Though DIN sockets are most widely used on 'consumer' and low cost equipment, the more professional end of the business isn't immune to their disadvantages. Sometime or other, we all have to meet with ill fortune... er, pardon... I mean wire up a DIN lead!! You see the DIN has fundamental design problems that make it the least popular connector in the business.

(1) Chaos. The common 5 pin DIN alone has over a dozen wiring configurations, so if you lose the maker's handbook giving the pinouts, making up new leads can involve a lot of hassle. Conversely, the chances of an existing DIN to XLR lead (say) mating up with DIN sockets it wasn't originally designed to suit are very slim.

(2) Even skilled wiremen find the tiny, cramped solder pins distasteful to wire up, especially when the plastic base melts and mixes with solder dross.

(3) Once wired correctly, the cable clamping is poor and stresses the terminations.

(4) On assembly, the mechanics are weak and the pins tarnish very rapidly. Nor do they wipe clean readily with use.

Tackling the pinout problem first, Figures 1 and 2 illustrate the original 3 and 5 pin wiring standards, whilst Figure 3 displays an alternative set of 5 pin connections relating to modern, voltage matched (Low impedance into High impedance) equipment. To understand how this mass of pinouts developed, let's take a historical look at the DIN.

History

The DIN plug originated in Germany in the 50's, DIN being the abbreviation for the name of the German standards organisation, analogous to our own BS (British Standards). At the time, it was a sensible concept, restricted to the interconnection of (valve) radiograms, tape machines (Grundig!) and amplifiers. Above all, this standard had been established just as the audio age was dawning, and not twenty years too late, as is often the case with most standards!

The DIN rapidly established itself as a Pan-European connector thanks largely to the backing of companies like Philips, but it was swiftly overtaken by new technology, such as stereo, and new matching concepts which demanded alternative pinout standards and/or plugs with more pins.

The basic scheme of errors is as follows: (A) someone decides to invent a universal audio connector. (B) It's given three pins, two for the basic connections, the other for capacitor microphone's polarising voltage or for balanced line operation. (C) For other, line-type connections, the third pin appears redundant, until, that is, a consumer goods manufacturer comes along and decides to use pin 3 for other, disparate or outright arbitrary purposes, in order to squeeze more interfacing facilities into fewer sockets.

Even at this juncture, the 3 pin mono standard (with five basic variations) had become unnecessarily difficult to memorise; by comparison, the 3 pin XLR which had the added complication of male and female versions was relatively standardised. Then came 'stereo', and rather than use separate 3 pin DINs for the two channels (as is normally the case with XLRs), two more pins were retrofitted to the 3 pin DIN to produce the now infamous 5 pin DIN.

The new stereo pinouts were by and large a logical extension of the 3 pin, the tuner output being an exception (see Figure 2). However, this retrofit meant that the new 5 pin DIN had a bizarre 1, 4, 2, 5, 3 pin numbering sequence, not to mention the inconvenience of bunching two cables into each plug.

Later, and looking now at Figure 3, the 5 pin plug became used as a combined stereo input/output connector on reel-to-reel tape recorders, whilst alternative connections arose for other equipment.

Line inputs, for example, could appear on pins 1 and 3 or pins 3 and 5. A means of getting around this was to link pins 1 and 5 together (see 'Line Input 1 - Universal' Figure 3), but this didn't alleviate another, more basic problem, in that outputs could be easily misconnected to other outputs. Under normal circumstances this was a harmless mistake, as the DIN standard involved putting large (100k) resistors in line with the outputs, but if you had removed them to achieve some response above 3kHz, you'd have discovered that the transistor circuits of the time were easily blown up.

Akin to this, the high impedance pinouts, associated with valve equipment, became obsolete in favour of 'voltage matching' (we will return to this in a future issue of Interconnect), and so pinout standards were further hacked around. The resulting mess can be surveyed in Figures 1 to 3. All that can be said with certainty is that pin 2 (in the centre) is always the earth/ground connection, at least on 3 and 5 pin DINs.

Reconciliation

So far the argument has concerned DINs in general, but in 90% of instances, the average home studio will have DIN connectors concentrated in two areas only. The first is cassette machines. Here, you should use the phono outputs, if available, but failing this you can be certain that the DIN socket on your tape deck will be wired according to the tape input/output pattern (see Figure 3). This is one standard you can rely upon, thanks largely to the cooperation between Japanese cassette manufacturers.

The second area is on microphones. Some mics, notably those from AKG, Beyer, Calrec and Sennheiser, have DIN terminations in their base, and here again the connections have a good chance of relating to the pinouts shown in Figure 1, though you'll need to know whether the mic is balanced or has a polarising voltage.

From time to time (to pay for your sins!) you'll have to wire up a DIN lead for an alien piece of equipment, without knowing anything at all about the pin connections. If this situation coincides with a "Hurry up, we've got to begin in five minutes!" scenario, then proceed calmly as follows: Draw a pin diagram of a DIN. Switch on the equipment. Rig up a test cable, one end being plugged into a test amplifier or mixer channel. At the other end attach 'crocodile' clips to the wire tails. Snip off two pieces of paper clip (or strip back some single core wire) and load these into the croc clips, then push the grounded probe into pin 2 (in the centre). By turning the channel gain up and monitoring on headphones, you should detect hum, hiss or some other indication of output as you try inserting the live probe into the other contacts, in turn.

