Tandberg TCA 3018A Preamp and TPA 3026A Amp (Equip. Profile, Apr. 1987)

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Manufacturer's Specifications:

Preamplifier:

Frequency Response: Phono, RIAA ±0.2 dB; high level, 20 Hz to 20 kHz, + 0,-0.1 dB.

THD (20 Hz to 20 kHz): Phono, less than 0.009%; high level, less than 0.005%.

Input Sensitivity (For 0.5 V Out put): MM phono, 1 mV; MC phono, 60 µV; high level, 90 mV.

S/N (A-Weighted): MM phono, 78 dB; MC phono, 74 dB; high level, 90 dB.

Maximum Input Voltage: MM phono, 290 mV; MC phono, 14 mV; high level, 20 V.

Maximum Output Voltage: Main, 5 V at 0.006% THD, 10 V at clipping; tape, 7.5 V; headphone, 20 V unloaded.

Crosstalk: Less than-70 dB.

Separation (100 Hz to 10 kHz): Phono, greater than 53 dB; high level. greater than 58 dB.

Output Impedance: High level, 47 ohms; headphone, 150 ohms.

Minimum Headphone Load Impedance: 4 ohms.

Subsonic Filter:-3 dB at 15 Hz, 12 dB/octave.

Phase Shift, High-Level Inputs: ± 0.5°.

Power Requirements: 115/230 V a.c., ± 10%; 50/60 Hz; 55 watts.

Dimensions: 17 1/8 in. W x 31/2 in. H x 13 3/4 in. D (43.5 cm x 8.9 cm x 35 cm).

Weight: 12.5 lbs. (5.7 kg).

Price: $1,695.

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Power Amplifier:

Power Output: 150 watts per channel, 20 Hz to 20 kHz, into 8-ohm loads; 210 watts per channel, 20 Hz to 20 kHz, into 4-ohm loads.

Rated THD: 0.05%.

S/N (A-Weighted): 94 dB re: 1 watt output; 115 dB re: rated output.

Frequency Response: 20 Hz to 20 kHz, + 0,-0.1 dB; 0.07 Hz to 1.5 MHz, +0,-3.0 dB.

Input Sensitivity: 110 mV re: 1 watt output; 1.4 V re: rated output.

Output Impedance: Less than 0.01 ohm.

Wide-Band Damping Factor:

Greater than 800 SMPTE IM: Less than 0.05%.

IHF IM: Less than 0 05%.

Channel Separation: Greater than 80 dB.

Slew Rate: 240 V/µS.

Rise-Time: 0.4 S.

Pulse Power: 1,000 watts into 1-ohm load.

Power Requirements: 115/230 V a.c., ± 10%; 50/60 Hz; 110 to 830 watts.

Dimensions: 17 1/2 in. W x 8 11/16 in.

H x 13 3/4 in. D (43.5 cm x 22.1 cm x 35 cm).

Weight: 30.4 lbs. (13.8 kg).

Price: $1,695.

Company Address: Labriola Court, Armonk, N.Y. 10504.






If you have $3,000+ to spend on a separate preamplifier and power amplifier, I can't think of a better way for you to spend your money than to purchase these two Tandberg components. The Norway-based company that brought us one of the first truly high-quality open-reel tape decks for serious home recordists has come up with another couple of winners. Indeed, the TPA 3026A power amplifier is actually the "junior" member of the latest family of Tandberg amps.

Its big brother, the WA 3016A, produces a couple of dB more power, can deliver up to 50 amperes of continuous current per channel (100 amperes peak), and is able to drive 0.5-ohm loads! Considering that the more powerful 3016A has a price tag of $3,295 all by itself, I'd be perfectly content with the combination I chose to test for this report, thank you. After all, 150 watts of power-especially the kind of clean power delivered by the TPA 3026A, with its high current capacity (more than 45 amperes per channel) and its total elimination of overall negative feedback loops does not leave one feeling deprived. At that power level and with that current capacity, the need for long-duration dynamic headroom is not particularly important, which is why Tandberg chose to use a very tightly regulated power supply in this amplifier.

I'll get to the TCA 3018A preamplifier presently, but first let's have a look at the heart of this two-piece system, the TPA 3026A power amplifier.

