Superpower = Super Low Noise

Scale adjusted RMS noise voltage measurement

Total unweighted noise across the audio band of 20Hz to 20KHz measures 27 µVrms, an excellent specification. Note that the units show mV because of a gain of 1000 (see below). Due to circuit variations for different output voltages, noise varies for different output voltages. This RMS value is noise measured for a +9V out Superpower, which equates to 3PPM of noise per volt out.

A noise spectrum shown below is from a Superpower with 9V out, sampled at 4.096K samples per second, 4K samples using a Blackman Exact window function. Load is approximately 5mA. Five samples are averaged to smooth the graph.

Superpower noise spectrum

To overcome noise floor limitations of the data capture instrument, a low noise preamp with a gain of 1000 is used to boost the noise to be measured:

Power to the amplifier and the regulator is delivered with batteries to eliminate any possible contamination from AC power supplies.

The test fixture also performs a bandpass function, limiting the measurement to the audio bandwidth of interest:

Bandwidth of noise test fixture

Superpower noise spectrum at 540mA load

Above is the same noise measurement made with the Superpower delivering a 540mA load. The spectrum is essentially the same as with minimum load seen above, and RMS value is 28µ.

With a gain of 60dB due to the test setup, the measured values were all scaled down by 60dB (= divide by 1000), so, e.g. a value at -90dB became -150dB. As a comparison, the spectrum of the fixture alone is measured to see the noise floor:

Comparison to Clark Kent

The blue trace is the Superpower spectrum seen above. The red trace is from Clark Kent as described here. The RMS value for this representative 9V device is 46µV. Note that the tested unit is inscribed with Ultra Low Noise.

Spectrum of measurement system

With gain = 1000, noise in the measurement system is almost non-existent, seen here in the -140 to -160dB range relative to 2V.