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Resource to calculate, building and measuring Hi Fi Loudspeakers and more...


Friday, May 18, 2012 28 users online

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Generator Frequency Hz	Phono Amp U_out	Phono Amp dB_out
20	9,23 volts	+19.30 dB
30	8,51 volts	+18.60 dB
40	7,76 volts	+17.80 dB
50	7,08 volts	+17.00 dB
60	6,38 volts	+16.10 dB
80	5,31 volts	+14.50 dB
100	4,52 volts	+13.10 dB
150	3,27 volts	+10.29 dB
200	2,57 volts	+8.20 dB
300	1,88 volts	+5.48 dB
400	1,55 volts	+3.80 dB
500	1,35 volts	+2.60 dB
800	1,08 volts	+0.67 dB
1,0k	1,00 volts	0.00 dB
1,5k	0,85 volts	-1.41 dB
2,0k	0,74 volts	-2.61 dB
3,0k	0,58 volts	-4.73 dB
4,0k	0,47 volts	-6.56 dB
5,0k	0,39 volts	-8.18 dB
6,0k	0,33 volts	-9.63 dB
8,0k	0,25 volts	-12.04 dB
10,0k	0,21 volts	-13.55 dB
15,0k	0,14 volts	-17.08 dB
20,0k	0,10 volts	-20.00 dB

The test circuit is built according to plan ( the scoop not really necessary ).

The sine generator is set so (out of balance can be no question), that appears at the output of the phono amplifier at 1kHz an AC voltage of 1V. In following the sine wave generator, only the frequency is changed, the amplitude remains the same.

Now, driven by the following frequencies and compare the measured voltage with the figures shown here. The closer the measurement result at this data, the better, with deviations of ± 0.12 volts quite acceptable.

When performing any tests on an audio system, some form of measuring device is essential. Digital multimeters are not useful, since they will not give the true picture of what is happening, and most have a fairly limited frequency range. An oscilloscope is the ideal tool, but not all hobbyists can afford the outlay for a scope.

Audio Generator - with a range of 10Hz up to 100kHz and high amplitude stabilisation
AC millivoltmeter - calibrated in dB - with a range of 30V down to 3mV full scale (80dB range)
Oscilloscope is ideal, but not all hobbyists can afford the outlay for a scope

RIAA equalization

reversed RIAA equalization

The previously described method for the measurement may, perhaps for one, two amplifiers are still acceptable, but if one more phono amplifier built, then the effort for this significant.

It would be better if they possessed a signal source, which already provides the distorted signal at the correct amplitude.

The frequency response of the current through the network formed by R1, R2, C1 - C4 corresponds to the inverse of the standard RIAA curve.
Resistor R3 determines the output voltage or the overall voltage gain.
R3 influences the frequency response at the upper end. If R3 becomes too high, high frequencies are reduced. With R3 = 1.5k the reduction is less than 0.1dB at 20kHz.

Circuit anti-riaa network

Component values

The use of close tolerance components in the filter network is absolutely necessary.

Desired Value:

IEA Series Closest Value Error Comments

E6 most capacitors, some inductors

E12 some capacitors, 10% resistors

E24 5% resistors

E48 2% resistors

E96 1% resistors

E192 0.5%, 0.25%, 0.1% resistors

How to measure the Phono Pre-Amplifier

Reversed RIAA EQ Network

This calculator finds the closest standard resistor or capacitor value.