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Anthem STR Measurements & Conclusion

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APx585All measurements were conducted using our Audio Precision APx585 8 Channel HDMI Audio Analyzer. Unless otherwise noted, all tests were conducted on the balanced connections of the STR preamp and power amp.

For more information about how we measure power amplifiers, please see:

Basic Amplifier Measurement Techniques

Anthem STR Measurement Report YouTube Discussion

STR Preamplifier Measurements

I verified the STR Preamp was able to deliver 3.3Vrms (RCA) and 6.6Vrms (XLR) unclipped as specified by Anthem.

At 2Vrms out via the balanced outputs, the STR exhibited a squeaky clean FFT output with the 2nd order harmonic being 104dB below the fundamental. I remeasured this via a 0dBFS digital source at the same output level and noted the 2nd order distortion of the FFT was about 2dB higher.

FFT-2vrms 

Anthem STR Preamp Out FFT Distortion Analysis @ 2Vrms

I directly compared THD (distortion) vs Frequency (Hz) of the analog direct path vs. converting the analog signal to digital (ADC) via the internal DSP. As you can see below, with DSP engaged, distortion rises slightly above 2kHz but still exceedingly low nonetheless.

STR Distortion DSP 

Anthem STR Preamp THD Analog vs DSP

In analog bypass mode the -3dB pt of the STR preamp exceeded the bandwidth of my test gear (80kHz) with +/- 0.41dB ch-ch deviation. But, with DSP engaged, the STR still exhibited excellent frequency response -2.5dB @ 78kHz.

  STR Freq Analog  STR Freq DSP

Anthem STR Frequency Response - Analog (left) vs DSP engaged (right)

I compared the HT Bypass feature vs. just a straight through cable and didn't measure any discernible differences, which should put every audio purist at ease that they can use this feature without any sonic, let alone measurable, penalties.

STR HT Bypass 

Anthem STR HT Bypass vs Straight Thru Cable Frequency Response

 HT Bypass FFT

Anthem STR HTBypass vs Straight Thru Cable FFT Distortion

Note: The residual harmonics shown in the FFT above the 1kHz test tone (i.e. -120dB @ 2kHz) are a limitation of the audio measuring equipment, not induced by the STR preamp.

STR Bass MGMT

Anthem STR Bass Management

I measured the HPF and LPF responses of the bass management circuits and measured the -6dB pt and perfect 24dB/oct slope of the LPF and -3dB pt and 12dB/oct slope of the HPF at the selected 80Hz crossover frequency. Most home theater receivers wish they offered precise bass management like we've seen here in this two-channel preamp.

 STR SNR 2Vrms

Anthem STR Signal to Noise Ratio @ 2Vrms - Pure Direct

With 1Vrms in and 2Vrms out, I measured 106dB SNR (a-wt) and 110 dB (a-wt) driving a digital input with 0dBFS and 2Vrms via the balanced output.

Anthem claims 120 dB (a-wt) for unbalanced and 118dB (a-wt) for balanced at 2Vrms output level.  They got these higher figures by driving the inputs at 2Vrms (unbalanced) and 4Vrms (balanced), respectively, while measuring 2Vrms output ,which is good for specmanship but not very practical in real world usage. You can see by simply altering the input level of my test from 1Vrms to 4Vrms, would yield a 12dB higher value or (106+12) = 118dB (a-wt) validating their spec for the balanced output. This measurement is very good nonetheless. The STR preamp has very low noise.

Editorial Note about Balanced vs. Unbalanced Connections

I noticed if I drive a signal to the unbalanced or balanced input on the STR preamp, I get the same level on either unbalanced/balanced outputs if the volume level is held constant. Typically, there should be a difference of +6dB going from unbalanced to balanced from the preamp and -6dB on the amplifier side going from unbalanced to balanced. I've never measured a preamp that maintains the same gain balanced/unbalanced before.

As a quick test, I drove the unbalanced input at 2Vrms and adjusted the master volume to -5.5dB to get 2Vrms output and measured the SNR to be 108dB (a-wt). I then switched to balanced, using the same 2Vrms input and measured 2Vrms on the balanced output with an SNR of 111dB (+3dB improvement). If this was a fully differential circuit, there should have been a +6dB improvement in SNR.

I inquired with Anthem about this and they replied as follows:

The XLR inputs go directly to a differential amplifier and then get converted to single ended. Subsequently in the pre-amp, the ADC’s and DAC’s are differential. Having a differential amplifier at the front end does a better job of rejecting common-mode noise on the input cables. Otherwise, any signal gain difference in the two paths degrades the common-mode rejection ratio.

I can't say I agree with their reasoning here, but I also can't deny the stellar measurements I've observed with the STR preamp.

STR XTALK 

Anthem STR Crosstalk vs Frequency

I did measure a difference in crosstalk between the left/right channels, but the levels were so exceedingly low that it's nothing more than academic to note. -90dB at 20kHz is an excellent measurement and proves the STR preamp has excellent stereo separation.

