Naturally Inspired

Solo Ultra-Linear Headphone Amplifier

If you're considering using the Solo Ultra-Linear headphone amplifier with In Ear Monitors click here

Our best selling solid-state headphone amplifier with around 1,000 highly delighted customers so far - it takes all the good points of valves/tubes, but won't wear out like valves/tubes, and drives low impedance headphones too!

Inherent headphone protection from damaging DC currents comes as standard with every Graham Slee headphone amplifier.

"It delivers ... a huge soundstage, a wealth of timbral nuance and subtlety, a totally immersive listening experience" said one customer who'd taken advantage of our free home trial. The Hi-Fi media has this to say...

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."

[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)

"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]

Whilst other headphone amplifier manufacturers follow a one-way trend of making micro-power speaker amplifiers, the Solo Ultra Linear headphone amplifier uses original thinking to take the headphone-specific Solo concept even further, so it reproduces music so precisely it naturally sounds more musical!

The Solo Ultra Linear headphone amplifier lets the music flow - it's timing is second to none. The bass is full but never loses control. The highs are free of grain and harshness. Stereo imaging is the best it can be without artificial cross-mix or width extension. Made for the best signal sources - the Solo Ultra-Linear headphone amplifier will be your best headphone amplifier purchase yet.

Read what our customers have to say here and here

Technically Speaking

The Solo Ultra Linear headphone amplifier is an improved linearity J-FET input - discrete transistor output-stage design which uses open-loop gain and bandwidth modified operational amplifiers to mimic valve/tube performance. The result is linearity in all areas that can only normally be provided by valves/tubes. However, the Solo Ultra-Linear headphone amplifier can directly drive low impedance headphones - as low as 5 Ohms - as well as high impedance headphones.

It also includes our proprietary headphone load feedback network which cancels much of the Solo Ultra-Linear current drive output impedance as well as controlling headphone cable capacitance and inductance so you should never need a cable swap to hear your headphones at their best.

The headphone load feedback network also makes it possible to swap from high to low or low to high impedance headphones without much change in volume control position or the need for a gain switch which could otherwise colour further the music.

"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)

Using your Solo Ultra-Linear headphone amplifier with In Ear Monitors (IEMs)

The Solo Ultra-Linear is a high voltage headphone amplifier designed for average sensitivity headphones. When used like this output noise (hiss) is sufficiently low at -78dB so as not to intrude on your enjoyment. When using In Ear Monitors which are extremely sensitive being intended for low voltage headphone amplifiers, the Solo Ultra-Linear output is considerably more than required. The whole output is magnified by 15 to 30 decibels depending on which IEMs you use, requiring the volume control to be set very low where, incidentally, all volume controls have poor channel balance. The output noise (hiss) is not reduced by the volume control and so it will be some 15 to 30 decibels louder and can therefore become intrusive on your listening pleasure. Several IEMs are supplied with "in-flight attenuators" because aircraft headphone sockets are also the high voltage type. If you use your "in-flight attenuator" with your Solo Ultra-Linear headphone amplifier and In Ear Monitors the output noise will not intrude any more and the volume control can be set to a more convenient position.

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An introduction to Ultra-Linear Technology

"It's been my intention to recreate the (original) valve sound for years simply because I liked the valve sound of yesteryear, but as I didn't fancy high tension voltages up my arm developing the circuits, I wanted to do it in solid state. Most people would think that's impossible but it isn't as I'll explain, but first I'll tell you why it was worth the effort...

Those who can recall the valve sound, or who listen using what I term a real valve amp, will be able to relate to this...

Valves sounded warmer but not over-warm - they rendered the bass much more naturally in a much less restricted way than solid state.

The valve scored in the presence band (what's now called midrange) communicating the feel of the music so you didn't have to try to get into it.

The highs sounded much clearer - not edgy - so you could easily discern between similarly sounding instruments

But mainly they made music something everyone enjoyed - families would gather round the valve set, listen, hear and enjoy, but I never saw that with solid state. The main thing I recall is being drawn into the music and being able to picture the images being painted in my mind. The valve always "told the story" better!

Good valve amps are pricey but solid state can be made much more affordable - wouldn't it be great if we could make it work?

Various arguments have been put forth as to why solid state cannot do the valve trick and the internet carries numerous points of view - some quite forceful, but still no solution. However, we touched on it to varying degrees with our earlier phono preamps but didn't fully understand how. In a way the Era Gold V and early Reflex phono preamps were almost there, with customers and reviewers suggesting they had valve-like qualities.

The Ultra-Linear technology is the result of two years almost solid research, exhaustive development and testing. We researched how to mimic all the valve’s characteristics to improve our products. What we found was that a number of op-amps (integrated circuits) could be made to perform just like valves - discrete transistor circuits being far less predictable. Graham Slee's products with Ultra-Linear technology feature significantly wider bandwidth (they go to higher frequencies) before negative feedback is applied - just like the best valve amps. What a breakthrough - valve sound at less than high-end prices!

We call this innovation Ultra-Linear because that was the tag used to describe the great performance of the best sounding valve amps that first made their appearance in the mid 1940's. These techniques vastly reduce the phase modulation distortion and linearity distortions that are hard for solid-state audio designers to perceive let alone measure. Ultra-Linear technology will feature in our top of the line products like the Solo Ultra-Linear headphone amplifier. More products will benefit from this new technology including the Reflex, Revelation and Gram Amp 3 Fanfare phono preamps plus the Elevator EXP MC step-up amplifier.

Natural like a valve: solid as a rock!

Graham Slee"

Connection Suggestion

The Solo can be connected in an amplifier tape-loop 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.

Solo Ultra-Linear Headphone Amplifier Specification

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) -78dB

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

Price

Solo Ultra-Linear headphone amplifier: £514.85 supplied with PSU1 power supply; Prices in GBP (pounds sterling) ex VAT/GST