K5synth

Hack update:
Since my last note I replaced the other two op-amps with socketed Burr
Brown OPA4228.  Replacing these two other op-amps did reduce noise
levels noticeably.  There is still some noise but with 1)the these
four super clean op-amps, 2)using Multi, 3)routing everything to a
sinlge output on the multi rather than mix, and 4)using my noise gate,
noise is really not an issue any more.  I would love to try and
replace the VCAs also, but I have not been able to track down a spec
sheet (or any other info on the) on them so I do not have a clue as
what might works as an upgraded part.
 
If anyone can help, the VCAs are part M5222L and they are from
the same off-brand Japanese JRC company that is used elsewhere in the
K5.  If anyone can help me with details on the M5222Ls I will see if I
can find a replacement parts.

My bottom line: If you are willing to lay-out $30 for the four BB
OPA4228 and sockets, and you if you are willing to remove some
tough-to-remove parts, I highly recommend this op-amp replacement
hack.  My K5 has much less noise and just sounds much warmer/classier
with the new parts.  I would love remove more noise, but right now it
sounds very good and I am not very motivate to continue hacking.  (I
do still plan on replacing the headphone circuit though since I
already made the new circuit and all I have to do is wire it up.)

An interesting aside:  After I did the latest op-amp replacement,
everything sounded great in multi, but when I went to single I had
serious problems.  Various ranges of the keyboard worked fine, while
other ranges sounds like a fried amp circuit.  It turns out that while
I was removing IC8 I accidentally pulled part of the circuit board
trace off that connected pins 1 and 2 on IC8.  This trace provides the
feedback loop between the (-) and output of line G2.  Once I tracked
down the problem I was able to reconnect pins 1 and 2 and then
everything in single mode worked great.  What I conclude from this is
that the K5 in single mode is splitting different ranges of the
keyboard to different op-amps.  I am not sure what K% is doing in 
multi but multi (ouput 1) DOES NOT use the opamp in IC8 pins 1-2-3.  

Hack on.      
     

--- In k5synth@yahoogroups.com, "antdes45dragonmaster" <antdes45@n...>
wrote:
> 
> Not exampe, example
> 
> --- In k5synth@yahoogroups.com, Antoine Deschênes
<antdes45@n...> wrote:
> > Removing the opamps one by one could help:
> > exampe. You remove the 2nd last opamp and there is no more noise,
then 
> > noise source is not at final stage.
> > 
> > nelsonj_sce@y... a écrit:
> > 
> > >
> > > Per one of my earlier notes,  I took out my BB opamp part U4 and
> > > replaced it with a rewired Tl074 where I lifted the ground pins
3, 5,
> > > 10, 12 and rewired them to a different ground.  Bottom line:
Using a
> > > different ground for U4 made very little improvement in noise. 
It did
> > > reduce it a bit, but the noise reduction is not worth the
effort.  I
> > > even tried 4 different new ground locations,including the main
ground
> > > by the xmfr, but none of the grounds resulted in any meaningful
noise
> > > reduction. 
> > >
> > > Anyway, this hack is not worth doing.  Back to the drawing
board...
> > >
> > > --- In k5synth@yahoogroups.com, Antoine Deschênes
<antdes45@n...>
> > > wrote:
> > > > Good opamps might not change the noise amout that much. But I
know
> > > wiaht
> > > > 2 opamps in parallel are doing with noise is like what 2
resistors
> > > in
> > > > parallel are doing: reduce it(noise in the case of opamps if
it's
> > > not
> > > > series, I've read this somewhere)
> > > >
> > > > antdes45@n... a écrit:
> > > >
> > > > > Well, in my case, the mixer is pretty niosy too(A Kawai MX8R
> > > mixer
> > > > > from the same year), and I've never found Multi louder than
Single
> > > nor
> > > > > Singles louder than Multi, nor that Mix is more noisy than
> > > > > Singles(Tried with VU meter too, maybe it's the same for you
since
> > > you
> > > > > changed your opamps, but maybe you haven't changed the 4
opamps
> > > as I
> > > > > did). I've already plugged the K5 directly in the SBLive
line
> > > in(Which
> > > > > is -90dB), but obtained a -46dB at the volume I get a -90dB
> > > without
> > > > > source on the SoundForge VU Meter.
> > > > >
> > > > > It's pretty noisy I know it, idtheory.com has a 6MB MP3 made
with
> > > 2
> > > > > K5s in 1991.
> > > > >
> > > > > nelsonj_sce@y... a écrit:
> > > > >
> > > > >>
> > > > >> You wrote: "I only use MIX output and headphones"
> > > > >> I don't use the MIX now, rather, I stack everything in a
Multi
> > > to a
> > > > >> single output , Out 1 usually.  It makes the sound cleaner
> > > because you
> > > > >> skip one of the op-amps.  You might want to try this trick
to
> > > help
> > > > >> clean up the sound.
> > > > >>
> > > > >> --- In k5synth@...m, Antoine Deschênes
> > > <antdes45@n...>
> > > wrote:
> > > > >> > You told a couple of replies before "I suppose you now
have
> > > socketed
> > > > >> > opamps, like me", well I don't have some, I forgot to ask
them
> > > at
> > > > >> the shop.
> > > > >> >
> > > > >> > "U1 if you use MIX"
> > > > >> > I only use MIX output and headphones. I don't have
time/want to
> > > build
> > > > >> > some 4 ½ m wires. And my mixer is 8 channels : 2 for
the
> > > first
> > > Roland
> > > > >> > D110, 2 for the second one, and 1 for the K5, if I would
do
> > > that, I
> > > > >> > would lose all the 3 other inputs, which I use sometimes.
> > > Also, I
> > > > >> don't
> > > > >> > use the K5 for recording or anything else, I modifiy it
even
> > > if I'm
> > > > >> just
> > > > >> > playing it when I've got nothing to do. The K5 is just a
kind
> > > of toy
> > > > >> for
> > > > >> > me(And my father owns it, and uses it rarely to use it
as a
> > > controller
> > > > >> > in Finale).
> > > > >> >
> > > > >> > nelsonj_sce@y... a écrit:
> > > > >> >
> > > > >> > >
> > > > >> > > 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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