THE PAT-5 is Dynaco's newest and finest stereo preamplifier. Matching the company's tuners in size and styling, the PAT-5 follows the Dynaco tradition of extracting the utmost in performance from relatively simple circuits. The PAT-5 has input switching for two magnetic phono cartridges, a tuner, two tape decks, and a SPARE high-level input. Small knobs are used for the balance and tone controls, with the latter mounted concentrically for independent adjustment of the two channels. The output of the power amplifier's speaker terminals is returned to terminals in the rear of the preamplifier, from which it is channeled by a front-panel switch to either, both, or neither of the two pairs of speaker systems that can be connected to speaker-output terminals on the PAT-5. The front-panel headphone jack is also driven from the power-amplifier outputs.
The power-switch lever is illuminated when raised to its ON position. This switch does not control the PAT-5 itself, for the preamplifier remains on as long as it is plugged into an a.c. line. The switch is designed solely for control ling the three switched a.c. convenience out lets in the rear of the PAT-5, and through them the power amplifier and other system components. There is also a single un switched a.c. outlet.
Eight pushbuttons are located along the lower portion of the front panel. One is the tape-monitor switch; when the MONITOR position has been selected, a second button connects either of the two tape decks to the tape-monitoring inputs (it is possible to dub from either deck to the other). Two other buttons, when released, place the preamplifier in its normal stereo mode. Pressing either one connects that channel to both outputs, and pressing both produces mono operation.
Low- and high-cut filters are activated by two buttons, and another connects the tone controls when pressed (normally the tone-control circuits are completely bypassed).
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In addition to the conventional rear-panel input and output jacks, the PAT-5 has terminals for the connection and switching of speakers.
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The last button is marked EPL (External Processor Loop), and it inserts into the signal path an external equalizer (such as is used with some speaker systems), a graphic equalizer, or some similar device for general signal processing. The PAT-5's rear panel is filled with connectors for the many inputs and out puts. There are two parallel sets of signal out puts to the power amplifier so that one can be used to drive a tape recorder with signals modified by the tone controls and filters.
Like all Dynaco products, the PAT-5 carries very complete performance specifications. Prominent among these is its very low distortion-less than 0.05 percent total harmonic distortion (THD) and intermodulation distortion (IM), and typically much less, at the rated output of 2 volts into loads of 10,000 ohms or higher. The maximum output is 7 volts into 10,000 ohms and 4.5 volts into 1,000 ohms. Hum and noise are rated at 70 dB below rated output through the phono in puts, and below 85 dB through the high-level inputs. The unit is free of phono overload for signal inputs of less than 100 millivolts (mV).
The PAT-5 uses surprisingly few components. Each phono-preamplifier channel has two transistors; two more are used in a unity-gain isolating stage, and two for the high-cut filter. The only other active device in the signal path is a single integrated circuit per channel that supplies a low-impedance output and includes the tone controls in one of its negative-feedback paths. A highly regulated power supply makes the preamplifier independent of momentary line-voltage fluctuations that can result when a high-power amplifier is used with inadequate a.c. house wiring.
The Dynaco PAT-5 is 13.5 inches wide, 4.25 inches high, and 11 3/4 inches deep; it weighs 11 pounds.
Price: $179 (kit), $289 (factory-wired).
Laboratory Measurements. We first tested a wired PAT-5. The output clipped at 9.7 volts into a high-impedance (100,000 ohms) load, and at 9.3 volts into 10,000 ohms (10,000 ohms is the lowest input impedance of any currently available power amplifier).
Distortion was not affected by load impedance. The total harmonic distortion (THD) at 1,000 Hz was below the noise level until the output reached 1 volt, where it measured 0.013 percent. From 2 volts to just below clipping at 8 volts the THD was between 0.004 and 0.007 percent. The IM distortion was 0.035 percent at 100 mV, 0.007 percent at 500 mV, and between 0.002 and 0.003 percent from Ito 8 volts output.
