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Old 24th April 2003, 03:19 PM   #1
TJtsj is offline TJtsj  United States
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Question RIAA Audio Standards

I have been working on the amplifier that has been mentioned in some other posts (http://www.astro.uu.se/~marcus/private/m250.html) and I am running into a few questions. Basically I just need to know what the standard signal levels for the RIAA are. Like what would come out of the line out of my home stereo.
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Old 24th April 2003, 06:51 PM   #2
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Out from the RIAA amp, you mean? 300-1000 mV. Line level is a floating value, have I noticed. It is also dependent of the pickup.

My monster RIAA amp has gain of 1848 = 65 dB at 50 Hz. This level is OK for my pickup (Ortofon FF15) and pre amp.
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Old 24th April 2003, 09:16 PM   #3
EC8010 is offline EC8010  United Kingdom
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There aren't any RIAA standards for levels, it's all down to how much level the cutting engineer is prepared to put on disc. Higher levels reduce recording time and risk mistracking on subsequent playback. Conversely, lower levels reduce signal to noise ratio, but allow you to cram Beethoven's 9th on one LP. Typical (equalised) peaks reach 12dB over 5cm/s.
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Old 25th April 2003, 12:07 AM   #4
TJtsj is offline TJtsj  United States
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Default Clarification

Ok so either Iím not getting the picture or I didnít make my question clear enough... I have the amp built that I mentioned in my previous post. It takes a 4.4Vp-p signal to make the output of the amplifier start clipping. I have learned that my CD player doesnít even come close to that. Itís more in the range of 500mVp-p. Is my CD player just odd or am I going to need a pre amp to get the full potential out of this amp?
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Old 25th April 2003, 12:35 AM   #5
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Default Standards? What Standards?

Hi,

From what I read I gather your a bit at a loss as to why your phono stage delivers more signal than your CDP?

Cheers,

EDIT:
Quote:
Is my CD player just odd or am I going to need a pre amp to get the full potential out of this amp?
Question is, what's the input sensitivity of your amp?
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Old 25th April 2003, 03:05 AM   #6
TJtsj is offline TJtsj  United States
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Hmmm, so I guess from what has been posted that every device from a home theater receiver to a CD player, to a computer has a different line-out peak voltage. Am I so far off that even GPS canít find me or am I finally making sense. So if there is no standard does that mean that I have to add an AGC (automatic gain control) to my amp so that I can get the full potential from it?
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Old 25th April 2003, 06:09 AM   #7
BrianL is offline BrianL  United States
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The thing you need is called a "volume control". Maybe also
a preamp.

CD audio is supposedly standardized so "full scale" output
is fixed (2V rms, I believe, or thereabouts; maybe it's 2V pk).
It's part of the nature of representing your signal in digital
form that there is a maximum full-scale "level" represented
by the bits.

Analog systems, be they magnetic tape, phono, broadcast,
etc., have no hard full scale limit -- it's somewhat "soft"
and dependent on many factors. (ulitmately, of course,
the circuitry can't put out a bigger signal than the power
supplies allow).

To use a somewhat defined standard, nominal "0 VU" on
professional tape machines are set to 180 nW/m or 250nW/m,
or even other standards depending on tape type, etc. But
even given that your machine is set to a particular one,
you can easily put peak signals onto the tape that are 10 dB
or more above this nominal operating level.

In analog, there are various reference levels such as the
above-mentioned tape levels or a phonograph disk level
of 1 cm/sec or broadcast standard of 100% modulation
(AM) or x kHz deviaion (FM), but these are just nominal
(and somewhat arbitrary) levels chosen for that particular
medium to use as a reference for technical performance
measurements. These do not represent the maximum
signal levels that can be put onto the medium.

There are some fancy preamps, both DIY and commercial that
give you a gain/attenuation adjustment for each input so
that you can have roughly equal volumes between sources
when switching from one to another.
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Old 25th April 2003, 06:33 AM   #8
TJtsj is offline TJtsj  United States
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Ok now I get it. I think all the EMI from the labs I have been working in has finally messed with my head. I have determined through testing that nothing other than a function generator seemes to put out the voltage i'm looking for. which means a pre amp is in order.
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Old 26th April 2003, 12:20 AM   #9
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I don't know if the situation is different in the USA, but down here in the Netherlands there are rather strict limits on the frequency deviation of FM transmitters. In the good old days +/-75kHz was the limit. Nowadays there is a spectral mask defining how strong you can modulate your transmitter without loosing your license, but for practical music signals, this spectral mask still corresponds to roughly 75kHz peak deviation.

On the other hand, for commercial reasons, many stations want to sound as loud as possible. That is why they use terrible multiband compressors and clippers to increase the perceived loudness while still complying with the spectral requirements. The pop music stations sound particularly dreadful.

Regarding AM: some transmitters cheat by increasing their carrier power somewhat in loud parts of the signal, but otherwise you cannot exceed 100% modulation without turning the signal into a kind of DSB instead of AM, which can no longer be properly demodulated with a precision rectifier.

However, there is no real standard for the demodulator constant of AM and FM tuners, so you can still get about any level out of your tuner.
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Old 26th April 2003, 02:11 AM   #10
TJtsj is offline TJtsj  United States
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Quote:
Originally posted by MarcelvdG
I don't know if the situation is different in the USA, but down here in the Netherlands there are rather strict limits on the frequency deviation of FM transmitters.

Ok....... um I never said that I was transmiting signals using FM or AM. I simply have an audio amplifer for my home speakers... people seem to be over analyzing my question. Not that I am not gratefull for the help people try to provide, but that's way far off topic.
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