Solo SRGII- Headphone Amplifier

 
Solo SRGII Headphone Amplifier

Dedicated To The Solo Headphone Listener

All of the Solo's amplification is concentrated into its single stereo ouput - it doesn't compromise on sound like multiple outputs will. If you listen on your own it's the ideal headphone amp!

The Solo SRGII headphone amplifier is the refined version of our legendary "green" Solo and it's a snip at £405.

Plus it offers an easy and simple upgrade path which involves swapping its outboard "green-energy" power supply to our PSU1.

SRG stands for Studio Reference Green. SRGII is the MkII version. It's available "in green" with its energy saving basic power supply - or go straight for the upgrade and buy it with the PSU1 power supply.

For more information continue reading after the purchasing options below.

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Specification Reviews

Delivering Wonderful Music Under Adverse Conditions

The Solo's have a long history of delivering wonderful music going back to 2001 as borne out in numerous reviews over the years - often beating off stiff competition from more expensive headphone amps.

The "green" Solo surfaced in 2007 as the first ever seriously hi-fi headphone amplifier to succesfully run off green energy otherwise known as switched-mode power.

It had to be done because legislation on energy using products was about to become a legal requirement by 2010, and switched-mode power supplies have since become the de-facto source of outboard power for economy product variants such as the less-expensive Solo SRGII option.

The problem earlier hi-fi products had was that switched-mode power has so much high-frequency distortion content, and as all amplifiers output what is essentially signal-modulated power, that distortion content ends up at your headphone diaphragms.

The complex behaviour of such distortion content with headphone diaphragm earpieces, not forgetting the amplifier itself, simply throttles the sound.

The "green" Solo, and now the Solo SRGII, overcame the problems switched-mode power caused, but went much further and the SRGII sound can fend off competition from more expensive headphone amplifiers using non switched-mode linear power.

Headphone Impedance Sensing

The Solo SRGII headphone amplifier has another trick up its sleeve, that being its headphone impedance sensing output.

Some output impedance is essential because headphone cables are highly capacitive, and without output impedance, amplifier phase margin is seriously compromised.

High impedance headphones with long cables (and there are plenty of them) can lead to phase margin reversal and that's why many solid-state amps don't work well with headphone impedances much greater than 30-40 Ω.

Exactly how much output impedance can be tolerated before a headphone stops performing well, will depend on the impedance of the headphone being used - and we can never know what the customer is using.

Headphones have impedance dips and peaks across their audible spectrum, needing more control at some frequencies more than others.

Zero output impedance would be ideal, but screwing down the high frequency performance to preserve phase margin is no good for outright musical performance.

Output impedance cannot therefore be a fixed value that suits all headphones. But, by sensing the headphone current, extra power can be delivered to the headphone to cover for impedance dips, and less power for impedance peaks - thus making for a smoother sound.

The actual output resistance can be kept constant guarding phase margin whilst output impedance will appear to be changing to compensate.

And that's basically how the Solo Studio Reference Green MkII achieves its really well-balanced sound regardless of headphone impedance.

And importantly for the most sensitive headphones, it doesn't hiss!

Swipe down for Specifications and Reviews.

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Specification

ItemMeasurement
Headphone impedance range16 to 600 Ohms preferred; 8 to 2,000 Ohms acceptable
Power output (rms, both channels fully driven) 32 Ohms: 27mW/channel; 600 Ohms: 23mW/channel
Distortion (THD plus noise, ref 1kHz)0.02%
Frequency response (-3dB) 32 Ohms load: 27Hz - 35kHz; 600 Ohms load: 10Hz - 39kHz
Output noise (20Hz-20kHz, CCIR quasi-peak)-84dB
Input sensitivity (for specified power output) 32 Ohms: 250mV rms; 600 Ohms: 775mV rms
Channel balancebetter than 1dB, "9 to 3 o'clock" positions
CrosstalkLeft to Right -57dB; Input to Input -68dB
MuteSignal off mute, non-shorting
Output StageBipolar class AB
Supply voltage24V DC
Size (approx.) W: 107 x H: 50 x D: 185 (mm) inc. controls

Specifications subject to alteration without notice in keeping with our continuous improvement policy.

Reviews

If you need your headphone amp to tell you exactly what is on a recording over and above anything else, you can stop reading the test now and go and buy the Solo SRGII. The detail retrieval it manages to conjure up is truly exceptional and this gives the Spektor and Melnikov pieces in particular an immediacy that is extremely impressive. It has no trouble discerning activities from the supporting strings in the Schumann piano trio that are lost in the mix elsewhere. This is then coupled with a tonality with voices and instruments that is unfailingly believable.
The really good news is that none of this seems to affect the Solo SRGII’s ability to pick up the pace and deliver with the two more uptempo tracks as well. It is able to deliver the thumping bassline of the Satriani piece with impressive agility and timing.
- HiFi Choice, November 2015

That super top end, a wonderfully open midrange and a low noise floor made everything I listened to sound great; the better the recording, the more I heard. So I plundered my CD collection for the best recorded tracks I own, including some SACDs that have been languishing in the drawers. The Solo did the business whether I was listening to Bob Dylan or Diana Krall or my copy of the Stockfisch Records demo disc or if I was working through stuff like Shelby Lynn or the Watson Twins. The Solo does a very good job of deconstructing music like this and laying it out clearly, along with any ambience, venue noise or low-level detail that has been captured, which enhances and expands the “head-stage” while allowing a listener to hear how the various parts of the recording fit together.
- ASHLEY KRAMER, Witchdoctor.co.nz, 2010

Reviewing the Solo MC in 2005 I wrote "The strengths of the Solo are in the extra high frequency extension, a superb transient response and an unsurpassed dynamic range." ...today’s SRG II is a significantly better performer than the Solo MC, with the biggest improvements in the bass and the all-important midrange. Maximum sound pressure levels are higher while the clean treble and lightning reflexes have been maintained. Distortion and background noise are lower than before, making it easier to listen to the music, to enjoy the texture of the instruments and voices.
- Phil Gold, Canada Hi-Fi, 2011

I have listened to a ton of music. This little amplifier has caused a wholesale reappraisal of my music collection. Some CDs never used to get much play because I thought they were poorly recorded. With the Solo, the superb stereo separation transforms them into gems. For example, The Velvet Underground aren't famous for leaving behind a legacy of hi-fi recordings. Their album 'The Velvet Underground and Nico' is a masterpiece of 1960's hiss and distortion. Despite the sonic shortcomings, however, the Solo separates everything in a way that allows the music shine through.
- forum member: DonutsAreGood

So far with such a limited burn-in and not using the PSU1 I can say:
- The soundstage width is huge! The depth makes the user feel he/she is in the stage w/ the musicians instead of in front of them.
- There is a lot of air between the notes.
- The mids are to die for w/ a level of clarity rarely heard in other amps so early in the burn-in process. At times I feel the musicians are in the same room as I am.
- The amp has great treble extension w/o any harshness or shrillness.
- The bass is tight and very well defined. I wish there was a bit more of it, hope that burn-in and the use of the PSU1 will provide the additional punch.
- forum member: mrarroyo