A 0.125-volt signal into the high-level in puts produced about a 1-volt output. The wide-band noise output was -76 dB, and with IEC "A" weighting it was below our minimum measurement capability of-80 dB referred to 1 volt. The phono sensitivity was 1.25 mV for a 1-volt output, with a wide-band noise level of -70 dB and a weighted noise below -80 dB. The phono circuits overloaded at 122 mV.
The frequency response with the tone controls set to their indicated flat positions was as flat as our test instruments, showing no variation from 20 to 20,000 Hz with the bypass button in or out. The bass control had a sliding inflection point, affecting frequencies be low 50 Hz with a slight rotation and gradually moving up to a maximum turnover frequency of about 300 Hz. The treble control curves showed a fixed hinge at about 2,000 Hz.
The low filter reduced the response by 3 dB at 50 Hz, with a 6-dB-per-octave slope below that frequency. The high filter, which uses active circuitry, was down 3 dB at 7,000 Hz and had an excellent 15-dB-per-octave slope. The extended RIAA phono equalization was with in ± 1 dB from 20 to 20,000 Hz and was essentially unaffected by cartridge inductance.
Some time after we completed this evaluation, a kit-built PAT-5 arrived, and we were able to compare its performance with that of the factory-wired unit. The two proved to be virtually identical. The THD for the kit was 0.004 percent at the rated 2-volt output and 0.007 percent at 8 volts; IM distortion was between 0.003 and 0.004 percent at rated output; and signal-to-noise ratio (unweighted) for a 1-volt output was 75 dB for the high level inputs, 70 dB for the phono inputs.
Comment. Although our kit builder was able to complete the kit during a single week end, he reports that the PAT-5 is appreciably more complex as a project than the earlier PAT-4. The construction manual is generally well done, although the sequence of steps makes a few tight corners inevitable. The instructions should be readily comprehended by those with no technical background whatever, so the PAT-5 kit can be recommended even to beginners who have the patience to work carefully and thoroughly.
A major reason for the "always on" design of the Dynaco PAT-5 is to eliminate the effects of turn-on transients, which could cause an annoying "thump" or even possibly dam age to speakers. It has the secondary benefits of keeping moisture from condensing on the PCBs and keeping the capacitors fully charged at all times, which should prolong their life. Current consumption of the PAT-5 under no-signal conditions is about 10 watts.
Dynaco's design makes possible several modifications to suit individual needs. The instruction manual, which is unusually complete and informative, lists the manufacturers' data on tone-arm wiring capacitance and optimum cartridge load capacitance for most popular arms and cartridges, and indicates how one can add the necessary capacitance to the PAT-5's negligible 10 picofarads (pF) on either or both sets of phono inputs. One or both of the phono inputs can also be modified to be a flat, high-gain microphone input, or the gain of either or both can be increased by 6 dB, with a simple resistor change, to handle the output of some very-low-output moving-coil cartridges. Another modification permits the EPL switch to be wired after the isolating stage so that long cables can used for connection to an equalizer without affecting the frequency response.
The power switch can also be wired to shut off the preamplifier as well as the switched outlets, although this is not recommended and the user is cautioned to turn the power amplifier on and off separately. The headphone circuit series resistors can be changed as required by headphone impedance and sensitivity and the amplifier power rating, and the usual mono (L + R) blending can be altered to a partial blend with 6-dB separation for a more appropriate spatial spread with head phones. Finally, the power supply can be wired for a 200- to 260-volt line instead of the usual 100 to 130 volts (either 50 or 60 Hz is satisfactory).
The measured performance of the Dynaco PAT-5 clearly ranks with that of the finest preamplifiers available, and its behavior in use confirms that judgment. Although it lacks some of the features of its more expensive counterparts, it does everything most people would expect from a preamplifier, and does it as well as modern electronic technology allows. To sum up, the Dynaco PAT-5 is a typical Dynaco product, offering unsurpassed performance and more than adequate operating flexibility at a bargain price even in factory-wired form. And in kit form, it could almost be considered a "steal."
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