FAQ to old CX3
*************
NEWS !!!
**********************************************
New old CX 3 diagnosis and repair web-site online
:
http://robert.weathergreen.com/bx3/
Parastream offers new support for SM304 chip
!
http://www.parastream.com/hardware/RP-SM304A.htm
Parastream offers now support for SM305 chips
too !!!
Parastreams
old CX3 FAQ
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Do you have SM 304/5 chips or CX3 parts for private sale ?
Write me an e-mail: richardon@nexgo.de to join this list.
Please contact salers directly
| 1 | SM 305 A | GERMANY | 12.2004 | Jürgen Frantzke | chatmecki@t-online.de |
| 3 | SM 304 | CANADA | 06.2004 | Mitton & Marg Tatam | tatamitton@yknet.yk.ca |
| CX3 boards | FINLAND | 01.2002 | Mika Tyrvaeinen | richardon@nexgo.de | |
In summer 2001 Mika Tyrvaeinen (Finland) and me Thomas Richardon
(Germany)
studied the funcions of old CX3 via e-mail contact. Here are some results,
that may be useful for other CX3 user. To understand more you should have
a look at the circuit
diagramms (SCHEMATICS) on this homepage !
Actually main interest of this FAQs are the functions of the board KLM-244
old CX3
You can studie our FAQ at once. If you prefer an overview of our questions click here !
What is chip SM304 doing ?
SM304 is a paralell to seriell data converter, scanning the keyboard
Why are there two SM304?
SM304 I, is scanning the keys C1-C3
SM304 II is scanning the keys F3-C5
How is data merged ?
SM304 I is connected to ES input of SM304 II
What data format is used ?
Explained on page 9, but we dont know exactly
What company build the SM chips ?
Seems to be SIEMENS
Are SM304 305 chips still available ?
Answer seems to be NO !
In summer 2001:
5 chips SM305A and B by KORG germany (35 $)
1 chip. SM305A by Bob overton TEXAS HOUSTON (70$)
0 chips by KORG america
Can SM304 be replaced by other components
?
Yes, Bob Overton offered a daughterboard for 299$
Parastream offers new support for SM304 chip
!
http://www.parastream.com/hardware/RP-SM304A.htm
Can SM305 be replaced by other components
?
Perhaps with a SX microcontroller.
Is there any information concerning SM
chips available in internet ?
Yes, but only on this homepage :-).
How is sound produced ?
Heart of Sound Generation is a Top octave generator.
TOC IC 7 dividing Master Oscillator Signal in frequencies for one octave.
To achieve all frequencies TOC signals are divided in SM305 chips.
What are they doing ?
A lot of ! Including
Seriell to Paralell data converstation of 304 input.
Octave dividing of TOC signals.
harping funcions
adding signals of one octave (still unsolved function)
What are diagramms D1-D3 describing ?
The Diagramms are explaining which Output of 305 is used,
depending on the pressed key
What means one line in the Diagramm ?
It stands for one Drawbar..
What are this strange footages 10-2/3
1/2 so on good for ?
They are good for nothing ! Not used !
Why are some pins of 305 connected via
resistor to 4 Volt ?
Thats the dust bin for the strange footages ! :-)
What means S1 , S2 and so on ?
It is the Name of the output pins of the 305 chips.
For each of the 3 chips there is an harping diagramm.
Therefore a better Name for S1 in D1 (305A-II) is II-S1
So one Drawbar is splitted in 5 S-Signals ?
Yes, for every octave the signal uses another S-output pin on 305.
What is further processing of the S-Output-Signals
?
They are Input for the 45 fixed Filters.
So every drawbar using 5 Filters ? Why
?
Yes, is explained in mathematics !
Where are the 5 filtered signals for each
drawbar added ?
Have a look at circuit diagramm KLM-244 !
At right side there are 9 mixer implemented with an operation amplifier of
Type
1/2 5458. Each having 5 Inputs.
Also you can see what S-Signal and filtertype F1-F10 was used.
