This is only a preview of the October 2007 issue of Silicon Chip. You can view 40 of the 112 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Items relevant to "Oscar: Electronic Noughts & Crosses Game":
Items relevant to "PICProbe: A Versatile Logic Probe":
Items relevant to "Rolling Code Security System; Pt.1":
Items relevant to "Simple Data-Logging Weather Station; Pt.2":
Purchase a printed copy of this issue for $10.00. |
DVD Players
By MAURO GRASSI
Just How Good Are They For HiFi Audio?
CD players are now relatively expensive so are there any
compromises in using a cheap DVD player instead? We
collected a bunch of players and put them through their paces
to find out.
T
HE CLASS-A STEREO Amplifier
described in the May to September
2007 issues is an ultra-low distortion
amplifier suitable for demanding applications. At $599.00, it’s not cheap
to build but that’s a price many people
are prepared to pay to achieve excellent performance.
10 Silicon Chip
By contrast, the prices of DVD players (most capable of playing almost any
format you can think of) have dropped
dramatically. As a result, you may be
tempted to use such a player to listen
to your CD collection through the
Class-A amplifier, particularly if your
CD player is old or “on the fritz”.
Part of the problem is that dedicated
CD players are no longer cheap to buy.
Nor are they as readily available as
they once were. To buy one, you now
have to go to a hifi shop and the prices
generally start around $400.00.
So how well do cheap DVD players perform as far as sound quality is
siliconchip.com.au
Equipment
Power Supply
Supply Type
Type
Signal Level
SNR (10Hz to
22kHz)
SNR (10Hz to
>500kHz)
THD+N (10Hz
to 22kHz)
Toshiba XM5302B
PC CD-ROM Drive
External
Switchmode
CD
1.079V
-118dB
-104dB
.03%
Sony CDP-XE300
CD Player
Internal
Linear
CD
2.083V
-97dB
-75dB
.003%
Tevion TEV1020
DVD Player
Internal
Switchmode
DVD
1.911V
-116dB
-105dB
.05%
Magnavox
MDVD50 DVD
Player With Tingle
Terminator
Internal
Switchmode
DVD
2.018V
-115dB
-95dB
.006%
Panasonic
DMR-ES10 DVD
Recorder
Internal
Switchmode
DVD
2.185V
-117dB
-94dB
.004%
Audio World AW8032 DVD Player
Internal
Switchmode
DVD
1.728V
-111dB
-93dB
.006%
Toshiba Satellite
A30 Notebook
DVD Drive (Via
Headphone Jack)
External
Switchmode
DVD
0.539V
-75dB
-55dB
0.3%
Table 1: typical audio characteristics of a range of equipment, as measured by our Audio Precision test set. All the players
are double insulated, differing only in the type of power supply (switchmode or linear). Players with THD+N of .05% or
higher can be expected to sound mediocre.
concerned? Can cheap DVD players be
used in place of much more expensive,
better quality CD and DVD players?
Is there a difference between CD and
DVD players in terms of audio performance, even for the better quality
units? We decided to find out.
Audio Precision gear
To obtain an idea of the audio quality of a range of equipment, we used
our Audio Precision Test Set to test a
selection of players owned by various
staff members of SILICON CHIP. The
players tested included DVD players,
CD players and CD ROM drives (including one in a notebook). The results
are summarised in Table 1.
All players were checked using the
1kHz 0dB sinewave track from the
Technics SH-CD001 CD test disc. In
each case, we measured THD+N (total
harmonic distortion) and SNR (signalto-noise) ratio.
In summary, Table 1 shows: (1) the
type of power supply used and whether it is inside or outside the case; (2) the
RMS signal output voltage; (3) the SNR
with and without audio band filtering;
and (4) the distortion with audio band
filtering (which is substantially better
than the distortion measured without
audio band filtering, especially for the
switchmode equipment).
Note that although the cheap DVD
players like the Tevion TEV1020 had
quite good SNR figures, they exhibited
siliconchip.com.au
Fig.1: block diagram of the Zoran Vaddis chip, version 888. It is a single
chip solution for DVD players and DV recorders. The device includes the
motor drivers, an RF amplifier and a processor, as well as various digital
interfaces for external memory and external memory cards. In addition,
there are input ports for video and audio, and output ports for 5.1-channel
surround sound and video. There are also optional connections to hard
drives (for DVR applications) and USB ports. Finally, there is a display
driver, button decoding and remote control inputs. Chips of this series are
found in many different DVD players.
relatively high distortion and audible
hum. The midrange DVD players like
the Magnavox MDVD50 and the Audio
World AW-8032 both had better distortion figures. The more expensive DVD
players like the Panasonic DMR-ES10
(a DVD recorder) also performed well,
with good distortion and SNRs.
