Tandberg TD 20A SE Reel To Reel Recorder Review

The Tandberg TD 20A-SE is a two-speed open-reel tape deck designed for the advanced amateur or semi-professional recordist. It is available with quarter-track heads for “7-1/2”/”3-3/4”- or “15”/”7-1/2”-ips operation. There is also a “15”/”7-1/2”-ips half-track version more suitable for professional applications. All three models accept either 7- or 10-1/2-inch reel sizes.

The transport of the TD 20A-SE is virtually identical to that of the TD 20A. A synchronous a.c. motor powers the belt-driven capstan, and there are separate motors for each of the reel hubs. A fourth motor replaces the usual solenoids for smooth, quiet operation of the tape gate, capstan pinch-roller, and brake mechanisms. Spring-loaded tension arms on either side of the head assembly compensate for any unevenness in tape winding, and a precision “scrape flutter” roller damps out the tendency of tape to vibrate along its length.

Separate ferrite heads of Tandberg’s own design and construction are used for erasing, recording, and playback. A shield on the playback head lowers hum pickup but also makes it somewhat awkward to mark editing splice points. A conventional mechanical four-digit counter indicates tape position, and an optical sensor stops the deck when the tape runs out.

Light-touch pushbuttons with LED indicators control all transport modes through a logic circuit that automatically prevents any possibly tape-damaging sequence of operations. Simultaneously pressing and releasing the stop and wind buttons places the deck in a “free” mode so that the reels can be manually rocked back and forth for editing or threading. If desired, the cue switch will cause the tape to be held against the heads even during fast winding, though the playback level must be turned down to avoid the possibility of burning out a tweeter. After threading, pressing the stop button momentarily energizes the reel motors in order to take up any slack in the tape.

The TD 20A-SE incorporates two highly original electronic features: the Dyneq Actilinear recording system and the “special equalization” (SE) from which the deck gets its suffix. The Dyneq (dynamic-equalization) system is designed to overcome a problem frequently encountered in slow-speed recording. Normal treble losses at slow tape speeds require a considerable high-frequency boost during recording in order to achieve flat frequency response overall. This boost, or “record pre-emphasis,” can lead to high-frequency tape saturation, however, if the treble content in the original signal is itself high in level. Saturation produces distortion and limits the tape’s high-frequency response.

The Dyneq system varies the amount of treble pre-emphasis during recording to take account not only of the frequencies in the incoming signal, but of their amplitude as well. If a given treble frequency would be driven into saturation with normal, fixed record equalization, the Dyneq circuit automatically lowers the amount of equalization supplied by just enough to enable the tape to hold as much high-frequency information as it can.

Tandberg’s SE circuit addresses another fundamental open-reel problem. Decades ago, when playback-equalization curves (which are usually stated in terms of microseconds for engineering convenience) were standardized for the various tape speeds, the very best available tapes of the time had severe treble losses, well beyond what any reasonable amount of record pre-emphasis could supply. The only place to insert the additional amount of treble boost required was in the playback section, where a 6-dB-per-octave treble boost was an inherent part of the playback head’s own operation (a 6-dB-per-octave rising characteristic means that the output from the head doubles each time the frequency doubles). While using this boost certainly helps compensate for treble losses on the tape, it unfortunately also increases any tape hiss.

Today’s improved tapes do not need nearly the amount of playback treble assistance that is built into the old standards, and now Tandberg has decided to run the commercial risk of providing an alternative set of playback-equalization settings. In brief, the “special equalization” of the TD 20A-SE uses time constants of 50 microseconds (treble boost beginning at 3,150 Hz) for the 33/4-ips speed; the current standard is 90 microseconds (boost beginning at 1,800 Hz). At 7-1/2 ips the SE is 25 microseconds (6,300 Hz) instead of the old 50-μsec (3,150-Hz) standard. And at 15 ips Tandberg proposes 10 microseconds (15,900 Hz) in place of the thoroughly obsolete 50-microsecond boost now mandated. A rather similar approach seems to underlie the “EE” (“extra efficiency”) system recently promulgated by Teac, Akai, Maxell, and TDK, except that EE requires a special high-bias (and rather high-priced) tape, while Tandberg’s SE is designed for high-quality regular open-reel tapes.

