NAD-PP1-riaa-sch 电路图 维修手册.pdf

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1、Phono preamplifiers are becoming less and less common in consumer audio equipment. Many preamps, integrated amps, and receivers are now made with- out a phono section, since most buyers wont use them, and manufacturers wish to keep costs down. In home-theater equipment, phono preamps are practi- cal

2、ly nonexistent. NAD has continued this trend in some of their recent audio products, including the excellent NAD 118 Digital Preampli- fier, which I reviewed in AE 6/97. The NAD PP-1 Phono Preamplifier (Photo 1) has been designed as a cost-effective add- on for products without phono circuitry, such

3、 as the 118. I doubt that any audio- phile 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 pre- tense at being a world-beater high-end p

4、hono 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 magnet- ic cartridgesthe PP-1 will not accom- modate low-out

5、put moving coils. If you are still convinced that LPs are inher- ently better than CDs, the PP-1 wont be a good choice. Like a lot of elec- tronics these days, the PP-1 is “made in China.” The PP-1 is utterly simple in function. There are no controlsnot even a power switch. The PP-1 is intended eith

6、er to be left on all the time or plugged into a switched outlet on existing equipment. An outboard “wall-wart” transformer with a built-in rectifier supplies raw DC to the PP-1 with a standard DC power connector. The chassis-mount input RCA connectors are what I call P.T. Barnum typethe shield is go

7、ld-plated, but the center contact (invisible to the con- sumer) is tin-plated. The output connec- tions consist of molded, gold-plated RCA plugs on a short, hard-wired cable. Circuit Details A schematic for the PP-1 is included with every unit (Fig. 1). I re-drew it using the CircuitMaker1Student Ve

8、rsion, since the supplied copy was not clean enough for publication. The design is ex- tremely simple. An NE5532 dual op amp is the active device, half used for each channel (my sample was supplied with a KA5532, PRODUCTREVIEW NAD PP-1 Phono Preamplifier Reviewed by Gary Galo NAD PP-1 Phono Preampli

9、fier. NAD Electronics International, 633 Granite Court, Pickering, Ontario, Canada L1W 3K1, 905-831-0799 (worldwide), 800-263-4641 (North America), nadNAD, www. . MANUFACTURERS SPECIFICATIONS Input impedance: 47k/220pF Input sensitivity: 2.5mV for 200mV output Signal-to-noise ratio (A-weighted, with

10、 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: 135 35 70mm / _ _ / CHASSIS CHASSIS -8.3V +8.3v D3 GREEN LED + C24 100uf/25V + C23 10

11、0uF/25V C26 100n C25 100n D2 17V D1 17V IN COM OUT U2 LM317 P1 LEFT OUT +20.4 VDC J3 POWER IN C21 100n J1A LEFT IN C1 220p C3 100n +C5 10uF/25V C7 220pF C13 6n8 C11 24n + C9 220uF/10V C19 1n5 C15 100n + C17 10uF/10v -8.3V +8.3V C28 100nF C27 100nF + U1A NE5532 R21 100R R24 2K2 R23 6K8 R22 6K8 R20 10

12、0R R19 62R R3 330k R5 56k R11 180R R7 130k R9 11k R15 22k R17 1k R13 82R FIGURE 1: Schematic of the PP-1. The power supply is essentially unregulated, since the LM317 is configured as a current limiter. PHOTO 1: The NAD PP-1 phono preamp. The output interconnect cable is hard-wired to the unit. Audi

13、o Electronics 3/001 RadioFans.CN 收音机爱 好者资料库 which is probably a Far-East equivalent). R7, R9, C11, and C13 form the RIAA feedback network, with R17 and C19 taming the ultrasonic peak that would otherwise occur. C9/R11 set the low fre- quency 3dB point at 4Hz. The 1kHz gain is set at 38dB. One percen

14、t metal-film resistors are used throughout, including the RIAA net- work, but the capacitors are film types, with no tolerance indication. The elec- trolytic input and output coupling capaci- tors are bypassed with film types. The car- tridge loading caps are ceramic disc (Photo 2). The wall-wart po

15、wer transformer is rated at 15V DC/300mV. Under the load provided by the PP-1, the unit outputs 21.5V DC. To keep the cost as low as pos- sible, NAD has derived positive and nega- tive supplies from a single LM317 (KA317 in my sample) three-terminal adjustable regulator. A phantom supply ground, con

16、- nected to the chassis, is formed at the junction of R22 and R23, which is also the junction of the power-supply capaci- tors. 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 config- uration the LM317 really

17、 functions as a current limiter rather than a regulator (see the National Semiconductor LM117/317 data sheet for similar 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 n

18、o 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 time. Even considering the cost of the PP-1, could not NAD have provided real supply regulation us

19、ing a pair of fixed, three-ter- minal 7808 and 7908 regulators? If it raised the cost a couple of dol- lars, it would still have been well worth the ex- pense. Im not sure why zener diodes D1 and D2 were included. Normally, these diodes would clamp the rails at 17V, should the regulator fail. But, s

20、ince the regu- lator isnt really a regu- lator, and each rail cant possibly go higher than half the raw DC voltage (or 10.75V), the zeners are totally unnec- essary (the 5532 op amp has an ab- solute maximum rating of 22V). Elimi- nating them would have freed up a few cents, which NAD could have put

21、 to- ward real supply regulators. Performance I ran a PSpice simulation of the PP-1s RIAA circuit (Fig. 2).2The circuit is ca- pable of RIAA accuracy of better than 0.25dB across the audible spectrum. Figure 3 shows the measured response of the review sample. The right channel is quite close to the

