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Someone used an instrument cable with my SVT Cl...

Discussion in 'Amps and Cabs [BG]' started by torza, Jul 10, 2016.

  1. torza


    Sep 20, 2005
    Yes, I ALWAYS use a speaker cable with my SVT CL. BUT...someone in the space I share (with quite a few other bands) not only attempted to use my SVT amp without asking, but hooked it up with an instrument cable. Now, luckily I walked in just as they were starting and they played maybe half a song before i gave them the axe and shut my gear down. (Yes, they have been kicked out.).

    Now, I know the amp was only used for maybe a minute, but is there any chance that any damage was done to my amp? I'm always super careful with my gear, so this is a bummer.
  2. BogeyBass


    Sep 14, 2010
    yeah you should return it straight away :)
    dude it's fine lol
    Clark Dark, 10cc and torza like this.
  3. torza


    Sep 20, 2005
    lol... I know it probably is! Just freaking out, of course ;)
  4. joebar


    Jan 10, 2010
    when we were kids just learning, we used anything that made an electrical connection and nothing got broke.
    tfer, AdamR, Catbuster and 12 others like this.
  5. So long as the instrument cable still works for guitar, should be fine.
  6. Rick James

    Rick James

    Feb 24, 2007
    New Jersey
    If it did you'd know it. The danger of instrument cords used for speakers is that they can't handle high current, so the insulation can melt, then the conductors short out, and that might mean death to an SS amp. It wouldn't bother a tube amp.
    bobyoung53 likes this.
  7. except if the shorting blew it open circuit and fried the tube amp.
    40Hz, Bassist4Eris and B-string like this.
  8. bobcruz


    Mar 10, 2004
    Disaster averted. Search around, there are threads about keeping other people in shared spaces from using your gear. I think there are locks that attach in the power cable socket, for example, but there were multiple good suggestions for disabling your amp without a lot of inconvenience.
    torza likes this.
  9. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    The moderate capacitance of an instrument cable on the output could make some amps prone to instability. I think this would be most likely in some amp designs where they omitted an output network in order to get a monstrously high "damping factor" to put on paper. There's a reason for that arrangement of resistors, capacitors, and coil(s) on the amp output. ;)
    leonard and Jim Carr like this.
  10. Guys - you're over-reacting. The facts are very simple, but always get embroidered into something terrible. Any reputable manufacturer who fits their products with jack sockets for connection has to ensure that they can cope with accidental disconnection and potential shorting. With everything biased in favour of the consumer now, warranty wise - if an amp was inherently susceptible to open or short circuit damage, it would be all over the net and the product would not have a decent reputation. So all the good ones can happily cope with a short circuit without any damage. That is simply good design.

    The other often quoted 'issue' is heating up the plugs and wiring, then melting then the shorting (dismissed above). Have any of you ever checked how much current is being drawn? It's always much, much less than you think. The PA people noticed it years ago - a rack with 5 or so 1K-2K amps. You can easily have five thousand Watts of amplifiers in the rack and have nowhere near five thousand Watts of power available.

    In the UK, with our higher voltage, 5K of amps can easily be run off a 13A outlet - capable of just over 3KW. Turning them all on at once will trip a breaker because as the transformers saturate on turn on - the surge can be pretty high - however, turning them on one at a time works. A 5KW amp rack playing hard rock music with the red peak lights about to come on rarely draws more than 2K, and on gentler and less busy music, less than that. A typical bass amp will not work that hard, and on paper some might appear to require 10-20A of speaker current, but in practice they don't. A typical cheap guitar jack cable can probably handle 3 or 4 amps worth of continuous current based on conductor size. Bass amps are good for music, they're pretty useless at heating up cables!

    I left my speak to speak cable for my 8 X10" cab at home. In the van I found a patch bay cable - moulded, cheap, flexible plastic. Played the gig - no issues whatsoever.

    Sure - you should use appropriate sized cable, but we are NOT talking welding here - the duty cycle on a typical bass waveform is surprisingly low. If you want proof - record a tone on your DAW and fire it down a thin cable for ten minutes and measure the temperature of the conductors. The physics is pretty straight forward, and the maths makes it pretty clear.

    It's not good practice - but it's not terminal!
  11. you're saying OP's SVT is immune to a open circuit? I don't think so.
    Last edited: Jul 14, 2016
    bobyoung53 likes this.
  12. I'm saying that this particular amp is well designed and because tube current can be adjusted in the design the actual monitoring of the tube current is pretty much going to stop damage. Oddly, they make the warning about using guitar type cables, but they also acknowledge that Speakons are better because of the connection unreliableness of jacks - which kind of acknowledges the possibility of shorts. I can't find the transformer spec, so can't work out the likely current.

    I do know that if I owned one of these amps, I'd really not be that concerned because clearly output monitoring is a well thought out, and the design can work into a virtual short-circuit anyway. It's possible that a cheap jack lead would have a distinct resistance anyway, that could allow decent current to flow - but again, my own experience of over-current faults in power circuits is that they tend to fail open circuit when the conductor melts.