Note that all these DVD players are
double-insulated with switchmode
supplies and for reasons to be explained shortly, produce audible hum
when connected to any earthed stereo
amplifier. By “earthed” we mean an
amplifier with a 3-core power flex and
3-pin plug.
On the other hand, the older Sony
CDP-XE300, a CD player rather than a
October 2007 11
This inside view of the Tevion TEV1020 DVD player shows just how few parts there are. The switchmode power
supply PC board is to the left of the disk tray with the arrow indicating the high-frequency transformer.
DVD player, uses a linear power supply. It produced no audible hum and
its distortion figure was a very respectable .003%, the lowest in the group.
But its SNR figure appears to be poor
at only -75dB when measured with
wide bandwidth (ie, >500kHz) and
quite good at -97dB when measured
with a 22kHz bandwidth (ie, restricting the noise bandwidth to the audible
spectrum).
This deserves some explanation.
Most CD players produce significant
noise above the audible spectrum and
this is usually filtered out during measurement to produce the manufacturer’s
Equipment
Case Potential
Relative To Earth
Tevion TEV1020
DVD Player
81.5V AC
Magnavox MDVD50
DVD Player
115.8V AC
Panasonic DMR-ES10
RVD Recorder
111.4V AC
Audio World AW-8032
DVD Player
117.3V AC
Table 2: these are the case potentials
we measured for a range of doubleinsulated switchmode equipment.
While the voltages are perfectly safe
in normal operation, they can give
you an electric shock.
12 Silicon Chip
typical specification of -96dB or better.
The out-of-band noise (ie, supersonic
noise) is mainly due to the switching
artefacts of the CD player’s DAC (digital to analog converter).
These switching artefacts will depend on the oversampling frequency
used by the DAC. For example, players
that use 2-times oversampling will
have their main switching artefacts
bunched at 88.2kHz and at the harmonics of that frequency.
The Sony CDP-XE300 appears to
have a 1-bit DAC and therefore its
main switching artefacts appear at
around 1.1MHz. Considering that its
wideband noise was only -75dB with
respect to 2V, the equivalent noise
signal at 1.1MHz is around 300 microvolts (300mV) or so. In other words, it
is quite a significant RF noise signal
to be injecting into the audio input
of any audio amplifier. We will have
more to say about this aspect, later in
this article.
Still on the Sony CDP-XE300, it is
about 10 years old and a look at its
internals revealed it uses 4558 op
amps in the output stages. Incidentally, these same op amps are also
found in the cheap Tevion TEV1020
DVD player, although they are surfacemount types.
As an aside, where a CD player or
DVD player is fitted with standard op
amps, it may be possible to gain an improvement in performance by retrofitting one of the latest high-performance
op amps such as have been featured
in recent SILICON CHIP designs; eg, the
National Semiconductor LM4562 or
the Burr-Brown OPA2134.
The Toshiba CD-ROM drive and the
Notebook CD-ROM drive both had
mediocre performance. However, the
latter’s output was measured via the
headphone jack, which might explain
its distortion and SNR figures.
DVD player problems
DVD players present two problems
as far as their audio performance is
concerned. The first is that they always
deliver a video output signal, even
when playing CDs. This can introduce
high-frequency noise into the audio
signal and although this may not be
audible, it can degrade the signal-tonoise ratio.
A more serious problem is the audible hum injected when a DVD player
with a switchmode power supply is
connected to an earthed amplifier.
These days many, if not all, CD players
also have switchmode supplies and so
they have the same problem.
siliconchip.com.au
The Sony CDP-XE300 CD Player has a linear power supply with a conventional mains transformer (arrowed).
Fig.2: the yellow traces in these scope shots show the voltage across an earthed 100W resistor connected to the case of the
Magnavox MDVD50 DVD player. The lefthand window shows the measurement when the Magnavox is floating and the
installed “Tingle Terminator” is disabled, while the righthand window shows what happens when the “Tingle Terminator”
is connected. The vertical scale is 20mV in both cases.
To understand the problem, we need
to refer back to our article on the “Tingle
Terminator” described in the July 2006
issue. This provided a simple solution
for preventing the mild electric shocks
that one can receive when using modern double-insulated equipment with
switchmode supplies.
Because double-insulated equipment is not earthed, the equipment’s
case can be at a large potential relative
siliconchip.com.au
to earth. While this is perfectly safe,
it can give you a mild electric shock
if you touch it.
