
ISSUE 1 -MARCH 2001
ZXCD1000
9
Itiswellknownthatthiskindofdistortionisparticularly
unpleasant to the listener. The two scope traces clearly
show the lack of such artifacts with the Zetex solution
Other Solutions - Stereo, Closed Loop and
Higher Powers.
STEREO
It is possible to duplicate the above solution to give a 2
channel stereo solution. However if the oscillator
frequencies are not locked together, a beat can occur
which is acoustically audible. This is undesirable. A
stereo solution which avoids this problem can be
achieved by synchronising the operating frequencies
of both ZXCD1000
’
s class D controller IC
’
s, by slaving
onedevicefromtheother.ThisisillustratedinFigure8.
Here OscA on the master is used to drive both
TriangleAandTriangleBinputsonthemaster.OscBon
the master is used to drive both TriangleA and
TriangleB inputs on the slave. In order to achieve the
increased drive capabilty required by the OscA/B
outputs on the master, 1.5k
pull down resistors are
addedfromthesepinstoground.Theslaveoscillatoris
disabled by connecting pin 4 (dist) to ground. Great
care must be taken when linking the triangle from the
mastertotheslave.Anypickupcancauseslicingerrors
and result in increased distortion. The best connection
method is to run two tracks, side by side, from the
master to the slave. One of these tracks would be the
triangle itself, and the other would be the direct local
ground linking the master pin9 ground to the slave pin
9 ground.
Audio A
Triangle A
Osc A
Dist
Cosc
Osc B
Triangle B
Audio B
Gnd
Out B
Gnd2
9VB
VCC
9VA
Out A
5V5
ZXCD1000
CX1
1.5k
Audio A
Triangle A
Osc A
Dist
Cosc
Osc B
Triangle B
Audio B
Gnd
Out B
Gnd2
9VB
VCC
9VA
Out A
5V5
ZXCD1000
1.5k
CX2
O/C
O/C
MASTER
SLAVE
Figure 8.
Frequency sync for Stereo Apps.
ZETEX Class D Solution. (10W into 4
)
Note lack of Crossover Artifacts
Typical Class D Solution.
Note Large Crossover Artifacts