Re: How to fix a noisy ground?

Buzzing in rear out is signal ground noise, all pcbs have sepparate 
analog grounds to PSU but linked together on the psu.

--- In [email protected], "nelsonj_sce" <nelsonj_sce@y...> 
wrote:
> 
> Antdes,
> Good information in the note below.  It sounds like the good news is
> that the digital (D) and analog (A) have seperate grounds.  From
> everything I have been reading that is good news.  If they had the
> same ground on the same PCB we might be completely out of luck.  
Today
> I ordered the latest OS ROM and schematics from Kawai so hopefully,
> once I have the schems, I make more informed suggestions on how to
> reduce the ground noise.
> 
> I did read something today that said that, although you should have
> separate A and D grounding, ultimately both the A and D should be
> grounded at the same point.  Otherwise, the D might inject noise in 
to
> the A ground.  Based on your note, this might be just what is going 
on
> in the K5.  
> 
> Based on this observation, one thing to try would be to take the D
> ground off of the power supply board and connect that ground 
directly
> to the A ground on the transformer.  We need to make sure the power
> supply board is still fully grounded even if we remove the D ground,
> but you should be able to check the schem and see if it looks like
> this is an easy move.
> 
> Anyway I don't want to do anything too fancy until I look at the
> schems, but if it looks safe, this is the first thing I want to 
try. 
> (Or if you feel adventurous you could try it and tell me if it 
works!)
> 
> Thanks for the note and let me know if you find anything else out. 
> 
>        
> 
> 
> 
> --- In [email protected], "antdes45dragonmaster" 
<antdes45@n...>
> wrote:
> > Digital Ground is plugged to one bridge's negative pole and 
analog to
> > 0v line of the transformer(Black wire). I know it's a noisy ground
> > because when I transfer MIDI between K5 and computer, I hear some 
low
> > volume beeps in the noise, and my intermittent inverter whines(Is 
on
> > DGround) in the headphones when it wants. I looked at the 
schemes, and
> > every different PCB's DGrounds are plugged together on the PSU
> > mainboard, but are going to it thru different wires.(Same for
> > AGround). Problem is I don't remember how to filter ground. 
Something
> > to try. Also, when I unplug the brown socketed black bus wire 
going to
> > outputs board, there is no signal from the headphones, but still
> > noise. So it's not coming from the opamps(Headphones noise). 
Might be
> > that the LM386's ground has no filter. While for the rear outputs
> > noise, the opamps might be too noisy(-45dB with some TL072 
instead of
> > some TL062, which might have not changed anything noise talking, 
using
> > some OPA????, don't remember which, will have to re-find the name 
on
> > DIYAudio, might be a lot less noisy, because a signal passing 4 
times
> > in pretty noisy OpAmps in series might not be really good). 
> > 
> > --- In [email protected], "nelsonj_sce" <nelsonj_sce@y...> 
wrote:
> > > It looks like you have already changed out the op-amps and 
found that
> > > the noise is still there.  Have you tried anythink to fix the 
noisy
> > > ground?  Is it that the digital and analog all share the same 
ground?
> > > Is there a way to "split" the ground or add a new ground plane 
and
> > > reroute say the digital chips to the new ground plane?  Are all 
the
> > > analog parts on a single board so that we could just cut the 
ground to
> > > that board and then wire up a new, "independent" ground?  Are 
there
> > > just a few key digital parts that are creating the noise that 
can be
> > > rerouted to a seperate ground plane? 
> > > 
> > > Has anyone at Kawai told you how to solve this problem?  Even 
if I can
> > > get a hold of the schematics, if Kawai or others can identify a 
few
> > > key components it should not be that hard to create a seperate 
ground
> > > for those parts.
> > > 
> > > Any thoughts?
> > > 
> > > --- In [email protected], Antoine Deschênes 
<antdes45@n...>
> wrote:
> > > > The LM386 doesn't produce any noise. Even if you unplug the 
signal
> > > there 
> > > > will still be some. Sctually the problem is a noisy ground. 
It's
> > > sharing 
> > > > the same ground for all the board(s).
> > > > 
> > > > nelsonj_sce@y... a écrit:
> > > > 
> > > > > Here is the latest, it is good news.
> > > > >
> > > > > Today I got my parts for DigiKey.  As below I replaced my
> backlight
> > > > > with a blue backlight from nightlaunch.  It worked with my
> stock K5
> > > > > inverter.  However, my stock inverter was very flakey, even
> after I
> > > > > did the resolder job so I decided to replace the stock
> inverter with
> > > > > the DigiKey part.  (Digikey part #289-1032-ND).  The good 
news
> > is that
> > > > > inverter works (even though it is only about 95V @ about
> 550Hz).  It
> > > > > is a slightly different color than before, but it still 
looks
> great.
> > > > > Also- THERE IS VIRTUALLY NO HUM! 
> > > > >
> > > > > The only warning is the Digikey part is not the exact same 
size
> > as the
> > > > > original inverter - it is a bit smaller in footprint and a 
lot
> > > > > shorter.  The stock inverter has only three connections 
(in -
> out -
> > > > > ground) and the new inverter has a fourth pin for mounting. 
> Because
> > > > > the part is smaller, I used the original hole for 
the "out", but
> > I had
> > > > > to wire up jumpers to the "ground" and the "in" - not a big
> deal but
> > > > > it is some extra work  - and you don't want to see pictures 
of
