PAO-A1HDCI Measurements and Analysis

The gain structure for this amp is right in line with every THX Ultra2 certified product I’ve measured:
Av = 23dB balanced
Av = 29dB unbalanced

Power Bandwidth & Distortion

Denon POA-A1HDCI Frequency Response at 1 watt & Full Power

The POA-A1HDCI displayed excellent frequency response uniformity with a ruler flat response in the audio passband and an unwavering -3dB point of 108kHz at every power level whether in normal or bridged modes of operation.

Denon POA-A1HDCI Power vs Distortion

I measured full bandwidth continuous power vs distortion by setting up a regulated sweep in my Audio Precision to automatically adjust input level until the maximum power output was achieved at < 0.1% THD + N. The POA-A1HDCI was plugged directly into an APC S-20 Power Conditioner with regulation to ensure the line never dropped below 116Vrms.

Power output: <0.1% THD + N

• 1CH, 8-ohms:                184wpc
• 2CH, 8-ohms:                180wpc
• 1CH, 4-ohms:                300wpc
• 2CH, 4-ohms:                285wpc
• 1CH, 8-ohms bridged:     340wpc
• 1CH, 4-ohms bridged:     *425wpc; 500wpc @ < 1%
• 2CH 8-ohms bridged         330wpc
• 2CH, 4-ohms bridged:       *405wpc; 470wpc @ < 1%

It is clear that the POA-A1HDCI easily hit the 150wpc power rating, delivering MUCH more than specified into 8-ohm loads in normal and bridged modes and about dead on specified power delivery for 4-ohm loads for normal and bridged modes of operation.

While the POA-A1HDCI was driving 4-ohm loads in bridged mode, I was able to achieve the 1% power numbers at <.1% THD + N in the above table at 1kHz but distortion went up significantly at the frequency extremes (20Hz and 20kHz). This is why I scaled the measurements back to ensure the amp delivered the measured power at <0.1% THD + N full bandwidth continuously.

Editorial Note on Bridged Power Measurements

What I believe was happening here was the power draw at low frequencies didn’t allow enough time for the capacitor bank to charge and at high frequencies the power density is much higher requiring a bigger transformer to achieve these sustained power levels. I couldn’t help to wonder just how much more power the POA-A1HDCI could have delivered if Denon chose to employ one massive power supply instead of multiple smaller ones for better channel to channel isolation. There are pros and cons to these different methodologies but I believe Denon struck a good balance here, yielding the best of both worlds with their hybrid mono block multi power supply approach while also keeping the box size reasonable for a high power ten channel amplifier. Keep in mind that this amp in bridged mode will yield a HUGE +6dB of dynamic headroom when driving a real speaker load with music, even though sustained power measurements aren’t all that much higher into resistive loads driven by continuous test tones.

When testing 2 channels bridged mode into a 4-ohm load, my APC S20 ran into an overload condition but did manage to keep the line regulated above 116Vrms. This goes to show you that continuous power testing consumes far more power than real world usage as I was never able to get my APC S20 to state I was using greater than 30% capacity even when I was blasting my system at sustained 110dB listening levels in 7.1 surround modes at my listening area.

Upon peering at the spec sheet for this amp, it was obvious that the manufacturer was specific about how they rated power. They specified full bandwidth power at < .05%THD + N for (150wpc, 300wpc bridged) for 8-ohm loads, but only 1kHz .7% THD+N (300wpc, 500wpc bridged) when driving 4-ohm loads. Under these circumstances, the POA-A1HDCI delivered as promised and then some, but as an Audioholic, I would de-rate the 4-ohm bridged continuous power specification by 15% or so and bolster the fact that you’ve got roughly +6dB of dynamic headroom.

Editorial Note on Audioholics Power Ratings

Keep in mind most review publications don’t do continuous power measurements and they usually publish power measurements into clipping at 1% THD + N at 1kHz. Our measurements are very conservative and are continuous full bandwidth.

For more info on amplifier measurements, see: The All Channels Driven (ACD) Test

Efficiency
With two-channels driven at full load, I measured about 47-49% efficiency which is good but not as great as I’ve seen in for other linear Class A/B amplifier designs. When the unit was idling with all amplifiers turned on, it consumed about 275 watts. It’s the idle power consumption of 10 channels that kills the efficiency of this amplifier. Too bad there isn’t a way to cut power on unused channels.

SNR Measurement
When the POA-A1HDCI was driven to full power into an 8-ohm load, I measured: -117.15 dB below 31.77 dBV Reference Level (at 0.09% THD+N) < 10Hz – 22kHz unfiltered and unweighted. This translates down to 94.3dB SNR @ 1 watt which is excellent and explains why this amp sounds so crystal clean and quite at low power levels.

