Manufacturer's Specifications
Power Output: 20 to 20,000 Hz; 75 + 75 watts (8 ohms); 115 watts (4 ohms). Distortion: Less than 0.1% THD and IM. IHF Power Bandwidth: 5 to 40,000 Hz.
Frequency Response: 15 to 40,000 Hz +0,-1 dB. Damping Factor: 50. Input Levels: Phono, 2.5 mV; Mic, 2.5 mV; High Levels, 100 mV. Impedances: Phono 1, 50 k; Phono 2, 30 k, 50 k, and 100 k. Hum & Noise: Phono, better than 75 dB; Mic, 65 dB; Others, 85 dB.
Dimensions: 19 3/4 in. W x 13 3/4 in. D x 5 1/2 in. H.
Price: $519.95.
There are several good 100 plus 100 watt integrated amplifiers around, but offhand I cannot think of any with all the features of the Sansui AU-9500. Consider this: There are not only tone controls for bass, mid, and treble, but each one has a choice of three turnover frequencies! Then there are switched two-position filters for both high and low frequencies, a loudness control, two phono inputs, microphone jacks, and provision for tape dubbing from one machine to another. There is a mute switch, another for the connection of a quadraphonic decoder, and yet another for a Dolby unit. Add to this a choice of three phono load resistors, preset input controls for AUX inputs, provision for using the pre amplifier and amplifier separately, and facilities for three speaker systems, and you have some idea how versatile this super amplifier really is.
Fig. 1-- 1-Back panel
Fig. 2-View of the chassis.
The front panel is black with satin trim and knobs to match-11 of them-plus eight lever switches. The first control on the left is the speaker switch which is combined with the ON/OFF switch. One can choose combinations of three speaker systems--A, B, or C, then A plus B or A plus C.
Under this knob are the two filter switches and two head phone jacks. Why two of the latter? Well, one mutes the speakers, one doesn't-I told you the 9500 is versatile! Next comes a group of six controls, the upper three being the tone controls and the lower three the turnover switches more about those .later. To the right is a large knob for volume, and underneath is the muting switch, followed by the balance control, then switches for loudness, four-channel adaptor, Dolby unit, tape monitor, and tape-to-tape. At the extreme upper right are the mode switch and input selector.
At the rear is a formidable array of input sockets including microphone jacks, a DIN socket and preamp-amplifier link connectors. There are also preset level controls for AUX already mentioned, and two more for tape recorders. The speaker connectors are the spring-loaded clip type (much easier to use than screw terminals) and there are two switched a.c. power outlets and two unswitched. Five fuses are also to be found at the rear-one in the a.c. power supply and four in the d.c. circuits. (See Fig. 1.) The massive power transformer can be seen in Fig. 2 and next to it are the four large (4700 uF) capacitors. The output transistors are mounted in their heat sinks placed at the sides instead of the rear. Workmanship appears to be excellent and all the components are of high quality. Incidentally, the 9500 turns the scales at 52 lbs.-it's no light weight so make sure that shelf will take the strain!
Circuit Details
The input stage is a PNP-NPN-PNP configuration with the usual equalization feedback loops for phono and micro phone. High level inputs are taken to the next stage-an FET which is coupled to an amplifier stage and an emitter-follower. This feeds a two-transistor tone control stage which in turn is coupled to another two-transistor stage for the filter circuits. Output from the preamplifier is connected to a parallel transistor which acts as a "turn-on" surge limiter.
The first stage of the main amplifier is a differential pair which is connected via pre-driver stages to Darlington pairs and the four-transistor complementary output stage. Two transistors are used for a standard current-sensing limiter circuit and two more are connected to a relay which switches off the speakers in the event of a short circuit or overload. The stabilized power supply for the preamp and driver stages uses no less than four transistors and the output stages are fed from separate bridge rectifiers. D.c. voltage is 49 plus 49. The grand total of transistors employed in the 9500 is 58--plus 42 diodes of one kind or another.
Measurements
Figure 3 shows the power output and distortion characteristics, using 4 ohm loads, both channels driven. Output at 0.1 percent THD was 120 watts and with 8 ohm loads, the figure was 87 watts. Power bandwidth extended from below 10 Hz to over 50 kHz (3 dB points) and the distortion versus frequency curves can be seen in Fig. 4. Overall frequency response was -5 dB at 100 kHz and 5 Hz, with-1 dB points at 10 Hz and 40 kHz. As might be expected, square wave performance was very good indeed with little degradation at both high and low frequencies. Figure 5 shows the square wave resolution at 100 Hz, 1 kHz and 10 kHz. The tone controls-all three of them-employ step switches giving 5 plus and 5 minus positions and the turnover switches each give a choice of three frequencies. Figure 6 shows the characteristics with the turnover set to 150 for bass and 6 kHz for treble, while Fig. 7 shows the results with a bass turn over of 600. Hz and treble of 2 kHz. The other positions (not shown) offer turnovers of 300 Hz and 2.5 kHz. The midrange control has a choice of three turnover frequencies--750 Hz, 1.5 kHz and 3 kHz, as shown in Figs. 8, 9, and 10.
