[linux-audio-user] Re: Digital Fidelity

[res0u2uc at verizon.net]

On Wed, Mar 01, 2006 at 10:43:15PM -0600, Paul Winkler wrote:
> On Thu, Mar 02, 2006 at 07:09:35AM +0900, res0u2uc at verizon.net wrote:
> > On Wed, Mar 01, 2006 at 04:52:33PM -0600, Paul Winkler wrote:
> > > The only exception I can think of is when there's a
> > > DC offset to the signal of sufficient voltage to force the
> > > signal always be positive (or always negative).
> > > But that would mean something's broken :)
> > 
> > Not necessarily broken. Class A amplifiers do their work
> > with sufficient DC offset that the signal never changes
> > direction. Even so, the music is carried by an AC
> > *component* which is present, and may be separated out by
> > using a transformer.
> 
> Or a highpass filter tuned very low - AKA a capacitor in series.  Which
> almost any modern electronic gear has on its inputs and outputs.
 
Hmm. Well, my knowledge here isn't great, but I think having
a capacitor at the output of a Class A amplifier would 
prevent it from operating with a DC offset. 

You're right about most gear using capacitors. Most
transistor amps are Class B or AB which output AC.  Older
tube amps, however are usually Class A to reduce the number
of tubes, and like my dad's old Heathkit, have a big
transformer on the output.

(Which, sad to say he threw out one fine day. The only
problem with that amp was that there would be a zhuuum
zhuuum sound pulsating with a period of a couple seconds.
Replacing one tube in the power amp would fix this for a
number of hours.)


> -- 
> 
> Paul Winkler
> http://www.slinkp.com

-- 
Joel Roth