PRODUCT REVIEW

NAD PP-1 Phono Preamplifier

Reviewed by Gary Galo

NAD PP-1 Phono Preamplifier. NAD Electronics International, 633 Granite Court, Pickering, Ontario, Canada L1W 3K1, 905-831-0799 (worldwide), 800-263-4641 (North America), nad@NA Delectronics.com, www. nadelectronics.com. Phono preamplifiers are becoming less and less common in consumer audio equipment. Many preamps, integrated amps, and receivers are now made without a phono section, since most buyers wont use them, and manufacturers wish to keep costs down. In home-theater equipment, phono preamps are practically nonexistent. NAD has continued this trend in some of their recent audio products, including the excellent NAD 118 Digital Preamplifier, which I reviewed in AE 6/97. The NAD PP-1 Phono Preamplifier (Photo 1) has been designed as a cost-effective addon for products without phono circuitry, such as the 118. I doubt that any audiophile who is heavily pro-LP would buy the 118 preamp, since all audio entering the 118 is converted to digital (heresy!). All control functions are accomplished in the digital domain. At $129 retail, the PP-1 makes no pretense at being a world-beater high-end phono preamp. NAD has clearly tailored this preamp to digital-oriented audiophiles who still own a collection of LPs that they wish to be able to play, but who arent too fussy about analog sound. The preamp gain is optimized for high-output magnetMANUFACTURERS SPECIFICATIONS
Input impedance: 47k//220pF Input sensitivity: 2.5mV for 200mV output Signal-to-noise ratio (A-weighted, with cartridge connected): 78dB Signal-to-noise ratio (unweighted, with cartridge connected): 72dB Input overload (20Hz/1kHz/20kHz): 55/63/580mV Rated distortion (THD, 20Hz20kHz): 0.04% RIAA accuracy: 0.5dB Dimensions: 70mm
ic cartridgesthe PP-1 will not accommodate low-output moving coils. If you are still convinced that LPs are inherently better than CDs, the PP-1 wont be a good choice. Like a lot of electronics these days, PHOTO 1: The NAD PP-1 phono preamp. The output interconnect the PP-1 is made in cable is hard-wired to the unit. China. The PP-1 is utterly simple in function. tions consist of molded, gold-plated RCA There are no controlsnot even a power plugs on a short, hard-wired cable. switch. The PP-1 is intended either to be left on all the time or plugged into a Circuit Details switched outlet on existing equipment. A schematic for the PP-1 is included An outboard wall-wart transformer with ever y unit (Fig. 1). I re-drew it with a built-in rectifier supplies raw DC using the CircuitMaker1 Student Version, to the PP-1 with a standard DC power since the supplied copy was not clean connector. The chassis-mount input RCA enough for publication. The design is exconnectors are what I call P.T. Barnum tremely simple. typethe shield is gold-plated, but the An NE5532 dual op amp is the active center contact (invisible to the con- device, half used for each channel (my sumer) is tin-plated. The output connec- sample was supplied with a K A5532,
C3 100n +8.3V C15 100n U1A 100nF NE5532 C27 + R5 56k
C5 + J1A LEFT IN C1 220p C21 100n 10uF/25V
C17 + 10uF/10v R13 82R R15 22k

R17 1k P1 LEFT OUT

R3 C7 330k 220pF

C28 100nF

C19 1n5

__ ///

CHASSIS

C9 220uF/10V +

-8.3V R7 130k

R9 11k

C11 24n

C13 6n8

R11 180R

U2 LM317

IN OUT COM

R19 62R

R20 100R +8.3v D1 17V C25 100n + C23 100uF/25V + R22 6K8

J3 POWER IN +20.4 VDC

R24 2K2 D3 GREEN LED

R21 100R

D2 17V

C26 100n

C24 100uf/25V

R23 6K8

FIGURE 1: Schematic of the PP-1. The power supply is essentially unregulated, since the LM317 is configured as a current limiter.

