Phono amp gain too high? (EAR 834p)

Thanks for all the information.  The specs provided on the Needle Doctor website show the following:

EAR 834P Specifications:
Input sensitivity for 1 volt out @ 1kHz:
MM 2.2mV - MC 0.22mV
Max output 30V
Noise (unweighted) -80 dB (1HF)
Tubes ECC83 x 3

Does this suggest that 2.2mV is the upper end of the range for a moving magnet cart?  Not sure I fully understand the above specs and how they would interact with a given preamp or integrated amp. 

Thanks for any clarification you can provide,Scott

Hi Scott,

No, it just means that 2.2 mv in (in MM mode) will result in 1 volt out, at 1 kHz. Based on those specs, the maximum input the phono stage could process without clipping, in MM mode and at 1 kHz, would be:

(30 volts/1 volt) x (2.2 mv) = 66 mv.

Obviously that represents a goodly margin relative to the maximum input any MM cartridge is likely to provide, and corresponds closely to Stereophile’s measured 1 kHz overload point of 69.2 mv.

The gain of the phono stage in MM mode, per those specs and expressed as a ratio, is:

(1 volt)/(0.0022 volts) = 454.5, meaning that the output voltage will be 454.5 times as great as the input, at 1 kHz, as long as the clipping point is not exceeded.

Expressing that gain in db:

20 x logarithm (1/0.0022) = 53.2 db.

As you’ll realize, that is about 4 db higher than what Stereophile measured. So either the spec is not quite accurate, or the design changed somewhere along the way, resulting in differences in gain among 834P’s that were manufactured at different times.

In the interests of simplicity I’ve neglected RIAA equalization in all of this, which does not affect 1 kHz but which compensates for a progressive increase in frequency response at higher frequencies and a progressive decrease in frequency response at lower frequencies that is introduced in the record-making process. See the first figure in this Wikipedia writeup.

Best regards,
-- Al

Al,  Thanks for all your help and valuable insight.  Some of it goes over my head as I haven't taken a math class in 30 years.  I just came across a phono amp that has the following as one of it's specs:

sensitivity 2 mV for 0.5 V rms o/p

What does that mean in terms of gain?  Sorry, I was a Spanish major to avoid taking math classes in college :)

Scott

Hi Scott,

"o/p" presumably means "output."  If 2 mv in results in 0.5 V out, since 0.5 V = 500 mv the gain is 500/2 = 250x (i.e., 250 times).

The ratio of two voltages expressed in db equals 20 times the logarithm of the ratio.  So 250x is a gain of:

20 x log(250) = 48 db

Best regards,
-- Al
 

Gracias :)