What do I need to connect my smartphone to a single speaker?
August 22, 2013 5:57 PM Subscribe
This should be so simple. I bought an classic but broken 1950s console TV to turn into a bar. I pulled the tube and all the electronics, except the speaker. Now I want to add a small amplifier to which I can connect a smart phone or iPod and which will power the single speaker. I bought this neat little stereo amp, but it turns out you can't just mash the lefts and right outputs together and attach them to a speaker. So what do I need to do this? Difficulty level: No electronics experience of specialized tools.
Best answer: LarryC's problem is you're not supposed to run the output from two amplifiers (with the left speaker output being one amplifier and the right speaker output the other) to a single speaker.
if trivia genius's idea doesn't work, you can try "mashing the inputs together" by using an adapter like this 3.5mm Stereo male to RCA mono female from your iPod/phone to one input of the amp and then just hook up the speaker to the corresponding output.
Your local Radio Shack or other electronics store should have something similar, although probably a few dollars more expensive.
posted by soundguy99 at 6:46 PM on August 22, 2013
if trivia genius's idea doesn't work, you can try "mashing the inputs together" by using an adapter like this 3.5mm Stereo male to RCA mono female from your iPod/phone to one input of the amp and then just hook up the speaker to the corresponding output.
Your local Radio Shack or other electronics store should have something similar, although probably a few dollars more expensive.
posted by soundguy99 at 6:46 PM on August 22, 2013
If you're handy with a soldering iron, you can make a very simple summing mixer box/cable for the output of the phone. This can be plugged into the amp, with one or both channels will have audio the summed (mono) signal. You would then only have to connect one channel of the speaker outputs to the speaker. The other simply remains unconnected.
This is somewhat similar to "mashing the inputs together". But using the two resistors might be a little safer, always presenting a load on each channel output.
posted by 2N2222 at 6:48 PM on August 22, 2013
This is somewhat similar to "mashing the inputs together". But using the two resistors might be a little safer, always presenting a load on each channel output.
posted by 2N2222 at 6:48 PM on August 22, 2013
Couldn't LarryC connect both positive outputs together into one lead and both negative outputs together into the other lead and then attach those to the terminals of the mono speaker? It isn't clear to me from his description that that is what he is doing.
My advice would be to return the amp to where you bought it and use the money to buy a cheap set of stereo computer speakers. The speakers will have the 3.5mm stereo plug already that would fit your smartphone's headphone jack. Take out the mono speaker and stick the speakers behind the speaker grill.
posted by Rob Rockets at 7:22 PM on August 22, 2013
My advice would be to return the amp to where you bought it and use the money to buy a cheap set of stereo computer speakers. The speakers will have the 3.5mm stereo plug already that would fit your smartphone's headphone jack. Take out the mono speaker and stick the speakers behind the speaker grill.
posted by Rob Rockets at 7:22 PM on August 22, 2013
Couldn't LarryC connect both positive outputs together into one lead and both negative outputs together into the other lead and then attach those to the terminals of the mono speaker? It isn't clear to me from his description that that is what he is doing.
That's generally not a good idea with power amp outputs. Especially the kind in the OP, which I think has some kind of bridged output topology for each channel.
It's much safer to sum the small signal levels from the iphone/ipod via some kind of resistive circuit at the very least, feed that summed (mono) signal to one or the other (or both) channel of the power amp, then simply use the speaker output with the summed signal to connect to the speaker.
posted by 2N2222 at 7:45 PM on August 22, 2013 [3 favorites]
That's generally not a good idea with power amp outputs. Especially the kind in the OP, which I think has some kind of bridged output topology for each channel.
It's much safer to sum the small signal levels from the iphone/ipod via some kind of resistive circuit at the very least, feed that summed (mono) signal to one or the other (or both) channel of the power amp, then simply use the speaker output with the summed signal to connect to the speaker.
posted by 2N2222 at 7:45 PM on August 22, 2013 [3 favorites]
Best answer: If you can't trust electronics advice from a user named 2N2222, who can you trust?
posted by Rob Rockets at 7:58 PM on August 22, 2013 [4 favorites]
posted by Rob Rockets at 7:58 PM on August 22, 2013 [4 favorites]
tl;dr The Straight Dope Tells you Rob Rockets is correct.
