# How to measure RCA out voltage?



## ZAKOH (Nov 26, 2010)

What's a cheap and good way to measure the voltages of RCA outs on a stereo? I believe the manufacturer specs for the full range outs, but I have some confusion about what's going on with the subwoofer outs.


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## minbari (Mar 3, 2011)

are you looking to just measure voltage out or freq range as well?

a DMM will measure voltage. if you have one that is "true RMS" those are a little more accurate.

if you want to measure freq response you would need a spectrum analyzer to get real results. if you just want a rough idea, then set the volume for 3/4 and connect your DMM. then start playing test tones, 1 hz at a time and write down the voltage. graph it and you will have some idea.


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## airseeker (Nov 13, 2011)

minbari said:


> are you looking to just measure voltage out or freq range as well?
> 
> a DMM will measure voltage. if you have one that is "true RMS" those are a little more accurate.
> 
> if you want to measure freq response you would need a spectrum analyzer to get real results. if you just want a rough idea, then set the volume for 3/4 and connect your DMM. then start playing test tones, 1 hz at a time and write down the voltage. graph it and you will have some idea.


correct me if I am wrong, but can't you use an oscilliscope if you can get your hands on one?


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## minbari (Mar 3, 2011)

yes, you can use an o-scope as well, and it will give you a more accurate reading on the voltage. It will give you accurate readings on the test tone you send it as well, but It will not do spectral analysis, so you would still have to manually sweep through the freqs to see what the output is doing.


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## ousooner2 (Jan 6, 2011)

So you can use a DMM and just put the leads in the RCA outputs to test for voltage output. I've always wondered what my 3sixty.2 is putting out


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## minbari (Mar 3, 2011)

ousooner2 said:


> So you can use a DMM and just put the leads in the RCA outputs to test for voltage output. I've always wondered what my 3sixty.2 is putting out


yes, you can do that. just be careful you dont short them out. best to take a junk RCA cord, cut the end off and strip the end off the wire.


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## ZAKOH (Nov 26, 2010)

minbari said:


> are you looking to just measure voltage out or freq range as well?
> 
> a DMM will measure voltage. if you have one that is "true RMS" those are a little more accurate.


I just want to know the voltage. The head unit is told to have 4V outs. However, I am confused about the subwoofer out. The subwoofer level control extends from -15dB to +15dB. I am confused about what happens when the sub control is in default position (0dB)


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## ousooner2 (Jan 6, 2011)

Sounds like a bass boost, not level (gain). I would think 0db would make it flat. Check the amp manual as most will say what freq. that boost is at


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## minbari (Mar 3, 2011)

ZAKOH said:


> I just want to know the voltage. The head unit is told to have 4V outs. However, I am confused about the subwoofer out. The subwoofer level control extends from -15dB to +15dB. I am confused about what happens when the sub control is in default position (0dB)


it is will put out 4V, then that is the max volts it will put out. (either RMS or peak, depending on how they rated it) the position of the virtual bass knob will simply reference it either higher or lower from the main RCAs. it will still have 4v output.


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## prince427c (Dec 7, 2010)

minbari said:


> it is will put out 4V, then that is the max volts it will put out. (either RMS or peak, depending on how they rated it) the position of the virtual bass knob will simply reference it either higher or lower from the main RCAs. it will still have 4v output.


IIRC, either Eclipse or Alpine units needed that to be set at +MAXdB on the subwoofer end to achieve full rated voltage output. 0dB ended up being something like 2V abouts.


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## chad (Jun 30, 2005)

Why? Are we fixating on numbers?


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## prince427c (Dec 7, 2010)

chad said:


> Why? Are we fixating on numbers?


Better to have it working at full potential, no?


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## minbari (Mar 3, 2011)

chad said:


> Why? Are we fixating on numbers?


because the numbers speak to us, man!


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## chad (Jun 30, 2005)

prince427c said:


> Better to have it working at full potential, no?


So with the number you get, you have nothing to go off of because min/max is pretty much a non standard measurement in gain increments 

A 0dBFS sine wave, WFO is the only max output you will get, I'll bet most people's 4V decks hover around 1V of output with real music.

The number is moot. If you set your gains for the deck's max voltage you will have a system that you will never be able to reach decent levels on.... ESPECIALLY if you listen to music that's properly recorded.


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## prince427c (Dec 7, 2010)

chad said:


> So with the number you get, you have nothing to go off of because min/max is pretty much a non standard measurement in gain increments
> 
> A 0dBFS sine wave, WFO is the only max output you will get, I'll bet most people's 4V decks hover around 1V of output with real music.
> 
> The number is moot.


Which is fine, but you can still determine whether or not 0db is full range max out, +12dB is full range max out, or if it's a bass boost at a certain frequency/range as mentioned. Remember, these are all test tones. It will never reach 0dB output on music unless it contains test tones basically. I would rather use +12db if it maxes out the voltage across the range instead of having the higher noise floor on 0dB. On a sub, this might not be audibly applicable, but possibly.


