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From: bill@videovax.tv.tek.com (William K. McFadden)
Newsgroups: sci.electronics
Subject: Re: line level and op amps
Keywords: op amp, line level
Message-ID: <6259@videovax.tv.tek.com>
Date: 9 Jan 91 07:23:51 GMT
References: <1991Jan8.072135.15225@wam.umd.edu>
Reply-To: bill@videovax.tv.tek.com (William K. McFadden)
Distribution: usa
Organization: Tektronix TV Measurement Systems, Beaverton OR
Lines: 30

In article <1991Jan8.072135.15225@wam.umd.edu> elwood@wam.umd.edu (Jim Bogard) writes:
>1. What exactly _is_ 'line level' defined to be?

For consumer products, it is usually somewhere in the neighborhood
of -10dBu=0VU, which is about 250 mV RMS.  Source impedances are
generally less than 10K, and load impedances are generally greater
than 10K

For professional gear, it varies.  The most common level I've seen
on tape decks is +4dBm=0VU.  +4dBm is about 1.2 V RMS and requires
600 ohm source and load impedances.

>2. What's the lowest noise op amp?

The king of the heap still seems to be the 5534 (single) / 5532
(dual).  It has a bipolar input stage that requires a lot of bias
current, and the supply current's kind of high, but it's very low
noise, low distortion, and can directly drive 600 ohm loads.  It's
also fairly old and hence fairly cheap.

There are some newer amps by places like Linear Technology that
have lower noise, but most applications have too high an impedance
to take advantage of it (most resistors generate more thermal noise
than some of these new amps).  Plus, they have either more distortion
or less output drive and cost more.
-- 
Bill McFadden    Tektronix, Inc.  P.O. Box 500  MS 58-639  Beaverton, OR  97077
bill@videovax.tv.tek.com,     {hplabs,uw-beaver,decvax}!tektronix!videovax!bill
Phone: (503) 627-6920       "The biggest difference between developing a missle
component and a toy is the 'cost constraint.'" -- John Anderson, Engineer, TI