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Old 30th Nov 2022, 11:27 pm   #21
Synchrodyne
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Join Date: Jan 2009
Location: Papamoa Beach, Bay of Plenty, New Zealand
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Default Re: Interconnect lengths.

Quote:
Originally Posted by Synchrodyne View Post
Somewhere I think I have a reference [to the origin of the DIN tape recorder interconnect system], but I’ll need to look for it.
Found it!

Here is the main reference, which explains the background and progression from the “diode” outlet:

Spring pp.142-145.pdf


And this is another example:

Diode Socket Plate.pdf


This WW 1962 September item indicates that BREMA issued a set of recommendations on the matter. I wonder if there is any archive of such BREMA recommendations, or are they lost to posterity?

WW 196209 p.434 BREMA Receiver-Recorder.pdf





Cheers,
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Old 1st Dec 2022, 10:20 am   #22
cmjones01
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Default Re: Interconnect lengths.

Quote:
Originally Posted by Synchrodyne View Post
Another ostensible reason for the DIN style radio-to-tape recorder connection was that back in the 1950s, not all domestic tape recorders had line inputs, but they all had microphone inputs. So taking the radio feed down to mic level, which is more-or-less what the DIN system did, was a solution.
Out of curiosity I looked up the circuit diagrams of two cassette decks I've used which had DIN connectors.

The first, a mid-1970s Sharp RT-442H, has a high/low input level switch which affects its input. In both cases the input is fed in to the microphone preamplifier, but in "low level" position it's attenuated by 32dB, and in "high level" by 52dB. Switching between mic and DIN input is done by the switch contacts on the 1/4" jack mic sockets. The DIN output is at what I'd call "line level" these days - a few hundred mV.

The second, the 1980ish Sony TC-K55 in its UK/European guise, actually feeds the DIN input straight in to the microphone preamplifier via a 3k resistor which gives very little attenuation. In this case it's actually necessary to switch the MIC/LINE switch on the front panel to the MIC position to get the DIN input to work! The DIN output is connected straight to the phono line outputs and is thus at high level.

I do find it a bit odd that the the inputs and outputs on the DIN socket on a machine like the Sony are not actually compatible with each other without attenuation.

Chris
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Old 1st Dec 2022, 11:15 pm   #23
Synchrodyne
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Default Re: Interconnect lengths.

That significant difference in signal levels between the DIN radio-to-tape and tape-to-radio directions was “baked in” from the start.

As noted above, the radio-to-tape signal was effectively attenuated – maybe by 30 to 40 dB – to avoid excessive loading on AM diode detectors. In the reverse direction, the tape recorder output was fed into the “gram” input, so needed to be at about the same level as the unattenuated signal that was fed to the high impedance divider. It couldn’t be otherwise unless an additional amplifier stage was incorporated in the radio receiver, and the economics of the time were against that.

Thus directly interconnecting two tape recorders via their DIN sockets (and a reversing DIN-to-DIN lead) could be problematical, unless they had output level controls or presets that allowed the signal level to be dialled down to match the respective DIN inputs.

I think that the tape input-output section of the Murphy A674R is illustrative:

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Presumably the tape out level was designed to match the radio input socket of the Murphy TR1 tape recorder (with its unlikely cascode input stage that makes one think that someone fired up the infinite improbability drive during that design exercise.)

One could say that the DIN system, at least on the radio (amplifier)-to-tape side, was used well beyond its “best by” date. By around 1970, the cost of adding emitter follower buffers to radio and amplifier tape output circuits would have been negligible, allowing them to supply “line” level signals without loading problems. Tape recorders might still have needed DIN inputs for compatibility with older equipment, though.

As a sidebar, although AM detectors were typically very load sensitive to the extent of needing resistive or active buffers for tape outputs, that was evidently not the case for at least some FM detectors. Thus, one finds some FM-only receivers (e.g. Ekco A274/A277/C274 and Hacker RV14 & RV20) where the tape outputs (which doubled as tuner outputs) were fed directly from the detectors, and so were at “line” level.



Cheers,
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Old 2nd Dec 2022, 11:17 pm   #24
jamesperrett
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Default Re: Interconnect lengths.

I don't know if it was part of the DIN standard but it is very common for line level inputs to be on pins 3 and 5 while low level inputs are on pins 1 and 4. Philips often made pins 3 and 5 dual purpose on their tape recorders. In play mode they would be an output while in record mode they would switch to being an input.
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