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## chad (Jun 30, 2005)

prince427c said:


> It will never reach 0dB output on music unless it contains test tones basically.


It will reach 0dBFS at least once.

although not in the defacto redbook standard it's generally a gentlemens rule of production that at one point, you will use every bit. You only have 16, may as well use them all.


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## chad (Jun 30, 2005)

prince427c said:


> Which is fine, but you can still determine whether or not 0db is full range max out, +12dB is full range max out, or if it's a bass boost at a certain frequency/range as mentioned. Remember, these are all test tones. It will never reach 0dB output on music unless it contains test tones basically. I would rather use +12db if it maxes out the voltage across the range instead of having the higher noise floor on 0dB. On a sub, this might not be audibly applicable, but possibly.


there was a thread here on headunit testing, it was pretty much determined that most if not all do not clip at WFO. In fact an alpine WILL NOT clip as when you increase gain on EQ it peels it off the final gain at the end of the volume control, as in the numbers increase, output will not. I have these testing numbers up here too, along with current draw, etc.


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## prince427c (Dec 7, 2010)

chad said:


> It will reach 0dBFS at least once.
> 
> although not in the defacto redbook standard it's generally a gentlemens rule of production that at one point, you will use every bit. You only have 16, may as well use them all.


True enough. In a proper recording, it should.


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## prince427c (Dec 7, 2010)

chad said:


> there was a thread here on headunit testing, it was pretty much determined that most if not all do not clip at WFO. In fact an alpine WILL NOT clip as when you increase gain on EQ it peels it off the final gain at the end of the volume control, as in the numbers increase, output will not. I have these testing numbers up here too, along with current draw, etc.


That may be true for things that actually add into the signal. If you defeat part of the signal though, that output WOULD be reduced, no. What I'm saying is if the output section is designed for full voltage output at +12dB, the 0dB setting would be a reduction of that(theoretically by half if there is a -12dB section.


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## chad (Jun 30, 2005)

yes and no, cuts will reduce, so if you dig the EQ into a hole it will not makeup gain, which would be sweet. But any boosts will not over drive it. Not many people actually have the entire passband below 0dB on the EQ, if they do, they need to learn how to EQ before worrying about output voltage.


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## prince427c (Dec 7, 2010)

chad said:


> yes and no, cuts will reduce, so if you dig the EQ into a hole it will not makeup gain, which would be sweet. But any boosts will not over drive it. Not many people actually have the entire passband below 0dB on the EQ, if they do, they need to learn how to EQ before worrying about output voltage.


Right. I guess what I'm getting at here is trying to keep the overall output equal across the Front/Rear/Sub. If your Front/Rear outputs are 4V, you don't want your sub section outputting 2V. It just seems like lost potential. I honestly don't remember what decks that were designed that way, I want to say they were Alpines, but it seems like a ridiculous design to make your actual rated output, in relation to the rest of the 0dB system, at the "highest boost" setting instead of doing what you're saying; pull back the rest of the output to put the highest boost at the highest voltage.


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## chad (Jun 30, 2005)

If you have your mids and subs doing 4V your tweeter output will NEVER ever, no way reach 4V.

That is if you plan to run active.


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## chad (Jun 30, 2005)

prince427c said:


> Right. I guess what I'm getting at here is trying to keep the overall output equal across the Front/Rear/Sub. If your Front/Rear outputs are 4V, you don't want your sub section outputting 2V. It just seems like lost potential. I honestly don't remember what decks that were designed that way, I want to say they were Alpines, but it seems like a ridiculous design to make your actual rated output, in relation to the rest of the 0dB system, at the "highest boost" setting instead of doing what you're saying; pull back the rest of the output to put the highest boost at the highest voltage.


Yeah it's alpine, the sub output goes from 0-15, 15 is wide open, It should be noted that the control is actually an attenuator..... Crazy Japanese  At least they don't call it +15, it just goes from 0-15. In reality all volume controls are simply attenuators when the output is fixed at WFO, nomesayin? Potato pootaato.

I have one of those alpines FWIW. I try to set the sub so it's "right" at about "ten" therefore if something is weaksauce I have a bit of room to go with it.


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## ZAKOH (Nov 26, 2010)

ousooner2 said:


> Sounds like a bass boost, not level (gain). I would think 0db would make it flat. Check the amp manual as most will say what freq. that boost is at


No. That's not bass boost. That's level. Bass boost is tuned with a different menu option.


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## Serieus (May 27, 2011)

you have a kdc-x995 right? i'd be interested in your results


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## TrickyRicky (Apr 5, 2009)

Chad some people just dont get it, they want to measure output with sinewaves but music is dynamic and there is no way in hell you can say "yeah I got 3.8v on my signal and 120vac on my power rails, 38vac on my subwoofer terminals, 28vac on my full range when playing lady gaga" or can you LOL.


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