Arcam A25 Integrated Amplifier Bench Test Results

Arcam A25 Integrated Amp Introduction - Good Things Come in Small Packages?

The Arcam Radia A25 is a 100 watt/ch Class G slimline stereo integrated amplifier with digital input connectivity and MM phono preamp output. The A25 features one toslink and two coax digital inputs along with USB-C for connectivity to a laptop for streaming high-resolution audio sources (including DSD). The A25 utilizes a very high quality ES9280A Pro DAC able to handle up to 192kHz/24 bit audio via the toslink and COAX inputs and 384kHz/32 bit audio via the USB-C input. The A25 also features Bluetooth which includes Qualcomm AptX Adaptive technology with 24-bit HD audio to ensure the best sound quality no matter what source you are playing either through your speakers or your wireless headphones.

Arcam A25 Internal View

The Arcam A25 employs a Class G amplifier topology with a large torodial power transformer and 2 x 6,800uF, 50V capacitors for the low rails and 2 x 10,000uF, 80V capacitors for the high rails. This allows the amplifier to maintain high efficiency at any power level compared to conventional Class AB designs.

Arcam A25 Backpanel View

A backpanel view of the Arcam A25 integrated amplifier reveals connectivity options for 4 sets of analog inputs (1 phono MM) and 1 set of analog outputs, two digital coax and 1 toslink inputs, 1 USB-C, a pair of high quality WBT style 5-way binding post speaker terminals, a detachable power cord receptacle, IR and 12V triggers.

This test report includes testing of the analog and digital circuit paths as well as the power amplifier section.

All measurements were conducted using our Audio Precision APx585 8 Channel HDMI Audio Analyzer. 

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

Basic Amplifier Measurement Techniques

Arcam A25 Preamp

Coax Input, Pre-Out

The Arcam A25 preamp outputs have exceedingly low noise and distortion (> 100dB SINAD) but the drive is insufficient if used in conjunction with most power amplifiers to reach full gain. The A25 clips at an alarmingly low output voltage of 1Vrms. I discussed this with Arcam engineering and they told me the preouts were mostly intended to be used as left/right subwoofer outputs to supplement a system with more bass if needed. However, this seems a bit odd considering the preouts have no bass management facilities or level/delay controls. Arcam informed me that they run the volume control at a high voltage level to keep the noisefloor extremely low and then back off the output to optimize drive level for the internal amp section. This was quite evident if you carefully observe the excellent SNR and distortion from the power amp section measurements in this report.

Arcam A25 Preout Output Voltage vs Distortion

Arcam A25 FFT Noise Spectrum (fs = 44.1kHz)

With a 44.1kHz digital input, I checked the stopband attenuation and found it to have a smooth rolloff below ½ Nyquist as expected with no residual out of band nasties. This is good housekeeping.

Phono In, Pre-Out

The Arcam A25 has a Moving Magnet (MM) phono preamp. Using the original 3-time constant RIAA curve, I EQ’ed the APx585 source to get the expected flat response of the phono preamp. The phono input was driven at 1mVrms and up to 5mVrms to determine frequency response, distortion and linearity.

 

Arcam A25 Phono Frequency Response (1mVrms input)

I was a bit surprised to see some roll off at low frequencies (-3dB at 20Hz), but my measurement were confirmed with Arcam engineering. As I increased drive level to 5mVrms, the -3dB point rose slightly to 24Hz.

 

Arcam A25 Phono Distortion vs Frequency Response (1mVrms vs 5mVrms input)

The distortion (< 0.09% THD+N) looks good across the entire audio bandwidth for the A25 phono preamp when driven with 1mVrms input but rises dramatically below 200Hz when driven with a 5mVrms input. MM cartridges typically produce 3-6mVrms output so you may want to check with your dealer on the particular cartridge you use on your turntable when mating with the A25 for optimal bass performance. Arcam could certainly improve the performance of their phono preamp section in future iterations of this product. However, it’s most likely users will be prioritizing digital sources with this product so it may be a non-issue for audiophiles that don’t embrace vinyl.

