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Thread: Speaker cable - Harbeth's recommendations to avoid "exotoc cable"

  1. #21
    Join Date
    Jan 2006
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    South of England, UK
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    4,271

    Default Amplifier stability and speaker cable - a cautionary tale

    Production dept. asked me to provide them with a new small power amplifier to be used on one of the test rigs. Only a few watts were needed, just enough to sweep-test every drive unit listening for buzzes by ear. The previous B&K oscillator (now faulty awaiting repair) had a speaker drive output stage, but the newer B&K doesn't have an inbuilt power amp.

    As It happens, I'd half assembled into a case a commercial "DIY" power amp module comprising of heatsink, power supply and circuit supplied in one neat resin-potted housing. It's a design that's been available for years and sold to the disco/pa market to drive long speaker lines.

    Assembly complete (wiring mains, phono input socket and psu transfomer) and hooking up to an oscillator and speaker and all seemed well. Until I turned the volume up more at which point there was a tell-tall audible distorted character to the pure tone: the character of circuit instability. I clipped the 'scope across the speaker feed to see, as expected, that one half of every sine wave had a burst high-frequency supersonic noise, which whilst inaudible itself, manifest as distortion in the audio band. Reduce the audio input and stability returned.

    Disconnecting the speaker so the amp was not actually generating power into a load, and again, stability. The solution was a 'zobel network' comprising a small resistor and capacitor in series soldered directly across the output terminals. Cost about GBP 0.10 (ten pence) and commonly fitted to amplifiers to partially-cancel the inductive/capacitive reactive load of a speaker cable and/or loudspeaker itself. But not this one.

    So the message from this is .... we want to assume that audio power-amplifiers are well designed and stable into the sort of loads that typical cables + speakers present, such as this combination. But that may be over optimistic on our part. Unless we have test equipment we cannot look for instability and if we identify it by ear, the damage may have already been done. There may indeed be latent instability which is only triggered on signal or transient peaks, depending upon drive level as in this case. The more exotic the speaker cable and/or the loudspeaker load the more we tempt instability. That's why I design Harbeth speakers to present as benign a load as possible to the amp and advise you to use simple, standard cable that looks like simple standard cable.

    If anyone is interested I'll take a photo off the 'scope to show the distorted waveform before the zobel was fitted.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  2. #22
    Join Date
    May 2011
    Location
    Australia
    Posts
    39

    Default Amp stability

    Quote Originally Posted by A.S. View Post
    Production dept. asked me to provide them with a new small power amplifier to be used on one of the test rigs. Only a few watts were needed, just enough to sweep-test every drive unit listening for buzzes by ear. The previous B&K oscillator (now faulty awaiting repair) had a speaker drive output stage, but the newer B&K doesn't have an inbuilt power amp.

    As It happens, I'd half assembled into a case a commercial "DIY" power amp module comprising of heatsink, power supply and circuit supplied in one neat resin-potted housing. It's a design that's been available for years and sold to the disco/pa market to drive long speaker lines.

    Assembly complete (wiring mains, phono input socket and psu transfomer) and hooking up to an oscillator and speaker and all seemed well. Until I turned the volume up more at which point there was a tell-tall audible distorted character to the pure tone: the character of circuit instability. I clipped the 'scope across the speaker feed to see, as expected, that one half of every sine wave had a burst high-frequency supersonic noise, which whilst inaudible itself, manifest as distortion in the audio band. Reduce the audio input and stability returned.

    Disconnecting the speaker so the amp was not actually generating power into a load, and again, stability. The solution was a 'zobel network' comprising a small resistor and capacitor in series soldered directly across the output terminals. Cost about GBP 0.10 (ten pence) and commonly fitted to amplifiers to partially-cancel the inductive/capacitive reactive load of a speaker cable and/or loudspeaker itself. But not this one.

    So the message from this is .... we want to assume that audio power-amplifiers are well designed and stable into the sort of loads that typical cables + speakers present, such as this combination. But that may be over optimistic on our part. Unless we have test equipment we cannot look for instability and if we identify it by ear, the damage may have already been done. There may indeed be latent instability which is only triggered on signal or transient peaks, depending upon drive level as in this case. The more exotic the speaker cable and/or the loudspeaker load the more we tempt instability. That's why I design Harbeth speakers to present as benign a load as possible to the amp and advise you to use simple, standard cable that looks like simple standard cable.

