (and how to troubleshoot them!). Interesting read, to
> say the least.
> 
>  
>    
> 
> 



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

So I neglected to order the SW1 on both of my Mouser orders because I thought I could transplant them from the original boards (I have three KLM-367s to replace). To my dismay the original part is a 6 pin DPDT and the new board requires a 4 pin SPDT. Can I still use the original part and just bend the middle two pins out of the way? I'd like to avoid having to place another mouser order and pay $8 shipping for $3 worth of parts ;) 
 
btw, what was the dilly with the headers? There was some discussion on here recently concerning those. Were adequate replacements found? That was by far the hardest part of this project, transplanting those damn headers from the old board!...that and transplanting the trim pots and fitting the originals into the new board. But I made it work. :)

A.....

============================================ 
Arturo Brisindi

[Musics]
mydadvsyours.com  |  soundcloud.com/arturo00
 
[Studios]
galleryrecording.weebly.com  |  arturo00.weebly.com

 		 	   		  

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

Hi Arturo,

I don't know the answer on the switches. Seems like you could do some
continuity testing to figure out if it would work in that configuration.

You can't really get those old-style switches anymore so we designed for new
stock...

On the headers, there is no solution that is as good as the original. You
just can't order any locking connectors like those from anyone. At least
neither Andy nor I could find any last year.

I used breakaway headers like these (they are on the parts list):
http://www.mouser.com/ProductDetail/Molex/22-28-4362/?qs=P7cO%252b%252bFDLzQWa7MZSY2QYA%3d%3d

<http://www.mouser.com/ProductDetail/Molex/22-28-4362/?qs=P7cO%252b%252bFDLzQWa7MZSY2QYA%3d%3d>Best
of luck in your build,

Jed

On Mon, Nov 15, 2010 at 10:15 AM, Arturo B <arturo00@hotmail.com> wrote:

>
>
>
> So I neglected to order the SW1 on both of my Mouser orders because I
> thought I could transplant them from the original boards (I have three
> KLM-367s to replace). To my dismay the original part is a 6 pin DPDT and the
> new board requires a 4 pin SPDT. Can I still use the original part and just
> bend the middle two pins out of the way? I'd like to avoid having to place
> another mouser order and pay $8 shipping for $3 worth of parts ;)
>
> btw, what was the dilly with the headers? There was some discussion on here
> recently concerning those. Were adequate replacements found? That was by far
> the hardest part of this project, transplanting those damn headers from the
> old board!...that and transplanting the trim pots and fitting the originals
> into the new board. But I made it work. :)
>
> A.....
>
> ============================================
> Arturo Brisindi
>
> [Musics]
> mydadvsyours.com | soundcloud.com/arturo00
>
> [Studios]
> galleryrecording.weebly.com | arturo00.weebly.com
>
>
>
> [Non-text portions of this message have been removed]
>
>  
>


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

Hi Arturo,

Personally if it was me I would not skimp and do the job right. After all
these boards are going to last someone another lifetime of their Polysix!
However, if you really can't reorder then two suggestions.

1. This switch is only used to set up the d/a convertor. Normally it is open
circuit. Why not just solder in four prongs of header in the corners of
where the switch should go and when you come to the d/a setup solder in two
wire links across the top lengthways to close the circuit.

2. You live in Ottawa, Canada, right? (I had a look at one of your
websites!). There must be someone on this board who lives near you who is
ordering some components some time soon. If you are out there make yourself
known to Arturo and help him out!

Cheers,
Andy

On 15/11/2010 18:49, "Jed Jorgensen" <jed.jorgensen@gmail.com> wrote:

> Hi Arturo,
> 
> I don't know the answer on the switches. Seems like you could do some
> continuity testing to figure out if it would work in that configuration.
> 
> You can't really get those old-style switches anymore so we designed for new
> stock...
> 
> On the headers, there is no solution that is as good as the original. You
> just can't order any locking connectors like those from anyone. At least
> neither Andy nor I could find any last year.
> 
> I used breakaway headers like these (they are on the parts list):
> http://www.mouser.com/ProductDetail/Molex/22-28-4362/?qs=P7cO%252b%252bFDLzQWa
> 7MZSY2QYA%3d%3d
> 
> <http://www.mouser.com/ProductDetail/Molex/22-28-4362/?qs=P7cO%252b%252bFDLzQW
> a7MZSY2QYA%3d%3d>Best
> of luck in your build,
> 
> Jed
> 
> On Mon, Nov 15, 2010 at 10:15 AM, Arturo B <arturo00@hotmail.com> wrote:
> 
>> 
>> 
>> 
>> So I neglected to order the SW1 on both of my Mouser orders because I
>> thought I could transplant them from the original boards (I have three
>> KLM-367s to replace). To my dismay the original part is a 6 pin DPDT and the
>> new board requires a 4 pin SPDT. Can I still use the original part and just
>> bend the middle two pins out of the way? I'd like to avoid having to place
>> another mouser order and pay $8 shipping for $3 worth of parts ;)
>> 
>> btw, what was the dilly with the headers? There was some discussion on here
>> recently concerning those. Were adequate replacements found? That was by far
>> the hardest part of this project, transplanting those damn headers from the
>> old board!...that and transplanting the trim pots and fitting the originals
>> into the new board. But I made it work. :)
>> 
>> A.....
>> 
>> ============================================
>> Arturo Brisindi
>> 
>> [Musics]
>> mydadvsyours.com | soundcloud.com/arturo00
>> 
>> [Studios]
>> galleryrecording.weebly.com | arturo00.weebly.com
>> 
>> 
>> 
>> [Non-text portions of this message have been removed]
>> 
>>  
>> 
> 
> 
> [Non-text portions of this message have been removed]
> 
> 
> 
> ------------------------------------
> 
> PolySix "Digiest" Page: http://www.acc.umu.se/~amber/Poly6Yahoo! Groups Links
> 
> 
>