Graham Slee Solo SRGII Headphone Amplifier Review

October 3, 2010
5 mins read


4 ½ stars

What you put between the cans and the source really counts, and this nicely priced Graham Slee headphone amp makes for gloriously grain free, clear-as-a-bell sonic pleasure

You can plug a set of cheap earphones into anything from an iPod Shuffle to an integrated amplifier and get exactly what you’d expect at the price. Once you move into the world of high-end headphones, however, you need to give serious consideration as to exactly what’s upstream in order to get the best results.

The better the ‘phones, the more they reveal of what’s in front of them, from the power and interconnect cables through to the source, the recording and especially the amplification. Most amplifiers and CD players with a headphone socket have it included more or less as an afterthought; the components involved aren’t top notch and the circuit design and implementation aren’t really put together with serious intent. After all, R&D and high spec parts cost money, which either comes off the bottom line (seldom) or gets passed to the consumer.

Some amplifiers such as my Yamaha A-S2000 have headphone stages that are sonically up to speed but even so, in most cases the best results come from dedicated headphone amplifiers like this one, the Graham Slee Solo SRGII (Studio Reference Green MK II).

Features and Construction

The Solo is assembled into a rather utilitarian but very sturdy silver anodized aluminium case. I’ve got no issues with the case design at this sub $1000 price point. Opting for a more solid bespoke case would only add to the retail price and the Solo is intended to be a high performance yet value for money proposition.

There’s a single full size 6.35mm headphone jack up front with a volume knob, a toggle switch and a small green LED. Two RCA inputs are provided, which are selectable from the toggle switch (which also mutes the amp) but there are no pass throughs, so you can’t run the Solo in between your source and your main system. This is no real hardship as I’ve found the pass throughs on other headphone amps inevitably degrade the sonics of the main system to some degree.

The “green” part of the full model name refers to the energy saving low power consumption wall-wart power supply unit (PSU) shipped with the Solo. The higher end PSU1 regulated power supply is available as an option at $499. It should theoretically improve the sound quality but it pushes the Solo into a much more substantial price range.

Just two inputs, a ground connector and a power socket

There’s no power switch on the Solo with the green PSU, so you’re either leaving it permanently powered up, in which case the green PSU is a good thing, or killing it at the wall every time. A ground connector is sited round back just in case there are any hum issues caused by interactions with the switch-mode PSU (I experienced none during the course of the review).

The Solo is designed to automatically cater for headphones of any impedance from 16-600 Ohms and to cater for input levels between 250mV and 1V, so no method of adjusting gain is required or provided.

Sound Quality

I initially ran the Solo with my Marantz SA8260 SACD player as the source, with a set of 0.5m Slinkylinks silver RCA interconnects in between and Sennheiser HD650 phones on the end. First impressions were average and I wasn’t blown away; the sound was restrained and flat. A three star review at best, but hold your horses, keep reading.

It turns out the Solo was brand new in box, and hearing anything in that state isn’t fair on the component or my overworked old ears. [Big old ears, too – Music Ed.] So Massive Attack’s Mezzanine went on repeat overnight. The next day proved the old truism that audio gear needs to be run in, some bits more so than others. The Solo was firing at a different level but it took a few days of on and off listening and running in before it felt like it had reached its peak.

I tried it on the Marantz, a Micromega Airstream, a Simaudio Moon 300D DAC and even a Well Tempered Lab Simplex turntable. Once it was run in, and it was a pleasure to listen to every time. First up, the treble on the Solo is something special; gloriously extended, grain free and as clear as you could possibly wish for – especially once I slotted a set of the Vitesse Audio Reference interconnects into the loop (yes, I know that two thousand bucks of cable is overkill on a nine hundred dollar amp but the Solo didn’t seem to mind).

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.

The Solo packs some slam and powerful dynamics as well, although these were the last aspects of the sonics to really manifest properly. Once the low end was present and correct in terms of depth and speed, the Solo had no trouble doing justice to more raucous stuff from Stanley Clarke, SMV, Massive Attack, Audioslave and Wild Beasts. The HD650 drivers must have been close to leaping off their moorings at times, because I really had the Solo cranked for a while and the sound never hardened or became congested. There’s a real sense of speed and control about the way the Solo makes music, notes stop when they should regardless of volume levels.


The Solo always needed some time to come alive if it had been left powered down for a while. An hour or so seemed enough but given the low power consumption, I’d advise leaving it on permanently.

The only other negative really comes down to personal preference and equipment matching. If you like an energetic, neutral but somewhat dry and lean sound, that doesn’t stray into being edgy, then you’ll really like the Solo/Sennheiser combination.

If you want richer, warmer sonics that take off the edges while mellowing your mood, then you’ll need to try some different cans or maybe look at an amp with a smoother nature. For example, I found my Perreaux SXH2 headphone amp to possess all of the Solo’s virtues with a marginally warmer overall character that might suit some listeners more, but then again, it does come at a higher price. I’ve got some high -spec Grados on the way and hope to try them with the Solo.

Another thing to consider is the new generation of Digital to Analogue converters that come with USB and Optical or Coax inputs and have built in headphone amplifiers. These units sell for money that seems silly but perform as if they were driven by demons. I’ve got two in for a review – the Zero DAC and the Firestone Audio Fubar 3. It will be very interesting to compare these versatile units to the dedicated Solo and SXH2 amplifiers.

Properly matched to your tastes, the Graham Slee Solo SRGII offers great bang for the bucks and is definitely worth a listen if you’re not inclined to drop way more than a thousand dollars on a headphone amp. ASHLEY KRAMER


  1. Couldn’t agree more with your description of it’s sonics.I love this amp as the clear sound suits my taste. I purchased the psu1 power supply for it also. That made a significant improvement and worth the $.

    Great HP amp and can see myself keeping it for many years to come.

  2. I use grado 325i’s and senn HD650’s, both are driven beautifully with the solo. With the Senns I think they sound better the more gain you apply. I have the volume set at about 3 o’clock to really drive it properly. Though with some digital devices I have to use a pair of inline -10db attenuators otherwise I can’t turn the solo up much past start as it is too loud.

    Since I’m talking headphones I’m dying to get a pair of senn HD800’s and visited 2 dealers trying to get a better price than the $2800 rrp. Both said there not allowed to discount and in fact the sale of them are so strictly controlled by sennheiser nz that they will only supply direct to customer after they have received the funds at rrp. The dealer gets his commission paid separately. I’m pretty sure it’s price fixing and it grates me even more when there selling on audiogon for US$995 new which at today’s rate is only about NZ$1700 and that’s including GST.

    I’m glad to get that of my chest it’s been annoying me all weekend 🙂

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