Ideally, the speaker will have some information printed on it. That information will include the wattage and impedance of the speaker. If you're lucky, it's a normal 8 ohm speaker and it's powerful enough to not die when the amp gives it . Since it's part of a non-user-servicable appliance, it could be whatever freaky impedance the manufacturer got the best bulk deal on.
None of that will help you tie the two channels together into one output channel. That needs to happen at the input stage (as described above) or in the amp, which may have a "mono" button.
Even if you put 8 ohm resistors inline to protect your amp, imagine a stereo signal where there is different information on the circuits. Left tells the speaker "-80% of full power", Right tells the speaker "+90%". The sound would be horribly distorted: sometimes amplifying and sometimes dampening the expected signal. And if it did push too hard, you would have a blown speaker (either due to thermal failure of the voice coil or mechanical failure from pushing the speaker cone too hard).
So, don't, you'll be dissatisfied at best with the results. If you really want to, go to Radio Shack and buy a dual-coil speaker of about the same size that matches the amp you have.
posted by Mad_Carew at 8:07 PM on August 22, 2013
Ideally, the speaker will have some information printed on it. That information will include the wattage and impedance of the speaker. If you're lucky, it's a normal 8 ohm speaker and it's powerful enough to not die when the amp gives it . Since it's part of a non-user-servicable appliance, it could be whatever freaky impedance the manufacturer got the best bulk deal on.
None of that will help you tie the two channels together into one output channel. That needs to happen at the input stage (as described above) or in the amp, which may have a "mono" button.
Even if you put 8 ohm resistors inline to protect your amp, imagine a stereo signal where there is different information on the circuits. Left tells the speaker "-80% of full power", Right tells the speaker "+90%". The sound would be horribly distorted: sometimes amplifying and sometimes dampening the expected signal. And if it did push too hard, you would have a blown speaker (either due to thermal failure of the voice coil or mechanical failure from pushing the speaker cone too hard).
So, don't, you'll be dissatisfied at best with the results. If you really want to, go to Radio Shack and buy a dual-coil speaker of about the same size that matches the amp you have.
posted by Mad_Carew at 8:07 PM on August 22, 2013
This Mini mixer mixes 4 mono inputs to 1 mono output. Not terribly expensive, and no soldering or electronics required.
posted by Jon Mitchell at 10:28 PM on August 22, 2013
posted by Jon Mitchell at 10:28 PM on August 22, 2013
absolutely seconding the mono 3.5mm cable and only using one channel of the amp. 20 watts will be MORE than enough for that speaker, and you won't hurt the amp by only using one channel. it was probably originally only driven by 5-9 watts or something. 15 if it was a big tv. Tube amps were always very low wattage, and the speakers used with them were generally quite sensitive.
I would be trying to use this old speaker as well. A lot of old speakers have a really fascinating sound signature to them, especially when playing old music from that era.
posted by emptythought at 10:28 PM on August 22, 2013 [1 favorite]
I would be trying to use this old speaker as well. A lot of old speakers have a really fascinating sound signature to them, especially when playing old music from that era.
posted by emptythought at 10:28 PM on August 22, 2013 [1 favorite]
Best answer: Soundguy99 has it, use an adapter to combine both channels of the ipod before it goes into the amp, then just use 1 channel of the amp. I've been doing the same thing as a sound guy/AV professional for decades when running music into a mono system. Don't buy any fancy mixers or summing boxes or whatever, just a tiny stereo to mono adapter will work perfectly for what you want to do.
posted by markblasco at 11:13 PM on August 22, 2013 [1 favorite]
posted by markblasco at 11:13 PM on August 22, 2013 [1 favorite]
Response by poster: The amp I bought has an aux in. So I buy Soundguy's recommended adapter, then wire it to a standard male 1/4 plug, stick that in the amp's aux in, then run wires from one channel only to the speaker. Is that right?
posted by LarryC at 12:11 AM on August 23, 2013
posted by LarryC at 12:11 AM on August 23, 2013
Best answer: One other little detail....
