joessportster Posted January 6, 2020 Share Posted January 6, 2020 I have a pair of 12" DIY sealed subs I am using with mainly music. Occasionally we throw in a movie and I would like to use the subs as DUAL purpose will it hurt anything to have 2 sets of wires going to the subs from 2 separate amps but only use 1 amp at a time 1 crown amp connected for music, and another crown amp connected for movies and only powering 1 at a time. I know bad things can happen if both amps got powered at once but there is really no scenario where that could / should happen. Thanks in advance Joe Quote Link to comment Share on other sites More sharing options...
rmlowz Posted January 6, 2020 Share Posted January 6, 2020 Hello, I did the same thing years ago with a Niles A/B switch Quote Link to comment Share on other sites More sharing options...
babadono Posted January 6, 2020 Share Posted January 6, 2020 Depending on the amps topology you MAY be OK. But better safe than sorry, install a switch. That´s my $0.02. 1 Quote Link to comment Share on other sites More sharing options...
ClaudeJ1 Posted January 6, 2020 Share Posted January 6, 2020 26 minutes ago, babadono said: Depending on the amps topology you MAY be OK. But better safe than sorry, install a switch. That´s my $0.02. I agree. Why take a chance of frying electronics, when a simple switch will do. https://www.ebay.com/itm/2-way-Speaker-Selector-Amplifier-Spiltter-Home-Stereo-Audio-Switcher-Box-Hub-/263721190621?hash=item3d670204dd Quote Link to comment Share on other sites More sharing options...
Tony Whitlow Posted January 6, 2020 Share Posted January 6, 2020 I agree. Why take a chance of frying electronics, when a simple switch will do. https://www.ebay.com/itm/2-way-Speaker-Selector-Amplifier-Spiltter-Home-Stereo-Audio-Switcher-Box-Hub-/263721190621?hash=item3d670204dd One amp would suffice for both. Switching would be from the pre-amp.Sent from my iPhone using Tapatalk Quote Link to comment Share on other sites More sharing options...
JohnA Posted January 6, 2020 Share Posted January 6, 2020 Modern power amps have very low output impedance, like 0.01 ohms. A figure near that would surely be there with the amp off. Paralleling 8 ohms with .01 ohms would make the unused amp look like a lot like a short. I wouldn't do it. There is no reason one power amp can't be used. Using 2 different pre-amps into separate power amp inputs on the same power amp is safer. Quote Link to comment Share on other sites More sharing options...
glens Posted January 6, 2020 Share Posted January 6, 2020 9 minutes ago, JohnA said: Modern power amps have very low output impedance, like 0.01 ohms. A figure near that would surely be there with the amp off. Paralleling 8 ohms with .01 ohms would make the unused amp look like a lot like a short. I wouldn't do it. That! Would likely cause damage to one or both amps. If not, at least will not be a pleasurable experience for you. If both amps have relays which disconnect their speaker terminals when powered off you'd be okay if you were certain to have them both powered off prior to powering only one on, but that's unlikely and it's unlikely you'd get it right every time - not to mention any other folks in your household... Quote Link to comment Share on other sites More sharing options...
babadono Posted January 6, 2020 Share Posted January 6, 2020 1 hour ago, Tony Whitlow said: One amp would suffice for both. Switching would be from the pre-amp. Sent from my iPhone using Tapatalk Yea but appearently that is not what the OP does. Quote Link to comment Share on other sites More sharing options...
babadono Posted January 6, 2020 Share Posted January 6, 2020 55 minutes ago, JohnA said: Modern power amps have very low output impedance, like 0.01 ohms. A figure near that would surely be there with the amp off ? I know there are people here much smarter than me. But how can you know this without knowing exactly which amps the OP is using? An un powered amp with no B plus and or B minus does not necessarily behave like a powered up amp, impedance wise. The output ddevices are biased off, who knows what the impedance will be without further analysis. That´s why I posted be safe, get a switch. 1 Quote Link to comment Share on other sites More sharing options...
ClaudeJ1 Posted January 6, 2020 Share Posted January 6, 2020 2 hours ago, Tony Whitlow said: One amp would suffice for both. Switching would be from the pre-amp. Sent from my iPhone using Tapatalk This is what I do. Quote Link to comment Share on other sites More sharing options...