Phono Preamp

 

STR Phono Freq 

Anthem STR Phono Preamp RIAA Curve Analog Direct vs DSP ADC Conversion

The ADC on the STR is again proven superb as can be seen by how transparent it is vs. the analog direct path in the above frequency response curve. using Inverse-RIAA EQ curve, I measured phono out with 30mVrms input, 2 Vrms output+-.05dB from 10Hz to 20kHz.

STR Phono curves 

Phono Preamp Frequency Response Curves

I measured the various phono response curves that the Anthem STR offers to show you exactly what each do. The EQ inverse RIAA curve was used to measure the standard response and all other curves were directly compared. For the majority of my vinyl listening, I used the standard RIAA EQ but those with a large collection of older jazz recordings may wish to experiment to determine what sounds best.

 STR Phono THD

Anthem STR Phono Preamp THD vs Frequency

Using a 10mVrms input signal, I measured distortion from the phono output (MM) at 2Vrms out, which was excellent as you can see in the above graph. Using the ADC to enable ARC room correction should NOT have any deleterious effects on sound quality as distortion at 20kHz is < .005% which is well below audibility (arguably around .1%).

 STR Phono SNR

Anthem Phono Preamp SNR @ 2Vrms

Once again my SNR #'s are much lower than Anthem's since they are apparently driving the inputs at near clipping to achieve their ratings.  If I exceeded 30mVrms input, HF at 20kHz rolls off and HF distortion increases so all my tests were done at 10mVrms input and achieve an excellent rating of 93dB SNR (a-wt). 10mVrms is more than sufficient drive to represent the output voltage of a MM cartridge. I believe Anthem spec'd their SNR at around 90 mVrms at 1kHz to achieve their 110dB (a-wt) SNR rating.

Power Measurements

Using our Audio Precision APx585 8-channel HDMI analyzer, we conducted a full barrage of multi-channel amplifier tests on Anthem STR per our Amplifier Measurement Protocol. We tested power using three methods all of which were taken at < 0.1% THD + N:

  • Continuous Full Power Bandwidth (CFP-BW) from 20Hz to 20Khz into 8 and 4-ohm loads (up to two-channels)
  • 1kHz Power Sweep vs Distortion (1kHz PSweep) - popularized by the print magazines, this is an instantaneous power vs. distortion test at 1kHz. The problem with this test is it often masks slew-related and or frequency response problems some amplifiers exhibit at the frequency extremes, and thus inflates the measured power results. It does provide an instant gratification # for consumers to argue over on the forums so we are now incorporating this test to please the masses.
  • Dynamic PWR - 1kHz CEA-2006 Burst Method testing. This is a dynamic power measurement adopted from the car industry, similar to IHF method only a bit more difficult for an amplifier and more representative of real musical content.

Keep in mind most review publications don't do continuous power measurements and they usually publish power measurements into clipping at 1% THD + N. Our measurements are very conservative as we use a dedicated 20A line with no Variac to regulate line voltage.  We constantly monitor the line to ensure it never drops more than 2Vrms from nominal, which in our case was 120Vrms. 

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

 STR Power BW

Anthem STR CFP-BW (2CH) Power Test - 8 ohms

With two-channels driven, the 400 watt/ch rated STR delivered 422 watts/ch for full bandwidth 20Hz to 20kHz at < 1% THD at 8 ohms and 622 watts/ch at 4 ohms under the same conditions.

 STR 1kHz Power  STR 1kHz Power 4 ohm

Anthem STR 1kHz ACD (2CH) Power Test - 8 ohms (left pic) ; 4 ohms (right pic)

With a 1kHz sweep test, the STR was able to muster an impressive 493 watts/ch at 1% THD and 468 watts/ch at 0.1% THD with 2ch driven into 8 ohms and 708 watts/ch at 1% THD and  671 watts/ch at .1% THD+N with 2ch driven into 4 ohms. This should be plenty of power to drive virtually any loudspeaker since I found the STR had no issues driving my own reference speakers (Status Acoustics 8T) which dip down to 2 ohms in the bass region.

 STR Dynamic Power

Anthem STR Dynamic (2CH) Power Test - 4 ohms

The STR performed well for 1kHz CEA 2006 short dynamic burst tests by delivering over 1 kwatt of power with 2ch driven at 4 ohms.

# of CH Test Type Power Load THD + N
1 CFP-BW 451 watts 8-ohms 1%
2 CFP-BW 422 watts 8-ohms 1%
2 CFP-BW 622 watts 4-ohms 1%
1 1kHz Psweep 499 watts 8-ohms 0.1%
1 1kHz Psweep 522 watts 8-ohms 1%
1 1kHz Psweep 723 watts 4-ohms 0.1%
1 1kHz Psweep 764 watts 4-ohms 1%
2 1kHz Psweep 468 watts 8-ohms 0.1%
2 1kHz Psweep 493 watts 8-ohms 1%
2 1kHz Psweep 671 watts 4-ohms 0.1%
2 1kHz Psweep 708 watts 4-ohms 1%
2 Dynamic PWR 651 watts 8-ohms 1%
2 Dynamic PWR 1043 watts 4-ohms 1%
*1 Instantaneous 800 watts 2-ohms < 1%

Anthem STR Power Measurement Table

* Note: The STR amplifier is rated at 800 watts/ch, 2 ohms (3 seconds), but I was unable to verify this with a sweep test without tripping the protection mode. I was able to verify the power claim by doing an instantaneous power test at 1kHz for under the time duration specified.

