Solo Ultra Linear Headphone Amplifier [Diamond Edition]

When only the best headphone amplification will do

  • Superior imaging and great musicality
  • Effortless dynamics
  • Powerful without sounding boomy
  • Valvey smoothness with detailed clarity
  • Ultra low noise [suitable for In Ear Monitors]
  • Input switch for two sources
  • Modestly affordable asking price

Spending hour after hour messing about with cables and headphones and IEM’s and amps and the variety of combinations you can make, the Solo Ultra just lifts everything it was hooked up to. Sure it couldn’t make a £30 IEM challenge a £200 one being played out of a meh source. It’s not a magic wand. It did however immediately offer a new layer, not only in quality and detail but it improved the acoustic layering. I feel almost a little spoiled in what it can do to things and then to go back to my old set up feels as though something has been stolen. That hint of life, of vibrancy, of dynamics, of nuance has just ever so slightly been taken away. Everything feels diminished and it makes me sad. The Solo Ultra Linear therefore stands quite easily head and shoulders above everything as the best amp I’ve ever encountered. It’s that simple. It is wonderful.
- mark2410, Head-Fi, June 2015

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 as a PDF download

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

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.
- forum member: DrHouse

Well ... I am finally listening to a Solo Ultra Linear with a PSU1! Straight out of the box and fed using a pair of RCA splitters from an inexpensive HLLY SMK-II with Apple Lossless files from an iMac running iTunes 10.4.1 I can say that versus a fully burnt-in SRGII w/ PSU1:
1. The soundstage is wider.
2. There seems to be more air between the notes.
3. There is more clarity and I suspect more treble extension (to be confirmed after more burn in).
Now, why did I wait this long?
- forum member: mrarroyo

I took a bit if a gamble and ordered a Solo Diamond Ultra Linear amp purely based on the wisdom from the forum and various reviews. It turned up an hour ago. Well, oh my God, or for the trendy, OMG, is the perfect phrase to describe my reaction! I'm completely bowled over! What an amazing, amazing, amazing sound, and the thing's not even burnt in yet! I can't wait! I've put together a dedicated listening setup with a comfy reclining chair; iPod Classic with Apple Lossless tracks, an Arcam drDock and Arcam rDAC, this gorgeous Solo UL amp and my Grado 325is headphones. I'm hoping to upgrade the headphones to Grado GS1000i cans soon. I'm getting so pulled in to the music that hours just float by, leaving a smile, ears tingling with joy and a wonderful emotional response to the music.
- forum member: Edmond_Terakopian

Some reflections on Solo UL and LCD-2. Overall I really like the range of sound, from the deep bass to the clear hi-hats and percussion. I can clearly hear all the parts in a pop mix, and the echoes in acoustic recording. There is a lot of detail but the sound is not crisp, which makes brighter mixes and those with enhancers or exciters more listenable. The depth and clarity of the bass and midrange makes drums and stringed instruments sound very good. For example some cello concertos come to life, upright and electric basses sound great. Drums sound great because the Solo UL/LCD-2 has real depth and is fast, kick/snare/tom parts are dynamic and I can hear the resonance of the toms.
- forum member: Fatmangolf

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


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Phil Gold, in a High End Headphone Amp Group Test wrote:

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.

Solo ULDE in show demo

Grado chose the ULDE to demo its headphones at the 2014 Bristol Sound and Vision Show after Grado's Brooklyn HQ started using one.

A headphone amplifier with an ideal balance of valvey smoothness with detailed clarity, and full frequency extension with "effortless" dynamics, makes the (solid state) Solo Ultra Linear Diamond Edition headphone amplifier a must-have companion for late night and personal headphone listening at home.

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.

If you have a Solo SRGII from mid-2004 onwards, you can upgrade to Ultra Linear Diamond Edition performance, with either our factory upgrade, or easy do-it-yourself upgrade. For full ULDE performance, don't forget to use the PSU1 linear power supply.


Headphone impedance range8 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 impedance37k 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 balancebetter than 1dB
CrosstalkLeft to Right -56dB; Input to Input -68dB
Input selector centre-off positionnon-shorting; -38dB at max volume with 2V rms input (ref: 1kHz and 10kHz)
Output StageBipolar class AB
Supply voltage24V DC unipolar
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.

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