By Gary Galo, Contributing Editor
NEW COMPACT DISC TECHNOLOGIES
COMPACT DISC PLAYING TIME is approximately 75 minutes, although a few companies have squeezed up to 80 minutes of music onto the medium. The extra 5 minutes or so are gained by narrowing the track pitch from the nominal 1.6m to 1.5um minimum tolerance. Whether the disc is stereo or mono normally does not affect the playing time, but one French label has set out to change that.
Rodolphe Productions, distributed by Harmonia Mundi, has introduced the world's first double-duration monaural compact discs. As a collector of historic recordings, I welcome this development since it doubles the available playing time of monaural discs without any loss of fidelity whatever.
I call these discs ‘two-track mono’ CDs, a term I borrowed from two- and four-track monaural reel-to-reel tapes- convenient, but not technically accurate when applied to the compact disc. Left and right channel stereo information is not recorded on separate ‘tracks’ on a CD, unlike the LP record, cassettes and reel-to-reel tapes. Digital information on a CD consists of a single spiral of digital data, which periodically switches back and forth between the left and right channels. Since the separation between the channels is more than 90dB, the CD can be considered free of any channel cross talk. The only limiting factors are the design and layout of the analog circuitry and power supplies in the CD player.
Nearly any reasonably well-designed CD player should have more than adequate separation to allow you to listen to pro gram material on one channel without audible crosstalk from the other.
The double-duration CD, therefore, puts one monaural program on the left channel and a completely different monaural program on the right. You must play the disc through twice, monitoring the left channel the first time and the right channel the second, using one of several available methods.
My preamplifiers have separate left right mono switching. When I press the left button, the left channel signal is routed through both the left and right preamp outputs of the power amp and loudspeakers. The right source signal can be similarly routed.
If you don't have separate left-right mono switching, you can rotate your balance control hard over to the left side for the first pass, and hard over to the right for the second. Unfortunately the sound will appear only in one loudspeaker each time. I personally prefer monaural recordings reproduced through two speakers. In my normal listening chair, the sound appears to come from one spot centered between the speakers, which I certainly prefer to having the sound come first from one corner of the room, then from the other.
If you purchase Rodolphe Productions' seven-CD set of Wagner's complete Der Ring des Nibelungen (yes, the entire Ring fits on only seven discs) you'll receive free, shrink-wrapped to the package, a switchbox that allows separate left-right mono switching. Rodolphe recommends inserting the switchbox in the signal path between the CD player and the preamplifier. Unfortunately, the box is cheaply made and will degrade the sound quality of any good system. I recommend inserting the switchbox in a spare tape monitor or external processing loop, accessing it only when you need it for the double duration discs; your purist cabling and connectors will remain intact when playing high-fidelity CDs.
---- FIGURE: Left-right mono switch.
You can easily construct your own switchbox. I've included a schematic for such a device; again, I recommend inserting it in a spare loop on your preamp.
You could, of course, use gold-plated connectors, silver contact switches and premium quality wiring, but you're still adding extra switch contacts in the signal path and increasing the chances for reduced channel separation on your stereo/ hi-fi CDs. I'd avoid this; you can mount the switches and connectors in a small aluminum box, or permanently install such an arrangement in your preamp, space permitting.
Perhaps the best news about the Rodolphe CDs is their considerable musical value. In a seven-disc set (of a work normally requiring 14 or 15 CDs) Rodolphe has preserved a live 1953 Bayreuth Festival performance of Wagner's Ring Cycle conducted by Clemens Krauss, a conductor of major importance, primarily known for his association with Richard Strauss. This recording will resolve any doubts you may have about Krauss as a Wagner interpreter; it is one of the best conducted Rings on record and one of the most unified, coherent performances of it I've heard. Krauss has an uncanny sense of the musical architecture; from the beginning of Das Rheingold the performance moves with incredible continuity and direction.
Few performances have illuminated the wide variety of moods and emotions present in the Ring. Krauss' approach to the score may appear introverted com pared to the super-charged performance listeners have become accustomed to by Georg Solti in his classic stereo recording for Decca/London. Krauss is never short on dramatic impact when it's required, however, and you'll have to turn to Wilhelm Furtwangler and Hans Knappertsbusch for a depth of understanding in his league.