 STR FFT 1 watt

Anthem STR FFT Distortion Analysis (1 watt, 8 ohms)

The Anthem STR amplifier produced a very low noise floor (-120dB). At 1 watt, the 3rd-order harmonic residual dominates but it's exceedingly low at -102dB below the 1kHz fundamental. 

STR XTALK pwr 

Anthem STR CH-CH Crosstalk (1CH, Undriven)

The channel-channel crosstalk was excellent measuring -90dB at 20kHz again proving the STR series has superb stereo separation approaching true monoblock performance from a 2ch package.

Recommendations

Mic positionSetting up a system like the Anthem STR separates requires a good deal of knowledge about audio equipment along with the desire to carefully take full advantage of its capabilities. It would behoove anyone serious about achieving state-of-the-art two-channel playback to find a reputable dealer with deep knowledge of how the STR series of products works, especially with regards to ARC room correction. I've seen some bizarre recommendations about how one should calibrate a system such as ARC not only from consumers but from professional installers that really don't understand basic physics. You can't just place the microphone in the room at random locations to allow ARC to calibrate and expect good results. Instead, best results are achieved when following our recommendations listed in this review. Post calibration is also critical in getting the most out of this system. Find a reputable dealer that will take the time to set this system up correctly in your room.

Conclusion

Anthem RackSpending the last couple of months with the Anthem STR preamp and power amplifier was a true delight. It's rare that I get to test out state-of-the-art two-channel gear these days and boy is it refreshing when equipment like this shows up at my door that not only bench tests extremely well but sounds impeccable too.

The STR preamp is perhaps one of the most flexible and diverse two-channel preamplifiers I've ever seen.  It offers state-of-the-art performance in every mode of operation handling analog and digital sources with equal ease. The connection options the STR preamp offers are virtually limitless and the home theater bypass mode is a Godsend for those wanting to merge home theater and two-channel systems together in perfect harmony.  The STR amplifier puts forth impressive power figures for an amplifier in such a reasonably sized package that is refreshingly manageable to transport. The system works seamlessly together to reproduce music with fidelity at the very highest level, especially if care is taken to set up ARC properly.

About the only thing I found I wanted in the STR preamp was the ability to view the front panel display of both products from a Smartphone or web browser. I sit about 20 ft away from the stack making it very difficult to read the displays of both units. The compact brushed aluminum remote is a bit Spartan and is only useful at digging deep into the OSD if you're close enough to the STR to see it. The STR amplifier was a powerful beast but I couldn't help wondering if Anthem would ever consider coming out with a model that offers a parallel bridged configuration of 4 amplifier modules per channel to bring the house down for those wanting the equivalent of a small nuclear power plant to power their speakers.

I'm so impressed with how the Anthem STR separates components work in my reference system that I've decided to make them a permanent fixture. I now understand the fanboy appeal to Anthem products that I often see on the forums. It's well warranted if you’re able to float the rather spendy asking price Anthem is requiring you to invest. Highly recommended!

The Score Card

The scoring below is based on each piece of equipment doing the duty it is designed for. The numbers are weighed heavily with respect to the individual cost of each unit, thus giving a rating roughly equal to:

Performance × Price Factor/Value = Rating

Audioholics.com note: The ratings indicated below are based on subjective listening and objective testing of the product in question. The rating scale is based on performance/value ratio. If you notice better performing products in future reviews that have lower numbers in certain areas, be aware that the value factor is most likely the culprit. Other Audioholics reviewers may rate products solely based on performance, and each reviewer has his/her own system for ratings.

Audioholics Rating Scale

  • StarStarStarStarStar — Excellent
  • StarStarStarStar — Very Good
  • StarStarStar — Good
  • StarStar — Fair
  • Star — Poor
MetricRating
Frequency Response LinearityStarStarStarStarStar
Measured Power (4-ohms)StarStarStarStar
Multi-channel Audio PerformanceStarStarStarStar
Two-channel Audio PerformanceStarStarStarStarStar
Bass ManagementStarStarStarStarStar
Build QualityStarStarStarStar
Fit and FinishStarStarStarStarStar
Ease of SetupStarStarStarStar
FeaturesStarStarStarStarStar
Remote ControlStarStarStar
PerformanceStarStarStarStarStar
ValueStarStarStarStar
About the author:

Gene manages this organization, establishes relations with manufacturers and keeps Audioholics a well oiled machine. His goal is to educate about home theater and develop more standards in the industry to eliminate consumer confusion clouded by industry snake oil.

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