Seta L20 - Large-Signal Square Wave, 0.1 Hz to 1 MHz
This is a test using large-output-amplitude (ca. 17 volts peak to peak) square waves from 0.1 Hz to 1 MHz.
Input level and preamplifier gain were adjusted to give an output level of approximately 17 volts peak to peak.
The apparent minor variation in output level is due to the resolution limit of the 8-bit scope's ADC and measurement noise.
This is an extreme torture test.
Higher amplitude square waves also are handled well, but aren't a useful test since clipping cannot be discerned easily with square waves.
To view the ca. 6 dB larger (36 volt peak to peak) output capability of the L20, see the large-signal sine wave measurements.
- 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.
0.1 Hz
The above proves the L20 is direct-coupled; no droop in the square wave from low-frequency roll-off.
Each half-cycle of the square wave has a duration of 5 seconds.
1 Hz
10 Hz
100 Hz
1 kHz
10 kHz
100 kHz
1 MHz (1000 kHz)
At first glance, the above 1 MHz large-signal square wave test appears ugly. It's actually quite remarkable!
It demonstrates the L20's behavior during an extreme high-frequency overload condition.
To properly design and understand an amplifier one must understand its behavior under overload conditions, not just when presented with normal signals. Ideally, a manufacturer should show a potential customer what conditions it takes to make the amplifier reach its limits.
- The slew-rate limiting evident in the output is clean and well-behaved.
- No oscillation, overshoot (leading edge) or overhang ("sticking" on the trailing edge).
- The above shows that the input to output slew rate of the L20 is over 50 volts per microsecond!
Links to other Seta L20 measurements
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