K5synth

You wrote: "They connected the non-inverting(+) input(if I'm right) to
the DG?!?"
Not directly.  The schem show that the (+) is connected to the AG, but
it appears from the wiring board layouts that the AG and DG have
ground planes that connect in several places.  So basically, there is
no physical seperation of the AG and DG ground planes on board MI-004.
 As a result the (+) is connected to this single ground plane that has
both A and D parts on it. 


You wrote: "What's the VCA's ground?"
The same dirty AG/DG ground as that of U4.  The VCAs are parts IC6 and
IC7.  The ground is pin 3, there is also a ground through a cap on on
pin 5 but this look like protection rather than ground.  I am not sure
if pin 3 is the third pin from the top or from the bottom, but pin 4
is -A6.  It can't hurt to move the VCA's grounds to a clean ground
also.  Note that it looks to me that the VCA's do not play the role of
traditional synth VCAs, but rather the are connected directly to the
main volume slider via pin 5.  They don't seem to have any other
control voltages so my guess is that all the VCAs do is control the
overall volume of the keyboard.  If that is the case, I am note sure
that a dirty ground will inject noise.  But again, it can't hurt to
make sure they have a clean ground. 

So here is my plan: Step 1 is change the ground on U4 (and U1 if you
want to use the Mix output).  Step 2 is change the ground on the VCAs.
 Parts U8 and U9 are set up as non-inverting amps and do not have any
direct connections to ground so no grounding to change here, but they
have that shielding that we may be able to improve as Step 3.

I may be able to do step 1 tonight - it all depends on how sleepy my
baby is! 


--- In k5synth@yahoogroups.com, antdes45@n... wrote:
> Pulling the DG from the boards not PSU board(Impossible, without
removing a bridge rectifier), I've already used the PSU without the
big brown connector full of wires for power and ground of the boards.
> 
> They connected the non-inverting(+) input(if I'm right) to the DG?!?
> Well, sure it will make noise, if that ground is that much noisy,
that would be like to plug a phono playing in the input and wondering
why you hear it.(Well, that's what I think)
> 
> What's the VCA's ground?
> 
> Also, they put two mono DACs for 4 channels, so (My theory) the
analog sound is passing thru a kind of flip-flop that switches rapidly
the input from 1 to 2 to 1 ... and the other with 3 and 4. As I only
have a part of the output board, the opamp section and the PSU(Thanks, 
> 
> 
> "nelsonj_sce" <nelsonj_sce@y...> wrote:
> 
> >
> >Antdes,
> >Ok, I still have more work to do but I did look more at the schems
> >while on a plane today. Some thoughts...
> >1) DO NOT simply remove the DG ground on the power supply and reroute
> >it to the AG (black transformer wire).  If you do this the inverter
> >for the backlight (as well as several caps and part D6 WILL NOT BE
> >GROUNDED.  Basically the DG does not terminate on MI-010, rather
> >MI-010 needs the connection <CN1> in order to be grounded.  I am still
> >looking at things but it seems the main ground for the MI-003 &MI-004
> >comes from where they are screwed in to the K5 case.
> >
> >2) Although I am not 100% sure, it appears that for some reason, on
> >board MI-004 the DG and AG are actually connected.  Board MI-003 is
> >all digital so the ground is pure digital.  If I am correct, and the
> >AG and DG grounds are not separated on MI-004, this may be the source
> >of the noisy ground.  The bad news is that there is no quick way to
> >separate the grounds on MI-004.
> >
> >3) Part U4 (the op-amp right after the VCA that we have both replaced)
> >has my attention.  It has four inverting op-amps, where the "+" of
> >each amp is connected directly to the dirty ground.  It is possible
> >that the dirty ground is basically injection noise to these amp.
> >
> >I think we both have replaced this op-amp and it is now in a socket. I
> >plan on taking out the amp(this is a total hack but if it works I can
> >make it look nice later), and then bending connections 3, 5, 10, 12
> >(the grounds) out so that they do not connect to the socket/dirty
> >ground on board MI-004. Then, I will wire these connections directly
> >to the K5's case to try and get a clean ground.
> >
> >4) If that does not help lower the noise, I am looking at lines g0-g7
> >that feed the op-amps U8 and U9.  These are the only analog signal
> >lines that have Faraday shielding.  These are low level lines early in
> >the analog signal chain.  If nosie gets in to these lines, the nosie
> >will get amplified in each of the following amp stages.  Perhaps there
> >is a way to improve the shielding on these lines or to change the
> >grounds related to these singal paths...but I have to think about how
> >to do it.
> >
> >Anyway, I will let you know what happens after I reground U4.
> >
> >
> >
> >
> >--- In k5synth@yahoogroups.com, antdes45@n... wrote:
> >> That's it, AG is analog ground, DG digital ground, +A6V dc analog
> >6v. . .
> >> The kind of fork for the analog ground is an other sign for ground,
> >maybe they mean different connection places, as the fork like is used
> >for antenna too. But I think it's just a country/continent difference.
> >>
> >> "nelsonj_sce" <nelsonj_sce@y...> wrote:
> >>
>               . . . Cut the file, was 62k.
> 
> -- 
> Antoine Deschênes
> aka DragonMaster
> http://thehotcom.deep-ice.com/
> Files:http://angelfire.com/ca7/hotcomcenter/
> 
> 
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