As is almost a hallmark with Tandberg, the record-level indicators of the TD 20A-SE are peak-reading equalized meters. They not only register signal peaks, but reflect the record treble pre-emphasis as well. This facilitates using the meters for their intended purpose, namely recording at as high a level as possible without encountering distortion.

Four separate record-level controls plus an overall master control permit full mic/line or line/line stereo mixing, and an adjustable detented ring on the master control permits easy resetting after a fade-out. As on professional decks, separate record-ready switches are used, and “flying start” recording is possible. Toggle switches also control the selection of standard or special equalization, source/tape monitoring, edit/cue functions, and a sync facility that enables a recording made on one channel to be synchronized with a second recording made on the other. Separate left- and right-channel playback controls are provided, and a switch permits routing either channel to both headphones or regular stereo listening. Pushbuttons are used to select either high or low speed and to set the proper tape tensions for large or small reels.

The rear panel of the TD 20A-SE contains the normal input and output jacks, which are recessed to permit either vertical or horizontal operation. Hub adaptors for NAB-type 10-1/2-inch reels are provided, and a remote-control accessory is available. The TD 20A-SE measures 17-1/4 inches wide, 17-1/2 inches high, and 6 inches deep, and it weighs 37-1/2 pounds. Price: $1,595.

Laboratory Measurements

Tandberg indicated that our sample of the TD 20A-SE had been factory adjusted using Maxell UD-XL tape, so we used it for the tests. We also tried top-line tapes from TDK, Scotch, and Memorex with almost equivalent results. The TD 20A-SE has front-panel access to a pair of bias-trim controls that can flatten out the response of nearly any tape, but the user must supply his own test equipment to take advantage of this feature.

Playback response (using the “normal” equalization, as there are no calibrated tapes available for Tandberg’s “special” equalization) was checked using both Am-pex and MRL test tapes. Overall record-playback frequency response at a level of — 20 dB showed very close tracking between the normal and special equalizations, though at a 0-dB level high-frequency response fell off"-more sharply when using the SE, which subjects the tape to increased record equalization. At 0-dB the equalized peak-reading meters deflected far off scale on higher-frequency test tones. In practical use, this would warn a user to reduce the level. Incidentally, the tape overloaded before Tandberg’s recording amplifier did.

Third-harmonic distortion of a 1,000-Hz tone recorded at an indicated 0-dB level measured between 1.1 and 1.2 per cent, and the 3 per cent distortion point was reached at a level of + 3.5 dB, just above the highest calibration on the meter scale. While this does not appear to provide the usual “leeway,” it is again an intentional part of the Tandberg design for its meter operation. A large differential between an indicated 0-dB and the onset of serious distortion is required only when the meter does not really indicate the exact signal level. With reference to the 3 per cent distortion point we measured unweighted signal-to-noise ratios ratios at 7-1/2 ips of 59.8 and 60.8 dB with the normal and the special equalization, respectively, and IEC A-weighting increased the readings to 67.4 and 70.8 dB. At the 3-3/4-ips speed the comparable unweighted figures were 56.4 and 58.8 dB, improving to 63.7 and 67.4 dB with A-weighting.

Wow-and-flutter, using the stringent DIN peak-weighted standard, measured 0.08 per cent at the higher speed and 0.12 per cent at the lower speed. High-speed winding time for a 3,600-foot (10-1/2-inch reel) tape was 115 seconds in each direction. An 1,800-foot (7-inch reel) tape could be shuttled from one end to the other in 83 seconds. A 38-mV (0.038-volt) signal was required at the line-1 inputs for a 0-dB indication, with an output level of 1.4 volts. The microphone input required only 0.18 mV and began to show signs of overload with an input of 25 mV.

Comment

As a top-grade, innovatively designed recorder the TD 20A-SE left little to be desired. Its tape handling was excellent, and it could make copies of a wide variety of listening material (including a first-generation dub from a live digital master) with virtually no degradation.

The special equalization does produce a definitely quieter tape, with far less indication of treble overload than the 0-dB test curves would imply. At the same time, getting the rest of the industry to accept a proposed new standard will not be easy, so at least for now tapes made with the new process will be primarily for playback on one’s own machine rather than for exchange with others. Overall, we would rate the Tandberg TD 20A-SE as well worth its price, an excellent deck that should give its owner many years of trouble-free musical satisfaction and fine performance in semi-pro mastering work.

Read all

Tandberg reviews

Read all