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supply regulation using Total harmonic distortion measurea pair of fixed, three-ter- ments were also well under the manufacminal 7808 and 7908 turers spec of 0.04%, 20Hz20kHz. I regulators? If it raised measured 0.011% at 1kHz, 0.012% at the cost a couple of dol- 20Hz, and 0.012% at 20kHz in the left lars, it would still have channel; the right channel was identical been well worth the ex- except at 20kHz, which measured pense. 0.013%. Noise was 80dB relative to an Im not sure why zener output of 2V; NA D specifies the undiodes D1 and D2 were weighted signal-to-noise ratio as 72dB, but i ncluded. Nor mally, they do not give the reference output for these diodes would this measurement. In operation, the unit clamp the rails at 17V, was subjectively silent. should the regulator I think it would be rather silly to give a fail. But, since the regu- detailed sonic description of the PP-1, PHOTO 2: Inside view of the PP-1. A 5532 dual op amp is the lator isnt really a regu- relative to some absolute sonic benchonly active device in the RIAA phono preamp. The + and lator, and each r ail mark. For $129 you cant expect highsupply rails are derived from a single LM317 regulator. cant possibly go higher end performance, and you dont get it. which is probably a Far-East equivalent). than half the r aw DC voltage (or The PP-1 offers sound quality comparaR7, R9, C11, and C13 form the RIA A 10.75V), the zeners are totally unnec- ble to the phono sections of typical Far feedback network, with R17 and C19 essar y (the 5532 op amp has an ab- East receivers and integrated amps. The taming the ultrasonic peak that would solute maximum rating of 22V). Elimi- PP-1 doesnt do anything nasty to the otherwise occur. C9/R11 set the low fre- nating them would have freed up a few music, and the casual LP collector will quency 3dB point at 4Hz. The 1kHz cents, which NA D could have put to- find it quite listenable. ward real supply regulators. Six years ago Victor Campos, then Digain is set at 38dB. rector of Product Development and EnOne percent metal-film resistors are gineering at NAD, lent me a prototype used throughout, including the RIAA net- Performance work, but the capacitors are film types, I ran a PSpice simulation of the PP-1s of a phono preamp NAD hoped to sell with no tolerance indication. The elec- RIA A circuit (Fig. 2).2 The circuit is ca- for between $200 and $250, but the trolytic input and output coupling capaci- pable of RIA A accuracy of better than product never materialized. This pretors are bypassed with film types. The car- 0.25dB across the audible spectrum. amp used a pair of A nalog Devices tridge loading caps are ceramic disc Figure 3 shows the measured response AD743 op amps for the RIA A preamp (Photo 2). of the review sample. The right channel and a power supply based on Linear The wall-wart power transformer is is quite close to the simulation, but the Technology LT317 and LT337 three-terrated at 15V DC/300mV. Under the load left shows an error of +0.5dB at 20Hz. minal adjustable regulators. A movingprovided by the PP-1, the unit outputs This is probably due to R7, the 130k re- coil input was also included, with the additional preampli fication accom21.5V DC. To keep the cost as low as pos- sistor, being slightly out of tolerance. sible, NAD has derived positive and negaMy simulations show that an R7 value plished with a built-in head amp based tive supplies from a single LM317 (KA317 of 135k will produce this error. Nonethe- on Analog Devices AD797. This preamp was several orders of in my sample) three-terminal adjustable less, the left channel is still well within regulator. A phantom supply ground, con- the manufacturers 0.5dB spec. This is magnitude better than the PP-1, and I nected to the chassis, is formed at the quite respectable RIA A performance for firmly believe that most music lovers would have been willing to pay the extra junction of R22 and R23, which is also such an inexpensive preamp. the junction of the power-supply capacitors. The input raw DC ground becomes the negative regulated supply rail. Note that the output of the LM317 is taken from the adjust pin. In this configuration the LM317 really functions as a current limiter rather than a regulator (see the National Sem iconductor LM117/317 data sheet for si m ilar topologies). I checked the supply rails with a scope and found that both had 6 to 7mV of peak-to-peak ripple. I also plugged the wall-wart into my Variac and found that there is no supply regulation using this schemethe DC rail voltages vary with line voltage. At a line voltage of 117V, the rails measure 9V DC. This is one of the sleaziest power supplies Ive seen in a very long FIGURE 2: PSpice simulation of the PP-1s RIAA response. The simulation shows that time. Even considering the cost of the the circuit is capable of accuracy within 0.25dB, 20Hz20kHz. PP-1, could not NAD have provided real

