Line voltages for audio

Thread Starter

bloguetronica

Joined Apr 27, 2007
1,359
I need to confirm if the line voltage for RCA connectors (for example, the ones used for audio output in TVs) is actually 0.350V RMS. Am I right?

Also, is it correct to assume that the line voltage for headphones is 0.316V RMS?

Thanks in advance.
 

studiot

Joined Nov 9, 2007
5,003
A quick shufty at the specifications pages of some audio equipment will show that 'line levels' can vary between 0.1 and 1 volt in normal operation.

Don't forget that impedance level also play a part 600 ohms, 47k ohms or 10k ohms being common input values.

This applies to both domestic and professional equipment. That is why we have input potentiometers.
 

Thread Starter

bloguetronica

Joined Apr 27, 2007
1,359
Thanks for you reply, studiot. But I need to know the exact standard RMS voltage as used in low level RCA sockets, like the ones found in the back of TVs and VCRs, or in the back of audio amplifiers.

Also, what is the standard RMS voltage for use with headphones?
 

beenthere

Joined Apr 20, 2004
15,808
The RCA connector has no bearing on audio levels. Audio signal levels are somewhat standardized - http://en.wikipedia.org/wiki/Line_level.

Headphones are driven by amps fed by audio sources at standard signal levels. The amp will have a fixed gain, so the audio signal will be attenuated by means of a level pot.
 

Thread Starter

bloguetronica

Joined Apr 27, 2007
1,359
So I can assume that the standard nominal voltage normally used in headphones is 0.316V RMS.

And what is the standard nominal voltage normally found in RCA connectors? Is it the same? Or is it 0.350V RMS?
 

bertus

Joined Apr 5, 2008
19,944
Hello,

Here I found an atricle on line level:

Line level


  • For domestic application Pre-Amplifiers (input selectors and tone controls) are combined with Power-amplifiers in one box
  • Pre-amplifiers for professional applications are described as signal processing.
    Mixers. EQ. Graphics. Processors. Effect systems. etc.
  • For professional applications Pre-amplifiers are separated from Power-amplifiers.
Line Level (0VU volume units) or (0dBm) is 775mV. Line level is slightly less than 1Volt, and was adopted as the standard in early audio history for all signal processing, prior to Power-amplifiers.
This standard only applied to past valve technology, in the broadcast industry, where equipment was interconnected with line transformers, referenced to 1 milli-watt into Z 600ohm. Solid-state technology has no need for this reference, which now only loosely applies.
The Line level standard should revised from 0dBm (775mV) to 6dBV (2V) to solve signal to noise problems.

This quote comes from this page:
http://lenardaudio.com/education/11_cable.html

Greetings,
Bertus
 

studiot

Joined Nov 9, 2007
5,003
At the risk of repeating myself

Look at the specifications for the particular equipment concerned.

Here are some quick ones

Sony Audio in/out -7.5 dBs ( 0 dBs = 1 vrms into 47k)

Panasonic Audio in -10 dBv Audio out - 8dBv both more than 47k headphone -30dBv into 8 ohms

Yelo 5.1 channel 0.5 volts pk to pk stereo mix 2volts pk to pk

As you can see they vary from manufacturer to manufacturer. There is no standard.

As I also noted before you also need the impedance to calculate voltages. This is very important.
 

Thread Starter

bloguetronica

Joined Apr 27, 2007
1,359
At the risk of repeating myself

Look at the specifications for the particular equipment concerned...
I'm not analysing any equipment in particular, but I'm projecting an amp that uses a pair of RCA sockets and a TRS jack socket as inputs. You can choose the input you want (RCA or TRS) via a selector switch. I believe they use different voltage levels. Hence my question.

I want to base myself on standard "should be" values, and not on the values measured from any particular equipment. I've heard that values for RCA plugs can be 0.775V RMS, others say they are about 0.350V RMS. I cannot base myself on suppositions.
 

studiot

Joined Nov 9, 2007
5,003
Do you understand what I said about impedance?

I though you knew more about electronics?
 

Thread Starter

bloguetronica

Joined Apr 27, 2007
1,359
Just found out that for RCA sockets, the standard line level is 0.5V RMS (if you take it from a SCART plug).
 

studiot

Joined Nov 9, 2007
5,003
If you say so it must be true.

However if you connect the output of a Panasonic Nv-DX110EG to the input of a Sony EV-C2000 and measure the 'voltage' you will find it is three times the 'voltage' if you connect the same Panasonic to a Tascam 424.

This is because the input impedance of the Sony is 47k and the Tascam is 10k, the output impedance of the Panasonic is the same 47k in both connection cases.

I won't waste my time again if you don't want to discuss sensibly.
 
All good replies to the OP. Even the old professional standards aren't so standard any more. It used to be that you could drive a 775 mV rms sine wave into an amp and that gave the maximum output without clipping. Now it seems the line levels are higher, presumably to minimise interference pickup on the long cable run between the mixing desk and the amp.

There are no connector-specific line levels that I've come across. OK SCART is now 2 V rms into 10 kΩ, but then SCART is more of an integrated system than a mere connector. And it still varies - all my SCART sources are at slightly different levels. Consumer audio gear is -10 dBV in theory, but in practice the levels are impossible to match with any degree of accuracy as the equipment manufacturer has no control over the levels of the source audio, whether that's CD, tape, radio, DVD or whatever.

There are no standards for headphone levels either. Maybe you need to think in terms of peak audio levels at the input, and match that to the peak power level the headphones will take, and then back it off a tad. 'Scoping up a CD source would probably be safest, as they've got a good dynamic range and will have a higher peak:rms ratio (or crest factor). The latter is a whole 'nother can of worms, but needs to be considered as an rms line level doesn't guarantee a maximum peak level.
 
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