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28 Nov 04 - 08:30 AM (#1341073) Subject: Dumb question about PA amps From: Big Al Whittle Recently I saw a folk duo doing a small pub and they only had room for one PA speaker, so they plugged just one speaker in. Now many years ago I was told that you could 'do some damage to the amp' and that you should always plug a jack into the empty socket in the amp - even if you didn't plug it into a speaker. is this an old electricians tale. I need to know cos I'm thinking of doing the same gig and it is very small. |
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28 Nov 04 - 08:49 AM (#1341080) Subject: RE: Dumb question about PA amps From: Leadfingers From the depths of (very old) involvement in electronics I would say the problem would be the loading of the output stage of the amp ! It would depend on what the output on the amp is , but it would only be a problem at 'full' volume on most amps . The imbalance would not help the sound , and I would rather put both speakers on for safety's sake . If space is a serious problem just put one speaker on top of the other ! |
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28 Nov 04 - 09:20 AM (#1341093) Subject: RE: Dumb question about PA amps From: mack/misophist A jack that's not connected to anything wouldn't change the characteristics of the system. ie. It might as well not be there. I guess the best compromise would be to put a large resistor across the plug at the speaker impedence. But my training was decades ago, too. |
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28 Nov 04 - 09:41 AM (#1341106) Subject: RE: Dumb question about PA amps From: Hand-Pulled Boy Put the other speaker in the toilet but make sure it's plugged into the amp. You'll reach a whole new audience in there! |
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28 Nov 04 - 01:56 PM (#1341261) Subject: RE: Dumb question about PA amps From: s&r If it's a stereo amp, turn down the channel that's not plugged in. If it's a mono amp the jack connectors are likely to be in parallel. No harm will result from using only one speaker. Stu |
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28 Nov 04 - 05:03 PM (#1341392) Subject: RE: Dumb question about PA amps From: George Seto - af221@chebucto.ns.ca It might have been a problem in Tube situations. It's been a LONG time! |
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28 Nov 04 - 05:56 PM (#1341429) Subject: RE: Dumb question about PA amps From: Grab If there's no speaker connected, plugging in a cable does nothing, so it can't affect the amp at all, so that's bogus. *Unless* this was some home-brew amp which had some bizarre switching arrangement or a strange screwed-up output stage that required *some* loading (in which case there would have been a cable with a load resistor, not just an unconnected cable). Bottom line - if it ever was true, it isn't now. Graham. |
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28 Nov 04 - 06:28 PM (#1341445) Subject: RE: Dumb question about PA amps From: treewind Some valve (tube) amplifiers used not to like operating with no speaker connected. With any transistor amplifier should be totally harmless to operate it with nothing plugged in the speaker connector. Anahata |
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28 Nov 04 - 06:31 PM (#1341449) Subject: RE: Dumb question about PA amps From: Big Al Whittle Right got the message. If I disappear in in a puff of smoke in the middle of the gig. I will take a most serious view of the matter. thanks for all contributions best wishes al |
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28 Nov 04 - 09:57 PM (#1341609) Subject: RE: Dumb question about PA amps From: GUEST,Songster Bob Older tube amps with output transformers need a load on each (if they're stereo), so you'd need a plug with a resistor across it for the second channel. Solid state amps are not liable to such damage, and can have any number of speakers attached. I have one with two output jacks, but you can use just one, even daisy-chaining the speakers if you have two and room for 'em. So the amp can be between the speakers (using both jacks) or at one end of the speaker chain. Bob |
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29 Nov 04 - 08:14 AM (#1341912) Subject: RE: Dumb question about PA amps From: mkebenn Stu was on point. Never run a stereo amp without both speakers connected. Lack of resistance can damage the amp. Mono amps are safe as there is only one channel, and only one speaker is needed to provide the load. Mike |
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29 Nov 04 - 05:22 PM (#1342448) Subject: RE: Dumb question about PA amps From: Bernard Just to get technical... Yes, stereo amps need a load on both channels, though if you can prevent the side with no speaker from being 'driven' - turn the volume off! - it will be okay as the load is only required when a signal is present. Putting a shorted jack into the effects loop (on a mixer-amplifier) may also cut off drive to that channel, but be sure you know what you are doing!! Don't short the amplifier output!! If it's a slave amp, just don't plug the input lead in on the unused side... Mono amps are okay with just one speaker, but you must be sure the single speaker can handle the extra load... Two eight ohm speakers on a 100w amp must be able to handle 100w between them, but one eight ohm speaker on the same amp is likely to be subjected to around 70w because the load is inductive, not resistive. In other words, Ohms Law doesn't strictly apply - there are other considerations. Ooops! Another can of worms!! ;o) |
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29 Nov 04 - 06:06 PM (#1342494) Subject: RE: Dumb question about PA amps From: Richard Bridge Let's keep it simple. Valve amps: do not EXCEED the recommended resistance (no speakers-infinite resistance) Trannies, do not go below the minimum resistance. |
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29 Nov 04 - 06:18 PM (#1342518) Subject: RE: Dumb question about PA amps From: s&r Impedance Stu |
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29 Nov 04 - 06:45 PM (#1342556) Subject: RE: Dumb question about PA amps From: fiddler It used to b*gg(r the old HH amps to ru n with onloy one speaker - I don't know why it jsut did! I desn't bother newer amps! Andy |
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29 Nov 04 - 07:00 PM (#1342573) Subject: RE: Dumb question about PA amps From: s&r I could nit-pick about some detail here , but it's a good straightforward summary Stu |
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30 Nov 04 - 06:57 AM (#1343023) Subject: RE: Dumb question about PA amps From: The Fooles Troupe If it really was a shorted plug being plugged in, then it is possible that it was a mono amp intended for 2 speakers in series, and the shorting plug just allowed one speaker to be omitted - in that case the thing would not work without the second speaker connected - the plug may also have had a loading resistor inside to help things. |