Amplifier Circuitry and Control Layout

To understand why anyone would pay $1,695 for a conservatively rated 150-watt-per-channel power amplifier, you need to understand the design philosophy behind the product. You also need to understand the new demands made upon a power amplifier by today's dynamic program sources and by some of the more popular loudspeakers currently favored by knowledgeable listeners. To begin with, the TPA 3026A, while rated at 150 watts per channel into 8 ohms and at 210 watts per channel into 4 ohms, can in fact produce short-term peaks of nearly 1,000 watts into 1 ohm.

Speaker impedances, far from being constant, vary with frequency, and it is not uncommon for the impedance of some speakers to dip well below 4 ohms when reproducing specific tones or frequencies. When this happens, an amplifier must be able to supply high current levels if it is to deliver its rated power at such low impedances. The TPA 3026A has an impressive peak-current rating of 45 amperes per channel, and it is this enormous current capacity that gives the amplifier the ability to play highly dynamic music on speakers with difficult impedance characteristics.

This kind of performance is made possible by the use of a tightly regulated power supply that has a toroidal transformer and large current-storing capacitors, and by the use of MOS-FET output devices whose operating characteristics obviate the need for signal-degrading protection circuits.

In terms of circuit design, the amplifier employs no negative feedback anywhere in the system. When only the static performance of amplifiers was measured, feedback was thought of as a distortion-reducing cure-all. However, excessive negative feedback has more recently been considered to produce subtle but nevertheless audible forms of distortion when reproducing actual music signals. A proprietary circuit which Tandberg has dubbed a Thermic Servo Loop keeps speaker-damaging d.c. components from reaching the output terminals, without interfering with the actual audio signals.


Fig. 1-THD vs. power and frequency, TPA 3026A amplifier driving 8-ohm load. THD scale is logarithmic.


Fig. 2-Same as Fig. 1 but with 4-ohm load.


Fig. 3-Response to 20-kHz square wave.

TPA 3026A amplifier.


Fig. 4--Repeating pulse output into 2 ohms. TPA 3026A amplifier. Peak-to-peak amplitude of this 10-RS pulse was 80 V!

The TPA 3026A is attractively finished in matte black with optional rosewood end panels or 19-inch rack-mounting adaptors. Heavy metal structures at each end of the chassis serve as heat-sinks. There are no user controls on the front panel other than a large rocker-type power switch; this is flanked on either side by left- and right-channel peak clip ping indicators and thermal overload indicators. The clip ping indicators glow when output levels exceed the amplifier's rating. The overload indicators illuminate when safe operating temperatures have been exceeded; when this occurs, a thermal switch disconnects the speaker terminals from the output stages. When safe, normal operating temperatures are restored, the output is automatically reconnected to the speakers.

On the rear panel, input jacks are located at the extreme left and right, and polarized speaker terminals are at the center. A fuse-holder containing an 8-ampere fuse is accessible from the rear, as are a line voltage switch and a connector for the separately supplied power cord.

Preamplifier Circuitry and Control Layout

Tandberg describes the chassis of the TCA 3018A as a "highly refined purist version of Tandberg's innovative and widely acclaimed TCA 3008A preamplifier." The TCA 3018A is a "direct path" preamplifier without tone controls. Discrete circuitry, including polypropylene capacitors and metal-film resistors, are used throughout. Like the TPA 3026A power amplifier, the TCA 3018A employs no negative feedback. Its high-level inputs use no capacitors in the signal path and have a signal headroom of 20 V before any evidence of overload. There are buffer stages between the high-level inputs and the volume control so that input signal sources see a constant load impedance regardless of master volume control settings.

Separate six-position "Record" and "Program" selector switches are provided, and bi-directional dubbing between two connected tape decks is possible. No negative feed back is used even in the phono preamplifier/equalizer section; instead, passive networks provide the required RIAA playback characteristics. Separate power-supply sections for right and left channels, each fed by a separate winding on the power transformer, are used to provide maximum interchannel isolation.

Tandberg has given special attention to this preamp's circuit-board design as well. Possible r.f. interference and audio noise levels are reduced to a bare minimum by a glass epoxy motherboard which is copper plated on its reverse side to form a ground plane for maximum shielding.

Also, as you might expect, input and output jacks are all gold plated for long-term, low-resistance contact reliability.

The TCA 3018A is finished in matte black and is available with optional rosewood and black Lucite end panels. The front panel has a bare minimum of controls. The power on/off pushbutton is at the extreme left, with a headphone output jack and its associated volume control nearby. Large master volume and balance rotary controls are concentrically mounted at the extreme right of the panel. To their left is a subsonic filter on/off switch and the separate six-position selector switches for "Program" and "Record" modes.