ClaudeJ1 Posted January 6, 2020 Share Posted January 6, 2020 20 minutes ago, babadono said: ? I know there are people here much smarter than me. But how can you know this without knowing exactly which amps the OP is using? An un powered amp with no B plus and or B minus does not necessarily behave like a powered up amp, impedance wise. The output ddevices are biased off, who knows what the impedance will be without further analysis. That´s why I posted be safe, get a switch. Yes indeed. Sorry is a sorry word in case this turns out to be a sorry situation! Quote Link to comment Share on other sites More sharing options...
JohnA Posted January 7, 2020 Share Posted January 7, 2020 See the attached gif of a simplified amp. The path from the collector to the base is the low resistance path to ground when the transistor in not powered. Were there several in parallel, the parallel resistance would drop further. Crown commercial amps usually have several output transistors. In the case of a DC300, a capacitor across the outputs connecting the + to ground somewhere above DC. https://adn.harmanpro.com/site_elements/resources/974_1425479991/DC-300AII-Schematic-MI250D-Schematic_MI250D_original.pdf Quote Link to comment Share on other sites More sharing options...
joessportster Posted January 7, 2020 Author Share Posted January 7, 2020 Ok looks like a switch is in the works, I can not use a single amp, My cary pre does not have a HT bypass and my antiquated reciever for movies has no pre out. I use an older yamaha receiver for DVD/Blu-ray movie playback it has sub outs and I have a spare crown XLS1002 not in use except for the sub duty during the rare movie playback. I ALONE touch the Audio / Video in that room, No one else cares to learn. Really appreciate the responses. I will get or make a switch Thanks Joe Quote Link to comment Share on other sites More sharing options...
joessportster Posted January 7, 2020 Author Share Posted January 7, 2020 This should do the trick thanks again https://www.ebay.com/itm/Two-2-Amp-Receivers-to-1-one-Pair-of-Speakers-Selector-Switch-Combiner-SP-71/274019322515 Quote Link to comment Share on other sites More sharing options...
glens Posted January 7, 2020 Share Posted January 7, 2020 I don't know just what all that other stuff signifies, might identify you when the link is followed - don't know. Usually, if you omit the question mark and everything following it, the link becomes totally benign, like: https://www.ebay.com/itm/Two-2-Amp-Receivers-to-1-one-Pair-of-Speakers-Selector-Switch-Combiner-SP-71/274019322515 which switch looks like it would fit the bill. If you're handy, you could make your own. All you need is a four-pole double-throw break-before-make switch of sufficient capacity, though an industrial switch of that description may cost half as much by itself as that complete unit. Quote Link to comment Share on other sites More sharing options...
joessportster Posted January 7, 2020 Author Share Posted January 7, 2020 4 hours ago, glens said: I don't know just what all that other stuff signifies, might identify you when the link is followed - don't know. Usually, if you omit the question mark and everything following it, the link becomes totally benign, like: https://www.ebay.com/itm/Two-2-Amp-Receivers-to-1-one-Pair-of-Speakers-Selector-Switch-Combiner-SP-71/274019322515 which switch looks like it would fit the bill. If you're handy, you could make your own. All you need is a four-pole double-throw break-before-make switch of sufficient capacity, though an industrial switch of that description may cost half as much by itself as that complete unit. Appreciate the info I could not figure out why it posted the link like that. I figure to buy the parts would run at least 1/2 the price of the switch and with the aggravation to build anything like that with my hands. its totally worth the price Quote Link to comment Share on other sites More sharing options...
rplace Posted January 7, 2020 Share Posted January 7, 2020 Joe, Does the pre/processor for TV/movies have a 12v trigger out? If so get a used Niles SPK-1 on eaby. The "A" side is on by default nothing to do for music. When you turn on the source with the 12v trigger is sends a signal to the switch and changes over to "B" side. When you are done watching the movie and back to music it is back to A because you turned off the source with trigger that was making it send the signal to B. Nothing to do on you end but turn on the source that you had to turn on anyway. I can send you one to play with if you like. I've got a couple I'm not currently using, but can't think of parting with them because I might "need" them some day. Quote Link to comment Share on other sites More sharing options...
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