Speaker switch project

[MarginWalker]

After buying a couple of speaker switches which have ended up breaking and trying to find a well built, reasonably priced one with decent quality binding posts without success I have decided (after a recommendation on here) that having a go at building one myself might be the best solution.

Other than adding new interconnects to my turntable I haven't done any soldering or circuit building since GCSE physics so am looking for some advice. I need the switch to allow me to play one or both sets of speakers at the same time. One set is 6ohm and the other is 8ohm. My first question is do I need to include resistors or is it simply a case of wiring up the binding posts to the switches?

if anyone has made anything similar or can offer me any advice on my first DIY hifi project I would be very grateful.

Thanks,

Phil

[Lawrence001]

Phil, not related to this but please clear your inbox. Thanks, Lawrence

[StanleyB]

I need the switch to allow me to play one or both sets of speakers at the same time. One set is 6ohm and the other is 8ohm. My first question is do I need to include resistors or is it simply a case of wiring up the binding posts to the switches?

If the two pairs of speakers are of different impedance I would not recommend that you try to play both sets at the same time, from the same amp.

Did you try my TC-7220 speaker/amp switch by any chance?

[nthall]

I would add an extra set of binding posts to the amp and put an a/b switch on it like integrated amps have. I agree that running dual impedances isn't the best idea.

They do sell pre-made switches that balance different loads automatically. They really aren't that expensive.

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[Qwin]

Doesn't the amp just see a combined load?
Plus drivers are anything but a constant load anyway.
At some frequency the nominal 6ohm will probably be more than 8ohm etc.

A three way speaker system quite often has drivers of differing impedance eg Celestion 66 monitors. The amp just sees the overall nominal of 6oms in that particular case.

I would be more concerned about putting switches in the signal path, go for the best you can afford, or go for a peg board switch over, like an old fashioned telephone exchange. If I'm reading you right, one set of speakers is on all the time and the other is on in addition occasionally. You only need switch one terminal on each speaker to stop it working so your switching just two circuits in or out. Most switch over boxes I have seen have been poor quality, so whichever way you go, making it yourself with decent parts is the thing to do.

The other question to ask is whether your amp will run two sets of speakers?

[Reffc]

Doesn't the amp just see a combined load?
Plus drivers are anything but a constant load anyway.
At some frequency the nominal 6ohm will probably be more than 8ohm etc.

A three way speaker system quite often has drivers of differing impedance eg Celestion 66 monitors. The amp just sees the overall nominal of 6oms in that particular case.

I would be more concerned about putting switches in the signal path, go for the best you can afford, or go for a peg board switch over, like an old fashioned telephone exchange. If I'm reading you right, one set of speakers is on all the time and the other is on in addition occasionally. You only need switch one terminal on each speaker to stop it working so your switching just two circuits in or out. Most switch over boxes I have seen have been poor quality, so whichever way you go, making it yourself with decent parts is the thing to do.

The other question to ask is whether your amp will run two sets of speakers?

This is not quite correct Ken. Hooking up two loudspeakers to the same amplifier output puts both pairs in parallel, so the amplifier sees a load equivalent to the two sets of impedances in parallel. If those loads are nominally 6 Ohm in the bass, then the minimum impedance can be less than this...down to 4 Ohms even, so the amp could well see a combined 2 or 3 Ohm load. Not a good idea.

3 way speakers may have current demands at varying frequencies that occur all at once, but hooking two pairs up is different because you're presenting two bass unit plus two mid unit impedance to the amp at once, per channel, unlike single channel 3 way systems, with the current loads that would demand. Also, the crossovers in between the drivers for 3 way systems means that you are splitting the frequencies so worst case for a "nominal" 6 Ohm load would be a "nominal" 6 Ohms! (or 4, or 5 or whatever the lowest case might be) and NOT the summation of the parallel loads of all three or more drive units.

Impedance will rise with frequency, but it matters less at higher frequency if you get a lowish impedance, as current requirements are less. It's the low frequencies all the way up to 1 or 2 KHz that demand most current. Combine that with difficult phase angles, and it could be a recipe for a blown amp.

[struth]

Agree, not a good idea. 1 or other but not both.

[MarginWalker]

Thanks all. To be honest, I usually play through one or the other and have only played through both at once at quite low volumes. Anyway, it sounds like an excuse to buy a new pair of 8ohm speakers!

[chris_s]

I can wholeheartedly reccomend Stans Speaker Selector:-

http://www.homehifi.co.uk/S/tc-7220.htm

Although just moved mine on, had it for 2yrs to switch my main speakers between main AV amp and Quad Amp when playing Vinyl.

Really can't fault it at all and superbly well made AND it can handle bi-wire.

Chris.

(not paid or sponsored by Stan to say that!)

[Qwin]

This is not quite correct Ken. Hooking up two loudspeakers to the same amplifier output puts both pairs in parallel, so the amplifier sees a load equivalent to the two sets of impedances in parallel. If those loads are nominally 6 Ohm in the bass, then the minimum impedance can be less than this...down to 4 Ohms even, so the amp could well see a combined 2 or 3 Ohm load. Not a good idea.

3 way speakers may have current demands at varying frequencies that occur all at once, but hooking two pairs up is different because you're presenting two bass unit plus two mid unit impedance to the amp at once, per channel, unlike single channel 3 way systems, with the current loads that would demand. Also, the crossovers in between the drivers for 3 way systems means that you are splitting the frequencies so worst case for a "nominal" 6 Ohm load would be a "nominal" 6 Ohms! (or 4, or 5 or whatever the lowest case might be) and NOT the summation of the parallel loads of all three or more drive units.

Impedance will rise with frequency, but it matters less at higher frequency if you get a lowish impedance, as current requirements are less. It's the low frequencies all the way up to 1 or 2 KHz that demand most current. Combine that with difficult phase angles, and it could be a recipe for a blown amp.

Actually Paul I think you helped make my point, which I made toward the end, which was, is the Amp capable of driving two pairs of speakers, due to the parallel loading you point out.
Whether both pairs are the same, 6 or 8 ohm is less of an issue, though obviously effecting the combined parallel sum, providing the Amp will drive them in the first place. ;)

[nthall]

I can wholeheartedly reccomend Stans Speaker Selector:-

http://www.homehifi.co.uk/S/tc-7220.htm

Although just moved mine on, had it for 2yrs to switch my main speakers between main AV amp and Quad Amp when playing Vinyl.

Really can't fault it at all and superbly well made AND it can handle bi-wire.

Chris.

(not paid or sponsored by Stan to say that!)
Do you have any pictures of the insides? I'm curious how it handles the load both amps are turned on and only one set of speakers is turned on. I'm assuming is has some sort of dummy load built in.

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