Monoblocs - relative length of cables, interconnect vs speaker

Discussion in 'TAG McLaren Audio Owners' Forum' started by tjobbins, Aug 14, 2005.

  1. tjobbins

    tjobbins
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    Hi guys,

    The manual for the Tag 125M lists as one of its advantages the fact that the monoblocs can be placed very close to the speaker it is driving, thus allowing for a very short length of speaker cable. This would then require longer interconnects from the pre-amp to the monobloc.

    I was wondering if everyone follows this design, or whether there are advantages to reversing the lengths - having short interconnects and long speaker cable.

    Intuitively it seems to me that it is better to minimise the length of the interconnect: the interconnect carries a low voltage signal, so any interference added at this level will then be multiplied by the power amp. This is not true if the same amount of interference is added to a speaker cable.

    Therefore interference on the interconnect will have a greater proportional effect on the signal than intereference on the speaker cable.

    I don't know if this argument can be expressed in simple numerical terms, but:
    if we assume the interconnect carries a signal level of '10', which is amplified 100 times to '1000', then adding an interference signal of level '1' results in a 10% effect if applied to the line-level cable versus only a 0.1% effect if applied to the speaker cable.

    Any of that make sense?


    Tom
     
  2. bushy30

    bushy30
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    Hi Tom,

    Don't let Udo hear you say that LOL

    The manual is correct ! I know this from doing PA work, always keep the power next to the speakers, the signal goes miles to the mixing desk and back in comparison !

    I can't remember the exact technical reasons, but if you look at recent posts in the TAG owners forum, Udo actually explains it !

    Cheers

    Bushy
     
  3. tjobbins

    tjobbins
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    Hehe, thanks Bushy. I certainly did not mean to impune Tag's recommendations! I was more wondering why this is the case, as it seems counter-intuitive to me. But then I am probably missing something important!
     
  4. bushy30

    bushy30
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    No worries,

    Graham, Steve et al will probably be able to answer it too !

    Cheers

    Bushy
     
  5. pjskel

    pjskel
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    It boils down basically to the fact that nearly all interconnects have a screen to mop up all manner of RF and EMI, whereas the speaker cables tend not to have any screening. Mind you, I've had plenty good results from longer lengths of Purist Audio speaker cables.
    A lot will depend ultimately on the construction of the cables being employed, and if stereotypical in design, longer line level connections won't unduly affect the signal, providing the screen has been properly gounded.
    Used to love the Furukawa cables of yesteryear with their flying grounding leads attached. Never got to try a full system's worth of it sadly.
     
  6. johnson

    johnson
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    Hi
    Also more recent TMA monoblocks have balanced inputs to negate the influence of noise.
    Regards
     
  7. Kenny Glasgow

    Kenny Glasgow
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    Tom

    Get yourself a good set of interconnects from Mark Grant in the Power Buys of the cable section "above". I can't recommend them highly enough :thumbsup:

    I've always wondered why people have long runs to their subs via interconnect and the have long runs of speaker cable to their speakers :confused:
     
  8. Dr Udo Zucker

    Dr Udo Zucker
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    Hi Tom, when it comes to signal impurities then there is more to it than signal amplitude. We need to look at the way interference can "attach" to the signal and ways we can prevent interference (addition) and signal degradation (distortion). Let’s do this:



    Looking at the connection from a preamplifier to a power amplifier, we have, as you rightly say a small signal, but actually not that small. Typically there might be a voltage between say 1V and 2V. The purity of that signal has to be maintained, no doubt, hence it is output (in most designs) by a low impedance pre-amplification stage, then “carried” via the cable before fed into a high impedance input stage at the power amplifier. That way (high mpedance input) we have almost no current flow, hence the cable’s resistance is of no real interest and almost more importantly we can now safely screen the connection cable without detrimental effect to the signal. Now, screened and voltage based, it is very difficult to interfere with or distort the signal whilst it “carries along the cable”. However, it is getting better: The low output impedance at the preamplifier prevents that any potentially interfering signal has a real chance to add significantly to the signal. We therefore can safely say that the chosen design allows the “clean” transport of the audio signal over a long distance between preamplifier and amplifier and it will be (almost) only mains hum issues we might suffer from due to the reference grounds being a long distance apart and therefore often different. Of course that effect can be eliminated by using a balanced input stage at the power amplifier end.



    The situation at the power amplifier’s output is different. Here the issue is less with noise (as the signal is large- didn’t you say it!) and the amplifier’s output is really, really low impedance. However, we have to make sure that the power amplifier is driving the speaker and partially the speaker cable. Therefore we have to prevent inductance (L), capacitance (C) and resistance (R). Well, the best way to achieve this is to remove the cable all together: L=C=R=Zero. If that isn’t possible we need to minimise each parameter. We could make the cable “thicker” to reduce R; we do not screen the cable to drop C (we accept the added noise) but reducing L isn’t easy and most frequently adds C. Of course speaker cables can be constructed to minimise these parameters for any given length, but no measure taken/money spent will have the same effect as simply reducing the cable’s length. Therefore, why spending so much time/money designing a long speaker cable, if we simply have to shorten it to get an even better result? The shorter, the better- it is simply that.



