Tandberg TPA-3016A and TCA-3018A Preamplifier and Power amplifier Review

Tandberg’s power amplifier, the 3016A, is a no-holds-barred design aimed at the demanding (and affluent) audiophile. Its unconventional circuitry and choice of internal components strongly suggest a perfectionist attitude on the part of its designers.

The 3016A is a large, heavy, and powerful amplifier. It is rated to deliver 220 watts per channel into 8-ohm loads from 20 to 20,000 Hz with no more than 0.05 percent total harmonic or intermodulation distortion. It is also rated for 400 watts per channel into 4 ohms. Its rated A-weighted noise level is — 94 dB referred to 1 watt (into 8 ohms), and its rated frequency response is + 0, -0.1 dB from 20 to 20,000 Hz and down only 0.2 dB at 1.5 MHz.

The special qualities of the Tandberg 3016A are not visible externally. It consists of two entirely separate mono amplifiers, with separate power supplies and transformers, that share only the line cord, power switch, and cooling fan. Each output stage employs eight MOSFET transistors, without any current-protection or limiting circuits. According to Tandberg, the dualmono amplifier can deliver up to 100 amperes into a 0.5-ohm load during a 3.5-millisecond burst, and it carries a pulse-power rating of 2,500 watts into 0.5 ohm. The massive current capacity of the amplifier is supported by a total of 120,000 microfarads of power-sup-ply filter capacitance.

The output transistors are mounted on heavy, finned heat sinks along the sides of the amplifier. Sensors on the heat sinks gradually turn on the electronically controlled fan as the temperature begins to exceed 70°C (it does not come on at all in normal operation). The capacitors in the signal path use polypropylene as a dielectric material, which is thought by many to give better sound than other dielectric capacitor materials. Selected metal-film resistors are used exclusively, as are discrete transistors— there are no integrated circuits. Other construction features not often found in home amplifiers include heavy circuit boards with copper ground-plane layers on both sides, to minimize common ground paths and the resulting noise and distortion, and gold-plated input and output sockets.

Probably the most unusual circuit feature of the 3016A is its “feedforward” design. Most amplifiers use negative feedback to reduce their inherent distortion and noise and to lower their output impedance for better speaker damping. In recent years there has been much controversy concerning the alleged undesirable effects of negative feedback, especially in the large amounts commonly used in high-fidelity amplifiers. Negative feedback has been claimed to produce various forms of transient intermodulation distortion, although the audible significance of such distortion in real-world home music reproduction is open to question. In any event, many amplifier designers now use much less negative feedback and resort to other means of reducing conventional distortions to acceptable levels.

One such approach is Tandberg’s “feedforward” design. Instead of returning a portion of the output signal to the input stage, comparing it with the input signal, and amplifying the difference between them (the distortion) to cancel out most of the output distortion—the negative-feedback approach—it is possible to use a low-power, highly linear (Class A) amplifier to drive the speaker load at low power levels, gradually augmenting its output as needed for higher signal levels with the higher current available from Class B output transistors. Such a feedforward amplifier is inherently free of crossover distortion (a low-level phenomenon common to Class B amplifiers), so that there is virtually no need for critical bias stabilization and matching of the output transistors. The linearity and gain of the amplifier are essentially determined by a bridge of passive components, effectively removing output-transistor nonlinearity from its transfer function.

The Tandberg 3016A uses no overall negative feedback in its signal path. The amplifier is direct-coupled throughout except for a blocking capacitor at the input (which can be bypassed if your preamplifier has no d.c. component in its output), and its d.c. stability is maintained by a thermal feedback system that monitors the transistor temperatures and corrects the operating conditions of the affected stages to maintain a zero average d.c. output voltage. In normal feedback amplifiers, this is sometimes maintained by a d.c. feedback loop, but Tandberg’s engineers apparently felt that the longer time constant of the thermal loop accomplishes the desired result with no possibility of audible side effects. Although this circuit can be viewed as a form of negative feedback (at low infrasonic frequencies), it is not in the signal path and thus does not violate Tandberg’s principle of avoiding overall negative feedback in the 3016 A.

The only front-panel features of the Tandberg 3016A are a large, rocker-type power switch with a small red LED pilot light and four LED’s on the upper section of the panel that light to show peak-clipping and the operation of the thermal protection system (marked term overload), presumably the activation of the rear-mounted fan. Separate warning lights are provided for each channel.

The Tandberg 3018A control amplifier (preamplifier) is a companion to the 3016A power amplifier, which it matches in styling and all black finish. The 3018A shares many design features with its companion, including the exclusive use of polypropylene capacitors, metal-film resistors, and discrete active devices (transistors instead of integrated circuits).

Like the power amplifier, the control amplifier uses no negative feedback, depending on close component tolerances and a special circuit topology to maintain the intended performance. The same design approach is carried over into its RIAA phono equalization, which is accomplished by means of passive components used with separate “blocks” of gain instead of the common practice of building the equalization network into a negative-feed-back loop of the phono preamplifier. A toroidal power transformer is used because of its very low external magnetic field.

