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Binson Echorec Head Adjustment

Given that Binson ceased operations in the 1980s it seems reasonable to surmise that there must be many old ‘Echorec’ echo machines out there that are no longer functioning at their optimal performance as they did when they came out of the factory back in the 50s and 60s. Time marches on and over the years the heads wear, become misaligned during transportation or the machine may have been incorrectly tampered with at some point. Head misalignment of a few microns or a few degrees off axis will make the difference between the Echorec reproducing a swirl of rich, crystal-clear repeats or the machine sounding weak, muffled and not having much effect on the signal at all. This article takes a detailed look at the intricacies of head adjustment on the Binson Echorec ‘B2’ and ‘B1’ ‘Export’ echo models and aims to help eliminate the guess-work from this critical and vitally important part of setting up the machine.

Wear in Drum and Tape Echo Machines

At best, adjusting the heads on an ‘Echorec’ delay machine can be quite tricky for the novice and requires an abundant supply of patience and time. At worst the heads and the drum can be irreparably damaged resulting in repair costs of many hundreds of pounds. Head alignment is one of those skilled jobs from a bygone era, a time when men (not women) would set up the tracking force of the tone-arm on their prized ‘Garrard’ record deck or the points on their Ford ‘Escort’ automobile (horseless carriage). Although the physical principles of operation of an Echorec are identical to those of a reel-to-reel magnetic tape or delay machine, the setup is significantly more critical as there’s much more at stake. This is because the storage medium utilised on the Echorec is a aluminium drum with hard magnetic wire wrapped around its circumference—incorrect head adjustment will result in adverse (and even catastrophic) wear between the hard surfaces of the head and the drum, drastically shortening the life of the machine.

binson_echorec_head_on_drum_320px — Metal on metal: Close-up photograph showing Echorec record head against the surface of the magnetic drum.

Repair costs can be horrifying. Again, this is no exaggeration, Binson, UK were charging £700-00 for refurbishing the memory system, that’s the heads and drum fixed on the mounting plate, back in 2009.

The risk of adverse head wear in a tape machine is significantly reduced in comparison to an Echorec because the magnetic plastic tape is so soft and fragile in comparison to the metal heads, which are manufactured from a tough hardened alloy. Additionally, the plastic tape is a relatively inexpensive part of the machine system and can be regarded as being disposable or sacrificial—if it snaps it can be replaced or spliced. It’s the weakest part of the system and will fail preserving the more expensive parts of the machine. The worst case scenario of poor head adjustment in a reel-to-reel machine is poor audio reproduction.

watkins_copicat_head_alignment_is_easy_320px — An engineer’s dream: Fixed heads on the Watkins Copicat tape delay make alignment a breeze – there’s nothing to adjust!

Not only is head alignment more critical for an Echorec than tape delay machine, it’s also more complicated. Head adjustment in a tape machine usually involves aligning the ‘azimuth’ and ‘height’ of the head relative to the tape, which often involves little more than tightening or loosening a single adjustment screw. In some machines, such as the Watkins Copicat echo, there is no adjustment to be made at all as the heads are hard-mounted to the chassis. As much as I admire the classy Italian styling and sound of a Binson, it has to be said that the CopiCat is an engineer’s dream—there is no hassle with set-up or expensive recording mediums which can potentially destroy the heads.

If the tape wears or breaks, simply replace it. There is no such elegant simplicity with the Echorec. Everything about this machine is demanding and difficult—especially adjusting the heads.

Visual Head Alignment on the Echorec

The fascinating thing about head alignment is that although we live in three dimensional world, Echorec head alignment involves adjustment of five parameters. No, it doesn’t transcend the laws of physics, nor is it a time machine. The dimensions additional to x, y and z orientation in 3-D space are force of the head against the drum and relative alignment to the other heads. The diagram below shows there’s quite a lot to consider.

binson_echorec_head_alignment_640px — 1. Azimuth 2. Height 3. Zenith 4. Rotation 5. Force

The alignment requires extraordinary precision. This is because the head ‘gap’—the part of the head that reads/writes signals to/from the magnetic drum—is only 5 microns width, a mere 5 thousandth of a millimeter and much thinner than human hair. The gap is actually just a tiny insulation space between the two polished end pole pieces of the magnet (or core) inside the tape head. The gaps of all five heads (1 record and 4 playback) must be aligned correctly and identically on the drum face to obtain strong, clear repeats. When set up properly the machine will sound wonderful with beautiful clear echoes that repeat indefinitely and into infinite self-oscillation with only a gradual degradation of each repetition. A nice example crystalline repeats in a well set-up Echorec can be heard on Pink Floyd’s track ‘Time’.