In practice, the case can sit anywhere between 80V and 120V – see
Table 2. By contrast, compare the
values in Table 2 with a measured
case potential of just 22V for the Sony
CDP-XE300, a double-insulated CD
player with a linear supply.
The “Tingle Terminator” was a
workaround to the shock problem. It
used a 22nF capacitor to couple the
case to earth, effectively removing
the shocks. In fact, with the capacitor in place, the case voltage drops
dramatically to anything between
2V and 5V.
The “Tingle Terminator” was design
ed as an add-on to existing equipment,
whose installation did not require
opening the case or modifying the
October 2007 13
Fig.3: the yellow trace of this scope shot shows the output
from the Tevion TEV1020 DVD player for what should
ideally be a clean 1kHz sinewave but which instead
has superimposed noise. The red trace is the Fourier
transform and this shows that higher frequencies are being
superimposed on the output by the switchmode power
supply. Notice the large spike at around 146kHz. Each
division represents 25kHz.
Fig.4: the yellow trace shows the noise output of the Tevion
TEV1020 DVD player when it is paused. The red trace
is the Fourier transform and this indicates that a range
of high frequencies are present in the signal, beginning
with the first peak at 27MHz (the crystal frequency of the
main IC). High signal amplitudes at higher frequencies are
also present right through the FM band and beyond. Each
division represents 100MHz.
2-pin mains plug. This was done to 134mA is flowing. The large highcircumvent possible issues with void- frequency spikes have disappeared
ing the warranty.
and the current flowing to earth has
Fig.2 shows the “Tingle Termina- dropped by 17%, yet the 50Hz mains
tor” at work. The yellow trace shows fundamental is still visible. This is
the voltage across an earthed 100W what produces the hum in the audio
1% resistor connected to the case of signal, even with the “Tingle Terminathe Magnavox MDVD50 DVD player. tor” installed.
This signal is essentially the 50Hz
Therefore, although the “Tingle Terfundamental from the mains supply. minator” may be effective at removing
Large spikes and high-frequency noise the risk of shocks, it is not useful for
from the digital circuits inside are also removing the audible hum.
present.
Compare the top window, taken Switchmode power supplies
when the “Tingle Terminator” was
The power requirements of a typical
disabled, to the bottom window, when DVD player are +3.3V and/or +5V for
it is enabled. In the top window, the the digital system and ±12V for the op
RMS voltage is 16.1mV, meaning that amps on the analog side.
around 161mA is flowing to earth. By
For example, the Tevion TEV1020
contrast,
in
the
bottom
window,
the
DVD
player
supply
RF_SiliconChip_60x181mm.qxd 30/3/07 2:12
PM has
Pagea switchmode
1
RMS voltage is 13.4mV and around that produces ±12V for three 4558 op
amps plus a +5V rail for the digital
circuitry. This circuitry is based on a
single Zoran Vaddis-series chip (see
Fig.1), which is a common single-chip
solution for DVD players.
In older, conventional power suppl
ies (also known as “linear” supplies),
a transformer completely isolates
and “steps down” the 50Hz 240VAC
mains. By contrast, the output side
of a switchmode supply is isolated
via a high-frequency switching transformer.
While the primary side of a linear
supply is quite simple, a switchmode
power supply has quite a few components on the primary side of the
high-frequency transformer. These
typically include a dedicated switchmode controller IC, a switching
device and various passive compo-
ELECTRO CHEMICALS
Chemical Technology
14 Silicon Chip
• Dust Off • Freezing Spray • Electronic Cleaning Solvent No. 1
• Electronic Circuit Board Cleaner • Electrical Contact Cleaner Lubricant
• Video Head Cleaner • Ultrasonic Bath Cleaner • Isopropyl Alcohol
• Protek • Contact Treatment Grease • Contact Treatment Oil
• Solvent Diluted Oil • Contact Cleaning Strip • Circuit Board Lacquer
• Q43 – Silicon Grease Compound • Heat Sink Compound
Contact us to find your nearest distributor:
sales<at>rfoot.com.au Tel: 02 9979 8311 Fax: 02 9979 8098
Richard Foot Pty Ltd, 14/2 Apollo Street,Warriewood NSW 2102
siliconchip.com.au
Fig.5: the top left and top right windows show the noise output from the Class-A Amplifier at 20W into an 8W load, at a
vertical scale of 100mV and 20mV respectively. No discernible hum is present – the waveform is simply random noise. At
bottom left is the noise output of the Magnavox MDVD50 DVD player connected to the Class-A Amplifier (100mV vertical
scale). In this case, a 50Hz fundamental is present and can be heard as hum. Compare this with the bottom right window,
which shows the noise output of the Sony CDP-XE300 CD player in the same conditions. No audible hum is present.
nents, including capacitors connected to ground. As the switching element is either at saturation or off, the
efficiency is quite high.