22、simulation, but the left shows an error of +0.5dB at 20Hz. This is probably due to R7, the 130k re- sistor, being slightly out of tolerance. My simulations show that an R7 value of 135k will produce this error. Nonethe- less, the left channel is still well within the manufacturers 0.5dB spec. This i

23、s quite respectable RIAA performance for such an inexpensive preamp. Total harmonic distortion measure- ments were also well under the manufac- turers spec of 0.04%, 20Hz20kHz. I measured 0.011% at 1kHz, 0.012% at 20Hz, and 0.012% at 20kHz in the left channel; the right channel was identical except

24、at 20kHz, which measured 0.013%. Noise was 80dB relative to an output of 2V; NAD specifies the un- weighted signal-to-noise ratio as 72dB, but they do not give the reference output for this measurement. In operation, the unit was subjectively silent. I think it would be rather silly to give a detail

25、ed sonic description of the PP-1, relative to some absolute sonic bench- mark. For $129 you cant expect high- end performance, and you dont get it. The PP-1 offers sound quality compara- ble to the phono sections of typical Far East receivers and integrated amps. The PP-1 doesnt do anything nasty to

26、 the music, and the casual LP collector will find it quite listenable. Six years ago Victor Campos, then Di- rector of Product Development and En- gineering at NAD, lent me a prototype of a phono preamp NAD hoped to sell for between $200 and $250, but the product never materialized. This pre- amp us

27、ed a pair of Analog Devices AD743 op amps for the RIAA preamp and a power supply based on Linear Technology LT317 and LT337 three-ter- minal adjustable regulators. A moving- coil input was also included, with the additional preamplification accom- plished with a built-in head amp based on Analog Dev

28、ices AD797. This preamp was several orders of magnitude better than the PP-1, and I firmly believe that most music lovers would have been willing to pay the extra 2Audio Electronics 3/00 PHOTO 2: Inside view of the PP-1. A 5532 dual op amp is the only active device in the RIAA phono preamp. The + an

29、d supply rails are derived from a single LM317 regulator. FIGURE 2: PSpice simulation of the PP-1s RIAA response. The simulation shows that the circuit is capable of accuracy within 0.25dB, 20Hz20kHz. RadioFans.CN 收音机爱 好者资料库 price. NADs decision not to manufac- ture this preamp was most unfortunate.

30、 Summary The NAD PP-1 is an unpretentious prod- uct 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 line- stage preamp with a spare input. My main criticism

31、 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 includ- ed) will prefer something considerably better. But, if you are a casual LP listener, the PP-1

32、 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 per- formance of this modestly priced d

33、evice, 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 re- ceivers that are no longer supplied with a phono input, or as an

34、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 its own, with typical NAD warmth and dimen- sionality to the sound and excellent rejection of induce

35、d noise and RF interferencea com- mon 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 copy- right information that we consider confidential intellectual property. Se

36、condly, the OPAMP KA5532 and regulator KA317 are not “Far-East equivalents” of something better; rather, they are specifically chosen for their excellent perfor- mance. Both semiconductors are manufactured by Samsung. As noted in the review, the resistors are all 1% metal film types, and the capacit

37、ors are 5% film types, again specifically chosen for sound quality and accurate RIAA performance. It should also be noted that NAD uses the IHF- specified cartridge load, not a 1k resistor, when designing and measuring phono circuits. This complex load gives results that are much closer to what list

38、eners 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 con- cept of the product, and gives very good results. Mr. Galo has not analyzed the power supply schematic c

39、orrectly. We are using current regu- lation 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 dif- ferent typ

40、es and voltages of outboard power supplies (wall warts?) required by the many dif- ferent 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 re- dundant, but since many

41、different outboard supplies are possible, they are a very important failsafe feature. By employing an outboard un- regulated power supply and using internal cur- rent regulation, we were able to keep the chas- sis size small and, yes, the cost low. It is true that the PP-1 cannot be compared to the

42、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 avail- able only as a plug-in module for the NAD S100 line stage preamp ($1,199), which supplies high regulated DC from its own rathe

43、r 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 sec- tions of todays typical Far East receivers. Far from being an afterthou

44、ght or a bullet point on a spec sheet, the PP-1 is a very musically satisfy- ing product that requires no apology for its technical specification. I Greg Stidsen, Director of Sales and Marketing NAD Electronics of America Audio Electronics 3/003 NAD PP- 1 MEASURED RIAA RESPONSE - 1 - 0.75 - 0.5 - 0.

45、25 0 0.25 0.5 0.75 1 20501005001k5k10k20k FREQUENCY IN Hz DEVIATION IN dB LEFTRIGHT References 1. CircuitMaker is a superb schematic drawing pro- gram, with integrated SPICE, for the Windows 95/98 platform. A fully functional student version is available for free from the manufacturers web site, The

46、 student version is limited to 50 parts per drawing, but is otherwise im- pressively loaded with features. A full-featured ver- sion and the companion PC board program cost $299 each ($549 if you buy them together). If you are looking for a Windows-based schematic pro- gram, a visit to this web site

47、 is a must. I have or- dered 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 sup- plied by LT on a floppy disk to demonstrate the per- formance of a number of their op amps. Walts RIAA p

48、rogram 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, products/pspice/eval_f.htm. FIGURE 3: Measured RIAA response of the PP-1. The review sample easily meets the manufacturers RIAA spec of 0.5dB, 20Hz20kHz. RadioFans.CN 收音机爱 好者资料库