I dont understand !
There are 10 Filtertypes but you mentioned 45 Filters. 5 for each drawbar
!
There are 45 fixed filters on CX3 ! For each drawbar 5 filters ! 9*5=45.
But some of the filters are identical, so there are only 10 different filter
types !
Isnt it silly to use 45 filters, (some
identical), 10 filters could do the same job ?
Its 1979 ! 10 filters could only do the job if each drawbar would be able
to
controle amplitude of all five s-outputs simultaniously. Thats no problem
for
digital simulation. Using 45 filters for digital simulation of CX3 would be
very silly.
In 1979 seemed to be more convinient to implement 35 silly filters, than one
drawbar controling 5 amplitudes ! I am not shure, perhaps the KORG
engineers really had a bad day :-)
Its assumed that SM305 producing square
wave. Mika still has some doubts !
What is fourier sinus transformated of
bipolar square wave, normalized to 0..2*Pi ?
Its 4/Pi * (sin(t) + sin(3*t)/3 + sin(5*t)/5 + ...
shorter:
4/Pi * SUM(k=0..infinit, sin((2*k+1)*t)/(2*k+1).
Why is every Drawbar for each octave
processed with another filter ?
Solution is fourier sinus transformated of square wave, only containing odd
harmonics !
Therefore the filter can be adjusted to the first square overtone sin(3*t)
Signal being square wave a full octave can be filtered !!!
Why is one filertype passiv ? That means 6dB/octave
Hi Hi old CX3 is using an additional filter, thats your ear ! :-)
The simple passiv Lowpass is used in CX3 for high frequencies !
Human ears are including Low Pass Filter of 12-16 kHz.
Assume to be older than 30 years, 12 kHz may be right !
Remember square waves first overtone is 3 times higher than
ground frequencie. Therefore if you are older than 30, you will almost hear
no difference between 4 kHz sinus or 4 kHz square function !!!
BTW: what is physical aspect fishes have
other ears than animals not living
in water ?
Expecting your answer
Mika and me also disussed square wave
synthesis. I suggested Eulers method of
"little square" for synthesis. In this case integral over product
of square waves with
different frequencies has to be computed. I suggested to write square function
as
sum of sinus functions, using orthogonal character of sinus function, a formular
can
be achieved.Soulution is constant / littlest common divider of frequencies.
I solved the integral introducing a new method of square wave synthesis.
Later getting aware that the solutioen is already used by walsh/wavelet/ transformation.
The reason I didnt completed my Euler mathematics site.
In spite of that: My Euler site is funny .Please take 5 Minutes of u time
for Euler !
How can SM304 be replaced ?
I still prever simply connecting a midi cable to RS 232 Port of SX
controller, using midi data format.
Easy way to drive old Cx3 as an simply sound expander !
What is the actuall state of your replacing projekt
?
Its still crazy ! Consider, that every S-ouput is a mixture of 12 frequencies
of one octave !
Second problem is to reduce 45 S-outputs to 40 outputs. SX microcontroller
with 40 IO Ports exists !
Interest to join our discussion, and
expand this FAQ ?
Comtact Thomas Richardon
regards
Mika Tyrvaeinen
Richy Richardon
Some theoretical thoughts ( an E-mail
to Aaron: )
Percussion is using the 4' and 2 2/3' Signals of the
tone generator.
The On/Off switches are named as gates.
That could be the FET Transistors T8 and T9 on KLM.
Here you'll find a VR called Decay time, so should be the right place.
I dont understand all functions of this circuit. There should be a gate and
an envelope generator.
But i cant locate this functions. The envelope generator could be build up
with a monoflop,
triggered by SM chip.
This could be the NE555 on KLM. The (in 80's famous) NE555 could do this job
easy.
To split the percussion
you have to find, where its mixed to the other signals.
Aha, the overdrive circuit seems to have an additional function.
Mixing main signal, keyclick, percussion.