The 3018A is a “minimalist” control amplifier, with no tone controls or similar features. Its basic front-panel operating controls consist of a single large volume knob, with a concentric balance lever, and two small knob-operated switches that independently select the program source to be heard and the source being supplied to the two sets of tape-recording output jacks on the rear apron. Also on the front panel are a pushbutton power switch with LED indicator, a headphone jack with a small volume knob (the headphone output is completely independent of the main volume-control setting), and a subsonic filter button with indicator light. Although the fact is not specifically mentioned in the instruction manual, the filter operates only with phono sources.

The program inputs are identified as aux, DD (for digital disc), tape 1, tape 2, tuner, and phono. As in the 3016A, the signal input and output jacks in the rear of the unit are gold-plated. There are separate inputs for moving-magnet (MM) and moving coil (MC) cartridges, selected by a toggle switch between them. A second three-position toggle switch near the MM input selects the capacitance, shunting the standard 47,000-ohm input resistance in parallel with 150, 330, or the normal “0” picofarads to suit the requirements of the cartridge. In addition, the d.c. blocking capacitor at the output can be short-circuited if desired when the 3018A is used with a power amplifier, such as the Tandberg 3016A, whose input already has a series capacitor.

The technical specifications of the Tandberg 3018A are extremely detailed and follow the requirements of the IHF A-202 standard (now incorporated in EIA RS-490). The rated frequency response is unusually flat: +0, —0.1 dB from 1.6 to 250,000 Hz through the high-level inputs and ±0.2 dB from 20 to 20,000 Hz through the phono inputs. The exceptionally low noise and distortion ratings are equally noteworthy, as is the input-overload rating of greater than 20 volts for high-level inputs and 290 millivolts for the MM phono input.

The Tandberg 3016A power amplifier measures 17-1/8 inches wide, 8-3/4 inches high, and 13-3/4 inches deep, and it weighs 62 pounds. The 3018A control amplifier’s dimensions are 17-1/8 x 3-1/2 x 13-3/4 inches, and it weighs 12-1/2 pounds. Optional black Lucite or rosewood end pieces, or rack-mounting adaptors, are available for both units. Prices: TPA-3016A, $3,295; TCA-3018A, $1,695.

Lab Tests

The Tandberg 3016A is a hot amplifier in several ways. Not only did the standard one-hour preconditioning make its top surface uncomfortable to the touch, but we also found that it became warmer than most amplifiers we have used even when idling or during normal system operation. On the other hand, at no time were we able to make the cooling fan come on, indicating that the critical temperatures within the unit never reached 70°C. The practical implications of this are all positive: unlike most fan-cooled amplifiers, the 3016A will not intrude on your listening pleasure with an annoyingly loud fan.

In its performance, the 3016 A was one of the most nearly ideal amplifiers we have seen. Specifically, its distortion level, though always negligible, decreased as the power was reduced. Many amplifers have more distortion at a few watts output than at full power due to crossover effects, which are absent from the 3016A because of its feedforward design.

With loads from 2 to 8 ohms, the 3016A’s 1,000-Hz distortion was typically 0.002 to 0.005 percent under 100 watts output, reaching about 0.02 percent at rated power. At 22 watts, the distortion was less than 0.002 percent from 20 to 500 Hz, rising smoothly to 0.014 percent at 20,000 Hz. At the rated 220 watts, it was a constant 0.018 percent from 20 to 7,000 Hz and reached 0.027 percent at 20,000 Hz. The slew factor was 13.

An input of 0.1 volt produced a reference 1-watt output, and the A-weighted noise was 93 dB below that level. The amplifier’s output clipped at 300 watts per channel into 8 ohms, 485 watts into 4 ohms, and 665 watts into 2 ohms. Because each channel has its own power supply, these readings apply equally to single-channel and dual-channel operation. The clipping headroom for 8- and 4-ohm operation was 1.35 and 0.84 dB, respectively. Our dynamic power measurements showed the clipping level to be 324 watts into 8 ohms, 578 watts into 4 ohms, and an impressive 990 watts into 2 ohms. The respective 8- and 4-ohm dynamic headroom measurements were 1.68 and 1.59 dB. We were unable to verify the manufacturer’s claim of a 90- to 100-ampere short-term current output into a 0.5-ohm load. The lowest load impedance we could provide for this test was 1 ohm, into which the amplifier delivered about 35 amperes RMS (1,250 watts) during short tone bursts.

At no time in our use or testing of the amplifier were we able to light up the clipping indicators—even hard clipping into 2 ohms did not turn them on. Tandberg informs us that at the time our test unit (a very early production sample) was manufactured, there had not been a final decision made at the factory concerning the proper setting of the clipping-level adjustment. In current production models, this will be set so that a small amount of waveform clipping will activate the indicators.