Make sure you have a clear workbench and there is plenty of available light—an ‘Anglepoise’ lamp and magnifying glass are essential tools to aid visual alignment of the heads. But first, before attempting to align the heads, it’s important to examine them to check if they require relapping (re-profiling)—there’s certainly no point going to all the trouble of aligning them if they’re worn-out or damaged and, even the slightest adverse wear profile will prevent you from setting them up properly. The photograph below shows an unused new old stock head on the left and a worn head on the right. Although heavily worn the head on the right was relapped which facilitated easier alignment and also significantly reduced friction between the drum face and head.

head relapping — An unused new old stock Echorec head on the left and a well worn head on the right. Note: the 'gap' is clearly visible on the worn head - this head is still usable after it's been relapped, however the high-frequency response will be curtailed a little.

Further, another hour or two will almost certainly need to be spent removing all the old nail varnish from the mounting hardware and screws. This is achieved by soaking them in isopropyl alcohol which softens the nail varnish allowing it to be flaked off with a small stiff brush. Take a great deal of care not to damage the heads of these small M2 screws whilst attempting to remove them as it’s pretty much mission impossible to obtain exact replacements. New vibration dampers will need to be fitted too as the old ones will have stiffened with age and even begun to crack and fall apart—use ‘Hellerman’ rubber sleeving here.

Azimuth Alignment

The gap must be aligned so they are perpendicular (at a right angles) to the drum surface to prevent loss of high-frequency response. This is known as ‘azimuth’ and is adjustable on most tape and echo machines with a single screw which alters the height of one side of the head by means of a spring-loaded mechanism. There is no such ease of adjustment on the Echorec though, where adjustment can only be made by loosening a tiny screw which allows the whole head assembly to pivot and drop—a primitive arrangement and terribly fiddly to get right. As the head assembly pivots the height of the head will also change slightly as well. It’s very tricky to set correctly though as just applying that additional bit of force to tighten the screw more often than not causes misalignment and the whole process has to be undertaken again.

Zenith Alignment

Unlike plastic magnetic tape, which is flexible enough to follow the contour of the head to a certain extent, the hard surface of the Echorec drum is very unforgiving. This makes zenith alignment even more critical. Just a few degrees misalignment (Fig below shows 5° off axis) is enough to prevent the core poles of the head from making proper contact with the magnetic wire on the drum—the head face must be aligned exactly parallel with the drum surface. If not then there will be a loss of output signal from playback heads or the record head will ‘print’ only a weak signal on the drum. This results in a poor signal no noise ratio on the echo swells, however that’s not the worst of it. A head with bad zenith misalignment of just a few degrees only contacts the drum on one edge. The head tracking force is not distributed evenly across the pole surface, and all the force is focused at one edge causing adverse wear on the drum—effectively wearing a groove in the drum.

Rotational Alignment

It’s essential to adjust all the head faces so they are radially aligned and tangential to the drum surface. The idea to ensure both poles make good contact with the magnetic wire on the drum. Again, just a few degrees misalignment will result in huge signal loss when writing and reading to and from the drum. In the figure below just 5° misalignment is enough to prevent the one of the poles from making any contact with the drum at all.

Height Alignment

Quarter inch tape heads are fairly forgiving when it comes to height alignment as the track is quite wide allowing some margin for misalignment between the heads. However it pays to make sure they are all lined up as accurately as possible to maximise the strength of the playback signal level to achieve best signal to noise ratio from the machine. Although the playback amplifier circuitry inside the Echorec might be able to recover or boost the gain of a weak playback signal to achieve reasonable echo swell volume levels, it will also amplify noise from the drum.

Head height in the Echorec is mostly determined by the length of the hexagonal mounting pillars on which the five head assemblies (the metal strip and head) are mounted. The pillars for all five heads are accurately machined to be the same length so that the heads line up, however there will be some small height variation between heads when setting azimuth alignment. Although some degree of height misalignment will not damage the drum in the short term, it will adversely affect the performance of the machine in the long term as the parts ‘bed-in’ over time. That is, over many, many hours of operation the drum and heads will gradually wear and settle into an optimum, harmonious relationship, but only if they are set-up correctly to begin with.