Separate input jacks are provided on the rear panel for a moving-magnet and a moving-coil phono cartridge. Accordingly, if you own two turntables (one with an MM cartridge, the other with an MC pickup), it is possible to connect both to this control amplifier. Switching between the two types of cartridge is done by means of a rear-panel slide switch.

The input impedance for the moving-coil cartridge is 50 ohms, while the input impedance for the moving-magnet cartridge is 47 kilohms, in parallel with either of two switch-selected capacitances (150 and 330 pF) or with no extra capacitance at all. Should you find it necessary to substitute other impedance values to match your cartridge, the owner's manual provides very explicit instructions on performing the required "minor surgery." If you are handy with a soldering iron and other tools of the electronic technician's trade, you can tackle the modifications yourself. Otherwise, Tandberg recommends that you have an authorized service shop do it. Tandberg's booklet even tells users how to short out the output coupling capacitor if your power amplifier has an input capacitor for d.c. isolation.

The remaining high-level inputs and two sets of tape outputs are neatly arranged across the rear panel. Tandberg still refers to the CD input as a DD (Digital Disc) input, but the intended purpose of these input jacks is clear. In a sense, I have always sort of wished that the rest of the industry had settled on "digital disc" instead of "Compact Disc," which doesn't really tell the most important part of the story to uninitiated music lovers. After all, the old 45-rpm records were also "compact." Amplifier Measurements The amplifier produced quite a bit more than its rated power when driving 8-ohm loads: 181 watts per channel at mid-frequencies and more than 170 watts per channel at 20 Hz and 20 kHz for its rated harmonic distortion of 0.05%.

When connected to 4-ohm speaker loads, the amplifier delivered an impressively high 280 watts per channel, as against 210 watts claimed by Tandberg. At maximum power output, the TPA 3026A consumed in excess of 800 watts; when not delivering power to speakers, it consumed just over 100 watts.

Figures 1 and 2 show how harmonic distortion varied with frequency and output power level when the amplifier was driving 8- and 4-ohm loads, respectively. At rated power of 150 watts per channel into 8 ohms, distortion measured a negligible 0.006%, and SMPTE-IM and IHF-IM distortion were both under 0.03%.

Frequency response was absolutely flat within the audio range from 20 Hz to 20 kHz. I couldn't detect so much as one-tenth of a dB of variation! Of course, response extended way beyond the audible range-out to well over 1 MHz, in fact, for the-3 dB cutoff point. To appreciate just what this means in terms of rise-time and slew rate, look at Fig. 3.

The input was a 20-kHz square wave; there is barely any curvature evident in the rising portion of that waveform. Or consider the output pulse shown in Fig. 4. The peak-to-peak amplitude of the pulse was around 80 V, and for this test the load resistance was reduced to 2 ohms. During the instant of time when the pulse was being reproduced, peak instantaneous current drawn from the amplifier was therefore 40 amperes per channel.

A-weighted signal-to-noise ratio, referred to 1 watt of output, measured an outstanding 95 dB, and input sensitivity for that same output level was 110 mV, exactly as specified. Translated to rated output, the noise level was-116 dB, and 1.4 V of input signal would be required to drive the amplifier to its rated output. Damping factor was probably well above the 500 which I measured, since my setup required several feet of 14-gauge wire between the amplifier and the loads. That bit of cable probably presented more of an impedance than the entire internal impedance of the amplifier. The high damping factor is all the more remark able when you consider the fact that there is absolutely no negative feedback used in the TPA 3026A. Normally, high damping factors (which aid in suppressing extraneous speaker vibrations or "overhang") are achieved by using great amounts of negative feedback; Tandberg has obviously gotten the same results without the deleterious effects of such feedback.

Preamplifier Measurements

Frequency response for the TCA 3018's high-level inputs was flat within 1.0 dB from 5 Hz to 500 kHz. An attenuation of 3 dB was reached with input signals at 2 Hz and above 1.0 MHz. Total harmonic distortion, with a 1-V signal applied and with the volume control set for 1 V output, was 0.005% at mid-frequencies; this increased slightly to a still-insignificant 0.008% at 20 Hz and 0.007% at 20 kHz. SMPTE-IM distortion measured only 0.005%. With gain set to maxi mum, 1 V of input signal applied to the high-level inputs resulted in an output level of 6.3 V for a gain of approximately 16 dB. At this higher output level, THD was still a very low 0.017%. (Bear in mind that no power amplifier I know of can handle so high an input signal level unless it is equipped with its own input attenuator.) Maximum output level at clipping was 12.0 V, 2 V higher than spec.

