- Written by Stephen Hornbrook
- Published on 07 July 2014
Meridian Prime Headphone Amplifier / Prime Power Supply Review Highlights
An incredibly compact and beautifully designed USB DAC and headphone amplifier from Meridian. Costing more than double the recently reviewed Sony UDA-1, the Meridian Prime offers similar functionality, sans the built in speaker amp, but with much higher performance. It may be small, but this little guy manages to power Audeze planar magnetic headphones with a clean and neutral sound.
Meridian Prime Headphone Amplifier / Prime Power Supply Highlight Summary
- • Able to drive even the toughest high impedance headphones
- • Provides a neutral, yet musical sound
- • Very compact, small footprint
- • Terrific build quality and beautiful modern design
- • DAC handles PCM up to 24bit/192kHz
- • Excellent analog preamp
Introduction to the Meridian Prime Headphone Amplifier / Prime Power Supply Review
With 25 years of experience in DSP Loudspeakers, products such as the first “audiophile” CD player, and Meridian Lossless Packing, Meridian has been on the forefront of digital sound engineering. So when Meridian announced a new high-resolution USB DAC / headphone amp, you better believe I raised my hand, with a grin full of excitement, to ask for a review unit.
MERIDIAN PRIME HEADPHONE AMPLIFIER / PRIME POWER SUPPLY REVIEW SPECIFICATIONS
Meridian Prime Headphone Amplifier
- Inputs: 1x stereo line input (2x gold-plated RCA phonos) / 1x stereo line input (3.5mm jack socket) / 1x USB input (mini-B USB connector) Outputs: 1x stereo line output (2x gold-plated RCA phonos) / 2x 1/4in TRS A-type jack sockets (tip=left) / 1x 3.5mm stereo jack socket (tip=left) Relay-controlled power up/down muting on all outputs
- USB DAC Input: 24 bit/192 kHz sampling Meridian Resolution Enhancement technologies including upsampling and Apodising (the DAC does not decode DSD files)
- Interface-powered: Disconnecting USB powers-down all digital subsystems
- Analogue Spacial Processing: Audio processing circuits provide “outside the head” headphone listening resembling listening to speakers / Two different modes plus bypass / Analogue switching / Short audio path
- Controls: Alps analogue volume potentiometer with flexible shaft coupling from the front panel controls all outputs / Input selector button: push to select between line level, 3.5mm jack and USB / Analogue Signal Processing selector: i, ii or Bypass
- Indicators: 1x, 2x, 4x digital sample rate indicators / A/B/Bypass Analogue Signal Processing / RCA/mini-jack/USB input selector / Power button illuminates blue in standby, white with all outputs active, green when preamp output disabled (hold button down to toggle)
- Power: Plug-in PSU provided; may also be powered by Prime Power Supply for superior performance
- Construction: Silver metal finish uniform with G Series
- MSRP: $2,000 USD
Meridian Prime Power Supply
- Inputs: 1x IEC C3 3-pole connector / 1x USB input for audio pass-through
- Outputs: 5x latching 3-pin mini-DIN connectors providing 12V dc at up to 500mA 1x USB output for powering external devices, delivering 5V dc at up to 1A. Passes USB data supplied via the pass-through input Outputs include two stages of regulation
- Controls: Front panel power button
- Indicators: Illuminated power button shows blue in standby, white when active.
- Power: Available models include 110–120V ac and 230V ac Consumption 60W max
- Construction: Silver metal finish uniform with G Series
- Dimensions: 2" H x 6.3" W x 5.9" D
- Weight: 3.5 Pounds
- MSRP: $1,250 USD
- SECRETS Tags: Meridian, Meridian Prime, Power Supplies, Headphone Amplifiers, DACs
With the Explorer, Direct DAC, and now the Prime, Meridian is targeting the headphone crowd head-on with its digital expertise. I am not one to complain either, as I am a big fan of their little portable Explorer USB DAC. The Prime is a considerable step up from the portable Explorer as it can drive anything from in-ear monitors to the most taxing planar magnetics. At $2000, Meridian is asking a lot for this compact headphone amp, and that doesn’t even include the optional Power Supply Unit for $1250 that stacks below the Prime. While it won’t win a budget conscious value award, there is no denying the Meridian Prime produces a lovely neutral, yet musical sound.
