Country of Manufacture:Netherlands
Release dates:1964 - 1967
Speeds: 1 7/8, 3 3/4
Max Reel Size("): 7"
Number of heads: 2
Head Composition: Permalloy
Head Configuration: Mono - Full Track
Frequency Response:3¾ ips: 60Hz - 13kHz
Wow and Flutter:0.6% peak to peak at 3¾ ips
Sound quality rating:5 / 10
Long-term reliability rating: 5/ 10
A quarter-track, two speed machine intended for home and family pleasure, the EL 3548 was a hybrid in that there was a marriage of solid state early stages with an ECL82 valve output and an EM87 magic eye record indicator, perhaps the best of both worlds in the mid 1960s.
Drive was achieved from a continuous-running capstan with wide flywheel, belt-driven from alternative pulleys for speed change which gave a very good wow and flutter specification.
The placement and marking of controls in three groups of three made operation simple and easily learned.
from The Tape Recorder, April 1965
A recorder of home and family pleasure, economical in tape and reasonable in price, backed by name and know-how …. Tape without tears, in fact … this is a fair description of the Philips EL3548, such as its own advertisers might use. Perfectionists and other (hi-) fry need not apply – it does not record stereo, and needs extras to replay it; the machine has no 7½ ips nor will it follow CCIR or any other characteristic with bloodhound accuracy; its output will not shake floors unaided, neither will it enjoy internal tinkering.
It does offer; ease in setting up; real simplicity and versatility in use; smart modern design with performance and facilities to match. The makers have kept size and weight down, but unlike other slow speed models the spools are not thereby limited to 5¾ inches or less; seven inch diameter reels are accommodated, giving really long uninterrupted runs.
The circuit is a marriage of solid-state early stages with an ECL82 valve output and EM87 magic eye – perhaps the best of both worlds at present. The mains transformer and single motor with their hum-fields are located as far to the rear as possible, and a close fitting shield is brought up to the record/playback head outside pressure pad; one might expect a higher signal to noise ratio than the 40 dB claimed; measurements gave 39 dB at 1ips, 42 dB at 3¾ ips.
Performance at either speed can be assessed by taking figs 1 (a) and (b) in conjunction; extending measurements rather beyond audibility in (b) points the causes of the somewhat restricted response from tape (a). Normally one would expect a test tape (replay only) at the higher speed to give the best showing; the dotted curve obtained in this way is in fact the least extended, the overall record-play curves being better at both speeds – 3¾ ips the solid line, 1ips the circles.
After checking azimuth and possible errors, I attacked the anomaly by plotting straight through response in the record and play modes, with results shown in fig. 1 (b). The lower curve shows recording gain with frequency test oscillator fitting the diode socket (input pin) and valve voltmeter across the monitoring headphone sockets, with resistive load. This curve divides into two steep treble peaks at 17kHz (3¾) or 11.5kHz set to 1 7/8 ips, the LF performance been unaffected. The upper replay curve also divides in the treble for each speed, and was obtained by matching the generator in place of the tape head and measuring at the diode output.
The picture now clears – best slope of the replay curve is less than the desired 6dB per octave, being 5dB per octave around 500 cycles and 2.5dB or less per octave below 200Hz. At the treble end, lift does not begin in earnest until 10kHz and upwards, except for the record equalisation at ips whose effect is mirrored in the flattening at “F” of the circled record/play curve before its final demise. At each speed the bass end of the overall curve in fig 1 (a) is 3 – 4 dB up on test tape, showing the effect of bass emphasis in recording.
What does all this add up to for the listener? There will of course be a scarcity of true bass, replaced by “middle bass”, but if driving fairly large extension speaker in open cabinet, with bass resonances around 100Hz – not uncommon in a domestic set up -the response makes best use of available output by minimising overload and cross-modulation from the true-bass end, and may even be turned to advantage -shades of ‘tailored response’. Likewise, any treble shrillness will be much less obtrusive, especially as the microphone knob becomes an unusually smooth treble-cut tone control on replay via speaker-not on the diode output, leaving the pre-amp user free to make up treble and bass as desired. The smooth declines of the test-tape curve make feasible a close approximation to flat response into an external power amplifier by these methods, for replaying, say, three and three-quarter ips pre-recorded tapes.
The EL3548 uses a continuous-running capstan with wide flywheel, belt-driven from alternative pulleys for speed-change, and I would expect rather better wow and flutter figures than those claimed in the specification. In fact the meter showed (RMS) total waver at 3¾ ips – 0.25% (flutter 0.2%, wow 0.15%): at 1ips -total 0.3% rising in slow cycle to 0.4%, flutter component again 0.2%, wow now 0.25%, (0.2% RMS). Use of pre-recorded known low-wow tape on the machine showed a slight audible improvement, but as the measured figures are not far off the specification, I suppose we must be satisfied. However, even these low figures are susceptible to a sensitive ear, and I did find a rubber inter-wheel driving take-up clutch with noticeable tyre eccentricity and warp; also, grinder-marks are to be seen on the capstan shaft.
