Impedance matching, why?

Why are some preamps not good with a specific amp / vice versa. ?



2 preamps listed below.......

Line Amplifier Section
Gain: 21.5 dB
Bandwidth: 0.5Hz-300 kHz + 0,-3dB
Maximum Output: 8.0 Vrms
Harmonic Distortion (THD): less than .1% at 2.5 Vrms output Hum and Noise: 100 dB below 2.5 Vrms output
Signal Polarity ("Absolute Phase"): Non-Inverting
Output Impedance: less than 100 Ohms
Input Impedance: 13.5 kOhms


Optional Phono Stage
MM Phono Sensitivity: 5mv for 0.5v @ 1kHz
MC Phono Sensitivity: 0.9mv for 0.5v @1kHz
MM & MC Phono Overload: 200mv
MM & MC Phono Input Capacitance: Adjustable (minimum = 100pF) MM & MC Input Load Resistance: Adjustable (maximum = 47.5k ohm) MM S/N: -80dB relative to 10 mv input
MC S/N: -75dB relative to 100 mv input



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Frequency Response

-3 dB at 5 Hz and 200 kHz

Noise

Greater than 100 dB below 1 volt reference

Distortion

Less than 0.002% from 10 Hz to 40 KHz @ 5 volts peak into 600 ohms or higher, shunted by 1,000 pF or less

Output Impedance

50 ohms, non-reactive, balanced or single-ended

Phono Input Impedance  

User adjustable between 47,000 and 100 ohms. Default setting is 47,000 ohms

Phono Input Capacitance  

User adjustable between 50 pf and 1,200 pF. Default setting is 50 pF.

Input Impedance

47 kohms, balanced or single-ended

Gain  

User adjustable up to 18 dB. Default setting is +8 dB

 Maximum Output  

 10 volts peak

Crosstalk

Greater than 70 dB from 20 Hz to 20 KHz

Power Supply

Independently regulated with shielded toroidal transformer and 20,000 uF of capacitance

Power Consumption

10 watts

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Amplifiers listed below (2)

Input Impedance: 13 kOhms
Input Sensitivity: 3.1 Vrms
Voltage Gain: 27.4 dB
Frequency Response: -3dB @ .5 Hz, 65 kHz Signal-to-Noise: 112 dB
Harmonic Distortion (10 watts, 1 KHz, 8 ohm load): .1% Signal Polarity ("Absolute Phase"): Non-Inverting
Power Requirements (117V/60HZ): 0.7 Amps /84 Watts @ idle
6.8 Amps/ 820 Watts @ clipping (8 ohms) Dimensions: 19" W x 6 7/8" H x 15 D"
Weight: 61 lbs.