Design and Setup of the Meridian Prime Headphone Amplifier / Prime Power Supply
Upon arrival I was met with elegant packaging that I can only describe as “if Apple went to the Darkside.” The Meridian Prime and its optional power supply come in black boxes wrapped in a thin band of matching blackness, accented by a silver Meridian logo. This careful attention to detail made for a worthwhile unboxing experience.
After getting the prime out of its bed of darkness, the first thing to cross my mind was how small it is. Even with its matching power supply, the Meridian Prime barely takes up more room than a large coffee mug and coaster. It's small enough to fit on any desk no matter how messy it may be. I will say that it is a bit of a relief not having a full size box taking up room on my desk. In fact, I was even able to carry the Prime with me to and from the office. With desktop real estate in high demand, if the Prime delivers performance akin to its price, then its small stature is extremely beneficial.
Those familiar with Meridian products will feel at home with the Prime’s styling. The unit is finished in textured silver to match their G-series with a shiny black face plate. Tiny blue LEDs light up when in standby and white is used for the active state. Two small buttons that feel like ball bearings are used to toggle input mode and Analogue Spatial Processing (ASD) modes. The tapered volume control knob turns smoothly with a bit of resistance. It is a high quality Alps-type control mounted towards the rear of the unit.
Front output consists of two ¼” and one 3.5mm mini jack for the lesser demanding load of in-ears. On the back, output is limited to one volume controlled stereo RCA, that can be disabled for pure headphone listening. For analog input there is one stereo RCA and a 3.5mm mini jack. Digital input is limited to USB and the internal DAC can handle up to 24bit/192kHz. The reason for only having a USB and no coax or optical input is to allow all digital circuitry to be powered off when USB is disconnected. This is because the digital section is powered via USB. It is also another reason having the Prime Power Supply increases fidelity since USB runs through the power supply before entering the Prime.
The DAC has dual oscillators, allowing it to handle 24/96, 24/88.2, 24/176.4, and 24/192. It also utilizes Meridian’s lauded Apodising filter to upsample 44.1 and 48kHz signals to 88.2 and 96kHz before hitting the DAC. The filter is designed to avoid digital pre-ringing, an unpleasant artifact of the digital process.
The Meridian Prime comes standard with a wall wart plug but for increased performance they offer an optional Prime Power supply. The Meridian Prime Power Supply is the exact same dimensions as the Prime and stacks beautifully underneath it. The Prime Power Supply is a high-current design based on the same linear power supplies Meridian developed for their 800 Reference Series. The Power Supply uses a low-profile, high-mass, hand-assembled toroidal transformer, low noise linear regulators on the outputs, and a high-efficiency low-dropout linear regulator with less than 5 μVrms output noise in the range 10 – 100k Hz on the USB supply.
The Meridian Prime Headphone Amplifier / Prime Power Supply In Use
Can the Meridian Prime handle the heavy loads of today’s star headphones? It most certainly can. While overall I found the pairing of Audeze LCD-X headphones with the Meridian best, the Prime was able to handle the HiFiMAN HE-6. Halfway on the Meridian Prime with the LCD-X headphones and your ears might be complaining later. It is loud, punchy, and dynamic.
Overall I would characterize the Meridian Prime as neutral, detailed, and prim and proper, like a perfectly executed Viennese waltz. The tonality is wonderful, especially on piano recordings. When listening to 24bit content via the Prime, the only thing left to criticize is the recording itself. The increased resolution leaves little for the recording engineers to hide behind and the Meridian Prime has enough transparency to expose those lousy recordings.
On Buena Vista Social Club, the various hand drums surround my head and emanate from an entirely different plane than the vocals and guitars. When the trumpet solo begins it cuts through with clarity and presence. Terrific dynamic range on the Meridian Prime, as vocals on “La Bayamesa” flow from delicate to boisterous with ease.
The romantic compositions of Ennio Morricone came alive on the HE-6 planar magnetics. Cinema Paradiso’s strings sounded like lush velvety chocolate mousse. The Meridian Prime is capable of producing wonderful depth like the piano on The Good, The Bad, and the Ugly. It easily could have been all the way behind the stage, with myself listening from the nosebleeds. The flute solo on the theme to The Mission retained an incredible airiness over the horns, harp and string background accompaniment.