The cast is uniformly good, with several excellent performances by singers familiar from other 1950s Bayreuth performances. Wolfgang Windgassen, in his vocal prime, shows how Siegfried can be sung from beginning to end using intelligence and a superb technique. Hans Hotter's vocal performance is fresher than with Solti 10 to 12 years later, and no bass-baritone has ever provided a more probing portrayal of the role of Wotan. The Brunnhilde is Astrid Varnay throughout, not the steadiest or easiest soprano on record, but a voice of enormous power and dramatic impact.
Gustav Neidlinger shows why he was the most respected Alberich of his day, and the Donner and Gunther of Hermann Uhde are an added bonus.
The catalog number is RPC 32503.9; the four operas are not available separately. The lowest price I've seen is $111, from Record Masters Inc. ( 711 W. 40th St., Baltimore, MD 21211, 1-800-727 DISC); Tower Records in New York is charging close to $150. If you're looking for a reliable source for mail ordering classical CDs, RecordMasters has an enormous selection, fast service and competitive prices.
Other double duration offerings from Rodolphe include a live October 12, 1953 performance of Beethoven's Fidelio, con ducted by Wilhelm Furtwangler (RPC 32494). The Salzburg Festival cast includes Wolfgang Windgassen, Otto Edelmann and Gottlob Frick, with Martha Modl delivering an admittedly strained Leonore. Only a few days later the same cast and conductor recorded a famous studio version for EMI, but technical considerations aside, the performance does not match this one. Typically, Furtwangler's intensity in a live performance is rarely matched by his studio recording.
Clemens Krauss' 1944 Munich Staatsoper performance of Wagner's Der Fliegende Hollander has also been issued by Rodolphe; Hans Hotter is superb in the title role. Viorica Ursuleac's singing of Senta is painful (she was married to Krauss and thus appeared in many of his performances), but the performance is otherwise excellent.
The monaural sound on all these Rodolphe discs is an example of well recorded in-house opera from the 1950s.
The source material is not hi-fi demonstration quality, certainly not the equal of early fifties Mercurys, but the sound is clean, reasonably quiet and has excellent balance between soloists and orchestra. Only the 1944 Hollander is be low par, originating from German Magnetophon tapes, with their somewhat coarse quality in the midrange and high frequencies. It's perfectly listenable, however, and anyone desiring this performance should not hesitate to purchase it I applaud this new technique for issuing monaural material and hope other manufacturers follow suit. I hear rumors that Philips (co-inventor of the CD) is not pleased and has put pressure on its licensees not to manufacture double duration discs. Rodolphe's discs are manufactured by Sonopress, apparently the only European plant that would do so.
The double-duration CD is a technically viable concept. A ‘not invented here ’ attitude is not appropriate. I would urge Philips to reconsider its opposition and make this format an industry standard for monaural issues.
Italy's Hunt Productions has introduced another technique for doubling the playing time of CDs. The packages say ‘double-sided ’ compact disc and initially I wondered how they managed to squeeze two aluminum layers into a single CD. Closer examination revealed two CDs glued back to back. The first Hunt disc I encountered was another Furtwangler Fidelio, from the 1950 Salzburg Festival, with Kirsten Flagstad in the title role. I also found a Salzburg performance of Weber's Der Freischutz conducted by Furtwangler. Are you get ting two CDs for the price of one? Certainly not-two New York stores were charging $31 for a ‘single ’ double-sided CD.
These double-thick discs cause problems. Many CD players simply jam when the transport attempts to load the discs, much like many disc dampers. A salesperson at Record Hunter ( 507 Fifth Ave., New York, NY 10017) told me that nearly all the Fidelios were returned as unplayable. The store finally gave up and returned all 90 in stock to Qualiton Imports, the US distributor. Another danger-even if they will play-is that you can easily scratch the top side of the disc. The single-sided concept was well thought out and prevents such a mishap if you exercise normal care when handling the disc.
The double-sided CD is not new technology; it is more of a technical kludge.
Hunt should consider dropping this idea altogether and adopt Rodolphe's technique for doubling the playing time of monaural CDs, or at least separate the two discs into normal, single-sided CDs.
As long as you're paying for two discs anyway, what's the point in gluing them together so they won't play? Don't ignore the Hunt label altogether; the company also issues normal, single-sided CDs, some of which contain historic performances, but avoid the double-sided discs.