Arcam A25 Power Amp

Frequency Response & FFT Distortion Tests

 

Arcam A25 Frequency Response @ 100 wpc, 8 ohms

The Arcam A25 exhibits ruler flat frequency response from 10Hz to 72kHz (-3dB pt) when driven by an analog or digital source (Fs = 192kHz). The frequency response remains consistent with 8 or 4 ohm loads and various power levels (1 watt and max rated power of 100 watts).  I measured +- 0.058dB CH-CH deviation at full power (20Hz to 15.3khz) which is excellent.

 

Arcam A25 1 kHz FFT @ 2.83Vrms (1 watt, 8 ohms)

The Arcam A25 exhibited a bit of power supply hum after the rectifier circuit but it was down -100dB which is inaudible. The FFT from the amplifier output is nice and clean with 2^nd harmonic down -109dB below the fundamental when driven with 2Vrms on the analog inputs. Curious when the same test was repeated with a 0dBFs signal on the COAX input, 2nd order harmonic rose to -95dB below the fundamental. Rest assured that low level details will not be masked by any audible harmonic nasties from this amplifier.

Arcam A25 Power Sweep Tests

For the Arcam A25, I 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) (2 second sweep time, typical)

• 1kHz Power Sweep vs. Distortion (1kHz PSweep) - popularized by the print magazines, this is an instantaneous power vs. distortion test at 1kHz. The sweep time is 1 second duration, 31 points.

• 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.

All tests were conducted on a 120Vrms, 20A dedicated outlet. Line voltage was constantly monitored 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

Arcam A25  1kHz PSweep (2CH) - 8 ohms

The Arcam A25 exhibited impressively low distortion from the amplifier section as you can see with SINAD approaching 100dB below 80 watts. With 2CH driven, the A25 delivered 113 watts/ch at 0.1% THD+N and 119 watts/ch at 1% THD+N into 8-ohms. You can see the slight bump in distortion around 25 watts where the A25 switches from low to high rail. It’s almost unnoticeable even on my Audio Precision analyzer.

 

Arcam A25  1kHz PSweep (2CH) - 4 ohms

The A25 maintained impressively low distortion even when driving 4 ohm loads. With 2CH driven, the A25 delivered 157 watts/ch at 0.1% THD+N and 167 watts/ch at 1% THD+N into 4-ohms. The rail switch is a bit more obvious in the 4-ohm test but still imperceivably low. Arcam did a good job with this power topology.

 

Arcam A25 CEA 2006 Dynamic Power – 4 ohms

The Arcam A25 exhibited impressive dynamic power test results able to deliver 155 watts/ch into 8-ohms and 260 watts/ch into 4 ohms. That’s almost 2dB of dynamic headroom over its rated power. Impressive. Most impressive.

Arcam A25 Power Table

# of CH	Test Type	Power	Load	THD + N
2	CFP-BW	100 watts	8-ohms	0.1%
2	CFP-BW	150 watts	4-ohms	0.1%
2	1kHz Psweep	119 watts	8-ohms	1%
2	1kHz Psweep	113 watts	8-ohms	0.1%
2	1kHz Psweep	167 watts	4-ohms	1%
2	1kHz Psweep	157 watts	4-ohms	0.1%
1	1kHz Psweep	216 watts	4-ohms	1%
1	1kHz Psweep	200 watts	4-ohms	0.1%
2	Dynamic PWR	155 watts	8-ohms	1%
2	Dynamic PWR	260 watts	4-ohms	1%

Arcam A25 Power Measurement Table

Test Bench Observations for the Arcam A25

The Arcam A25 hit or exceeded it’s power ratings in all of my testing. I did notice anytime I ran the amp to near its power rating on the test bench, you could hear components singing inside of the unit. I initially believed it could be caused by a piezoelectric effect from insufficient damping on the power transistors causing them to ring. However, Arcam engineering explained to me that when substantial currents are abruptly shifting from the power supply lifting from low to high rails in tune with the input test signal, this could happen. It's the sharpness of the transition (which needs to be in the order of microseconds to perform effective envelope following at high audio frequencies) that can cause the capacitors in the lifter circuit to "sing". This is observable when using an AP to test the system into passive loads but in normal use the volume level in the room will be huge and the noise would be masked.

