Possibly a very stupid question. But one that's puzzled me. It would be madness and dangerous to have a cable in the home with. a regular 13amp plug on each end. I remember seeing on at high school once and when one of the teachers saw it in use went mental at someone for it even existing.
So how come we use speaker cables with amplifierss with a male connector at each end. Aren't we connecting it to a lot of power? After all a 100w amplifier is a powerful thing - how much power is coming down that cable to the speakers? Surely one could be easily shocked by a speaker cable.
Or if not much power is coming down those cables to the speakers then where is all that power going? Two hefty transformers in a 100w head - all that electricity must be going somewhere?
And on that subject, why two transformers in a valve amp? Can't we make one do all the work?
y.
Thanks for anyone taking time to ask these baby questions.
Edit: To answer myself slightly. Of course I just realise 100W amplifier head sounds crazy powerful. But that's like an old lightbulb isn't it. So it isn't that much power.
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However, operating a valve amp with no speaker connected at the sort of volume setting where that voltage can be generated is likely to be quite a brief exercise...
The two transformers are the power transformer (PT) which converts the incoming mains power into voltages the amp needs internally (hundreds of volts for the signal part of the circuit), and the output transformer (OT) which converts those high voltages back to lower ones that the speaker needs. Solid-state amps don’t need the OT because transistors operate at voltages low enough to be directly connected to the speaker.
You’re absolutely right that if a speaker isn’t connected to the OT, the energy can’t just go nowhere - it then causes very high voltages to be developed in the winding which can arc through the insulation and destroy it. (Or if you’re lucky, it may arc in the valves instead and blow those.)
And really, you’re quite right that 1/4” telephone plugs (what they were originally designed for) are a very poor choice for speaker connections! But they’ve become an industry standard and it’s hard to change that now - at least for amps with power ratings below about 300W. Most modern bass and PA amps of higher power than that use Speakon connectors, which were purpose-designed for higher voltage and current levels, don’t have exposed contacts, and lock into place.
These aren’t stupid questions by the way .
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
So all the internal stuff like valves and stuff - they are using more power than the speakers are?
Yes. An amplifier isn't 100% efficient. More like 40-50% for a push pull amp. They get warm - that's power from the mains being turned into heat, not driving the speaker. Plus of course valves have to be heated in order to work, more 'lost' power.
There are other losses in the circuitry too. A valve amp is often no more than about 20% efficient in terms of input power to speaker power - low-powered ones worse than high-powered, because the filament power is a more significant fraction. A modern switch-mode/Class D audio amp can be up to about 80% efficient, possibly even higher.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
Rather than one where you could just use any old cable because it fits - not because it's the right cable to use.
Unless @ecc83 has just beaten me to it , Blackstar use a similar sort of system except that it still uses 1/4" plugs - but there is a standby circuit in the amp activated by putting a plug into any of the speaker jacks, so it at least covers that end of the cable. Fender used to do it a cruder way by simply having a shorting switch in the speaker output jack - a valve amp is safer into a dead short than an open circuit, especially if only briefly.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
Also doesn't have a standby switch - it goes into standby with no input jack in. This confused the hell out of me originally trying to use just the FX return with a modeller as I couldn't get any sound until I put a headphone adapter plug into the input.
To pull some figures from the air - not exact but they will be in the right ballpark - if a 20W valve amp uses 90W, a 50W Class AB solid-state amp uses 100W, and a 100W SMPS/Class D amp uses 120W, but they're all the same perceived volume in a real musical situation, which is the most efficient?
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein