[78-L] EQ ideas for transferring acoustic 78s?

[J. E. Knox]

Greetings from FixitLand!

DanKj wrote:

>  That is correct - we hear 120 because the "60" refers to how many  
> times the
> electrical current is reversed each second ...

Power frequency in the US is 60 cycles per second (or, nowadays, 60  
Hz). Each cycle is typically measured from one positive-going zero  
crossing to the next positive-going zero crossing, thus one cycle has  
a positive peak and a negative peak. If the current reversal occurred  
60 times each second, the frequency would be only 30 Hz since each  
cycle encompasses two polarity reversals -- one going positive that  
defines the beginning of the cycle, and the other at mid-cycle as the  
polarity goes negative.

We hear 120 Hz in many cases because full-wave rectification is  
frequently used in power supplies (because it's more efficient); by  
"flipping" the negative-going halves of each cycle to positive-going,  
a 120-Hz pulsating DC is output from the rectifier. Insufficient or  
failing power-supply filtering causes 120-Hz ripple to be heard in  
audio. Harmonics of that frequency are prevalent, because the ripple  
component is usually not sinusoidal.

> ... - it doesn't refer to a sound frequency.


I don't understand this statement. 60 Hz is in fact quite audible (a  
"sound frequency"). Hook a speaker to the secondary of a 115V:6.3V  
filament transformer, and plug in the primary, and you'll  
*definitely* hear it!

Thanks for the comments on various power frequencies; interesting.

Take care,


Joe
--
It's my cats' world. I'm just here to fill their food dish.