If VR2 set to zero mixing level is around R8/RX. (R8=500k)
Key click : RX=R12 =100k ( Signal forced to ground with VR5)
Drawbars : RX=R43-R46 =100k
Percussion: RX=R11 =100k corrected to 180k (was it too loud :-)
This R51 connected to +6V is strange. As said
the Opas are driven unipolar.
Perhaps the 6V lifting the Input to half of Vmax=12V.
Cutting off the line leadin from C15 to R46 would cut off the 6V too. So u
cant do that.
Take (cut) the signal behind C15 instead.
Now we need a new mixer (OPA) behind the
Leslie circuit.
Block diagramm showing, there must be a mixer adding leslie and dry signal.
Ok looking for MN 3004 (BBD=Phase Shifter, Eimerkettenspeicher ?)
Not easy to find
the mixer.
I think its IC3. The dry signal directly leading to this OPA via R95=150k.
6 Volt offset provided by R1.
Therefore it should work to connect the percussion / click signal to the connection
point of R94, R95.
Of course only in theory. I am not shure, no guaratee.
( Dont damage the SM chips ! Only 4558
is still available ) How about not to cut the percussion line ?
Just leading via VR additional dry percussion signal to the IC3 ?
ARONS EASY SOLUTION :
i discovered today that if i pass both
the "send" signal and the hi output" through a simple
passive mixer (just jacks connected together), i can use the cx-3 volume knob
to mix
"clean" and "r.e." until the r.e. is quieter. great!
Send is clean and not influenced by the volume knob.. interesting effect:
when you turn the volume
knob down, "send"
stays almost the same and "output" gets quieter, but when you get down to
the
lowest range, both signals disappear together.
... so it is almost as if the percussion has bypassed the "chorus"!
Another E- mail to Aron, describing some
unexpected mathematical facts
concerning dissortion of sinus organs.
Hi Aaron
My cx3 is actually in the practice room, so I can make no tests. Some suggestions:
If the dissortion is caused by "too high levels", it would depend on the absolute
level of the drawbars.
EG 888 would produce more dissortion as 444. Perhaps you are listening to
an acoustic phenomena,
well known to tune an instrument, but in other cases often forgotten.
Two frequenzies sin(w1) and sin(w1+dw) producing an amplitude modulation with
cos(dw) because
(a) sin(x)+sin(y)=2*sin( (x+y)/2)*cos( (x-y)/2 ).
Perhaps you could listen, that this formular exist for all x and y, this Christmas.
Two flutes playing Christmas songs, produce frequencies products
(x+y)/2 with (x-y)/2, making pain :-)
(Nearly my whole family playing flute at christmas :-) It can be heard, because
Flutes are producing
triangel waves very close to sinus ! (only few overtones)
Both sides of equation (a) describing the same.
Tunnig an instrument we hear the "Right side" But it seems to depend on several
Parameters,
we hear the "Left side" two frequencies, or the "Right side" one frequencie
in an Enveloppe,
or a mixture I just tested it with 2 sinus generators.
So isnt it this, you are describing as dissortion ? That would need to modify
your ears or brain :-)
Some computation:
****************************
A4=4*440
Hz=1760 Hz
D5=1760 Hz*2**(5/12)=2350 Hz
F5=1760 Hz*2**(8/12)=2790 Hz
****************************
Differenze is 440 Hz
Differenze/2 is 220 HZ Thats A1 isnt it :-)
Exactly the additional frequenzy you are describeind as dissortion.
ciao richy
PROBLEM OF JOHNS CX3
> I have a problem with my old Korg Cx-3 that nobody has been
able to help me
> with. Perhaps you can help me. My CX-3 has started to generate sounds when
> the keys are not pressed down. It's not pink or white noise. It's actual
> organ tones. It's not just one key. It sounds as if all the keys are being
> played together. It sounds almost like a huge but faint diminished chord
in
> the background. The condition appears to be getting worse. When the drawbars
> are pushed in, the sound disappears.