THE DYNAMIC RANGE POTENTIAL OF THE PHONOGRAPH By Ronald M. Bauman his article describes a new transmission standards of even lower added to the quietest passages by the approach for analyzing the quality than our current CD standards. cartridge-preamplifier combination dynamic range of the phono- Unless these standards are dramatical- should be essentially inaudible. graphic playback system, in which the ly upgraded (in terms of information Similarly, the cartridge-preamp sys- cartridge and preamplifier are treated content), we may never have a source tem should be able to clearly repro- as an integrated system. I analyzed of music for our homes that sounds ducd the loudest sounds on record the dynamic range potential of several better than the phonograph. without distortion, compression, or combinations of phono cartridges and Are analog records inherently better clipping. preamplifier amplifying devices and in some sense? Your ears may already The same should be true of CD compared the results to CDs. be telling you that analog can sound playback. The quietest passages Additionally, I speculate about the better than today's digital. I will should be reproduced without added drawbacks of frequency domain char- provide quantitative reasons this may noise or distortion of the rnusic acterizations of musical audio compo- be so. caused by amplitude steps, or sam- nents and suggest that the time pling intervals that are too coarse, or domain may be a more natural frame Qualitative Requirements by filter phase shifts and ringing. The of reference for audio instrumentation The subtlety of detail in the grooves of loudest peaks encoded, as for analog development. an LP record is astounding. Quiet, yet records, must be reproduced without clearly audible, details (such as the distortions, compression, or clipping. lntroduction reverberation characteristic of Car- Why should anyone still be interested negie Hall) are represented by stylus Definitions in the analog phonograph? The reason motions of less than an ultraviolet For CD players, dynamic range is is simple: today's best record playback wavelength (1/100,000,000 of a essentially the ratio of the loudest pos- systems sound better than today's meter)-a dimension approaching the sible output signal to the quantization best CD players. (CD playback is size of a complex organic molecule. noise, i.e., the noise corresponding to improving, though maybe not faster This submicroscopic motion may be the round-off error of the least signifi- than turntable, arm, and phono car- superimposed on an orchestral cant bit. For the 16-bit standard CD tridge developments.) Moreover, crescendo involving stylus motions format, this is 96dB dynamic range. many analog record treasures are thousands of times larger. Over the To parallel the previous CD defini- unavailable on CDs or other available last ten years, the ability of modern tion, I define the dynamic range of a and anticipated digital music sources. cartridges, arms, and turntables to phono cartridge as the ratio of the After all, standards to transmit digital resolve this ultra-fine detail, particu- loudest sound to the background music (and video) directly to our larly during loud and complex music noise referenced to the preamp output homes are developing. This will open peaks, continues to improve beyond terminals. Crucial to this definition is a vast library of musical selections for all expectations. understanding that there is an inti- our potential enjoyment. Ideally, to reproduce the dynamic mate relationship between the car- I believe that commercial considera- range inherent in the groove modula- tridge and the first preamplifier stage. tions and the limitations of today's tion of a fine LP with the least possible Each interacts with the other to estab- digital technology will establish digital degradation, the background noise lish dynamic range; neither the car- tridge nor the preamplifier stand alone. Oddly enough, the preceding defin- ition is not the conventional one, ABOUT THE AUTHOR Hon Bauman received his BSEE from Lehigh University. He is founder and owner of inSound, which produces high- end audio amps, preamps, and, in partnership with Mapleshade Electronics, the Omega Mikro line of digital and analog interconnect, power, and speaker cables. Ron also specializes in personal and meteor burst communica- tion systems design. With his wile Marcia, he is raising his FIGURE 1: Simplilied noise model of phono cartridge and preamplifier. sons Marcus and Mitchell. His hobbies include music, beer-making, llying, and restoring old Volvos. l6 Audio Electronics 4/96 which is simply signal-to-noise ratio equivalent circuit parameters of the age of the cartridge resistance in volts; (S/N) at some arbitrary cartridge out- cartridge. For the above three car- e, is the equivalent