Binson Echorec Head Adjustment
by Phil Taylor
The author suspects there are many old Binson Echorec delay machines that are not set-up for optimal performance. Over time the heads wear, become misaligned during transportation or the machine may have been incorrectly tampered with at some point. A head misalignment of a few microns or a few degrees off axis will make the difference between the Echorec reproducing a swirl of rich, clear repeats or the machine 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
Adjusting the heads on an ‘Echorec’ delay machine is not a task to be undertaken lightly. It demands an abundance of patience and time – it’s no exaggeration to describe it as highly skilled and an art that is fast becoming forgotten. 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. 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.
Adverse head wear is myriadly reduced in a tape machine 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.
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.
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 length, 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 repitition. 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.
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 undetaken again.
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 poor a 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.
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.
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.
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. Once the correct tracking force has been set the pillar should be locked in position with low strength thread-lock such as ‘Loctite 222′. 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 will only get you so far when dealing with dimensions that are in the order of just a few microns one way or another. Also subjective audio tests by listening can be hit and miss too. The most fool-proof method of setting the machine up is to use a test signal generator and oscilloscope. The signal generator is used to feed a pure sinewave signal into the input of the Echorec and the ‘scope is used to monitor the ‘wet’ signal output from the output. The internal ‘mix’ trimpot needs to be adjusted fully clockwise so that only the wet signal from the playback amplifier is seen at the output. You can manually sweep the frequency of the signal generator to test the frequency response of the memory system and observe output levels. Each of the playback heads can be tested individually using the selector knob on the Echorec. Much more on this coming soon…