    If anyone is interested I'll take a photo off the 'scope to show the distorted waveform before the zobel was fitted.
    Thanks Allan for the suggestion,i use a high strand direct copper cable for my Harbeth P3ESR's have never tried anything else.
    But for my interconnects I use Morrow Audio MA-1's http://www.audiosold.com/ma1interconnect.htm

    Should I try something more simple then these,I know the cable looks very slim,would this be doing justice to my setup or should I just buy some basic copper interconnects from the supermarket.

  3. #23
    Join Date
    Oct 2010
    Location
    Holland
    Posts
    115

    Default Naim no Zobel?

    Hmm...I use a Naim amplifier which doesn"t has a Zobel network claiming this results in a better sound. Mr Shaw's experiment has proven the opposite as I understand it.

    {Moderator's comment: is that really true? That will certainly mean that the type of cable and speaker connected to it will entirely define the technical performance, and probably audio performance too. Can't understand why they designed like that unless to sell their own cable and own speakers i.e. a marketing tactic.}

  4. #24
    Join Date
    Oct 2010
    Location
    Holland
    Posts
    115

    Default Naim with own cables

    Don"t think so...Although NAIM does advice to use their own Speakercable and connectors they are so cheap that I guess there's hardly any profit.

  5. #25
    Join Date
    May 2009
    Location
    England
    Posts
    846

    Default Naim: stable into normal cable

    Very early Naim amps had to use the appropriate cable in a run of 3.5 mtr minimum to provide the correct amount of inductance to keep the amp stable. In practice, this wasn't a problem as any 'normal' cable will supply the recommended characteristics.

    All Naim amps made during the past 15 years are completely stable into any cable unless it's very highly capacitive but there are very few such on the market. In practice, you don't need to give it any thought.

    Naim's own speaker cable is very good and reasonably priced, making it a good choice to partner Naim amps or any other for that matter.

  6. #26
    Join Date
    May 2011
    Location
    US
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    32

    Default Standard cables are fine...

    Greetings from Chicago! I agree that speaker cable should be DECENT, not expensive. I have 25' (8M) runs to my Super HL5s with quad 14 gauge Belden cable (I think I paid $75US). Anyway, by merging the - and + wires the result is 11 AWG. The sound is terrific. DON'T waste your money on fancy speaker wire. Regards, Steve

    {Moderator`s comment: you should explain carefully what you mean by `merging the wires` in case readers accidentally short out their amp}

  7. #27
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    May 2011
    Location
    Canada
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    18

    Default

    Agreed, can you elaborate?

    Quote Originally Posted by QChicago View Post
    Greetings from Chicago! I agree that speaker cable should be DECENT, not expensive. I have 25' (8M) runs to my Super HL5s with quad 14 gauge Belden cable (I think I paid $75US). Anyway, by merging the - and + wires the result is 11 AWG. The sound is terrific. DON'T waste your money on fancy speaker wire. Regards, Steve

    {Moderator`s comment: you should explain carefully what you mean by `merging the wires` in case readers accidentally short out their amp}

  8. #28
    Join Date
    May 2011
    Location
    US
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    32

    Default Explaining about using quad core wire as standard pair

    By "merging" the wires what I mean is this: The "quad" (Canare) type wire consists of four separately insulated wires (two + and two -). I do not "bi-wire," as it's useless to do so IMO.

    Accordingly, I twist together the two + and connect them to the corresponding + terminal of the speaker; and I do likewise with the two - wires and connect them to the corresponding - terminal.

  9. #29
    Join Date
    May 2011
    Location
    US
    Posts
    32

    Default Simple is best

    Haligonian: I'm not sure what to elaborate about here.

    Basically, I believe that expensive speaker cables are not necessary to achieve the best sound and that money is much better spent on other parts of our audio systems (such as components) that DO make a SQ difference. I also believe that bi-wiring does nothing to improve SQ. I follow the Harbeth suggestions: DECENT (not expensive) cabling of suitable gauge and single wiring of the speakers.

