Ramblings
May / June 2007 By David A. Rich

CD Recorder Reliability An Oxymoron?

  I recommended the Sony RCDW500C CD recorder in Issue 108, but have since discovered that the unit's reliability is suspect. Two units of which I have direct knowledge went south within a window of 6 to 12 months. Both refused to record or finalize, giving error codes instead. Amazon.com and other user experience blogs report a similar frequency of failures. Unplugging the unit might be a quick fix, but who wants to risk the unit malfunctioning in the midst of a critical recording. Sony's press representative could not provide any additional information on the products reliability. Consumer-grade CD recorders are not a common item. Better reliability might be obtained by purchasing a player designed for the semi-pro market. These start at $500 on the web for single-drive units (the Sony had a separate player and player / recorder). For example, I used the Tascam CD-RW900 for the cartridge and turntable evaluations in this issue. The unit has geographic reach, having been assembled in China, but with a Japanese-sourced internal mechanism from Teac (of which Tascam is a division). One of Teac's core businesses lies in data storage and disc publishing. D&M Holdings also has a similar semi-pro, single well, CD-R recorders offering under the Marantz brand at a similar price. I have not had direct access to this unit or others in the category.

Teac's consumer-grade offering, the CD-RW880 (~300), is a new device. Designed for ease of use, it lacks some pro-quality features for disk labeling and editing. Also missing is a SPDIF digital output. The unit takes both analog and digital in, but only analog comes out. The Teac CD-RW880's drive looks less robust than the one in the CD-RW900; however, I had fewer problems rearranging tracks from the former with Sonic Record Now (see my article for more information on the problems I had with the Tascam). The analog specifications for the 880 are lackluster, with less than 14 bit equivalent dynamic range and 12 bit equivalent full-scale distortion. The CD-RW900 is strictly semi-pro and offers slightly more than a bit equivalent better performance. The real deal, Tascam's professional CD-R with genuine 16 bit performance, requires deep pockets at $1200. When I record, I want absolute assurance that the never-to-be-heard-again live FM broadcast is captured intact. For that, you need a system with no moving parts, and I will examine one of these next time: the compact flash-based Marantz Professional PMD66O.

 

Sangean HD FM Tuner: I cannot wait to give you a preview

This is the first reasonably priced HD FM rack sized tuner (no amps or speakers) of which I am aware. For $200, the unit not only captures the core stations transmitting HD signal well, but also captures stations at the fringe in analog. When operating to potential, it delivers performances akin to long discontinued super tuners costing three times or more. The only problem I have found so far is when the HD signal is only captured marginally, the unit slides back and forth between digital and analog with noticeable discontinuity. More information on this unit will be in Issue 113.

 

Red-Faced Dr. Rich

In my review of the NHT active speaker, the power rating of the power amplifiers was given in units of RMS (i.e., root mean square). I cannot tell you how many times I have taught my students in EE101 that power is not measured as an RMS quantity. Just to make sure they do not forget, I repeat a small derivation in almost every course I teach.

The output power of an amplifier is an average measurement. When a resistive load is driven by a sinusoidal voltage waveform or a sinusoidal current waveform, the average power dissipated by the load is calculated from an RMS voltage measurement. Typically, a voltmeter will express an AC voltage as an RMS quantity.

I will briefly explain what this RMS thing is about. If a DC voltage is applied across a resistor, the power thrown off by the resistor as heat can be measured. If the DC voltage is replaced with an AC sinusoidal voltage, and the AC sinusoid has a peak voltage equal to the DC voltage, then the resistor only throws off half as much heat because the instantaneous power across the load is not constant when a sign wave is applied. When the sine wave crosses zero, no power is supplied to the load; only when the sine wave is at its peak is the instantaneous power applied to the load equal to the DC power. For all other positions of the sine wave, the instantaneous power dissipated by the resistor is greater when driven by a DC source.

Circuit designers typically want a uniform average radiated power of a load whether it is driven by an AC source or subjected to a DC voltage. To do so, requires fiddling with the scale factor of the sinusoidal voltage. An RMS voltage is approximately 70% of the peak voltage. Thus, when the AC line voltage is measured with a meter, the meter registers 115 V RMS. On the oscilloscope, the peak voltage is 170 V Peak. Yes, the maximum voltage at your wall outlet is 170 V Peak but we are nonetheless familiar with the 115V number because that is the standard for calculating average power and most of the things we connect to outlets are rated in power.

In sum, RMS scaling factors for sinusoidal AC currents and voltages ensure that average power calculations using RMS values will yield the same constant power as if a DC voltage of the same value were applied to the load. It is all about calculating average power. RMS power has no meaning.

 

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Coming Attractions

Equipment in the test queue includes the Velodyne DD-10 subwoofer; Audyssey Sound Equalizer; NHT multi-channel controller and power amplifier; and Yamaha RX-V2700 AV receiver. On the TSS development agenda for future issues, we will have more pocketbook-friendly gems from both established and up-and-coming manufacturers.

-DAR