Interconnect lengths.
 

Hi all

I have a mid-range hifi separates collection which works just fine for me. My one problem is interconnects - I never seem to have enough, or enough long enough.

So, to deal with this I have just sent off for a new one (to check the quality) and I want for a long length so I can use it with whatever source I choose and have some slack instead of a taught cable.

Then I wondered if there's any down side to having long interconnects besides messy cabling round the back.

The cable I bought is cheap enough to spend a couple more quid on a bit more length (we are not talking gold and diamond coated run-in by aliens stuff here).

Martin

Re: Interconnect legths
 

It's unlikely to make any difference over just a few metres, even with cheap poorly screened cable. The output impedances of transistor HiFi equipment are quite low.

Re: Interconnect lengths.
 

Yes.

The only thing you don't want excessively long in a set-up like yours is the leads from the turntable. Longer leads mean more capacitance which would cause roll-off of higher frequencies. They'd also be prone to hum pickup, as the output from a MM cartridge is much lower than from your CD player etc.

Re: Interconnect lengths.
 

Cheers chaps. The turntable is probably the shortest distance between source and amp and I don't need a cable for that. It's the additional tape deck, CD and so on - I end up borrowing a cable from here and there, which is rarely long enough, and lose track of what is missing a lead.

From what I gather the cable I am getting is pretty decent. I won't mention the brand name just yet in case I am disappointed.

Re: Interconnect lengths.
 

If you make up your own cables you can always get exactly what you want. I have a reel of shielded cable and a bag of nice Amphenol phono plugs. If it turns out the lead's too long, you can easily cut it down... :-)

Re: Interconnect lengths.
 

As above, fine for transistor equipment with outputs of low source impedance. I have often run 10-20m of unbalanced shielded cable from domestic -10dBV phono outputs.

Cable capacitance is more critical for line outputs from domestic valve equipment that has high output impedance, in which case long cables will form an RC low-pass filter that encroaches on the top of the audio spectrum and rolls off the treble. Professional valve (studio) gear solved this problem by driving all outputs with matching transformers to lower the impedance (and balance it) and make it uncritical of the interconnect capacitance.

Re: Interconnect lengths.
 

Excellent Advice.
I use good quality standard (EG Beldray) microphone cable twin core with separate shield and I've used every sort of RCA plug going over the years. can't say i have noticed any difference in audio quality although some plugs are more robust than others.
Luciens post also points out about lengths.
I have a very long 8m run of the aforementioned sreened mic cable between my valve preamps and a valve power amplifier and it performs with absolutely no audible impairment of performance.
One preamp has a cathode follower ouput with an output Z around 600 ohms and the other is a transformer output with Z around 25 ohms (I think, it's certainly less than 100 ohms) into amplifier input Z of either 100k or 1 meg depending on which Valve amp.
And I also get the same results when using any of my Silicon preamps either into a valve power amp or solid state power amp, usually a Quad405 but i have used others.
I hope that gives an insight Martin, I'd confidently use commercial connecting leads of 3m or more if necessary. Which it can be if you're thinking of connecting an analogue aduio output from a TV for instance to an audio system situated some distance from the Screen, I did this until we got a new telly that only had digital outputs and now luckily discovered that 7m of optical cable works into the DAC in the main system. Which I am led to believe is pushing it a bit.
Regards.
Andy.

Re: Interconnect lengths.
 

Thanks to everyone for their contributions. It seems my ambition of having more than long enough cables to all sources will be fine!

I am capable of making my own leads up but think for me it is easier and probably cheaper and time effective to buy what I need ready made.

Re: Interconnect lengths.
 

What everyone says. Unless it’s a DIN output, eg to/from a tape recorder, in which case they are high impedance, and cable capacitance is critical.

Many moons ago I had a B&O tuner/amp feeding a Ferrograph R-R machine through a 1mtr 4-way screened cable with a short break out cable at the Ferrograph end. There was a noticeable lack of treble, even with the monitor switches set so the signal went down the cable to the Ferrograph and back to the amp without going onto the tape. A different 1mtr 4-way cable much improved things. The first cable had much higher capacitance than the second cable or any other cables I had around at the time, and got itself a warning label attached. Turns out the B&O had a high value resistor (200k?) feeding the DIN socket.