    At the suggestion of the Moderator, I have explained what I meant by "merging" the wires in a previous post. HTH

  10. #30
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    Feb 2006
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    Malaysia/Singapore
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    435

    Default Keep more $ for music not accessories

    Appreciate QChigaco for sharing your experience. The good sound of Harbeth really no need exotic accessories....I am too still using my more than 10 yrs old MIT terminator2 speakers cable happily. I can keep my $ for more music..
    "Bath in Music"

  11. #31
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    May 2011
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    Canada
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    Default

    QChicago, thanks for the helpful response.

  12. #32
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    Sep 2011
    Location
    USA
    Posts
    2

    Default Fattening-up my P3ESRs?

    I am trying very hard to get the proper sound from these new P3esr speakers. I am running them from a Pass Labs XA 30.5 Class A amplifier at 30 watts. Actually much higher but you already know that!

    I am trying to find a pair of quality speaker cables that match with your speakers. I feel the sound just a tad on the thin side or I haven't adjusted my ears to "pure" sound of flawed recordings. I listen to the Stones to Lucinda Williams to Coltrane to Miles. James Taylor to The Beatles.

    Can you point me in a few directions for a pair of 8-9' cables.

    Nordost Red Dawn LS
    Kimber 8TC
    Crimson
    are the ones I am currently looking at.

    {Moderator's comment: we here at Harbeth UK are highly sceptical of using speaker cable to 'adjust' the sound of your system. That's really not the right approach. The P3ESRs as you will have read have a fantastic following, and if you are not achieving the natural sound they are capable of throwing money at the issue willy-nilly is not sensible. The first step is to live with the system as it is for weeks. The second step is to borrow another amplifier. The third step is to do some soul searching about whether natural sound is really what you want. It's not everyone's choice. We urge you to use bog-standard QED79 strand or similar cable as a benchmark to be sure your existing cables are not the culprit. In other words, remove all the variable and get back to basics.}

  13. #33
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    Feb 2006
    Location
    USA
    Posts
    148

    Default Basic cables

    Hey, 'drew.

    I'm going to go with the moderator here and ask what cables you're currently using, and what electronics are in front of the Pass amp. I have no problem with your amp, as I use a 15 watt Pass clone in front of my Monitor 30's. And they've never sounded thin.

    Of the cables you mention, I'd try the Kimber first - a no BS product.

    Let us in on the rest of your system.

  14. #34
    Join Date
    Jul 2011
    Location
    Singapore
    Posts
    43

    Default Basic cables

    Quote Originally Posted by Vooidudrew View Post
    I am trying very hard to get the proper sound from these new P3esr speakers. I am running them from a Pass Labs XA 30.5 Class A amplifier at 30 watts. Actually much higher but you already know that!

    I am trying to find a pair of quality speaker cables that match with your speakers. I feel the sound just a tad on the thin side or I haven't adjusted my ears to "pure" sound of flawed recordings. I listen to the Stones to Lucinda Williams to Coltrane to Miles. James Taylor to The Beatles.

    Can you point me in a few directions for a pair of 8-9' cables.

    Nordost Red Dawn LS
    Kimber 8TC
    Crimson
    are the ones I am currently looking at.

    {Moderator's comment: we here at Harbeth UK are highly sceptical of using speaker cable to 'adjust' the sound of your system. That's really not the right approach. The P3ESRs as you will have read have a fantastic following, and if you are not achieving the natural sound they are capable of throwing money at the issue willy-nilly is not sensible. The first step is to live with the system as it is for weeks. The second step is to borrow another amplifier. The third step is to do some soul searching about whether natural sound is really what you want. It's not everyone's choice. We urge you to use bog-standard QED79 strand or similar cable as a benchmark to be sure your existing cables are not the culprit. In other words, remove all the variable and get back to basics.}
    I am using 10 gauge belden cables terminated and sold by bluejeanscable on my P3esr. They are no nosense, afforable and feature ultrasonically welded banana plugs. Do a google for their contact.

  15. #35
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    Jul 2010
    Location
    USA
    Posts
    111

    Default Various cables

    From your list, I'd choose Kimber. I use Kimber PBJ interconnects, and Kimber 4TC's on my P3ESR's (I think mine are 8' runs). The Kimbers seem fine, someday I'll have to A/B them to my old Analysis Plus Clear Oval cables that I still have, from an older set up. I have a feeling they'll sound pretty much the same...

    I've used Blue Jeans Cable for digital interconnects - they're a good company to deal with, they're stuff seems pretty sound (no pun intended).

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