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Solo Ultra-Linear Diamond Edition Headphone Amplifier

Solo Ultra-Linear Diamond Edition Hi-Fi Headphone Amplifier

News Update: Solo Ultra-Linear Diamond Edition Chosen For Grado Again!

The Solo Ultra-Linear Diamond Edition headphone amplifier has been chosen again to demo Grado headphones at the 2014 Bristol Sound and Vision show, February 21st - 23rd.

A Solo Ultra-Linear Diamond Edition headphone amp also resides at Grado HQ in Brooklyn NY.

Solo Ultra-Linear Diamond Edition at Bristol Hi-Fi Show

Phil Gold said...

"The superior imaging and greater musicality on all the single ended phones in my collection make this component worth the extra money. You can't beat the sound at this price and this is the one I'm keeping.

[High End Headphone Amp Group Test Shootout!]

The Solo Ultra-Linear Diamond Edition headphone amplifier gives you the sound you always wanted from a headphone amp! A headphone amplifier truly capable of making good headphones deliver a lifelike, dynamic and breathtaking performance with a real 'out of head' three-dimensional stereo sound stage.

The Diamond Edition Solo Ultra Linear headphone amplifier has a lower noise floor for improved in-ear monitor listening and a new output stage for better performance with difficult and low impedance headphones, yet it has the clout to drive high impedance headphones too.

The Ultra-Linear voltage amplifier stage gives you the smoothness and warmth of a tube amp, yet with all the precision, fine detail, and punchy sound of the solid state amp it is. Plus, it won't wear out like tubes.

Make the Solo Ultra-Linear Diamond Edition your reference!

A factory upgrade to Solo Ultra-Linear Diamond Edition spec is available for all old Solo's from mid 2004 onwards - click here. A DIY upgrade is also available - click here. If your Solo isn't already equipped with a PSU1 power supply, it is highly recommended to bring out the true Solo Ultra-Linear Diamond Edition sound from your upgrade.

User Reviews

Excerpts taken from the Owners Club Forum:

"What the Solo UL does is carefully walk the tightrope in between too much and too little treble. On the metal tracks listed such as Lateralus, I can happily crank up with the introduction of loud distorted guitars with no fatigue whatsoever, and a solid midrange gave the guitars authority. Very often I found myself waiting for the inevitable ear grating treble of a guitar, but the Solo keeps this under control and the result is very pleasing.

With a good amp like this, it's not necessarily that it adds or improves on anything, it simply feels like it's been brought back to 'normal', to what it should have been from the start.

N.B. Just for anyone using an Audiolab M-DAC, the difference between that built in amp and this IS significant. Just thought I'd put that.

EDIT: after going back to some other equipment the Solo UL definitely adds significant kick to the low end.


"Mr Slee, this time I think you have absolutely nailed it, the Solo UL is absolutely superb. It delivers what the "green" tantalisingly hinted at, a huge soundstage, a wealth of timbral nuance and subtlety, a totally immersive listening experience, one that almost does not leave me wanting a "speaker fix". The AT cans absolutely love this amp and happily sing with whatever it delivers.

The entire musical spectrum and canvas seem to have been extended in both directions leaving sufficient space for each and every nuance and texture to be clearly and distinctly heard yet drawing the whole together into a cohesive and spellbinding musical whole. Overdubs and backing singers are more clearly placed and delineated, different voices in duets are easier to distinguish and the uniqueness of different voices, human and instrumental more readily heard.

Source for most listening, foobar/ASIO>Terratec DMX 6 Fire coax out>heavily modded Beresford Caiman DAC.


"Although still early days, my overall impressions of the U/L compared to the standard Solo are that the improvements are (at first hearing) subtle but become very significant. The more I re-visit familiar recordings, good or bad, the benefits of the U/L become increasingly apparent - great detail, great dynamics, natural tone and greater enjoyment of the music. Whether it's like a valve amp, I can't say, due to no point of reference. However, anyone thinking of taking the plunge with this piece of kit, either as a first time buy, upgrade or upgrade from Solo, would not, I think, be disappointed.


"The level of resolution of the UltraLinear I feel is excellent, just plenty enough to look into the different recordings, ambiances, etc... Sincerely, I have a hard time critising any aspect of the music reproduction through the UltraLinear. It has really become an essential part of my system which I feel is now completed, allowing me to just relax and enjoy as much music as I can (but still much less than I would like). A big thank you to Graham.


"Now I could close my eyes and be at a rave. Stomping house beats and nice attack from the synths. It won't turn your K701 into bass cans. Only when the music asks. Musically everything is still very good compared to the Solo 2007. With up-tempo songs you find yourself tip-tapping to the music. Instead of 1 song I listened to entire CD's. One song of Tori Amos' Little Earthquakes nearly brought me to tears. That has not happened before. This is where this amp really shines. Conveying emotions. All in all the Ultra-Linear gives the AKG K701 a fuller bass, and a much rounder, a bit warmer presentation. It also takes away some of the glare in the highs. But above all it makes you want to listen and immerse yourself into more music.


