SH-5 questions

[jhaible]

Hi,

I'm just going thru the SH-5 filter schemos. Looks like there's more
to that than I used to think. The LP section is *not* a 18dB 4pole
diode ladder, but a 5pole diode ladder - did anybody notice this?

At the moment I'm wondering about the HP mode. There is this obvious
1-pole HP section in front of the LP section. In BP mode, both are active.
In LP mode, the HP section is bypassed, and the LP output is boosted
(why? details see below), and (here comes the interesting part!) in HP
mode the LP section is *not* bypassed, but part of the LP input is
substracted from the LP output, and the 1-pole HPF is inside the signal
path, too.
I'm currently making PSpice simulations for this filter, and I suspect that
there is an error in the schemos. Two resistors are involved in both, the
substraction (HP mode), and the boost (LP mode), and they are numbered
R548 (180k) and R549 (22k). If these values were right, this would mean
that
the filter would be approx. 20dB louder in LP mode than in BP mode. This
is hard to believe. Different values here would also highly affect the
subtraction
result in HPF mode.

So I have a few question to SH-5 owners:

(1) Can anybody check the values of R548 and R549 ? 180k and 22k, like
written in the schemos ? Or rather 18k and 22k, or 180k and 220k ? This
would be more reasonable. How to find out ? If someone has an opened
SH-5 on his desk for service (very likely, I know (;->)), you might look
in the neighbourhood of IC506 on the VCF board. Or if someone has a full
service manual (I only have the one VCF page), you might double check
in the parts list (if there is one included ...)

(2) Can anybody *describe* the sound of the filter modes with words?
(only speaking of the multimode VCF here, not the additional manual BP)
Is the HP resonant, or is it just like the 1-pole HP function on later
Roland synths ? 
Is the LP mode only slightly louder than the BP mode, or is there a 10dB
difference ??
Anything else that could be important ?

It would be nice if someone could answer one question or the other.
But it's not crucial - so don't go and dismantle your vintage synths ...

JH.