In that era, field coil speakers were common. These are different than permanent magnet speakers you see these days. They required a DC supply to provide the magnetic field that powered the speaker movement. This won't work at all on current amplifiers. You will need to see if your speaker is such a beast. Usual give away is a smallish magnet area and 4 wires instead of just two in the connector. (Two are for the field coil and two for audio.)
FWIW, I actually do this by fixing the radio, finding insertion points for a mono audio signal, and using the vacuum tube amps. Did it on a Scott radio and a Capehart. Lovely vacuum tubes glowing in the dark. Yum. A little more involved, but oh, so satisfying.
I also use bluetooth speakers for a clever wireless hack.
Note, once you get the signal mono, you can use 1/2 the amp (i.e. right OR left channel). Perfectly legit approach.
posted by FauxScot at 1:29 AM on August 23, 2013
In that era, field coil speakers were common. These are different than permanent magnet speakers you see these days. They required a DC supply to provide the magnetic field that powered the speaker movement. This won't work at all on current amplifiers. You will need to see if your speaker is such a beast. Usual give away is a smallish magnet area and 4 wires instead of just two in the connector. (Two are for the field coil and two for audio.)
FWIW, I actually do this by fixing the radio, finding insertion points for a mono audio signal, and using the vacuum tube amps. Did it on a Scott radio and a Capehart. Lovely vacuum tubes glowing in the dark. Yum. A little more involved, but oh, so satisfying.
I also use bluetooth speakers for a clever wireless hack.
Note, once you get the signal mono, you can use 1/2 the amp (i.e. right OR left channel). Perfectly legit approach.
posted by FauxScot at 1:29 AM on August 23, 2013
There's no need to bother with any complexity at all if you're making a mono signal from the cellphone's headphone output by plugging a mono plug into the jack. Headphones are designed to work like that.
posted by ambrosen at 2:12 AM on August 23, 2013
posted by ambrosen at 2:12 AM on August 23, 2013
IMHO, just go to the local electronics store and buy a 1/2 decent pair of car speakers. Remove the current speaker and mount the pair inside the old TV/bar and viola!. A nice pair of JVC 5.25" could be as cheap as $40.00
posted by Gungho at 6:34 AM on August 23, 2013
posted by Gungho at 6:34 AM on August 23, 2013
Best answer: So I buy Soundguy's recommended adapter, then wire it to a standard male 1/4 plug, stick that in the amp's aux in,
This may be a typo on your part, but the amp you linked to has a 3.5mm (a.k.a. 1/8 inch) aux in, so no need to do anything with a 1/4" plug.
And my idea was even simpler than that - the adapter I linked to takes the separate left & right "hot" connections of a stereo plug and physically connects them to the single "hot" connection of an RCA cable.
So plug the adapter into the headphone output of your phone, then run a single RCA male to RCA male cable of appropriate length from the adapter to one RCA input of the amp, then wire from the corresponding output to the speaker.
posted by soundguy99 at 8:10 AM on August 23, 2013 [1 favorite]
This may be a typo on your part, but the amp you linked to has a 3.5mm (a.k.a. 1/8 inch) aux in, so no need to do anything with a 1/4" plug.
And my idea was even simpler than that - the adapter I linked to takes the separate left & right "hot" connections of a stereo plug and physically connects them to the single "hot" connection of an RCA cable.
So plug the adapter into the headphone output of your phone, then run a single RCA male to RCA male cable of appropriate length from the adapter to one RCA input of the amp, then wire from the corresponding output to the speaker.
posted by soundguy99 at 8:10 AM on August 23, 2013 [1 favorite]
Response by poster: Thanks! I'll post back here and let all know how it worked.
posted by LarryC at 10:11 PM on August 23, 2013
posted by LarryC at 10:11 PM on August 23, 2013
This thread is closed to new comments.
posted by trivia genius at 6:26 PM on August 22, 2013 [1 favorite]