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I don't know of a way to make 1/4" plugs permanent in the jacks. It might be possible, but I don't have the incentive to research it. If the amp has a 1/4" jack for the speaker connection, I just live with it, being careful to turn the amp off before removing or inserting the plug. Short circuits are never a good thing. I have 1/4" to Speakon adapters, but they're just one more thing to have to remember, and they're not all that much safer, because the problem is still the 1/4" jack in the amp. I'm not a fan of the 1/4" connectors, but we don't always get what we want. I just deal with what I have to deal with.
Originally Posted by RJVB
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02-21-2024 08:04 PM
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I don’t think there’s a shorting problem with the speaker out jack in the amp. The tip and shaft of the plug can both contact the grounded part of the jack body during insertion and removal, which will short the amp’s output if it happens at the speaker end. But it can’t short the amp’s output if it happens at the amp end, because the tip will be out of contact with the hot center jack contact before it can reach the body of the jack. Originally Posted by sgosnell
The problem with disconnecting at the amp while it’s on is that many amps (mostly tube) won’t tolerate an infinite load on the output. A short is basically a 0 Ohm load, and an open circuit has infinite resistance. An open output can lead to tube disaster. I’ve only had this once, but it was so dramatic I’ll never forget it. It was in a McIntosh audio amplifier and one output tube kinda blew up inside when I somehow managed to pull one of one channel’s speaker leads out of its connector.
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The easiest way would be to use a small drop of superglue on the base of the plug, I guess, but you could also use an l-shaped connector and lock it in place with a U-shaped brace or even just some velcro. For me the goal would mostly be to remind myself not to jank the jacks out without thinking. Originally Posted by sgosnell
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I've blown fuses in solid state amps by removing 1/4" plugs from the amp. Actually, just one, because that's all it took to convince me not to do that again. I don't need adhesives or Velcro to remind me.
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Oh, neither would I under normal circumstances. But distract or pressure me a bit and I might simply not notice the amp was still on or worse, think I'd already turned it off. I've learned to force myself to have to take a step back. (Of course even that doesn't always work...
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Many SS amps (and most older ones) will blow if there's no load on the output. And a lot of them are wired so that the chassis is not at the same electrical potential as the ground bus. So you had to isolate the speaker ground from the chassis ground or you'd blow a fuse if the speaker ground lead touched the chassis. Originally Posted by sgosnell
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Are Jack plugs a flawed design?
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I just checked, modern switchboards apparently use TRS (2 signal, 1 ground) jacks, but did those early ones already use 2-or-more connection jacks? Traditional telephone wires aren't shielded and in a switch/patch board the ground could be shared. Originally Posted by GuyBoden
Ah, this really takes me back to pre-USB days where you'd have to turn off both computer and peripheral to dis/connect. A hassle but the problems only started when we started to get used to buses that did support hot swapping.
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But it’s all low voltage, low current power in circuits that will not be harmed by open or shorted status. All of the unused preamp outputs are open in most audio equipment, including guitar amps that have them. Some have muting of preamp outputs and / or power amp inputs to prevent turn-on and turn-off thumps from damaging the speakers. The muting is often just a relay that shorts the output. This causes no damage because it’s a very low power circuit. Originally Posted by RJVB
Power amps are a different kettle of fish.
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Surely; I was just reacting to the (rhetorical?) question if jacks are a flawed design, and the accompanying image of an old switchboard. Originally Posted by nevershouldhavesoldit
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Sorry! No offense intended - It seemed like a very reasonable question to me, so I answered it. Originally Posted by RJVB
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Good info: Originally Posted by nevershouldhavesoldit
Power Amps with Jack Plug speaker connectors like this shown below were common in my era.
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No offense taken - but the actual question was whether those old switchboard even used the kind of jack was used in the old switchboard shown (and not rhetorical, though also not very urgent). Originally Posted by nevershouldhavesoldit
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Yes, telephone switchboards used the same 1/4” jacks and plugs that we use today. They were invented for telephony, which is which they’re called phone jacks and plugs. Originally Posted by RJVB
No offense taken - but the actual question was whether those old switchboard even used the kind of jack was used in the old switchboard shown (and not rhetorical, though also not very urgent).
The jacks in old style switchboards were TS, but the center contact was a flat spring that contacted either the ground lug or a 3rd lug when there was no plug inserted. The plug pushed it away from its contact so that the circuit wired to the plug was connected to the circuit wired to the jack.
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