    Personally I replaced a 2.5 m ultra-expensive Transparent Reference XL SS cable, which uses passive filters, with a 30cm TAG McLaren speaker cable. Now I have the “ultimate” speaker cable due to minimal length as little cost, whilst yet another two pieces of audio experience are “dusting” along in my cupboard.



    I hope above helps, although purists of the engineering society might say that I should have used a more scientific language.



    P.S.: Above is only true for intrinsically stable amplifiers. If that isn’t the case the speaker cable’s L is essential to stabilise the amplifier and hence such amplifier usually requires a very specific cable as otherwise it will self-destroy or oscillate. To sell amplifiers which are not intrinsically stable, whatever the their load, isn’t a good move in my opinion!


    Typo, spotted by Steve, has been corrected. Sorry for any confusion and my thanks to Steve!
     
  9. bushy30

    bushy30
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    Hey Tom !

    Hate to say I told you so ! :D

    Thanks Udo, I'll try and keep all that in my pea brain for next time !

    It's great to be able to discuss information like this, now I'm just wondering how I can get my 700:7R 30cm away from all of my 5 speakers !!!!!

    Bushy
     
  10. Dr Udo Zucker

    Dr Udo Zucker
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    Hi Bushy, it isn't difficult to place 5 speakers around a 700:7r using short cables, but rather an achievement to find a suitable listening position then. Maybe a good case for TMREQ (or is it ALREQ today) :D
     
  11. Stevesky

    Stevesky
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    I think there is a typo here as this is mixed around. The preamp output stage will have a relatively low output impedence, while the power amp input stage should have a relatively high impedence.

    For example an AV32R output impedence is 47ohms, while a 250MR input impedence is 25K Ohms.
     
  12. bushy30

    bushy30
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    WOW ALREQ !

    Maybe if I could pay John to do a software revamp.............

    :D

    Bushy
     
  13. tjobbins

    tjobbins
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    Absolutely it does, thank you! I do like to understand why something is the way it is - sometimes it has a practical benefit, othertimes just out of pure interest :)

    I am going to get the Mark Grant interconnects, place my amps at the base of my speaker stands, and connect them using 0.75m lengths of multiple CAT5 cables, home-made :) (Learnt that trick over at the Cables & Cabling forum!)

    Thanks again everyone, particularly Udo!
     
  14. Miron

    Miron
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    Steve, he is simply enjoying portuguese sun (and everything what comes on the top) for far too long :)
     
  15. Dr Udo Zucker

    Dr Udo Zucker
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    Hi Miron, not really - it was rather my 18month old son who came into my office with the clear intention to pull every book from the sheves and to push every CD ROM onto the floor :hiya:
     
  16. Miron

    Miron
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    Udo, hold on for two and a half more years and he will help you put all disks from smashed boxes into new ones (from personal experience :) )
     
  17. babaroga

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    hehehehe, welcome to the club ;)
     
  18. bushy30

    bushy30
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    Hi Udo,

    Apologies for mixing my threads but.............

    This is really good news ! can we expect in 20 years or so that there will be a continuation of the Zucker heritage, and some really outstanding, quality kit will be brought to the market ???? Maybe even ZuckerREQ !

    Waiting with anticipation !

    Bushy
     
  19. JohnDee68

    JohnDee68
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    Hi all

    At the moment I have my Hi-Fi placed between my speakers, but I have the option in the future to place the Hi-Fi in a different location leaving only the 125m's close to each speaker, but such a setup would leave me feeding one mono with about 2M of interconnect and the other about 4m of interconnect, would this difference in interconnect cable length cause any problems with the signal from the Pa20r to the 125m's?

    Thanks
     
  20. Dr Udo Zucker

    Dr Udo Zucker
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    Hi, whilst this isn't the best set-up for the audio purist, there will be no difference in performance assuming there isn't an issue with mains hum (just listen to the hum emission to decide) and any RF interference (just listen to any hiss if there is no signal).
     
  21. JohnDee68

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    Hi Udo

    Thanks for the reply, at the moment I don't have a problem with mains hum that I'm aware of, but Re the RF interference you mentioned, there is a very slight hiss from the tweeter when there is no signal, which is inaudible unless I'm right next to the speaker. Would this RF interference be increased if I were to use longer interconnects?

    Thanks - John
     
  22. Dr Udo Zucker

    Dr Udo Zucker
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    Hi John, that tiny hiss level, you are experiencing, is most likely the level produced by the amplifier itself (and not caused by any interference).
     
  23. JohnDee68

    JohnDee68
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    Hi Udo

    Thanks again for the reply, at least now I can think of introducing longer analogue interconnects without worrying about introducing possible problems with the signal. As well as the 125M Manual suggesting this setup, the manual for the speakers also suggest that the space between speakers is kept clear to aid soundstage reproduction.
     

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