It will be seen that the maximum lift and cut are each about 5 dB, or 10 dB total, which is more than adequate for most applications.
Fig. 3--Power output and distortion, both channels driven, 4-ohm loads.
Fig. 4--Distortion versus frequency.
Fig. 5--Square wave resolution. A is 100 Hz, B is 1 kHz, and C is 10 kHz.
Fig. 6--Tone control characteristics, 150 Hz bass turn over 6 kHz treble
turnover.
Fig. 7--Tone control characteristics, 600 Hz bass turn over and 2 kHz treble turnover.
Fig. 8--Midrange control, 750 Hz turnover.
Fig. 9--Midrange control, 1.5 kHz turnover.
Fig. 10--Midrange control, 3 kHz turnover
Fig. 11--High and low pass filters.
Fig. 12--Loudness control characteristics.
Fig. 13--Showing symmetrical clipping. Power is 145 watts.
Fig. 14--1 kHz sine wave at 10 milliwatts
Fig. 15--Hum and noise (phono) 70 dB
Now for the filter controls: Here we have a choice of two positions each-50 and 100 for the low frequency and 1.2 kHz and 6 kHz for the high frequency. All four are shown in Fig. 11. The loudness control characteristics at-10,-20, and-30 dB are given in Fig. 12.
At overload point, the clipping was symmetrical as shown in Fig. 13, which represents a power of 145 watts into 4 ohms. There was no sign of low level crossover distortion, and Fig. 14 shows a sine wave signal of 10 milliwatts. Hum and noise came out at a creditable 70 dB for phono (see Fig. 15) and 80 dB for high level inputs. High level sensitivity was 110 mV and phono, 2.6 mV. Dynamic range on the latter input was one of the highest we have found overload point was not reached until the input signal was increased to a whopping 280 mV! In other words, the phono input stage can handle more than four times the signal it is ever likely to get. (Many of the early transistor amplifiers could only handle signals of about 30 to 50 mV, which meant that there was some peak clipping and distortion when used with high or even moderate output phono cartridges.)
Listening Tests
Most of the listening tests were carried out with the lab standard speaker systems (dynamic-electrostatic combi nation) and AR LSTs. The program sources included records played via a Shure V-15 Mk III and a Thorens TD-125AB, tapes from an AKAI 4000DS open-reel recorder, and FM using a Dyna AF-6-now being tested. A cassette unit (Wollensak 4780) was also used for a period, mainly to transfer some tapes.
Using the aforesaid speaker systems, there was no particular need to switch in the tone controls, except for two or three recent recordings which I found to be "bass heavy" and here the 150 Hz turnover was just right to give the necessary correction-at least to my ears. I did connect up a pair of Hegemann systems which sounded a little distant due to a slight dip in the upper midrange, so I set the mid range control at 3 kHz with the lift control at position three and the difference in sound had to be heard to be believed! I found the 12 kHz filter position useful for dealing with some distortion present on some FM transmissions and, the 6 kHz filter had its uses too. The ordinary tone control just cannot reduce tape hiss and other high frequency distortion without removing a good deal of the music in the process! That 150 Hz bass turnover would be effective for equalizing the response of small bookshelf speaker systems without producing that "chesty" speech coloration caused by tone controls operating from the 1 kHz region. You might ask, will anyone use a small bookshelf system with such a luxury amplifier as the 9500? The answer is yes, if space is restricted, and in any case, even large speaker systems might be happier with a little bass lift on occasion. The only effective way of doing this is with an equalizer or a tone control system like the 9500's. With such an array of tone controls and filters, all kinds of things are possible-correction for program deficiencies, equalization for old tapes and records, the generation of special effects with electronic musical instruments and so on. The tape enthusiast will find the other features like tape-to-tape dubbing switch useful too, so will those who want to use a Dolby unit and/or a quadraphonic decoder. The 9500 is not only recommended for its versatility--it has other virtues. Like the almost immeasurable distortion, clean power output up to 100 watts and more, plus excellent signal-to-noise and wide bandwidth.
What else could you want in an amplifier? If the answer is more power, then you would have to buy separate units (a preamplifier and a power amplifier). But for many people, 100 plus 100 watts (times two for four-channel) is more than adequate--unless the loudspeakers are very inefficient or the listening room is exceptionally large.
--George W. Tillett
(Audio magazine, Jun. 1974)
Also see:
Sansui AU-D11 Integrated Amplifier (Equip. Profile, Feb. 1982)
Sansui Model SR-838 Direct-Drive Turntable (Feb. 1979)
Sansui PC-X1 PCM Digital Processor (Jan. 1984)
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