READERS' QUESTIONS
JVC Receiver Reception
I am an electrical engineering student who was recently introduced to your publication through the Journal of the Audio Engineering Society. I own a JVC receiver model RX-1 and the FM reception is terrible. Has TAA presented any past projects such as a signal amplifier that I can make to improve the reception? Also, where can I obtain the service manual for this receiver, or for my Onkyo TA-2028 tape deck? Since I am not familiar with the techniques in TAA, can you suggest any reference manuals I could use in assembling my projects?
Nick Schmansky; Powell, OH 43065
REPLY
TAA has not published any RF preamplifier projects, but inexpensive commercial amplifiers exist that may help. One is MCM Electronics' Non-Passive Amp (#33-917) and Power Supply (#33-915). This broadband amplifier (5-950MHz) provides 11dB of gain, is designed for 75-ohm operation, and ideally, should be placed as close to the antenna as possible. It won't fix a defective tuner, so if your JVC receiver is malfunctioning, repair it first. The signal amplifier will not compensate for a bad antenna system, either. If the signals on your antenna distribution sys tem are already noisy, the amplifier won't help unless you can increase the gain before the noise is introduced. If you simply need a bit more gain to quiet your receiver, it should work well.
The best (and often only) source for service manuals is the manufacturer, who usually will provide them for a nominal fee. The current addresses you need are: JVC, 41 Slater Dr., Elmwood Park, NJ 07407; Onkyo, 200 Williams Dr., Ramsey, NJ 07446.
Glenn White's The Audio Dictionary will help you become familiar with audio terminology (see Review: Books, TAA 2/89 p. 40). Since you are an EE student, you probably don't need an electronics dictionary. If White's book is not what you had in mind, perhaps you could send specific questions to Ask TAA. Back issues of TAA are also an excellent source of such information.
SAE 4000 Salvage
I recently bought an SAE 4000 active two-way crossover. I want to improve it, as follows:
1. Upgrade the Mylar 0.12 uF, 100V and 0.012uF, 400V capacitors in the multiplier circuit to 50V, 2% polypropylene;
2. Use Panasonic HF series electrolytic capacitors for input and output coupling;
3. Use polypropylene types for power supply decoupling;
4. Use metal film resistors throughout;
5. Maybe use an IC in place of the transistor regulators;
6. Upgrade the op amp to have better noise specs and a higher slew rate.
What should I use to replace the op-amp? I want to just drop in the new chip without any external compensation. Do you think a slew rate higher than 1 is really needed for audio? SAE said the original is a Motorola A1-4741-5, but I've only been able to find a prefix of MC for Motorola, not Al. The originals were covered with black paint, which I re moved, and it looks like a Harris quad op amp HA1-4741-5.
I also would like to know how companies such as Denon and Sansui can squeeze 80W per channel RMS into 8Q with only two output transistors per channel and small filter power supply capacitors.
I'm working on the POOGE-4 Magnavox CD mod (TAA 2/88). What is the purpose of diode D100 in place of 10 ohm R3331 (Fig. 3, p. 20)? Also, referring to R3 (p. 22, third column, second paragraph), what is a Class-A pulldown?
Jim Kakavas; Iowa City, IA 52242
REPLY
The op amp you sent us is manufactured by Harris and is its equivalent for the Motorola 4741. This device is nothing more than a quad version of the 741, a terrible audio device by any current standards. Fortunately, this device follows the standard quad pinout, so finding a replacement is no problem. I suggest Analog Devices' new AD-713, a quad version of its AD-711 Bi-FET op amp, a de vice praised in these pages by Walt Jung ( ‘Op Amp Meets CD, ’ TAA 3/86). This device is the most exciting quad op amp I've seen. You shouldn't consider slew rate independently of gain bandwidth product. Vy, of the AD-713 is 0.8V, eight times better than the 741. The resulting Vi (input dynamic range) is most important and Walt's article explains this in detail.
You could also use the older Texas Instrument TL-074, the quad version of its TL-071. Although a respectable per former, it falls short of the new devices from Analog Devices. The AD-713 may have sufficiently low DC output offset (5mV or less) to allow you to remove the output coupling capacitors completely.
Check the DC voltage on pins 7 and 14 of IC2 with a digital voltmeter with 1mV resolution. If it reads less than 5mV, you can safely remove the capacitors and replace them with jumpers.
