A brief introduction to DIN sockets on hifi

I regularly mess with all kinds of vintage hifi and audio stuff, but I have a particular soft spot for compact cassette decks and tape recorders, and a side effect of this fondness is that I'm somewhat frustrated by RCA cables. To put it bluntly, stereo RCA cables in their "modern" form are a blatant bodge. The plug can only carry one signal channel (since it was designed before the rise of stereo), so let's just use two of them. Yeah, maybe, if you're just putting something together quickly for a tech demo, but this solution adds a lot of unnecessary complication to hooking up tape recorders in the form of a frankly ridiculous number of wires and plugs¹.

An alternative solution in the form of the the DIN connector² has existed and was widely used in Europe for a while, but it has now faded into relative obscurity. This means there's not a lot of information about it on the internet, so when I tried using DIN cables I ran into some unexpected quirks. This page will hopefully save you the trouble of having to figure this out for yourself.

Pinout

The diagram below shows the usual pinout used by amplifier tape sockets. Playback only equipment (tuners, record players) will generally use the same pinout with the "rec out" pins unconnected.

The cables connect each pin to the same pin on the other end, so the socket on a tape deck will have a mirror image of this layout, the output is connected to pins 3,5 and pins 1,4 are used for input³. This has the side effect that you can't use an ordinary DIN cable to connect something like a tuner directly to a tape deck, but since that's unwise for reasons I'll get to later, that might be an intentional feature.

One thing to note is that while hifi equipment generally used this pinout, there wasn't an actual standard set down for this so other audio equipment like portable tape recorders could very well have some other pinout. As usual, when in doubt its best to consult a manual if you possibly can before plugging anything into it.

Cables

One difficulty in using DIN sockets on your equipment is that DIN interconnects aren't made anymore. There are plenty of cables around to connect a DIN socket to something else, usually RCA or an audio jack, but cables with DIN plugs on both ends seem to be made only for MIDI, which doesn't use all 5 pins and therefore MIDI cables often don't have all pins wired. As such, you either have to find some used cables or make your own from scratch. I personally went with the second option using some quality plugs made by Rean and a length of shielded microphone cable, because this is one of the rare cases of a home-made cable being much higher quality than anything I could buy.

Making your own cables also eliminates wiring headaches you could run into with second-hand cables. I have some old, home-made cables (courtesy of my parents' garage) with only the playback pins wired up and one such cable actually has its connections crossed. I have no idea if any such cables were ever sold commercially and if there was any standard in place for marking how a particular cable is wired. The only advice I can give (again) is that you should probably check the wiring of any unknown cables you encounter for yourself before using them for anything.

Levels

One thing you quickly find out if you connect to a tape deck using the DIN socket is that the output turns off during recording and for a fairly good reason. If I mess with my Sony reel-to-reel I reliably get a nasty high-pitched squeal by turning the monitor switch to "source" and turning up the level of the DIN/microphone inputs, even with no actual input signal. You might think this is down to the signal wires being packed close together in one wire and that certainly has to do with it. But there's one more reason which has to do with signal levels.

Turns out that while the output signal in DIN sockets is roughly equivalent to a line output and DIN inputs on amplifiers can generally be treated the same as a line input, the same is not true for cassette recorders. For reasons I can only guess (there's not a lot of information about this, that's why I made this page), tape recorder inputs have a much higher sensitivity, usually in the range of 1..10 millivolts. They are effectively as sensitive as a microphone input and in fact they are often connected to the microphone preamplifier of the tape deck.

This of course makes DIN inputs much more succeptible to interference or crosstalk from the output. However, it also means an ordinary DIN or line level output would overdrive them significantly, even at low volume or recording level. To solve this problem, the tape output pins are wired through a fairly high value (several hundred kiloohms) resistor on amplifiers with DIN sockets. This attenuates the signal to a level that the input on tape recorders can tolerate, although this arrangement of attenuating a signal and then amplifying it back seems like a good recipe for noise. Somewhat surprisingly it seems to work all right in practice as long as you don't want to monitor recordings.