FFT Distortion Analysis

Denon POA-A1HDCI FFT Analysis @ Full Rated Power

Denon POA-A1HDCI FFT Analysis @ Full Rated Power – Bridged Mode

At 1 watt into 8-ohms, the POA-A1HDCI displayed excellent results (+8.649 + 84.653)dBv = 93.3dBv or 100*alog^-1(-93.3/20) = .0.0022%. At full rated power the POA-A1HDCI again exhibited excellent distortion measurements (+30.355 + 61.821)dBv =92.2dBv or 100*alog^-1(-92.2 /20) = 0.0025%. With the POA-A1HDCI in bridged mode, it still achieved excellent distortion measurements (+33.594 +56.47)dBv = 90dBv or 100*alog^-1(-90 /20) = 0.0032%. This was among the cleanest amplifiers I’ve measured to date besting even the venerable Integra Research RDA-7.1.

While the overall amplitude of the primary distortion products remained similarly good for normal vs bridged modes of operation, it was interesting to note that the POA-A1HDCI even order harmonics seem to dominate in normal mode while the odd order harmonics seem to dominate in bridged mode of operation.

Amplifier Output Impedance & Damping Factor

Denon POA-A1HDCI Amplifier Output Impedance – Normal Mode

Denon POA-A1HDCI Amplifier Output Impedance – Bridged Mode

The POA-A1HDCI exhibited vanishingly low output impedance in normal and bridged configurations. This indicates good usage of negative feedback but also high quality output devices and a large enough power supply to be stable when driving low impedance loads at full power. It fell well below our desired 100 mohm or less mark for the entire audible bandwidth up to 20kHz and maintained itself even when driving at max sustained power levels into 8-ohm and 4-ohm loads. This proves that the POA-A1HDCI will sound consistently good no matter what loudspeaker load it is driving.

Denon POA-A1HDCI Amplifier Damping Factor – Normal Mode

Denon POA-A1HDCI Amplifier Damping Factor – Bridged Mode

The POA-A1HDCI amplifier damping factor is about what I expected based on the measured output impedance. It is uniformly good across the entire audio frequency range at around the 100 mark (50 is a minimum we like to see in all amplifiers of uncompromising design) when driving an 8-ohm loads. Into 4-ohm loads the Damping factor is exactly as expected, ½ the 8-ohm value and buttressing the argument that the POA-A1HDCI is happy to drive low impedance loads at full power.

Crosstalk

Denon POA-A1HDCI Crosstalk Measurement Adjacent Channels

Running a full range frequency sweep through the POA-A1HDCI amplifier at full rated power (150wpc @ 8-ohms), I measured channel to channel crosstalk on two adjacent channels where one channel was the disturber and the other was the Device Under Test (DUT). The Audio Precision plotted crosstalk of both channels over frequency by varying the Distruber/DUT channels. You can see the POA-A1HDCI produced very good crosstalk measurements (>81dB at 1kHz) with only a gradual rise with increasing frequency because of capacitive coupling. Anything greater than 60dB is deemed acceptable so this is quite good for a multi-channel amp that isn’t a true mono block design.

Denon POA-A1HDCI Crosstalk Measurement 4 Channels Apart

As expected, channel separation got better as you moved the Disturber/DUT channels further apart. It is interesting to note that varying the Distruber/DUT of the two-channels I tested produced a crosstalk measurement difference of over 20dB. While both measurements were very good, I couldn’t help to wonder how much better it would have be if a bit more careful layout was done to optimize trace routing and minimize their coupling paths on the circuit boards.

Denon POA-A1HDCI Crosstalk Measurement Bridged

For two-channel audiophiles wanting the absolute best performance this amplifier has to offer, I’d suggest bridging the two amplifier pairs on the opposite ends of the amp labeled “FL” and “FR”, respectively. This provides the maximum amount of separation between them which is critical especially during high power applications to minimize magnetic coupling. As you can see in this measurement, the POA-A1HDCI produced excellently low crosstalk measurements (>94dB @ 1kHz) with a slight rise at the frequency extremes due to magnetic coupling at low frequencies and capacitive coupling at high frequencies. Considering I was pumping over 300wpc during this test, I’d say magnetic coupling isn’t an issue of concern with this amplifier. Audiophiles rejoice as this is as close as you’re likely gonna get to mono block channel separation performance in a non mono block multi-channel amplifier design.