I'm designing a home-made amplifier and am trying to choose connection options for the speaker outputs; is there any reason that RCA plugs are inappropriate, assuming I control the full system, including making the correct cables? Can they cause interference of some sort? They would be more compact than banana sockets or terminal connectors, but seem rare - is this purely convention or is there a motivating technical factor?
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\$\begingroup\$ I had a commercial (but not high-end) system that used RCA plugs for speakers. So long as you didn't unplug/plug them with the power on, no problems. OTOH, at this point I'd use SpeakOns by default; they are made for the job and can't be mixed up with other connectors, nor are they easily shorted. Avoid the counterfeits. \$\endgroup\$– EcnerwalJan 22, 2016 at 14:21
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4 Answers
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It avoids accidentally connecting a speaker output (100W at 8Ω => 28V) to a line input (which may not be 28V tolerant).
answered Jun 27, 2015 at 23:11
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\$\begingroup\$ I did not think of that and I feel stupid now. I have seen audio equipment where line inputs and 'power' outputs used RCA though. \$\endgroup\$ Jun 28, 2015 at 7:54
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\$\begingroup\$ You have the same issue with jack plugs, which are commonly used for headphones, guitars etc. This is exactly why I would use 2-pin DIN connectors, which I have only ever seen on speakers. Certainly more convenient than terminal blocks. \$\endgroup\$ Jun 28, 2015 at 13:25
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1\$\begingroup\$ Yes, however headphones are close enough to line level that it doesn't matter, as long as the amplifier can accept a high-impedance sink. \$\endgroup\$ Jun 28, 2015 at 14:30
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RCA connectors typically have a maximum current rating of 2 amps.
For an 8-ohm speaker, that's 32 watts.
EDIT - Per a comment by Dwayne Reid, I have found that Switchcraft makes RCA connectors which are rated for 6 amps (I'm impressed). Those puppies will handle nearly 300 watts at 8 ohms (200 watts RMS to be conservative). On the other hand, I've found RCAs that are only rated for 0.5 amps, which amounts to 2 watts. So, you can use RCAs for your speakers as long as you are absolutely sure of your source.
answered Jun 27, 2015 at 21:50
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\$\begingroup\$ I hadn't even considered the current rating! (It's not necessarily a particularly professional amplifier) Thanks. \$\endgroup\$ Jun 27, 2015 at 22:00
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\$\begingroup\$ P = I^2 * R. Typical RCA jack & plug rating is 5 Amps or more. 5 * 5 * 8 = 200 Watts \$\endgroup\$ Jun 27, 2015 at 22:28
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\$\begingroup\$ @DwayneReid - My bad on calculating power. I have edited. However, RCAs are NOT rated for 5 amps. See belden.com/docs/upload/NP245.pdf, adam-tech.com/catalog/2012/page_224-228.pdf, service.powerdynamics.com/ec/Catalog17/Section%2015.pdf. The outer connection is good for lots of current, but the inner connection just isn't up to it. All the RCA data sheets I've encountered specified max current of 0.5 to 2 amps. You are, of course, free to provide counterexamples. \$\endgroup\$ Jun 27, 2015 at 23:41
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\$\begingroup\$ I'm on location and don't have access to my datasheet collection. But I have a very strong memory of Swichcraft rating their RCA jacks at 5 Amps. I generally specify Swichcraft or Neutrik connectors for the equipment I design and that my company builds. \$\endgroup\$ Jun 28, 2015 at 1:26
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1\$\begingroup\$ @DwayneReid - Well, I stand corrected. switchcraft.com/Specification.aspx?Parent=1006 says 6 amps. \$\endgroup\$ Jun 28, 2015 at 1:29
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There is no reason not to use RCA connectors for (small power) amplified outputs.
Plenty of professional equipment uses RCA for line level signals, that is more liable to pick up noise, with no problem whatsoever. Maybe they use some sort of fancy connectors like gold plated but you know... Doesn't really make a difference in your project probably.
The maximum power is somewhat limited but probably the cable you are going to use is the biggest problem. RCA plugs can carry some 2A, that is plenty of current for a satellite of an home made amp, just be sure to use appropriately sized cables and you will experience no problem.
answered Jun 27, 2015 at 22:10
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\$\begingroup\$ Thanks Vladimir - this will just be powering desktop speakers, so the wattage isn't an issue. I guess consumer systems just use posts because you can't supply custom length RCA-terminated cables. \$\endgroup\$ Jun 27, 2015 at 22:40
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I would never use anything other than XLR for a live show. RCA has exposed grounds, which can cause a 60hz hummm if your power to everything isn't filtered and perfect.
For any other reason like making a home amplifier... just make sure your ohms rating can be handled by the line, as @WhatRoughBeast suggested.
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\$\begingroup\$ The benefits of XLR for balanced audio don't hold for +/- connections to a speaker. \$\endgroup\$– DavidJun 28, 2015 at 15:23
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\$\begingroup\$ @David There are XLR speaker connectors too. Nothing to do with balanced lines. But that's hard to see how an exposed ground can cause a hum on a speaker connection. \$\endgroup\$ Jun 28, 2015 at 22:27
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\$\begingroup\$ proguitarshop.com/andyscorner/taming-60-cycle-hum @EJP 'Ground Loops' \$\endgroup\$ Jun 30, 2015 at 22:21
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\$\begingroup\$ @Relic Ground loops aren't an issue at speaker-levels, only at preamp levels. There is nothing in the article you cite about ground loops in speaker circuits. You can't cite anything from the electric guitar industry as a normative reference in an EE context. Mostly they simply don't know what they're talking about. \$\endgroup\$ Jan 22, 2016 at 16:19