Force Adjustment

The heads must be kept in direct physical contact with the surface of the magnetic recording medium (the drum) in exactly the same way that tape heads touch the magnetic plastic tape in a reel-to-reel machine. The head must only lightly touch the drum surface without even the smallest air gap between them otherwise there will be a drastic drop in record and playback signal levels. Contact is maintained mechanically by the small flat metal strip which serves as mounting bracket and spring to keep the head pressed against the drum with a force of no greater than 0.01N. The tracking force of the head is adjusted by rotating the hexagonal pillar using a low-profile 6mm spanner. Once the correct tracking force has been set the pillar should be locked in position with patented Binson anti-tamper locking compound (a.k.a. nail varnish – coloured red for 1950s machines, silver for machines manufactured from the 1960s onwards). Note: this procedure also affects rotational alignment as well as the tracking force, however this is compensated for by an adjustment screw on the head (see ‘Rotational Adjustment’).

Additionally, because the head and spinning drum are physically in contact it is essential that the drum surface is kept lightly oiled with fine sewing machine oil—not watch oil, as this is simply not viscous enough and will drip onto the idler wheel causing it to slip.

Electronic Test Procedures for Head Alignment

Visual alignment of the heads will only take an Echorec so far along the path to attaining its peak audio performance. The minute tolerances, dimensions that are in the order of just a few microns one way or another, required to align the head gap accurately against the drum are beyond human ability to resolve, yet alone manipulate. Or, to put another way, the task is somewhat akin to attempting to assemble a pocket watch, whilst blindfolded and wearing oven gloves. Further, subjective audio testing by listening alone is a hit and miss process, especially if using a guitar amp instead of a hi-fidelity audio reproduction system.

But there is an easier way of tackling the climb to audio nirvana where all the heads are perfectly aligned and the machine is producing crystal-clear repeats: use the same procedures that Binson used. Back in the day Binson production engineers utilised electronic test equipment, a signal generator and oscilloscope to measure the audio performance of the heads whilst the machine was operating. A pure sine wave signal from the generator is fed into the input of the Echorec and then the ‘wet’ signal level (from the playback amplifier circuitry) monitored on the ‘scope display. The frequency response of the memory system (heads and drum) can be determined by taking spot measurements at 1KHz and 10KHz (note: the Echorec’s bias oscillator circuitry generates an A.C. bias signal between 50KHz to 60KHz, setting the upper frequency limit of the machine at 10KHz to 12KHz).

Test point for head alignment on the model 'T5E'

The older model ‘T5E’ machines were fitted with a test point to facilitate connection of a ‘scope probe. Signal playback levels from each of the four playback heads could then be monitored individually using the selector knob on front panel of the Echorec. No test point is present on the newer ‘T7E’ machines however a connection can be made by soldering a wire on to the pole of the 12-way head selector switch. The signal level from the playback heads should be adjusted for maximum output level and matched to within 1-2dB. This is relatively easily achieved at 1KHz however the task is significantly more challenging at 10KHz where gap alignment becomes super-critical.

As an aside, you may notice a little bias ‘bleed’ superimposed on top of the audio on playback head 1. This is due to its physical proximity to the record head. The bias signal is effectively a L.F. (low frequency) radio signal and the wires to the record head act as an antenna launching (transmitting) the bias signal, which is then the picked-up (received) by the playback head connecting wires. Although this bias contamination can be seen on the ‘scope it cannot be heard as it it is outside human audible range and outside the upper frequency limit of a guitar amplifier.

In theory the head alignment procedure is fairly straightforward. First, position all five heads by eye so they are centered on the drum face as described earlier. Next, inject a 100mV 1KHz sine wave from the signal generator, use the ‘scope to monitor the output and power the Echorec up. Hopefully the scope will show at least some output signal from the heads. Now begins the game of carefully adjusting the heads to maximise the signal. Obtaining a 1KHz signal is not so difficult, however a 10KHz signal is much more frustrating and challenging. The entire alignment process can easily take the best part of day. So be warned. It’s skilled work requiring expertise and the patience of an angel, and there is a proverb about that—”Fools rush in where angels fear to tread.”

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Binson Echorec Head Adjustment