The Meridian Prime includes a feature called ASP, or Analogue Spatial Processing, that seeks to bring the performance outside of your head. My experience was quite the opposite as I felt turning the ASP on actually brought the music more inside my head. I prefer a wide as possible soundstage and the ASP tended to shrink this along with removing some of the bass response. Some will prefer the effect and some will not, but since it’s purely an option the user is free to make their own decision.
In terms of functionality I do have one complaint that could be easily solved. Make USB the default input. If you power the Meridian Power supply off, this shuts down the Prime and it forgets what input you were set at. Therefore, every time I turned it on I had to first select USB, which seems odd since the ideal way to connect music to the Prime is via USB.
As a preamp, the Prime does a wonderful job. The problem I see is that users won’t want to move the unit from one setup to another. Unless your headphone listening is in the same area as your main stereo, this isn’t a feature that will be heavily utilized. That said, it is there and performs very well, just be prepared to get up and walk over to the equipment rack in order to adjust the volume.
The performance of the Prime without the optional power supply is very good and adding it did not make a huge difference. By routing USB first though the Prime Power Supply, it also reduces any possible noise in the USB signal running from a computer. I did hear less noise at high volume levels with the Prime Power Supply, just not enough to warrant the extra cash. I say, if money is no object, then go ahead and purchase the full bundle.
The Meridian Prime Headphone Amplifier / Prime Power Supply On The Bench
Measurements by David A. Rich, Ph. D.
I did not have a schematic because I did request it in time so I will have to infer what is going on based only on the measurements. The measurements below were made with an Audio Precision APx585 analyzer which has been generously supplied for our use by Audio Precision.
The first thing I noticed about this product was the power supply voltage was only 20VDC. That is half what even a cheap preamp would have coming off the full wave rectifier. After the regulators a typical unit would have a supply of at least +/-15V referenced to ground.
This is a big deal since the 20V supply limits the maximum voltage that the headphone amplifier can supply. Let us assume the regulated rails take us to +/-9.0V referenced to ground and lets assume the amplifier needs 1.0V of headroom with no load. That brings us to +/-8.0V p –p or 5.6VRMS at clipping.
The curve below shows THD vs. measured level at the headphone terminal for loads of 330ohms, 150 ohms, 33 ohms and 16 ohms. The volume control was set to maximum which is provides a gain of 3.3.
At clipping (0.1% THD) the unit supplies 4.5VRMS into 330 ohms. A little less than the back of the envelope calculation above. Other headphone amplifiers we have tested made it past 10VRMS.
At 33 ohms the unit is current limited 3.2VRMS at clipping or 310mW average. At 16 ohms clipping is at 2.1VRMS or 275mW average. 300mW average is a very good result with many headphone amplifiers we have tested producing about twice the power but a couple could supply only 100mW.
What is very impressive is how fast the distortion declines if the unit is not driven to clipping. The graph below is 2V RMS out into 16 ohms. Here the volume control was set for unity gain not the maximum gain used for the graph above. Even at 20kHz for the worst channel the THD is 0.003%.
Keeping the output at a constant 2VRMS but increasing the load to 330 Ohms reduces the distortion at the frequency extremes by a factor of 2.
Making a measurement at the preamp out under the same conditions (100k Ohm load) looks almost identical.
For comparison the Emotiva XSP-1 had about half the distortion at line out. It was not tested at headphone out.
The Meridian uses a passive volume control (metal on carbon) arguing this yields lower distortion. The previously reviewed Benchmark, Funk, and OPPO make the same argument.
The passive volume control can impose an SNR penalty since the amplifiers gain is always in the circuit. A digital controlled analog volume control will apply the gain only when needed.
The SNR relative to 2VRMS was 109dB into a 330 ohm load at headphone out with a brick wall filter at 20kHz. The SNR measured 110dB relative to 2VRMS at the preamp output. The Emotiva preamp was 8.5dB better than this. We did not characterize the headphone amplifiers performance of that product however.
The spectra of 1kHz sign wave at preamp out is shown below at a 2VRMS signal level. Even the 2nd harmonic is at -114dB relative to the test signal. Note the X axis of the graph is in units of dbV. 6dBV has a value of 2VRMS. The 3rd is at -116dB down. Most of the higher harmonics are lower than the noise floor.
Line noise was -121dB down at 60Hz and -126dB at 180Hz (expanded graph below 1kHz not shown). No other spurs were seen above the noise floor. The external power supply made no difference. The headphone output has the same spur levels.
