Sound Quality

[Oren Beck]

>
>On Sat, 27 Dec 2003, Zscoundrel wrote:
>
> > That 'buzz' is probably a 60hz hum from the power lines.  Many of the
> > better turntables used a very sensitive electro-magnetic pickup that put
> > out a much lower line-level output than tape decks and stereo systems.
> > You probably need to get a pre-amp or just hook the turntable into a
> > stereo that is built to accept turntable level input and puts out
> > standard line-level out put.
>
>This is called matching amplifier impedances.  Each amplifier has been
>designed with a particular resistance and must be matched with its input
>or outputs for maximum efficiency.  If a 50 ohm microphone is connected to
>a 1,000 ohm amplifier input, the gain will have to be greatly increased to
>overcome massive loss.  The result is maximum noise in the form of static,
>hum, the switching of light switches, dimmers, and possibly local radio
>stations.
>
>A good amplifier should always state its input and output impedances and
>frequency response.  Sometimes the input impedance is measured vaguely in
>volts.  A one volt input gives a hint of a higher impedance, say 1,000
>ohms.  Our friends at the RIAA were involved in setting these wonderful
>standards in the old days...
>
>Speaking of frequency response, pick something that matches your
>application.  An ideal amplifier would cover the entire spectrum, but you
>wouldn't want the real low frequencies including DC voltage...
>
>When designed, an amplifier has a bias circuit that defines its input
>impedance... or its input resistance is infinite in the case of
>differential amplifiers.  The output impedance is usually much lower than
>the input as the final transistors often are driven directly from the
>power supply rails.

Good catch on the RIAA standards !

To my hazy recall the issue may be complcated by a pre-transistor era 
concept called

Pre and De Emphasis .

Simply IIRC the signal out  to the record cutting head was BOOSTED in 
certain defined parameters to compensate for nonlinear properties of the 
whole chain . At the pickup head amplifier or preamp point a matching CUT in 
certain parameters restored an essentially flat EQ end to end .

Now as the coffee cuts in I hit Google and found this :   
http://www.delback.co.uk/lp-cdr.htm
Which while sadly wincentric in the software area it may help . It covers  
things I forgot .

Oren

" How much of our world could you recreate from your memories "

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