(I have wondered whether the DIN current drive spec is the grain of truth behind all the magic cables audiofoolery)

Stuart

Re: Interconnect lengths.
 

Watch out for phono leads sold as screened ,which were not screened just twin wire , I found this out one day whilst repairing a record deck the lead passed over my soldering station tx producing a loud hum very strange I thought ,tried a different lead ok ,so I chopped the plug off the offending lead only to find no screening , admitted they were cheep but when sold as screened you expect a screen. Mick.

Re: Interconnect lengths.
 

If you make your own cables up, then you also know just what's gone into them, also by keeping a reel of cable and some connectors around, I can make up any combination I need without slowing a job waiting for things to arrive.

Yes, cables can affect the sound, but you have to have done something wrong to achieve this, and it's properly understandable once traced.

One thing I've noticed; "Interconnects" are always much more expensive than mere cables :-)

Audio cables may be coaxial in their screen, but they are usually bad mismatches to source and load impedances. This doesn't matter because they are such short fractions of a wavelength. So thy can be considered to act like lumped capacitors in loading sources, preamps, etc. You can get lower capacitance per metre by using smi-airspaced or foamed dielectric cable.

Some badly designed gear can also go unstable into capacitive loads but that's really the gear's designer's fault.

David

Re: Interconnect lengths.
 

That's very interesting Stuart. I had no idea, and have a number of tape decks that, when running, will need various DIN connections. I can see a search coming on when I need to make some up...

Is there a reference somewhere?

Re: Interconnect lengths.
 

I don't have a reference to hand, but I understand that the origin of the DIN current-driven audio interconnection was that originally the audio output (intended for tape recording) from an AM radio was taken straight from the detector diode. To avoid loading this too much, and thus flattening the selectivity of the final IF stage and spoiling the radio's performance, a high-value resistor was included between the detector and the DIN output. The gain was made up in the tape recorder.

So a "proper" DIN audio connector isn't just the same signals as on the phono connectors but wired to a different socket. There are electrical differences as well. However, there is a lot of equipment out there which just uses "line level" signals on DIN connectors.

Chris

Re: Interconnect lengths.
 

All this non-compliant DIN stuff was apparently a source of extreme frustration to the cassette deck reviewer of HiFi Choice in the late 1970s (Angus McKenzie?? https://www.stereophile.com/news/011...zie/index.html )

Re: Interconnect lengths.
 

Sound logic Martin.
If you don't anticipate needing to knock up lots of connecting leads once you've got your setup done, then buying modest but functional ready made stuff does make sense.
If a cable is a bit too long then its fine to coil a bit up and tie it with a twist wrap (Like your missus uses on freezer bags) for neatness. You aren't worried that you've just made a Choke balun for RF...................
The points made about some cheap stuff not having adequate screening are valid, but, and trust me on this, at line level unscreened wire can be very effective given the usual caveats on exposure to strong EM fields.
I have a few lengths of QED "Incon" leads bought in the 80's when the ideas about wires sounding different were gaining ground in the hi fi press....... These are simple 2 core unscreened wire,allegedly directional (yeah right) made from directionally drawn oxygen free pure copper (Yeah right again) and were modrately expensive but not in the league of modern snake oil at least QED charged a reasonable amount and the plugs were well soldered.
Anyway I have a 2m length and a few short 0.5m ones still and frankly they are just as good as line level patch cables as any of my other stuff, including a dalliance with some rather sexy looking PTFE wrapped and insulated 2 core and screen pure silver plated wire that I made most of the stereo system connecting leads with.
And My Lug 'oles are better than most of my age, I am cursed with a hyper sensitivity to high frequencies, somewhat ameilorated by the years but still better than a typical 65 year old.
Theres more to the way an audio system performs to the listener than simple extremes of frequency, some of which is as simple as personal taste, and a lot of which is rather subtle and hasnt got that much to do with "Accuracy".
Over to RW for thoughts on psycho-accoustics, and to the pro Audio and hi fi designers lurking here (And theres quite a few) They'll understand what I mean.
Andy.

Re: Interconnect lengths.
 

