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In Reply to: RE: Active vs passive phono preamp? posted by BCR on March 19, 2015 at 12:07:06
Don't think there are passive phono preamps. The purpose of a phono preamp is to provide gain, which a passive unit doesn't.
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The purpose of the phono preamp is to provide a very precise filter, called RIAA equalization, to the signal from a phonograph record. The filter boosts the low frequencies and attentuate the high frequencies on a specific curve with points along the curve at 50Hz, 500Hz and 2122Hz.
This RIAA equalization can be passive or active meaning that the amplifiers used to drive the filter can have the passive components either between the stages of amplification as in passive or within the feedback network of the driving amplifiers which would denote active.
A passive filter can not boost anything above the input signal, only active circuitry can do that.
In order to get the RIAA curve an ideal passive filter leaves the lowest frequency alone and applies varying amounts of attenuation to all other frequencies.
You can probably use a transformer to boost voltage at the expense of current and vice versa.
"A passive filter can not boost anything above the input signal, only active circuitry can do that."
Read my post again:
"the amplifiers used to drive the filter can have the passive components either between the stages of amplification as in passive or within the feedback network of the driving amplifiers which would denote active."
It should be obvious that gain stages are required to drive the passive filter network.
By the way it can be both 1/2 active and 1/2 passive.
with a 1 mV input sensitivity. ;)
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