Sound Quality
Oren Beck
oren_beck at hotmail.com
Sat Dec 27 18:55:08 CST 2003
>
>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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