Switchmode advantages
Switchmode supplies have several
advantages over linear types. They can
easily step up or invert voltages, they
are more efficient and they require a
much smaller transformer since they
switch at a much higher frequency
than 50Hz.
Their high efficiency in turn equates
to low heat and the smaller transformer
makes them cheaper and lighter than
conventional supplies. Most cheap
DVD players are extremely light for
this reason.
Noise is the problem
Although switchmode supplies are
siliconchip.com.au
efficient, they produce noise in at least
three ways. First, there is ripple at the
switching frequency (typically in the
kHz range) in the regulated output and
ripple injected into the unregulated
input supply. Second, there is also
radiated noise at the switching frequency and its harmonics. This noise
emanates from the inductors and the
high-frequency transformer.
Thirdly, as already described, the
switchmode supply configuration
introduces earth loops which in turn
causes hum problems. What happens
is that the capacitors on the primary
side of the switchmode supply couple
the mains input through to the signal
ground, which connects to the case.
As a result, when the signal outputs
are connected to an earthed amplifier,
current flows to the amplifier’s earth,
since the case of the double-insulated
equipment is at a high potential.
This earth current degrades the
SNR and causes audible hum in the
amplifier’s outputs. Note, however,
that this is only a problem if the amplifier is earthed and the switchmode
equipment is double-insulated (ie,
not earthed).
By the way, if you have this problem,
don’t even think of disconnecting the
amplifier’s mains earth to cure the
problem. That would only serve to create a potentially fatal situation in the
event of a fault in the amplifier.
Unfortunately, the noise problem
doesn’t end there. Since a DVD player
also produces a video output signal,
the noise component of its audio
signal is potentially of a much wider
bandwidth than for a dedicated CD
player.
To see how bad it can be, we measOctober 2007 15
Fig.6: the yellow and pink traces are the left and right channels respectively of the Class-A Amplifier. The cyan trace is
the distortion signal produced when the Magnavox MDVD50 DVD player, connected through the Class-A Amplifier,
is paused. In the lefthand window, the Magnavox is powered by its internal switchmode supply. By contrast, in the
righthand window, the Magnavox is powered by an external linear supply. Notice that the 50Hz hum present in the
lefthand trace has disappeared in the righthand trace.
ured the Tevion, the worst in our group
of DVD players. First, we measured the
radiated noise from its switchmode
power supply, as shown in Fig.3.
As shown, the yellow trace is the
audio output from the right channel
of the Tevion TEV1020 DVD player. It
should be a clean 1kHz sinewave but
it has a lot of superimposed noise. The
resulting measured distortion figure is
high at .05%, as indicated in Table 1.
Using a pick-up loop placed near
the switchmode supply of the player,
we measured the induced current
produced by the electromagnetic field
of the high-frequency transformer.
The resulting noise waveform had a
frequency around 130kHz, which we
assumed is the switching frequency
for this model.
The red trace in Fig.3 is the Fourier
transform of the 1kHz audio output
and it shows a large peak at 146kHz,
again close to the suspected switching
frequency, confirming that there is
noise being injected from the power
supply into the audio output.
It gets worse
It gets worse, however, when we
look at the higher frequency noise –
see Fig.4. The yellow trace is the noise
output from the right channel of the
Tevion DVD player when it is paused,
while the red trace is the rectangular
Fourier transform. The latter has its
first large peak at 27MHz, which is the
fundamental crystal frequency of the
main IC. Large peaks follow all through
the FM band, with smaller peaks then
following as the frequency increases
right up as far as 675MHz – that’s right
Equipment
Power
Supply
Switchmode
Signal
Level
SNR (10Hz THD+N (10Hz
to 22kHz)
to 22kHz)
Sony CDP-XE300
CD Player
Internal
No
12.65V
-77dBr
.003%
Magnavox MDVD50
DVD Player
Internal
Yes
11.28V
-82dBr
.009%
Magnavox MDVD50
DVD Player
External
No
11.28V
-94dBr
.012%
Tevion TEV1020
DVD Player
Internal
Yes
12.65V
-75dBr
.051%
Tevion TEV1020
DVD Player
External
No
12.65V
-100dBr
.052%
Table 3: the audio performance of various players connected through the
20W Class-A Stereo Amplifier. All are normally switchmode powered except
the Sony CD player. The table also shows the difference to the SNR when an
external linear supply is substituted for an internal switchmode supply in the
two DVD players. The signal level of 12.65V represents 20W into 8W load.