Media Reviews

Canada Hi-Fi Headphone Amplifier Review by Phil Gold "The Ultra-Linear is the warmer, more natural sounding model, but the differences are less apparent on A/B switching than on extended listening. I found the more expensive Ultra-Linear allowed me to relax more into the music, and appreciate the texture of the instruments and voices. More significantly, the imaging felt more three dimensional and realistic. The frequency response seems pretty much the same, with a very wide extension at both ends, but the treble is sweeter and the bass end has more presence... the Ultra-Linear sounded more musical. I think the extra $200 is well spent on the Solo Ultra-Linear...the volume control is calibrated quite differently than on a conventional amp, where you would expect a setting in the 9 to 12 o'clock range, and large amounts of distortion if you go too far clockwise. Here the whole range is usable to adjust to headphones of very different sensitivities. There were times with very inefficient headphones and a low output source that I was in the three or even four o'clock position, with no noticeable stress to the sound.

[Canada Hi-Fi (p:28), Graham Slee Solo SRGII and Solo Ultra-Linear Headphone Amplifiers by Phil Gold, August/September 2011] (also available in PDF - click to download)

KitGuru Must Have Award "This [review] would have been impossible without the Graham Slee Solo Ultra Linear Amplifier. This amplifier is a work of art, which significantly outclasses what we would assume possible from the very modest asking price. I am absolutely stunned that a large corporation hasn't offered to give Graham an extraordinary amount of money for his amplifier configurations. With the Graham Slee Solo Ultra Linear amplifier in the chain, the dynamics and musicality were presented with such a rich tapestry that it was often difficult to believe that a valve based amplifier was not somehow in the chain.

[Grado PS1000 Headphones & Graham Slee Solo Ultra Linear Amp Review, KitGuru, by Zardon, March 2011]

"I really can’t forget how I fall in love with it... I recommend Solo Ultra Linear Diamond edition for you if you like Classical music but don’t want your amp to sound bad in other genre of music, Solo Ultra linear Edition should be in your top buying list.

[Earmass, Su, August 2013]

Connecting the Solo Ultra-Linear Diamond Edition headphone amp in a tape loop


Ultra-low noise:the Solo Ultra-Linear Diamond Edition is now also ultra-low noise as well as being ultra-linear.

Higher output current: its output stage has been beefed-up to take control of the most difficult headphones with ease.

No dangerous DC on the headphone output prevents headphone damage: it only takes a small amount of DC offset to heat up the windings of headphone transducers. That heat softens the adhesive which keeps the "voice-coils" in place, and eventually your headphones don't perform all that well. All our headphone amplifiers block DC offset from reaching your headphones.

Tape monitoring: the Solo Ultra-Linear Diamond Edition headphone amplifier has two inputs and a non-shorting mute. Its input switching can be used in tape monitoring as shown here.

(An extra pair of interconnects are required as well as two phono tee-adapters inserted where indicated by the asterisks shown in the diagram)

When connected as per this suggestion, the input selector on the Solo front panel mimics a tape monitor switch. In position 1, the same source as selected on the amplifier is fed to the Solo; in position 2, the output from the tape recorder (or other recording device) is fed to the Solo.

Headphone sensitivity volume control: unlike conventional volume controls, this one is designed to be used over its full rotation to compensate for a wide range of headphone impedances and sensitivities. This avoids the use of gain switches which would otherwise result in differing performance characteristics depending on the gain setting.


Headphone impedance range: 8 to 2,000 Ohms / 16 to 600 Ohms preferred

Power output: (rms, both channels fully driven at 1% THD)
32 Ohms: 140mW/channel; 600 Ohms: 30mW/channel

Input sensitivity (for specified power output into 32 Ohms): 511mV rms

Input impedance: 37k Ohms at max volume; 50k Ohms at min volume

Distortion: (THD plus noise at 9 o'clock volume control setting (qtr power))
10Hz-20kHz: better than 0.04%; 10Hz-1kHz: better than 0.02%

Frequency response (±0,-3dB) 10Hz - 35kHz

Output noise: (22Hz-22kHz, quasi-peak/un-weighted) -95dB

Channel balance: better than 1dB

Crosstalk: Left to Right -56dB; Input to Input -68dB

Input selector centre-off position: non-shorting; -38dB at max volume with 2V rms input (ref: 1kHz and 10kHz)

Output Stage: Bipolar class AB

Supply voltage: 24V DC unipolar

Size: (approx.) W: 107 x H: 50 x D: 185 (mm) inc. controls


Solo Ultra-Linear Diamond Edition headphone amplifier supplied with PSU1 power supply:

£670.00 (including 20% UK VAT)

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