> > my ugly
> > > > > job.  :).  But so far so good.
> > > > >
> > > > > Also, I did the 147K resistor hack and it seems to have gone
> > well.  My
> > > > > K5 is a louder, but the headphones have even more noise 
now. 
> I have
> > > > > been looking things over and I think the headphone noise is
> because
> > > > > they use a cheap LM386 op-amp and a bad overall design for 
the
> > > > > headphone amp.  I am trying to see if I can replace this 
with a
> > better
> > > > > op-amp, otherwise I think the only good solution is to just 
bypass
> > > > > their circuit completely and make a better headphone amp and
> wire it
> > > > > up to the K5.
> > > > >
> > > > > Anyway, again the good news is that for less than $30
> delivered you
> > > > > can get nightlaunch backlight and a Digikey inverter and 
have
> a new
> > > > > backlight that does not hum!  :)  
> > > > >
> > > > > Now for the headphone amp...
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > --- In [email protected], "nelsonj_sce" 
<nelsonj_sce@y...>
> > > wrote:
> > > > > > Update:
> > > > > > Well today I ordered a new inverter from 
www.DigiKey.com.  I
> > > found an
> > > > > > inverter that looks like it will do the job - for those
> interested
> > > > > it is:
> > > > > >
> > > > > > Digikey part #      289-1032-ND  and it only cost $11.90 -
 not
> > bad.
> > > > > >
> > > > > > I am not sure if it will fit exactly in the same slots as 
the
> > > original
> > > > > > inverter so it might require some additional wiring.
> > > > > >
> > > > > > Anyway, I had my K5 open to look at the power supply to 
plan
> > the new
> > > > > > inverter install when my K5 started "humming", and guess 
what,
> > I now
> > > > > > have a beautiful blue backlight.  It looks great, a very 
cool
> > blue.
> > > > > > So it appears my inverter was not bad, but it just has bad
> solder
> > > > > > joints.  It is working for now but tomorrow I will likely 
take
> > > out the
> > > > > > board and redo all the solder joints. 
> > > > > >
> > > > > > Just some additional info I learned in researching
> backlights and
> > > > > > inverters.  The "brightness" of the backlight is a 
function
> of the
> > > > > > voltage and frequency applied to the backlight.  It 
appears one
> > > has a
> > > > > > lot of flexibility in selecting the inverter output 
voltage and
> > > freq.
> > > > > > For example, nightlauch says you can "test" the backlight 
by
> > > plugging
> > > > > > it directly in to a wall socket (120V AC @ 60 Hz here in 
the
> > > US)!  The
> > > > > > higher the voltage and freq the brighter the backlight.  
> > > However, the
> > > > > > backlight will "burn out" quicker the higher the freq.  
So there
> > > is a
> > > > > > trade off, high freq = bright but shorter life. 
> > > > > >
> > > > > > Right now my stock inverter is putting out about 102V @ 
380
> Hz.  I
> > > > > > think the inverter I ordered will put out about 95V @ 540 
Hz and
> > > > > > should work with a 3 - 6 V DC input.
> > > > > >
> > > > > > Next step, 147k resistors (also ordered from Digikey 
today). 
> > > > > >
> > > > > >
> > > > > >
> > > > > > --- In [email protected], "nelsonj_sce" 
<nelsonj_sce@y...>
> > > wrote:
> > > > > > > Well I replaced my backlight with one I ordered from
> > > > > > www.nightlaunch.com.
> > > > > > >
> > > > > > > It took less than two weeks from when I ordered and the
> > parts look
> > > > > > good. 
> > > > > > >
> > > > > > > Good news/bad news though on my backlight. 
> > > > > > >
> > > > > > > The good news:  I had no problems removing the LCD, 
taking out
> > > the old
> > > > > > > backlight and sliding in the new backlight.  The new 
light has
> > > some
> > > > > > > wires and a plastic "tab" that kind of gets in the way, 
so I
> > > soldered
> > > > > > > the backlight wires to where the wires connect to the 
LCD
> board.
> > > > > > > Hint:You have to cut the new backlight to size, so make 
the
> > > backlight
> > > > > > > a little longer (say 1/4 inch) than the original to make
> things
> > > > > easier.
> > > > > > >
> > > > > > > Bad news: My backlight does not work but I think my 
inverter
> > > is the
> > > > > > > problem.  I am only getting about 1/2 Volt at the 
output of my
> > > > > > > inverter, and I am supposed to get 120V @400Hz if I
> > understand the
> > > > > > > part correctly.  I tested my inverter before I did the
> backlight
> > > > > > > install and saw it had low voltage, but I was hoping 
that my
> > > existing
> > > > > > > "dead" backlight was causing the problem (i.e. it was
> > shorted.) I
> > > > > > > guess not because even with the new backlight I get 
very low
> > > voltage.
> > > > > > >
> > > > > > > Anyway, it looks like I need to get an inverter.  I can 
get an
> > > > > > > inverter from nightlaunch for $17.99+s/h but it needs 9V
> DC.  I
> > > > > > > understand the inverter in the K5 uses 5V DC.
> > > > > > > 
> > > > > > > Q1: Does the K5 inverter use 5V DC?
> > > > > > > Q2: If I measure the voltage on the two wires to the 
left
> of the
> > > > > > > inverter, should I get 120V if everything is working? 
(My
> > > Fluke says
> > > > > > > it is good <=1kHz)
> > > > > > > Q2: Does anyone know where to get a compatible K5 
inverter
> > and how
> > > > > > > much it will cost?
> > > > > > >
> > > > > > > Thanks again for all the help.  This group is great.
> > > > >
> > > > >
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> > > > >
> > > > >
> > >
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> > > > -- 
> > > > antdes45@n...





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