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soundbadger 3rd October 2007 03:32 PM

What Is Line Level????
 
Im trying to design a driver stage for a kt88 based SE amplifier. i've not done this before so its mostly new to me.

but i dont know what peak-peak input i am to expect so as i can work out how much gain i need for a desired voltage swing coming out of the driver stage.

i have found figures from 249mV rms to 2V rms :mad:

i did find a pdf on line levels which stated consumer audio products operate at -10 dBv which they stated was .249V rms,

but when you look at for example a cd players spec sheet on the web it often seems to state voltages around 2V rms.

can someone explain to me whats goin on,,, or is there really no logic here.

thanks in advance
soundbadger

AndrewT 3rd October 2007 03:48 PM

Hi,
older sources often have outputs in the range 200mVac to 500mVac. Modern units tend to be higher, ranging from 500mVac to 2500mVac.
The peak to peak will be around three times the Vac value.

A modern active pre-amp based on solid state devices can have a maximum output of over 10Vac.
Tube/valve gear can often cope with much higher levels than these. I have seen a phono pre that had a maximum output of over 30Vac simply because valves made that possible, but was it ever needed, I doubt it, but headroom is nice to have if no other compromise is needed to accomodate these high input/output levels.
Commercial gear line level is often specified to +20dbu (7.75Vac) to +24dbu (12.3Vac).

kevinkr 3rd October 2007 03:48 PM

You have to be somewhat careful about whose definition you use because for example the IHF definition of line level to which most US, and Japanese HiFi adhered to until the CD era is defined as 775mVrms which is 0dBu (not dBv). Many in fact still adhere to this standard. Note that -10dBu is almost exactly 249mVrms which corresponds closely to what DIN standards indicated line level to be - manufacturers such as Tandberg, Saba, and B&O used this definition.

Current line level is often based on 0dBfs for CD players which Philips - Sony defined in the early 1980's as 2.0Vrms.

I typically design my amplifiers for full output at 1.0Vrms - if you use a line stage with some gain ahead of the amplifier it is a none issue, if you don't and use either a passive controller or build the amplifier as an integrated you should plan on more gain to provide flexibility for lower level sources and program material that is recorded at lower than normal levels. In such a case a sensitivity of 250mVrms - 500mVrms might not be unreasonable.

Glowbug 3rd October 2007 04:15 PM

Re: What Is Line Level????
 
Quote:

Originally posted by soundbadger
Im trying to design a driver stage for a kt88 based SE amplifier. i've not done this before so its mostly new to me.

but i dont know what peak-peak input i am to expect so as i can work out how much gain i need for a desired voltage swing coming out of the driver stage.

i have found figures from 249mV rms to 2V rms :mad:

i did find a pdf on line levels which stated consumer audio products operate at -10 dBv which they stated was .249V rms,

but when you look at for example a cd players spec sheet on the web it often seems to state voltages around 2V rms.

can someone explain to me whats goin on,,, or is there really no logic here.

thanks in advance
soundbadger

There isn't a universal standard. Heck, in car audio I've worked on installs where the head unit had 8V unbalanced outputs, and sometimes 16V balanced ones...although there are few amps that actually can handle that kind of input voltage.


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