16 Silicon Chip
up in the UHF TV bands!
As a result, when connected to an
FM/AM stereo receiver in order to
play a CD, not only can it blot out all
AM radio reception from that receiver,
but it can blot FM radio reception as
well.
In addition, the same DVD player
can produce audible high-frequency
noise through the speakers of the
amplifier it is connected to. We don’t
know whether other cheap DVD players have the same problem but given
that they probably use the same Zoran
LSI chip, many equally cheap DVD
players could easily be just as bad or
even worse.
The hum problem
Let’s now go back to the main issue,
which is audible hum. Of all the players tested, only the Sony CDP-XE300
CD player (ie, the player with the linear
power supply) exhibited a quiet output
signal when it was paused while connected to the Class-A Stereo Amplifier. The other players, especially the
cheap DVD players like the Magnavox
MDVD50 and the Tevion TEV1020, all
exhibited audible mains hum under
the same circumstances.
Take a look now at Fig.5. The two top
windows show the noise output of the
Class-A Amplifier when the inputs are
shorted with a 1kW resistor. Two different vertical scales are shown: 100mV/
div for the left window and 20mV/div
for the right window. No hum can be
seen in the signal nor can any hum be
heard through headphones.
siliconchip.com.au
In the bottom left window, the
cyan trace shows the noise output of
the Magnavox MDVD50 DVD player
when it is paused while connected
to the Class-A Amplifier. Hum is now
clearly visible in the form of a 50Hz
fundamental sinewave and this comes
from the mains. The vertical scale is
set at 100mV.
Now compare this with the noise
output of the Sony CDP-XE300 CD
player, shown bottom right at the same
vertical scale. No discernible hum is
present, nor can any be heard.
To verify this, we connected one
headphone channel directly across the
amplifier’s speaker terminals, using
the circuit shown in Fig.8. This further
confirmed that the switchmode DVD
players produced hum while the linear
supply CD player did not.
Not satisfied with this, we performed yet another test – see Fig.6.
The yellow and pink traces are the left
and right channels respectively of the
Class-A amplifier. The cyan trace is
the distortion signal produced when
the Magnavox MDVD50 DVD player
is connected to the Class-A Amplifier
and paused.
There’s an interesting twist here
though. In the top window, the Magnavox was powered by its internal
switchmode supply. However, in the
bottom window, the switchmode supply was disabled and the Magnavox
was instead powered by an external
linear supply that we patched in. Notice that the 50Hz hum that’s present
in the top trace has disappeared in the
bottom trace!
Audio performance
Finally, we measured the audio performance of the Magnavox MDVD50
DVD player, the Tevion TEV1020 DVD
player and the Sony CDP-XE300 CD
player when connected to the ClassA Stereo Amplifier. Their SNR and
THD+N measurements are shown in
Table 3.
We measured the SNR of the Class-A
Amplifier at 20W into 8W to be -107dB
with 1kW shorting jacks. Table 3 shows
that changing the switchmode supply
to a linear one improved the audio
performance of the two DVD players.
For example, the Tevion TEV1020
DVD player had a SNR of -74dB when
connected through the Class-A Amplifier (at 20W into 8W) when using its
internal switchmode supply. However,
this improved by some 25dB to -99dB
siliconchip.com.au
Fig.7: this diagram shows the linear power supply we developed to replace
the switchmode supply in the Tevion & Magnavox DVD players.
earthed audio amplifier.
Even so, a cheap DVD
player may be an attractive proposition for
playing audio CDs in
non-critical situations.
This particularly applies
if your listening position
Fig.8: this circuit can be used to protect
is far enough away from
stereo headphones that are connected
the speakers to render the
directly to the outputs of a stereo amplifier.
The 10W resistors limit the current, while
hum inaudible.
the four diodes limit the maximum voltage
Substituting an exacross each earpiece to about ±0.6V.
ternal linear supply for
the internal switchmode
supply certainly gets rid
when it was powered by an external of the hum. In fact, we went so far
linear supply!
as to design a suitable linear supply
that could be retrofitted to cheap DVD
Conclusion
players.
These tests lead us to just one conIn the end, however, we scrapped
clusion. If you want the very best audio the idea – the audible hum problem
performance from your hifi system, was not sufficiently bad to warrant the
then a dedicated CD player with a lin- extra cost of the linear supply. It also
ear supply is the only way to go. DVD does nothing to improve a mediocre
players may cost a lot less but their THD+N performance.
switchmode power supplies introduce
If you want the very best, buy a good
SC
audible hum when connected to an CD player.
October 2007 17
|