CHANNEL D - Fun with the Seta L20

Seta L20 - Small-Signal Sine Wave, 1 kHz to 24 MHz

This is a frequency response measurement. The 1 kHz output level is used as the baseline.
Output level diminishes as the bandwidth limit is approached.
The amplitude measurement precision and accuracy are limited by the 'scope's 8-bit ADC.
The practical accuracy for measurements made in this way is within about 0.2 dB, which is sufficient for this purpose.

The input signal is the blue trace, output red trace.
The input signal is taken from the input of the balanced signal attenuator, shown in above photo.
The input signal level is the same for all measurements.
The signal's frequency shown on the display is measured by the 'scope's frequency counter.
The signal's output level shown on the display is measured by the 'scope's waveform measurement function.
These are all single-shot measurements. Signal-averaged measurements would be cleaner and prettier.
The "Flat" preamplifier output was used, since the RIAA filter would substantially attenuate any high frequency signal.

1 kHz

Seta - Balanced Direct Coupled Ultra Wide Bandwidth Phono Preamplifiers

0 dB (0.54 Volts peak to peak) at 1 kHz, sets baseline output level for comparisons

100 kHz

-0.16 dB (0.53 Volts peak to peak) at 100 kHz

1 MHz (1000 kHz)

-0.84 dB (0.49 Volts peak to peak) at 1 MHz

10 MHz (10000 kHz)

-1.8 dB (0.44 Volts peak to peak) at 10 MHz

Notice that the signal phase is inverted with respect to the input signal at this extremely high frequency.
This roughly corresponds to the signal propagation delay through the L20, about 50 nanoseconds
(the reciprocal of one half the wavelength, since delay is one-half cycle or 180 degrees out of phase at this frequency).
See the Signal Propagation Delay measurement for another way to determine the signal propagation delay.

20 MHz (20000 kHz)

-2.0 dB (0.43 Volts peak to peak) at 20 MHz

The L20 is specified to have a bandwidth of DC to 20 MHz.
Amplifier bandwidth is customarily defined as the -3 dB response point.
This measurement determines that the bandwidth of the Seta L20 is somewhat greater than 20 MHz.

24 MHz (24000 kHz)