2 Audio Electronics 3/00

NAD PP-1 MEASURED RIAA RESPONSE

-0.5 LEFT -0.75 RIGHT

-500 1k 5k 10k 20k

FREQUENCY IN Hz

FIGURE 3: Measured RIAA response of the PP-1. The review sample easily meets the manufacturers RIAA spec of 0.5dB, 20Hz20kHz. price. NADs decision not to manufacture this preamp was most unfortunate. its own, with typical NAD warmth and dimensionality to the sound and excellent rejection of induced noise and RF interferencea common problem with inexpensive add-on phono preamps. There are several factual inaccuracies in Mr. Galos review. First of all, the schematic is not included with every PP-1, as this is NAD copyright information that we consider confidential intellectual property. Secondly, the OPAMP KA5532 and regulator KA317 are not Far-East equivalents of something better; rather, they are specifically chosen for their excellent performance. Both semiconductors are manufactured by Samsung. As noted in the review, the resistors are all 1% metal film types, and the capacitors are 5% film types, again specifically chosen for sound quality and accurate RIAA performance. It should also be noted that NAD uses the IHFspecified cartridge load, not a 1k resistor, when designing and measuring phono circuits. This complex load gives results that are much closer to what listeners can expect in the real world outside the lab. We take strong exception to what is referred to as sleazy design of the power supply. This design is entirely appropriate to the overall concept of the product, and gives very good results. Mr. Galo has not analyzed the power supply schematic correctly. We are using current regulation for the power supply of the PP-1, not voltage regulation. We do not take the output from the adjust pin of the low-noise regulator; rather, this is the feedback input that regulates the current output. This circuit was chosen to accommodate different types and voltages of outboard power supplies (wall warts?) required by the many different countries in which the PP-1 is sold. This
circuit also has better ripple rejection and lower noise than a voltage regulator would have in this application. The zener diodes may seem redundant, but since many different outboard supplies are possible, they are a very important failsafe feature. By employing an outboard unregulated power supply and using internal current regulation, we were able to keep the chassis size small and, yes, the cost low. It is true that the PP-1 cannot be compared to the NAD prototype that Mr. Galo sampled several years ago. That phono section (in a much evolved form) is in production today as the S100/RIAA and retails for $299. It is available only as a plug-in module for the NAD S100 line stage preamp ($1,199), which supplies high regulated DC from its own rather complex power supply. The S100/RIAA accommodates both MC and MM cartridges and also includes provision for adjusting cartridge loading. It is too bad that Mr. Galo did not actually compare the PP-1 with the built-in phono sections of todays typical Far East receivers. Far from being an afterthought or a bullet point on a spec sheet, the PP-1 is a very musically satisfying product that requires no apology for its technical specification. s Greg Stidsen, Director of Sales and Marketing NAD Electronics of America

Summary

The NAD PP-1 is an unpretentious product that allows those firmly committed to digital audio to continue playing their LPs. As such, it is an ideal companion to the NAD 118 Digital Preamplifier, and will mate well with virtually any linestage preamp with a spare input. My main criticism of the PP-1, considering the price, is the poor power supply even at this price NAD should have used an acceptable regulator. Those who still own large collections of excellent-sounding LPs (myself included) will prefer something considerably better. But, if you are a casual LP listener, the PP-1 will fit the bill. For what it costs, and where its likely to be used, the PP-1 is a safe recommendation. Maufacuturers response: Thank you for the opportunity to comment on Gary Galos review of the NAD PP-1. While Mr. Galos measurements confirm the excellent performance of this modestly priced device, I am puzzled by the negative tone of the review. Our concept for the PP-1 was to offer very good phono performance (low noise, low distortion, and accurate RIAA tracking) to partner with our own low-cost integrated amps and receivers that are no longer supplied with a phono input, or as an upgrade to the many mass market receivers, whose built-in phono stages cannot match the musical performance of the PP-1. When compared to other similar products, we believe the PP-1 more than holds

DEVIATION IN dB

References
1. CircuitMaker is a superb schematic drawing program, with integrated SPICE, for the Windows 95/98 platform. A fully functional student version is available for free from the manufacturers web site, http://www.microcode.com/. The student version is limited to 50 parts per drawing, but is otherwise impressively loaded with features. A full-featured version and the companion PC board program cost $299 each ($549 if you buy them together). If you are looking for a Windows-based schematic program, a visit to this web site is a must. I have ordered the full package. 2. For the PSpice simulations, I used a modified version of a program written by Walt Jung for Linear Technology back in 1989. This program was supplied by LT on a floppy disk to demonstrate the performance of a number of their op amps. Walts RIAA program simulates the accuracy of a phono preamp he designed that is still featured on the front page of the LT1115 data sheet. I modified the code to operate under the text-based PSpice program supplied with MicroSyms DesignLab V.8 Evaluation Release, and replaced the LT1028-based circuit with NADs. Design Lab V. 8 is available for free from the OrCAD web site, http://www.orcad.com/ products/pspice/eval_f.htm.

