Ayre Acoustics MX-R Twenty monoblock power amplifier Specifications

Sidebar 1: Specifications

Description: Solid-state monoblock power amplifier. Inputs: 1 balanced. Output power: 300W into 8 ohms (24.8dBW), 600W into 4 ohms (24.8dBW). Frequency range: 0Hz–250kHz. Voltage gain: 26dB. Input impedance: 2 megohms. Power consumption: 45W (standby), 120W (operating/no signal).
Dimensions: 11" (280mm) W by 3.75" (96mm) H by 18.75" (480mm) D. Weight: 52 lbs (23.6kg).
Finishes: Silver, Black (add $500/pair).
Serial numbers of units reviewed: 14G0129 & '130.
Price: $29,500/pair. Approximate number of dealers: 25.
Manufacturer: Ayre Acoustics, Inc., 2300-B Central Avenue, Boulder, CO 80301. Tel: (303) 442-7300. Fax: (303) 442-7301. Web: www.ayre.com.

COMPANY INFO
Ayre Acoustics, Inc.
2300-B Central Avenue
Boulder, CO 80301
(303) 442-7300
ARTICLE CONTENTS

COMMENTS
Banana97's picture

The -112dBW unweighted residue noise is spectacular.
However, in figure 4, the 120Hz hum noise component is only -100dB below the 2.83V signal. Is it something going on?

John Atkinson's picture
Banana97 wrote:
The -112dBW unweighted residue noise is spectacular.

One of the best I have measured.

Banana97 wrote:
However, in figure 4, the 120Hz hum noise component is only [100dB] below the 2.83V signal. Is it something going on?

The apparently anomalous behavior stems from the fact that I measure S/N ratio with the amplifier's input shorted. There is therefore no signal current being drawn from the power supply. But in my spectral analyses of the low-frequency noisefloor, I use a more realistic condition, which is with the amplifier delivering at minimum 1W into 8 ohms. In this condition, the AC transformer is being asked to deliver greater current, and the 120Hz and 240Hz spuriae appear. But at -100dB, these are still negligible.

John Atkinson
Editor, Stereophile

dmusoke's picture

John:

You can't measure S/N with the inputs shorted otherwise where would you apply the signal? I believe what you meant to say is that you measured the amplifier noise floor with the inputs shorted. This makes more sense and is the correct way to do so.

John Atkinson's picture
dmusoke wrote:
You can't measure S/N with the inputs shorted otherwise where would you apply the signal? I believe what you meant to say is that you measured the amplifier noise floor with the inputs shorted.

The Signal/Noise Ratio is the measured level of the component's self-generated noise within a specified bandwidth referred to a specified level, in this case 2.83V into 8 ohms. The noise level is conventionally measured with the component's input shorted to ground.

The individual components of the noisefloor, examined in a separate measurement, are, of course, lower than the measured noise power used to calculate the S/N ratio, as the latter is the RMS sum of those components.

The poster's argument was that if spectral analysis showed that a supply component at 120Hz was present at -100dB ref. 2.83V, the unweighted RMS sum of the noisefloor components used to calculate the S/N ratio couldn't be less than 100dB.

John Atkinson
Editor, Stereophile

dmusoke's picture

So the left/right channel inputs are shorted together and both fed a 2.83V mono signal? Sorry being dense as I'm still confused where you apply the 2.83V level signal to perform these measurements. Thanks...

John Atkinson's picture
dmusoke wrote:
So the left/right channel inputs are shorted together and both fed a 2.83V mono signal?

No, this has nothing to do with connecting the left and right inputs together. (And this is a mono amplifier, please note.) The 2.83V is the reference level at the amplifier's output. It is equivalent to a power of 1W into 8 ohms. (Strictly speaking, it should be 2.82843V, but 2.83V is close enough for this kind of measurement.)

dmusoke wrote:
Sorry being dense as I'm still confused where you apply the 2.83V level signal to perform these measurements.

This the procedure I use to measure S/N ratio:

Feed the amplifier an input signal at 1kHz so that the output level is exactly 2.83V RMS into 8 ohms.

Set this as the analyzer's reference level.

Turn off the signal generator. With the Audio Precision system I use, this connects both the hot and cold phases of its balanced output to ground.

Read on the analyzer's screen what the level now is, in dB referred to the previous level of 2.83V. This is the S/N ratio for whatever analyzer bandwidth I have chosen. (The Audio Precision gives me the choice of flat response from <10Hz to >500kHz or from 22Hz to 22kHz, plus the option of applying a weighting filter, like CCIR or A-weighting.)

I hope this explanation clears thing up.

John Atkinson
Editor, Stereophile

dmusoke's picture

OK...thanks. That makes sense now. I wasn't aware that you ground the AP analyzer outputs after determining the reference AP voltage needed to produce a 1W amplifier output into an 8 ohm load. So the AP takes that reference signal level and divides it by the measured output noise when the amps inputs are grounded to calculate the S/N ratio. Is that about right?

John Atkinson's picture
dmusoke wrote:
So the AP takes that reference signal level and divides it by the measured output noise when the amps inputs are grounded to calculate the S/N ratio. Is that about right?

That's correct. The AP can display the noise level in dB vs an arbitrary reference, as in this case, as dBm, dBV, and other decibel-related ratios, or as the absolute level in milli- or microvolts.

John Atkinson
Editor, Stereophile

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