As you've indicated, other possible changes are to replace the rest of the capacitors with high-quality polystyrene or polypropylene types, as values dictate, or to replace all resistors with 1% metal films. The power supply leaves much to be desired. First, there appears to be no local bypassing. Add 330uF, 25V Panasonic HF series electrolytic capacitors as close to pins 4 and 11 of the two op amps as possible (four caps in all). If there is room for values, use larger caps.
Even 1,000 uF will not be overkill.
You should remove the 0.01 uF output bypass capacitors on the supply and re place them with HF electrolytic types, as well; again, if 1,000 uF will fit, use them.
Your problem now becomes the MPS A05 and MPS A55 regulator transistors.
These devices may not respond well to repeated charging of the higher value capacitors. Replace these two transistors with TIP-31 and TTP-32, rated at 3A each.
Finally, I'd replace the 16V zener diodes with 15V, 1W types. The 1N4744A should work fine. The transistors, diodes and Panasonic capacitors are available from Digi-Key. If the line fuse blows as a result of charging the increased capacitance, change it to 0.5A.
Regarding your amplifier question, these amplifiers probably can deliver 80W into 8Q provided the load is a resistor and the input signal is a sine wave. This is how power output is usual ly tested. Reactive loads often give very different results. A small power supply won't impair the static bench measurement, but when faced with real music conditions the amplifiers' dynamics and imaging probably will not excel. This is an example of the ‘spend no more than absolutely necessary ’ school of Japanese amplifier design.
The TDA-1541 D-A converter in the Magnavox CD players requires -5.25V at pin 26. Philips did not provide a separate - 5V supply, instead using the -6V supply, which also feeds the servo circuit. R3331 drops the -6V to the required value. In POOGE-4, the diode re places the resistor to achieve the required voltage drop without raising the supply impedance as much. A Class-A pulldown resistor simply re-biases the output stage of the op amp so it now operates Class A instead of Class-AB. The output stage is more linear as a result.
Building a Borbely
A few months ago I bought my second Borbely 60W power amplifier (TAA 2/82) from Old Colony Sound Lab. I have been using one I built in 1983 for the high level of my biamped main system; I like it. In 1986 I added a Borbely preamp with completely separate (two toroids) power sup plies.
In building my second Borbely 60W amp (for replacement), I would again like to have two discrete power supplies using separate toroid transformers. What I envision is a scaled down version of the power supplies for the Borbely Servo 100 ('Third-Generation MOSFETs: the DC 100 Part II, ’ TAA 2/84, Figs. 13 and 14, p. 22).
I need advice on what values to use on the two toroids. Is the Avel-Lindberg D1034, 160VA (35+35V RMS), 2.29A RMS too much? What size do I need for the four power caps? What kind of bridge rectifiers? What brands and sources? An Audio Aid by Hal Faulkner on a servo for the EB-60 (TAA 2/87, p. 40), indicated it might be available from OCSL as a kit or board. Is it? I would like to include this servo in my new venture.
Paul Foster Wilmington, NC 28405
REPLY
First, congratulations on your superb construction of the Borbely preamp. As I'm sure you realize, you'd have to spend thousands of dollars to get a commercial product built as well as yours.
Mr. Borbely specifies a 200VA trans former if both channels of the 60W amplifier are to be run from it. One channel could safely operate with a 100VA transformer, but I would be conservative and choose one with 160VA since the oversized transformer should improve the amplifier's dynamics.
The filter capacitors should still be rated at a minimum of 63V. I'd consider the Panasonic TS series 10,000uF/63V capacitors, available from Digi-Key (#P6495). I've always found filter banks greatly improve amplifier performance.
If space is no consideration, you might consider putting two or three in parallel.
If you stick with 10,000 uF caps, you can use a 25A bridge rectifier. A Digi-Key device (#BR-256-ND) is conservatively rated at 600 PIV and a 300A maximum surge current. The cost difference between a 200-PIV bridge and one at 600 PIV is only 60 cents and they're the same size physically. If you parallel several capacitors, use a 35A bridge. Another Digi-Key bridge (#BR-365) is rated at 600 PIV and a 400A maximum surge current.
I've safely charged 35,000uF of parallel capacitance directly from the bridge rectifiers, without using soft-start circuits.
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Also see:
A MULTI-TONE INTERMODULATION METER, PART 1