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INSTALLATION & OPERATION OF NAD PP 1
Please make sure all ancillary equipment is turned off, and that the NAD PP 1 is not yet connected to its dedicated Power Supply. Connect the leads from the turntable to the input sockets on the back of the NAD PP 1. Make sure you connect the Right channel to the Right input; the Left channel to the Left input; Normally, a Red connector denotes the Right Channel; White or Black denotes the Left channel. Connect a suitable lead from the NAD PP 1 to the amplifier or receiver. Always use a so-called 'Line-Lever input, such as CD, AIDE, Tuner or Tape. Never connect the lead from the NAD PP 1 to an input marked Phono or turntable. Again, make sure to connect the Red plug to the Right channel, and the White plug to the Left channel of the amplifier or receiver. If the lead from your turntable is equipped with a separate earth lead, connect this directly to a ground connection on the amplifier or receiver. Usually, the metal back panel of an amplifier provides grounding by means of a small terminal. If this is not available, you can connect the earth cable directly to the back panel, by means of placing the wire under a screw in direct contact with the metal of the back panel; for instance, the screw holding the lop cover to the back panel. Almost all receivers provide a ground terminal with the antenna input; this terminal is usually marked 'GND' or with the symbol ---|---. If an antenna is connected, you can simply add the wire to this terminal. Connect the dedicated Plug-in Power Supply to the NAD PP 1 (marked 15V). Insert the Plug-in Power Supply to a live mains socket; the green LED on the NAD PP 1's front panel will light up. Installation is now complete. As the power consumption of the NAD PP-I is negligible, it can always be left switched on. It is recommended however that you disconnect the Plug-in Power supply from the mains if you are not going to use the NAD PP 1 for a prolonged period of time (such as a holiday). To play a record: Ensure that the volume on the amplifier or receiver is set to a low level. Select the input on the amplifier or receiver to which the NAD PP 1 is connected, use amplifier or receiver and turntable as normal, set to desired volume level. Troubleshooting: Always turn down the volume to a low level or turn off all equipment before checking.

Problem

No sound
(LED is not lit) Power Supply not connected to either NAD PP 1 or mains socket (LED is lit) Wrong input on amplifier / receiver selected Plugs from turntable and / or lead from PP 1 to amplifier / receiver sockets not property fitted Plug in dedicated Power Supply

Solution

Select input to which NAD PP 1 is connected Check all connections (make sure to turn off all equipment beforehand)
Sound in one channel only
Plugs from turntable and / or lead from PP 1 to amplifier / receiver sockets not properly fitted No connection from turntable to ground Earth loop present Interference from nearby equipment
Check all connections (make sure to turn off all equipment beforehand)

Hum or Buzz noise

If present, connect earth lead from turntable directly to amplifier / receiver If present, disconnect turntable's earth lead from amplifier / receiver Move NAD PP-I and cables further away from other equipment

SPECIFICATIONS

Input impedance (R and C) Input sensitivity (ref. 200mV output) Signal to noise (A weighted, with cartridge connected) (Unweighted, with cartridge connected) Input overload (20Hz/1kHz/20kHz) Rated distortion (THD 20Hz - 20kHz) RIAA response accuracy Dimensions excl. Power supply (W x H x D) 47 k + 220pF 2. 5mV 78dB 72dB 55/63/580mV 0. 04% +/-0.5dB 135 x 35 x 70 mm

NAD ELECTRONICS LTD

DESIGNED AND ENGINEERED IN LONDON. ENGLAND MODEL: PP 1 PHONO PRE-AMPLIFIER _______________ CUSTOM MANUFACTURED TO NAD SPECIFICATIONS
NOTE: NAD reserves the right to change specifications or design at any time without notice. All specifications are those in effect at time of printing. Packaging NAD Electronics Limited 1997