For standard output conditions (0.5 V), input sensitivity measured 1.0 mV for the moving-magnet phono inputs, 55 µV for the MC phono inputs, and 80 mV for the high-level inputs. Signal-to-noise ratio for the MM phono inputs was 80.5 dB referred to 0.5 V output and with 5 mV of input applied. Amazingly, the MC signal-to-noise was almost identical to the MM figure; it measured 80.0 dB referred to 50 µV input and 0.5 V output. This is the first time I have encountered a preamplifier whose MC S/N measured this way was as low as the MM S/N measured in accordance with the accepted standard. Users of MC cartridges can, at last, overcome one of the disadvantages ascribed to their pickups in the past: Higher noise levels. Moving-magnet phono input overload was 260 mV at 1 kHz, marginally short of the 290 mV claimed, but overload for the MC inputs was 20 mV, considerably higher than claimed.

It was pretty clear from my measurements that Tandberg must be using components of extremely tight tolerance in their passive RIAA equalization networks. It's not too difficult to achieve accurate RIAA curves using negative feedback equalization. However, it is quite an achievement to come within 0.2 dB of the precise RIAA characteristic over the entire audio range, as this preamp does, using fixed, passive "tosser" networks. I might mention, too, that both channels were measured and both were equally accurate.

Assuming that your other stereo components are well balanced from channel to channel and that your listening location is well centered between your loudspeakers, you are not likely to need the balance control on the TCA 3018A regardless of where you set your volume control. That's because the tracking of the master volume control's two sections proved to be accurate within 0.4 dB from maximum down to a-60 dB setting.

Use and Listening Tests

Tandberg's typically modest claims for the TPA 3026A amplifier are exceeded by far, not only in terms of specifications but in terms of sound quality. With this amp coupled to a pair of high-quality loudspeakers, and with appropriate program material fed via a suitable preamplifier such as the TCA 3018A, any serious music lover would be hard pressed to find a better-sounding amplifier at any price.

Having lived with these two Tandberg components for several weeks now, my reaction to them can best be summed up by the fact that I am very reluctant to return them. Though my own reference power amplifier delivers considerably more continuous power to my low-efficiency speakers than does the TPA 3026A, I never encountered amplifier overload during my auditioning of this system.

Transients were unmistakably superb.

Since Tandberg boasts about the "straight-line" design philosophy of the TCA 3018A, I rigged up a little switching arrangement which allowed me to bypass the preamplifier entirely and to compare sound obtained that way against sound quality when the signal was passed through both components. Having an output level control on my reference CD player made this A/B comparison practical once the preamplifier settings were adjusted for unity gain. Admittedly, the test was not strictly a double-blind experiment, but I could hear no degradation of musical sound quality when the TCA 3018A was in circuit.

My record collection has been collecting dust lately, but for the purpose of these tests I resurrected some of my old favorites, plus a couple of recent additions that I commend to you. Try listening, through this Tandberg pair, to the digitally mastered London LP of Blue Skies (414666-2), in which Kiri Te Kanawa sings some Cole Porter classics. The clear and utterly velvet-smooth voice of my favorite New Zealander never sounded better. Or mount the Classic Masters Christmas at the Church of St. Luke in the Fields (CMS-1006), which was mastered using Teldec's DMM (Direct Metal Mastering) technique, if you want to hear organ and choral sounds that bring you as close to "being there" as anything I've yet heard played on an analog turntable.

Using both my favorite moving-magnet cartridge and a long-idle moving-coil pickup, I was impressed by the ultra-low noise of the preamp during my listening tests. But the sound quality of these Tandberg components goes beyond low noise and wide frequency response. There is a purity and overall clarity of sound that is evident on all of the several program sources I used.

Many readers and others interested in audio ask me if there's really an audible difference between run-of-the-mill (a substitute phrase for "medium-priced") components and high-end (read "high-priced") components. There's no general answer to this question; some high-priced components have little to recommend them except the fact that they were produced in small numbers by inefficient production methods. Others, like these units, offer sound quality and reliability that fully justify their price. Tandberg had an advertising campaign a while back that talked about the "Scandinavian Alternative." If money were no object, I'd look upon the TCA 3018A/TPA 3026A combination not as an alternative but as a "first choice."

--Leonard Feldman

(Source: Audio magazine, Apr. 1987)

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