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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