P801 Power Amp

Alan March

Founder of March Audio
Staff member
Hi everyone

We are releasing our new flagship monoblock at the Australian HiFi Show in a few weeks time. Just thought I would share a little test data.

Below is a plot of the P801 running at 5 watts as you would typically see on sites such as ASR. Distortion levels beat anything I have seen.

The SINAD (THD+N) is noise dominated. We cant actually measure an accurate SINAD figure because our measurement signal source, although very good, is too noisy! In reality the noise floor, and SINAD is around -115dB to -116dB.

Please note that our new "ultra buffer" is designed to provide overall gain options of 23dB or 29dB. Here we are set at 23dB. This gain level is required to make the amp hit full rated power output into 4 ohms with a standard balanced XLR 4 volt rms input signal. 29dB is required when using a 2 volt RCA source.

Just be aware/wary when comparing SINAD figures that some manufacturers rely on very low gain levels to obtain their results. This is using the basis that lower gain equals lower noise and therefore higher SINAD. Often they just use the power amp module gain (13dB) where you would require an input signal of 10 volts or more to drive the power amp to full output.

Very few domestic signal sources can do this, particularly with suitably low noise and distortion.

To put it into context, a typical DAC or streamer with 4 volt XLR output would only drive this amp with a 13dB gain setting to 80 watts output into 4 ohms. Only 20 watts with a 2 volts RCA source.

1000011276.png
 
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Another thing to note about the P801 is that we use a custom power supply to ensure the amplifier delivers its full output power and performs to the highest levels with minimum noise and distortion.

The PSU is a new design that has 2 quadrant operation and active synchronous rectification. This means the output voltage stays much more stable and won't suffer from bus pumping.

The PSU can also output 1500 watts which means it will power the Purifi 9040 to its full 2 ohm load capability.

Other manufacturers still use the outdated Hypex supplies which will only drive the Purifi 9040 module to around 1100 watts short term.
 
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I wrote above about the SINAD figure for the P801 being higher than indicated in the measurement. This being due to our signal generator source, although excellent (<1uV 20Hz to 20kHz), being too noisy.

The P801, with 23dB of gain, is essentially amplifying the noise that is present in the source. The measurement is showing this noise, and not what the amplifier is actually capable of.

Just to demonstrate this, below is a measurement of the noise floor of the P801 with its input shorted.

We can see that the noise, measured 20Hz to 20kHz is at -116.5dB (7uV rms). 6dB better than with the signal source attached.

p801 noise floor.png

From the first measurement we know that the THD is -126.4dB.

1000011276.jpg

From these 2 figures we can calculate the SINAD, which works out at -116.0dB.

So to accurately measure the SINAD of the P801 a signal generator source would need to have a noise level below about 0.4uV.
 
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