To check on the possibility that the machine was not standard, I unobtrusively tried a 3kHz good tape on another 3548 in the local dealer’s and it sounded much better. Regret no fluttergrams-difficult to take under the circumstances, and was Christmas-crowded too…
A fair review must mention also that rewind is rather slow-the 1200 ft 5¾ inch tape supplied took 2½ minutes to wind on to similar spool (tight wind) and 2¾ minutes on rewind (one packslip). The location counter is four-figure, instant reset, and showed an error of only three final digits over the distance. But bearing in mind the recorder’s purpose, may one also give due weight to the following:
The placing and marking of controls in three groups of three, six large tablets and three knobs for everything, make operating simple and easily learned. The left-handed knob switches on, and the red left-hand RECORD tablet is pressed; advancing the remaining knobs shows the incoming signals on the magic-eye-microphone on right-hand knob and mixing in radio/gram or another recorder by the centre knob. The transparent red centre-clip on the eye simplifies level setting; signals can be heard at any convenient volume by advancing the combined on/off switch and gain control on this is also the straight-through amplifier mode. Three finger control on either group of tabs from now on-to record, still listing, press the outer tabs together in the left-hand group (RECORD and PLAY). Pressing PLAY alone releases the red tab, as a safeguard against accidental erasure.
The centre tab of this trio (PAUSE) gives temporary stop and may be held or locked down without scraping of oxide against the capstan; the tape angles prevent this in play while offering a straight drop-in slot when loading. Pause action is duplicated by optional foot control, a not-electrical Bowden-cable action which screws in at the rear. The run completed, tape can be fast-wound either way – without necessarily stopping -by three-finger control of the right-hand group of tabs: REWIND at the left, fast forward WIND to the extreme right and STOP in between, which cancels all. WIND and REWIND cancel RECORD/PLAY instantly, without smearing the the recording at the reversal point, and tape-wind can be reversed at will for inching by alternating pressure on the outer pair. Hardly any single motor machines have had this feature to date; interlocks are usually arranged to prevent one operation running into the next, operation of the stop button been mandatory each time.
For editing, chinagraph-pencil marking is made easy by a lid on the front head-cover which slides forward and unclips. One screw releases the back section for cleaning heads, etc. Four more screws are removed for international attention, one behind each spool and one each side, and I have never seen a domestic machine whose ‘works’ can be uncovered so elegantly. Instead of a drop-in chassis, top-plate and sides of the cabinet are integral, and once the knobs are pulled off the complete ‘overcoat’ lifts away. The carrying handle slides away through the socket cut out at the right to ease the unveiling.
To replace the output valve or the fuse beside it is even simpler: the plastic bottom-plate only is removed (four bolts in the feet) and this carries a rubber beading all round its edge to engage plastic finger-moldings on the cabinet sides when replaced, eliminating cabinet buzz at high volume.
Many electrical devices in one-room flats, etc, are used from bayonet adaptors or other two-pin sources, and Philips provide twin mains lead (no earth-wire) -hum-loops at least are unlikely with the arrangement, and earthing, if required, can be taken to the lower wander-plug (headphones); the sockets is marked with the earth symbol, and makes through to chassis. There is no exposed metal apart from sockets, and their mounting plate is shielded by an engraved plastic fascia. A final point – do not press WIND and REWIND together; the interlocks are ingenious, but not that clever, and the motor will promptly stall, stretching the unfortunate tape in the process!
Further to feelings that the specimen I tested might possibly be an unlucky one, was glad to have the opportunity of testing another sample kindly provided by Philips. The procedure was to take another series of measurements for the more interesting parameters and re-plot them, and of course, to measure the wow figures again of depending on aural assessment.
The differences found were no more than might be attributed to to the normal spread of tolerances in production. In fig 2 (a) the same test tape failed once again to give as wide or even response as the overall record play results, for the same reason of pre-emphasis already discussed in the body of the article, and visible in the new version of fig 2 (b) curves. The straight portion of the replay response is also shown, and its float of 5.2 dBs per octave is only marginally better than the 5 dBs per octave of the original.
The appearance of the salient parts of the tape transport was much better, and the wow figures showed an improvement. They are RMS in all cases: 3¾ ips, flutter 0.16%, wow 0.15%, total 0.2% to 0.25%; 1, flutter 0.2%, wow 0.25%, total 0.25% to 0.35%. The values for total waver in gaining showed the same slow cycling between the figures given, as various components came in and out of step.
Remaining impressions were substantially the same, except for two very small faults. Pressure of the PLAY tab to its bed while using the diode socket to feed external systems on replay caused disappearance of the external signal – without, however, affecting sound from the internal loudspeaker. Also it is not advisable to snap home the cover to the mains cable stowage compartment, relying on the locking spring to latch home with click: it flew off with a snap, owing to the plastic pips which secure it shearing off. Am hopeful of what Araldite may do …
Valve complement: ECL 82 and EM 87, solid state preamplifiers / Rewind speed: 1200ft in 2½ minutes (5¾ inch-reel) / Audio output power: 2.2 watts / Inputs: diode, gram and microphone / Outputs: diode, external speaker, headphones and stereo / Speaker(s): internal 4″ (10cm) / Dimensions: 15¼ x 13¾ x 6¾” (387 x 350 x 171 mm) / Weight: 18 lbs (8.2 kg) / quarter-track mono