SNR & Crosstalk

 

Arcam A25 SNR @ 1 Watt (a-wt)

I always measure amplifiers at 1 watt so that apples to apples comparisons can be made between different products that have different maximum output capabilities.  If you want to know the SNR at rated power, then you simply take the 1 watt rating and add 20* log (V*R)^1/2 / 2.83) where V = Vrms and R is the load. With a 0dBFs input signal, I measured 95dB (a-wt) at 1 watt (8 ohms) which is a superb figure. This is an extremely low noise floor I rarely measure in power amplifiers costing substantially more than the A25. I tested the analog circuit path with 200mVrms in at 1 watt output and observed 90dB (a-wt) which again is just excellent.

 

Arcam A25 SNR @ 50 watts Per Spec

Arcam spec of SNR is 110dB (A-wtd, ref. 50W, 0dBFs input). I recreated this test scenario with a digital source of 0dBFs and measured 108dB which is about 2dB shy of their spec but still a phenomenal result, nonetheless. Arcam also provides a spec of 106dB SNR via the analog inputs under the following test conditions (A-wtd, ref. 50W, 1Vrms input). I measured 105.7dB which is pretty much spot on.

 

Arcam A25 SNR @ 50 watts from Phono Input

Through the phono preamp, SNR was 73dB with a 5mVrms input and 1 watt output and maxed out to 75dB at 50 watts. Arcam specs this at 80dB under the same test conditions, so I'm unsure why my measurements came up about 5dB short. Irregardless, this is a decent measurement for a phono stage but not among the best I’ve measured.

 

Arcam A25 CH-CH Crosstalk (1CH, Undriven)

The channel-to-channel crosstalk of the A25 was very good measuring at > 85dB at 1kHz at full rated power and 75dB at 20kHz. I find anything > 60dB at 20kHz to be acceptable and the A25 beats that by a healthy 15dB.

Arcam A25 Conclusion

The Arcam Radia A25 is NOT a powerhouse product. It’s a sleek elegant solution for a audiophile tight on space and wishes to have a competent piece of audio gear that looks the part to compliment any room décor. I absolutely love the yellow theme from the chassis to the halo LED lit volume and input selector to the remote control. The chassis isn’t the standard generic black box you see from competitor products. This unit just looks expensive despite its modest $1,500 asking price. You can proudly display the A25 on your credenza and make your audiophile friends envious when they sit down to listen.

The A25 produced some impressively low noise and distortion measurements that actually surprised me. I typically see SNR and distortion degrade through the power amp sections of other integrated amplifiers or stereo receivers but not so much with the Arcam A25. The fact that it was able to achieve almost 100dB SINAD at near full rated power (80 watts) and an SNR of 95dB at 1 watt demonstrates that Arcam prioritized a very clean signal path that audiophiles could take FULL advantage of for high resolution digital audio sources.

The only warts that I could complain about were the low preamp output drive clipping at 1Vrms and the ho-hum phono preamp section. However, the A25 was not designed to be a standalone preamp so I doubt many users would find this limitation to be off putting. I also believe the phono preamp is fine for casual users but if you’re a diehard vinyl lover, you may want to add an external phono preamp into the mix since the analog circuit paths of the A25 are certainly good enough to benefit from a better one.

Going with a Class G amplifier topology was a smart move on Arcam’s part for both efficiency (less heat) and space savings. I would confidently recommend the A25 to power reasonably sensitive bookshelf or tower speakers of nominal impedance of 6 ohms or greater for small to medium sized rooms. In fact, I think an excellent pairing for the A25 would be the JBL HDI series, particularly the HDI-3600s or HDI-3800s which have good bass response, and high sensitivity or the Polk Reserve R700s which are another great option that won’t break the bank, sound great and also look the part. 

I plan on doing a full report with listening test results on the Audioholics Youtube channel so please be sure to check back for updates in the near future.

Unless otherwise indicated, this is a preview article for the featured product. A formal review may or may not follow in the future.