Having located the output(s), mark these on your diagram and make the output test connection more robust with a narrow strip of gaffer tape or Blu-Tack - otherwise, you'll find that the probes keep falling out. You can then proceed to confirm input(s) by pushing another probe against the remaining contacts, listening for a hum or buzz. Incidentally, if you're dealing with a 3 pin DIN, it's wise to make a quick check with a meter for possible DC polarising voltages. With a 5 pin (stereo) DIN, you may also want to note down how the inputs and outputs relate.

Formats

The cheapest DIN plugs are held together by a thin, plastic insulating cover and are therefore very fragile, to the extent that slight mechanical damage often strains or rips off the internal connections. They also fall apart when tugged too hard from a tight fitting socket. Put simply, they're best avoided. If you do have to use them, then don't recycle them: if you come to rewire a lead, throw the DIN away unless it's still in pristine condition.

RS Components produce more rugged DINs. These have solid brass bodies, a rubber strain-relief bush, and screw-together construction. Whilst a great improvement, in practice the bushing tears off easily and the fixing screw frequently falls out because the brass used is too soft to allow proper tightening. Furthermore, the cable clamping is primitive, and subjects the connections to an unacceptable strain whether it's gripped before or after soldering. A latching version of this DIN is also produced, which suffers the same design complaints.

Put in perspective, the RS DIN is fine, indeed excellent, for semi-permanent patching inside 19" racks, for instance, but not where it's going to be subjected to regular aggravation. Making the best of RS DINs involves either locking the screw with a fixing compound or placing a rubber sleeve or some tape over the screw to prevent it from escaping should it work loose.

If these setbacks sound unappetising and you're prepared to look for a better product, one likely candidate comes from Preh, an original German manufacturer of DIN connectors. The Preh DIN series, available from studio suppliers like Canford Audio and Future Film Developments, comes solely in a latching version, with a strong, bayonet-style locking ring. (The latching ring can be removed from plugs if you need to interface them with conventional DIN sockets). There's also a grounding contact, which comes hand in hand with a more positive connection between case and chassis. This reduces noise, whereas lesser DIN plugs will often cause rustling noises when wobbled in their sockets. Last, but not least, the mechanics and cable bushing are altogether more robust. Confirmation that they're tough enough to survive on a studio floor comes when Preh DINs are spotted being used to supply power to DI boxes and to connect up mics. Preh devices cost no more than the inferior so-called 'professional' latching types from RS, and are strongly recommended for mic leads or any other situation where DINs are likely to be trampled on.

Another more esoteric DIN product is the Bleecon L1904A series made by Belling-Lee. All the plugs feature a push-pull latching system which sometimes plays up, but otherwise provides a very firm, vibration-proof yet readily uncoupled connection - rather like latchless XLRs. Bleecons are also available with moisture tight rubber covers which find applications in gear used outdoors, for example, on portable recorders.

Matching

One aspect of the DIN system not discussed so far in detail becomes evident when you examine the inside of a cassette recorder fitted with both DIN and phono sockets: the DIN socket terminals often have resistors soldered in line with their connections. The reasons for this relate back to valve and early transistor technology, where matching involved the concept of a constant current transfer eg. 1 millivolt of signal per 1k of load resistance (input impedance).

The practical implications of this are two fold. Firstly, output (source) impedances are often much higher than they need be, giving rise to increased crosstalk, noise and often serious high frequency loss. Input impedances may also be excessively high with identical results. Secondly, on the plus side, the system is partly self-compensating as regards sensitivity, given that high level sources will tend to have lower source impedances. Also, outputs are almost immune from damage, which is fortunate because it's so easy with the DIN system to accidentally feed signals into outputs.

DIN Laws

(1) Avoid using DIN outlets whenever alternative connectors can be used.

(2) Try to avoid involving DIN sockets in regular interfacing. If the wiring to equipment with DIN sockets has to be repatched regularly, consider wiring the DIN plug(s) into a termination box or patch panel thus allowing everyday connections to be made, or changed, via XLRs or B gauge jacks. With such a set-up, the DIN connection becomes semi-permanent so it will survive longer and hopefully give fewer problems. Some products feature DIN sockets in awkward places, so this external termination will also help access.

(3) Many DIN plugs have silver-plated pins which tarnish very quickly. These should be cleaned regularly with a polar solvent like alcohol; stronger organic solvents will probably melt the plastic mouldings. Abrasives will quickly strip down the plating, so when you come to clean sockets, don't poke bits of wire up them. A sliver of matchstick soaked in meths or alcohol will do a much better cleaning job without damaging the plated layer. If the pins are seriously contaminated, unwire the socket, you'll then be able to release the pins by twisting, and then remove them for cleaning.

(4) If your DIN terminations give impedance-related problems (such as treble loss), remove the constant-current resistors and wire direct. Alternatively, by reducing the resistors in series with the output to about 100 ohms, you can retain a measure of idiot protection without incurring HF losses.

That about sums up the DIN connector for now. If possible avoid DIN connectors like the plague, but if you are forced to use them, then the information made available to you here should help make life a little more bearable. Good luck.