In testing the 3018A preamplifier, our measurements were made with it driving an EIA-standard load of 10,000 ohms in parallel with a 1,000-picofarad capacitance. The output-voltage waveform clipped at 12.5 to 13 volts from 20 to 20,000 Hz. The frequency response through a high-level input was perfectly flat from 10 to 100,000 Hz, falling to —0.5 dB at 5 Hz and —3 dB at 450 kHz. (Removing the EIA load extended the high-frequency response to 2.82 MHz at the — 3-dB point.) The input sensitivity, for a 0.5-volt output, was 78 millivolts (mV) through a high-level input, 1.1 mV through the MM phono input, and 0.066 mV through the MC phono input. The respective A-weighted noise levels, referred to 0.5 volt, measured — 90, — 80, and -76.5 dB.

The MM phono input overloaded at inputs between 210 and 277 mV, depending on frequency. We were unable to measure the high-level input-overload limit (rated at 20 volts), but up to the 10-volt maximum output of our signal source there were no signs of clipping in the output waveform. The MM phono-input impedance was 47,000 ohms in parallel with 140 pF, and the capacitance added by the rear-apron switch was approximately as rated. The output distortion (THD + N) was slightly larger at 0.1 volt output than at higher levels, reflecting the greater contribution to the measurement of the small amount of noise present in the amplifier output. At 1,000 Hz, the distortion was 0.027 percent at 0.1 volt, 0.0062 percent at 1 volt, 0.016 percent at 3 volts, and 0.0245 percent at 5 volts. It consisted almost entirely of second harmonics and random noise, and the levels were not significantly different at 20 and 20,000 Hz.

The 1,000-Hz headphone output at the clipping point varied from 17.5 volts into an open circuit to 9.4 volts into 200 ohms and 0.73 volt into 8 ohms. The maximum power (440 milliwatts) was developed with a 200-ohm load, which is typical of many of the better stereo headphones. The 3018A’s headphone volume should be more than sufficient with headphones of any impedance.

The RIAA phono equalization was extraordinarily accurate, and we had to plot it on a ten-times-expanded scale TQ measure its deviation from the ideal characteristic. It was flat within 0.15 dB overall from 20 to 20,000 Hz, a reading comparable to the accuracy of our measurement system and certainly the best we have yet seen from a preamplifier. We extended our measurement of the phono response to establish its limits: it had dropped a mere 0.2 dB at 5 Hz and began to roll off slightly above 30,000 Hz. The subsonic filter reduced the response by less than 1 dB at 50 Hz, 2.5 at 20 Hz, and about 12 dB at 5 Hz, with a 12-dB-per-octave slope below 5 Hz.

Comments

The combination of the Tandberg 3016A and 3018A was as impressive to listen to as it was to measure. We certainly could not fault the sound of the two units with speakers and sources of comparable quality. We have never heard better sound in our own listening room. We were also impressed with the output level from the 3018A’s headphone jack, which would have been consistent with driving phones from a power amplifier (this is not too surprising in view of the healthy fraction of a watt delivered by the separate headphone amplifier).

Our only “lukewarm” reaction to these superb components concerned their installation requirements. They are so closely matched in appearance and size that stacking them seems to be a logical procedure, but there is a catch. Unlike many preamplifiers that run stone cold, the 3018A gets hotter than many power amplifiers or integrated amplifiers. And the 3016A also runs surprisingly warm to the touch. Neither poses any problem in itself, but when we stacked the two (in the open, though against the manufacturer’s recommendations), they became distinctly hot in a short period of normal (low-level) operation. While the temperature rise might not cause any problems, heat is the enemy of all electronic circuits, so it would be advisable to find some well-ventilated place where the power amplifier can be located by itself.

Tandberg has taken an unconventional approach to amplifier design in these two products, which are clearly aimed at the high-end enthusiast. By any objective criteria, both these components are outstanding performers. Tandberg’s engineers have demonstrated decisively that an amplifier can meet or surpass the most critical performance requirements without using negative-feed-back loops. The question of whether the 3016A and 3018A sound “better” than other amplifiers is one that each listener must answer for himself.

Although the 3016A’s ratings are not significantly different from those of some other very fine amplifiers, its actual measured performance far exceeded Tandberg’s claims. It was totally silent, both mechanically (acoustically) and electrically, and it is hard to imagine any home listening situation that would even come close to probing its limits or causing its protective fan to come on.

The 3016A has the ability to deliver many hundreds of watts into almost any conceivable speaker load. Even the Apogee speaker, with its 1-ohm impedance, is unlikely to make the 3016A breathe hard, let alone collapse as many other fine amplifiers do. Along with this output capability comes a noise level 93 dB below 1 watt, or 116 dB below rated power. These numbers define a dynamic range exceeding that of a CD by a comfortable margin. From this we can infer that the 3016A is unlikely to be found wanting when handling any program source and driving any speaker in any home.

We find it reassuring to know that products like the Tandberg TPA-3016A and TCA-3018A exist, and our experience with them was totally enjoyable. Who could ask for more?

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