There’s a further gotcha with DIN connectors for tape recorders. On the 5pin DIN sockets for connecting amplifiers to tape recorders, the pins which are inputs on the amplifier are outputs on the tape recorder and vice versa.

Hence the default 4-way DIN cable is electrical “crossed”, ie pin 1 (4) at one end connects to pin 3 (5) at the other end. (Pin numbering going round the arc of a 5 pin connector goes 1,4,2,5,3 to maintain pin number compatibility with the 3 pin connector, the centre pin, pin 2, is the signal ground).

This is fine for connecting a tape recorder to an amplifier, by far the most general case. If you want to connect two tape recorders together, eg to copy tapes, you need an uncrossed cable - sometimes confusingly called a crossed cable.

The DIN 5-pin audio connections are very convenient for users with a ”standard” setup: you have one cable to connect your tape recorder to your (nearby) amplifier, and one cable to connect your record deck. With phono connectors you have to work out left and right, input and output etc, DIN sorts out all that for you, and even lets you have separate ground connections for signal and chassis (pin 2 and the outer shell), useful for record decks. If you want to do anything non-standard, eg long leads or connecting two tape recorders together, you’re probably better off using phono connections.

Automation is wonderful until you want to do something different.

Isn’t there a quote about a camel being a horse designed by a committee?

Stuart

Re: Interconnect lengths.
 

Err, no.

As you said, the output pin on an amplifier is an input on a tape recorder and vice versa. So to connect a tape recorder to an amplifier, you need a straight-through cable. For example pin 3 on the tape recorder is left channel output, pin 3 on the amplifier is left channel input, and you want to connect those together.

To interconnect 2 tape recorders you need to connect inputs to outputs as usual, so you need a cable that connects pin 3 at one end (left output) to pin 1 at the other (left input), etc. That is the crossed cable.

I feel it would have been better to always have pin 1 as an output, pin 3 as an input, etc and thus always need crossed cables. But it's not done that way.

I've seen it recommended that all long-ish DIN cables should be wired straight, and that you should have a short adapter lead, 5 pin DIN socket to 5 pin DIN plug wired 'crossed' which you fit onto one end of the long cable if you need crossed connections. At least then you don't get confused as to whether the long cable is crossed or not.

Re: Interconnect lengths.
 

The trouble with Angus in those days is that whenever a DIN type plug/socket was used, he 'assumed' that the accompanying electronics should be to the DIN standard (for valves!), when in truth that plug socket arrangement was simply being used for simplicity or the choice of the designer. DIN plugs and sockets are not the most versatile, and they were plagued by some poor quality ones on the market, but personally I've never had a major problem with them and apart from what I've mentioned, never had a problem with them; they're plug and play, as they say..

Re: Interconnect lengths.
 

Somewhere I think I have a reference, but I’ll need to look for it. That’s basically my understanding. One additional point is that originally, a high impedance potential divider was used at the radio receiver end. But at some stage it was realized that the tape recorder input itself could serve as the bottom leg of the divider, meaning that that part of it was not required in the receiver.

Diode type AM detectors tend to distort quite noticeably if the AC load impedance is much below the DC load impedance, which will happen if a parallel load, such as a tape recorder output, is added. And back in the valve days, the use of a buffer stage (cathode follower) was usually out of the question economically. So the high impedance divider was an economical solution. I think that Murphy did this on some of its late 1950s receivers, with something like a 3M3 upper leg.

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.

That I think explains for example the input labelling on the Revox A77 tape deck. “Radio” had a sensitivity of something like 2.5 mV, and a moderate impedance, and was essentially configured to take the input level from a DIN-style source. “Auxiliary” had a sensitivity of around 35 mV, and was essentially the line input. It also had a high impedance, 1M, in deference to the fact that at the time it was released, it was likely to be used at times with valve amplifiers whose unbuffered tape outputs typically liked to see 500k or higher. In those days, the domestic hi fi "line" level was often around 100 mV at 30% modulation – although the upward migration to around 300 mV average programme was probably already happening.


Cheers,

Re: Interconnect lengths.
 

Oops, senior moment. You’re right Tony, I’ve got my cables crossed. Long time since I was doing tape to tape transfers, but I knew it needed an odd cable.

Sorry for the confusion everyone, Stuart