Using a speaker switch - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Phil__G · 25th Jan 2023, 2:55 pm

How about this, no breaks, no 2 ohm parallels, no resonating...
This is one channel, repeat for the other...

Nickthedentist · 25th Jan 2023, 3:14 pm

Agree with David et al.

I too would never switch speakers on a transistor amp without switching off (and ideally waiting a couple of seconds) first. It's just not worth the risk, especially as genuine vintage replacement transistors are now almost impossible to source.

lesmw0sec · 25th Jan 2023, 3:44 pm

I would suggest that all that is required, is to turn the volume down to zero when changing over. Turning the amp. off should not be necessary.

Radio Wrangler · 25th Jan 2023, 3:48 pm

Many amplifiers are DC coupled and give several milliamps DC into a typical speaker. If not well adjusted this can be quite a bit more. Low risk, but not zero. Unlikely enough to be a killer.

David

mhennessy · 25th Jan 2023, 4:09 pm

I have an Arcam Alpha 2, which uses the same power amplifier as the 3.

It has current limiting and "catch" diodes, as well as output fuses. I would have no concerns about using it "live" with a speaker switch. I routinely change speaker connections without powering down amplifiers, and have never had an issue. No competently designed amplifier should be bothered by sudden disconnection or accidental short circuit when silent or playing quietly. Remember; a just a couple of volts is a lot of noise given that speakers generally produce anywhere between 80 and 90dB when driven with 1 watt.

In the highly unlikely event that the Arcam does suffer, it's an easy amp to repair as it mostly uses transistors that are easy to source (TIP2955/3055, BC547, etc). The exceptions are the drivers, VAS and VAS current load, being FST239/240 and MPSA056, but it won't be impossible to find substitutes.

Obviously, I have this viewpoint because I'm able to do a repair if necessary, so the "consequence" part of the risk assessment (likelihood-times-consequence) is just a minor irritation for me. If you have to pay someone to repair an amplifier that fails, the consequence is higher. But as the "likelihood" side of the equation remains vanishingly small, it's still a very low risk, whatever your position.

It's worth saying that power-cycling amplifiers is not completely risk-free either...

And please don't wire speakers systems in series! Remember that the impedance varies wildly with frequency, so they won't sound anything like the designer intended. Parallel is fine. I used that Arcam to power a 4 ohm subwoofer for many years - it never complained.

Diabolical Artificer · 26th Jan 2023, 10:28 am

I had one of these speaker switch boxes, it lasted about a month before the switches failed. I now use 4mm banana jacks with a "U" shaped patch to sw between my various amps, no issue's so far.

Some of the lads over on DIY audio have built quite complex speakers sw's using relays, no idea if they're any better than the speaker sw boxes comercially available.

Andy.

Edward Huggins · 26th Jan 2023, 3:45 pm

I hope that this does not appear as too intrusive, but noting Martin's comment in his Post #5, surely using two other speakers as speaker "stands" is not the best possible way to enjoy decent stereo sound?

25th Jan 2023, 2:55 pm	#21
Phil__G Hexode Join Date: Mar 2011 Location: North Yorkshire, UK. Posts: 431	Re: Using a speaker switch How about this, no breaks, no 2 ohm parallels, no resonating... This is one channel, repeat for the other... Attached Thumbnails

25th Jan 2023, 3:14 pm	#22
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 16,901	Re: Using a speaker switch Agree with David et al. I too would never switch speakers on a transistor amp without switching off (and ideally waiting a couple of seconds) first. It's just not worth the risk, especially as genuine vintage replacement transistors are now almost impossible to source.

25th Jan 2023, 3:44 pm	#23
lesmw0sec Octode Join Date: Jul 2009 Location: Carmel, Llannerchymedd, Anglesey, UK. Posts: 1,317	Re: Using a speaker switch I would suggest that all that is required, is to turn the volume down to zero when changing over. Turning the amp. off should not be necessary.

25th Jan 2023, 3:48 pm	#24
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 20,886	Re: Using a speaker switch Many amplifiers are DC coupled and give several milliamps DC into a typical speaker. If not well adjusted this can be quite a bit more. Low risk, but not zero. Unlikely enough to be a killer. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

25th Jan 2023, 4:09 pm	#25
mhennessy Dekatron Join Date: Jul 2007 Location: Evesham, Worcestershire, UK. Posts: 4,108	Re: Using a speaker switch I have an Arcam Alpha 2, which uses the same power amplifier as the 3. It has current limiting and "catch" diodes, as well as output fuses. I would have no concerns about using it "live" with a speaker switch. I routinely change speaker connections without powering down amplifiers, and have never had an issue. No competently designed amplifier should be bothered by sudden disconnection or accidental short circuit when silent or playing quietly. Remember; a just a couple of volts is a lot of noise given that speakers generally produce anywhere between 80 and 90dB when driven with 1 watt. In the highly unlikely event that the Arcam does suffer, it's an easy amp to repair as it mostly uses transistors that are easy to source (TIP2955/3055, BC547, etc). The exceptions are the drivers, VAS and VAS current load, being FST239/240 and MPSA056, but it won't be impossible to find substitutes. Obviously, I have this viewpoint because I'm able to do a repair if necessary, so the "consequence" part of the risk assessment (likelihood-times-consequence) is just a minor irritation for me. If you have to pay someone to repair an amplifier that fails, the consequence is higher. But as the "likelihood" side of the equation remains vanishingly small, it's still a very low risk, whatever your position. It's worth saying that power-cycling amplifiers is not completely risk-free either... And please don't wire speakers systems in series! Remember that the impedance varies wildly with frequency, so they won't sound anything like the designer intended. Parallel is fine. I used that Arcam to power a 4 ohm subwoofer for many years - it never complained.

26th Jan 2023, 10:28 am	#26
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 6,922	Re: Using a speaker switch I had one of these speaker switch boxes, it lasted about a month before the switches failed. I now use 4mm banana jacks with a "U" shaped patch to sw between my various amps, no issue's so far. Some of the lads over on DIY audio have built quite complex speakers sw's using relays, no idea if they're any better than the speaker sw boxes comercially available. Andy. __________________ Curiosity hasn't killed this cat...so far.

26th Jan 2023, 3:45 pm	#27
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 7,730	Re: Using a speaker switch I hope that this does not appear as too intrusive, but noting Martin's comment in his Post #5, surely using two other speakers as speaker "stands" is not the best possible way to enjoy decent stereo sound? __________________ Edward.