The 19kHz – 20kHz IM spectra is equally impressive as the single tone distortion results. Both test tones are at 1VRMS. Everything in band is below -130dB. This preamp is free of any dynamic distortion process. Even the out of band 2nd harmonics are below -100dB.
USB performance to preamp output.
For a 24/192 sample, the input the digital reconstruction filter limits the frequency response to 40kHz. Only bats need worry about this.
Shown below is the THD from preamp out with the volume control set for 2VRMS at 0dBFS. It is good but does not provide the excellent performance of the preamp with an analog input. The distortion is at 0.005% in the midband but rises to an average 0.02% at 20Hz and 20kHz. At 30kHz the digital reconstruction filter come into play.
The 1kHz spectrum correlates with the 0.05% THD. The 2nd harmonic is -88dB down relative to 2VRMS (6dbV). The other harmonics are below -102dB and do not contribute much to the THD value. Compare this spectrum to the equivalent analog measurement above which has a 2nd harmonic at -114dB down ref 6dBV.
The 19kHz – 20kHz IM spectra is not as extraordinary as the analog preamp (graph shown above) but all inband spurs are -110dB down. The out of band harmonics are at -90dB. Both test tones are at 1VRMS (0dBV). The level needs to be reduced since the two synchronous tones will have the same peak amplitude of a single test tone at 0dbFS.
The rise in the noise floor of the spectra compared to the analog measurement is correlated with the SNR performance. The SNR is down 3dB to 107.5dB. This is 17.5 bits equivalent. This is about a 1.5 bit less than the best products we have tested with a cascade of a DAC and a preamp. The best DAC box we measured with no preamp (the more expensive Auralic Vega) had a noise level of -123dB. Analog preamps are the limitation at the present time. The Auralic Vega used the ESS ES9018 a DAC also used in the Oppo USB DAC / headphone amplifier. I was not supplied with any information on the DAC used in the Meridian.
On the positive side (no pun) the power supply components were below -125dB down from dbFS with the internal power supply. Any other spurs were covered by the noise.
The noise can be seen in the time domain spectrum of a 1kHz sine wave at -90dBFS with a 24bit depth.
The spectrum of this waveform is free of any spurs above the noise floor.
The effects of the noise can be seen in the deviation in level as the signal generator is reduced digital full scale. A 1dB change occurs at -104dBFS and a 3dB change is at-108dBFS. For a different prospective the Yamaha CX-A5000 11.1 channel Pre/Pro at a similar price to this unit with external power supply had a 3dB change at -112dBFS. The Yamaha used the ESS ES 9016 DAC.
For Auralic Vega DAC box (no preamp in the system) had a 3dB change occurring at -124dBFS.
To sum up the measured performance of the analog preamp is excellent with the exception of the SNR which was 4dB below the best. The headphone amplifier is not far behind within its limited voltage swing for higher impedance headphones. If you have a high impedance headphone, that is not efficient, you want to check the Meridian can produce the level you want to achieve. Low impedance headphones will present no problem for this unit.
The DAC adds more noise into the system. The only thing that could be identified between the Meridian and the best available technology in a blind test with closed back headphones would be the noise. I must note the volume level might have to be set to the point that a full scale digital signal would cause hearing damage.
The $1250 external power supply made no difference. It does not increase the 20V DC power rails which represent a significant design compromise in headphone amplifier.
Conclusions about the Meridian Prime Headphone Amplifier / Prime Power Supply
Most office desks are cluttered, with little to no extra space. The mere thought of adding a headphone amp and separate power supply is laughable for many. Even if you are one to keep a clean, minimalistic desk, the last thing you want is to clutter it up with a big amp. There is something to be said about how small the Meridian Prime and Prime Power Supply are. This is a case where bigger isn’t always better and even though you are certainly paying a premium for its small stature, you get a lot of quality components and brilliant engineering inside.
I found the Meridian Prime to match up very well with the Audeze headphones and should definitely be on the audition list for users of those cans. The Prime’s clean and neutral sound played well with the LCD-X’s warm and lush tone. With its 6.35mm and 3.5mm headphone outputs, the Meridian also makes a great amp for those with a variety of headphones and in-ear monitors. Don’t let its size fool you, the Meridian is a force to be reckoned with, do check it out.