input RMS put lcvcl wcll bclow thc louclcst. tridgc.s, thc significarrt cir.ctrit paralnc- voltagc noisc gcncrator of the pream- Often, preamplifier noise is character- ters are the series resistance and plifier in volts; ized with the input shorted, which, as point2 inductance. The values are: Blue i* is the equivalent input RMS cur- you will see, is an incomplete and 108C1, 190pH;MCZ 70Q, 9mH; and rent noise generator of the preamplifi- useless way to measure preamplifier MC 100 34, negligible inductance. er in amps. noise. This conventional definition led None of the manufacturers states a The output S/N ratio is (1) divided to the widespread notion that phono need for a loading capacitor. Small bv (2): dynamic range is only 60-70dB. If loading capacitors and cable capaci- true, this means LPs are about tance and inductance have a second- Vo2/No = ec2l[eR2 + N2er2 + [ir?Nltlz.l2]l 25-35d8 more compressed than CDs, order effect on the equivalent electri- (3) an amount of compression so severe cal noise anyway, so I neglected them that you would notice a real in the following analysis. Notice that the input impedance of "Muzak"-like loss of dynamic impact Figure 1 shows a simplified equiva- the preamplifier has dropped out, in LPs relative to CDs. lent circuit for analyzing the noise and, therefore, does not direitly affect In fact, serious listeners find the performance of a phono ca"rtridge and the S/N ratio. opposite is true. Using LP and CD preamplifier, or pre-preamplifier. The Shunt resistances placed across the issues of the same performance, they circuit model is based on the Rotl-re- preamplifier input increase the noise have carefully and empirically com- Dahlke3 theory of noisy fourpoles (in power of the voltage and/or current pared state-of-the-art (SOA) phono which the preamplifier has one input generators. Such resistors can only systems to SOA f;ljfback CD players. port and one output port). In this decrease dyrlamic range by increasing LP playback is generally considered model, amplifier noise originates, at noise. Motchenbacher and Fitchena either better or eclual to CDs in macro- audio frequencies, as two uncorrelat- show that the output S/N ratio is dynamic impact. LPs are usually supe- ed generators: an ideal noise voltage maximized if the rior following is true: in subtle microdynamic shadings. generator, e*, and an ideal noise cur- rent generator, i*. These generators N2[e*/ir]= lZ.l ohms (4) Examples interact with the cartridge impedance To help quantify dynamic range for to establish the basic noise level of the Substituting (4) real phono - into (3) and simpli- playback systems, I use phono playback system. fying yields: three modestly priced examples: a The figure includes a transformer to Surniko Blue Point, a high-output show the effects of coupling very low moving Vo2lNo = eczllen2 + [eri, lZ"l]l (5) coil; a Grado MCZ, a fixed coil output-moving coil cartridges to pre- with moving magnet; and an Ortofon amplifiers. You assume the trjns- Assuming optimum noise coupling, MC 1091 a very low output moving former is - ideal, but you can represent the output noise is dependent on the coil. Although better-sounding car-- its losses by increasing the power of product of the basic noise generators tridges are available, I chose theie for the preamplifier noise geneiators. To of the preamplifier and the magnitude modest price and convenience, not to apply the diagram to transformerless of the cartridge impedance. Equation mention that I own one of each. preamplifiers, simply set N, the turns (5) shows that the preamp,s e*in, To estimate the dynamic range ratio, to one. parameter is useful for choosing capability of the vinyl Lp, first i estab- To calculate the S/N ratio at the low-noise preamplifier; the lor.ier lish the cartridges' sensitivity and the preamplifier output, first calculate the e*i*, the greater the potential S/N. largest signal amplitude it must han- desired output signal as follows: Therefore, consider using e*i* as dle. The sensitivity figures in units of an appropriate figure for any ampUfy- mY /cm/s are: Blue Point, 0.85; MCZ, Vo2 --A,2 [e.2/N2] [tZ(Z+ ft)t2] votts2 (1) ing device in which low noise is 0.42; and MC 100, 0.018. The worst important. I find it more useful case (loudest) recorded than sound on a where: Vo is the desired output sig- noise figure because record in the the parameter literature is 105cm/s at nal in volts; contains information 7kHz.1 necessary to e-a is the open circuit output voltage _ noise-match to a source and compare Of these three cartridges, the largest of the cartridge in volts; two devices. signal available to the input of the N is the turns ratio of the coupling Of course, as with noise figure, preamp is 0.85mV/cmls x 105cm/s, eri* transformer; varies with frequency, bias cur.eiri, or 89mV.