    When you spend decent money on a decent amp - you expect it to not fall over and wave it's legs in the air. After all, amps have to cope with the terminals of speakons coming loose and the conductors touching, they have to contend with speaker shorts when they burn out and melt the turns together - both of which I have seen many times. I've not yet seen a guitar cable kill and amplifier, and most are not protected as well as this one!

    The manufacturers warn customers not to do things, but they're human. Holding a dead short (and of course the silence) for an extended time is stupid, and the high current does stress the tubes, but they can take a bit of abuse without suffering. This amp actually allows you to deliberately stress the tubes as part of the design - so if it then falls over to accidental abuse, that would be funny!

    The rule is always don't short out your amps. Second rule is use proper sized cables and connectors. Third rule is rules are fine to break occasionally.
    I thought I'd have a go to see what happened when you put current through a guitar cableNot to be recommended but I had a couple of old quite plasticky ones. I bodged some crock clips to a couple of chassis jack sockets and tried a couple of items. A 1500W load at 230V - so that's 6.5A. 3 minutes. No heating I could detect, but the cable was a little more flexible (I think). Increased the load to 2.5Kw and after 3 minutes it was warm and very flexible. Tried one last test on 3KW - that's the full 13A we can get from our power outlets. 35 seconds and it went bang, and interrupted the current - not a short, open circuit when the conductor melted. The metal tags in the jack were also hot. The sockets I used were actually fine - not damaged at all. This kind of power just isn't available from a typical amp. You'd have to work hard to melt the cable.

    As for being immune to an open circuit - that would not concern me at all. The only warnings are about going below 2 Ohms.
    tfer likes this.
  13. Don't ever take on the third rule by shorting a SS amp. No forgiveness with that one.
  14. BogeyBass


    Sep 14, 2010
    lol pretty much hosa used to make 8 cable snakes for 25 bucks instead of buying one instrument cable I'd buy 8 and I've literally used those cables in a pinch to tie stuff to my roof and they still worked. I've powered my 810 with 700 watt amps with dirt cheap instrument cables. I had a red hosa cable holding my license plate on for a year. it was tied in knots and turned
    pink from uv damage. ggetting drunk one night at the studio somehow we questioned if that old pink cable on my license plate worked.....lol it did
  15. Just for the record - if anyone is confused about this and regardless of what other jabberwockey may have been expressed- please don't operate your SS amp with the output shorted or your tube amp without a load (and preferably one of proper impedance).
  16. Rick James

    Rick James

    Feb 24, 2007
    New Jersey
    I wouldn't have brought it up if I had not seen it with my own eyes. Not all insulations are rated for 90C, especially those used in cheap instrument cables, nor do all cheap instrument cables use at least 22 gauge conductors. Then there's the matter of 1/4" plugs, which were never intended for high current handling. There's many reasons why Speakons are better, not being able to mistake an instrument cable for a speaker cable being only one.

    As for the capacitance issue that Bob mentioned, that can be a real problem with long speaker cables used for PA, and that's why speaker cables aren't shielded. Of course if you decide to slap a cheap 30 foot instrument cable between your amp and cab then it might be a matter of what toasts your output transistors first, a short circuit or runaway ultra high frequency oscillation. Neither would happen with a QSC amp, but not all amps are built to QSC standards.
  17. Guys - I'm not prescribing using guitar cables for speakers as an everyday thing - but simply that using one does NOT mean instant incineration.

    Has nobody here ever tripped over a cable and had a speaker jack fall out, or accidentally forgotten top plug in the cab? These things are planned for by the manufacturers.

    One of the speaker production periods for pro products was the Bose 802 - which had jacks fitted for years. Shure did the same on their early tube amp ranges. Shorts causing damage seemed to become an issue when semi-conductors first started to take over from tube designs, when they were very sensitive to mismatches and accidental shorts. By comparison, tube designs are pretty tough - but I expect the transformer output coupling helps them. In fact, I wonder if the transformer windings are more prone to overheating via excess current than thin speaker cable.

    When power amps used XLR 3 pin connectors, it was accidentally very easy to use a mic cable for speakers.

    This topic started when somebody had palpitations because somebody used his amp with the wrong cable. No harm was done. Thank the amplifier designers. My point was that the chances of lasting damage are very low. That's good design. Stop the outgrabe and tulgey.
  18. I have used guitar cables for whole gigs with a 70's SVT before I realized it was not a good thing to do and had no problems but would I do it now? Not on your life. I ran an SVT @ 8 ohms without realizing it for a year once and it wore out the power tubes prematurely and sounded like krap when it was loud but otherwise did no damage, would I do that again? Not on your life.
  19. steveinohio


    May 27, 2007
    It seems that the biggest amount of damage that it did has been contained to this thread!
    LoDownSinner likes this.
  20. I'm afraid that I have always treated anything with tubes in as a product that costs you to run - unlike products that are solid state. You can tweak the amp to give years or months on a set, depending on what you like. Let's face it - worrying about a cheap cable is less likely to cause grief than some idiot knocking over your flight case, or simply heaving the thing up on tip of the cab - 'helping' you.

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