GSP Solo Ultra-Linear headphone amplifier with PSU1
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"
So what's the Solo Ultra Linear secret? Well, there are many, but for one its distortion is quite unlike any other solid state headphone amp: solid state distortion increases in proportion to frequency, so when there's lots of highs the distortion increases and that's highly noticeable playing complex music. The distortion from the Solo Ultra Linear remains consistently low throughout the audio spectrum. Why? Because its bandwidth is exceptionally wide before the application of a thing called negative feedback. Solid state headphone amps use negative feedback as a fix for distortion as well as noise but also to widen the bandwidth, but all it succeeds in doing is adding glare. The highs also affect the sound at bass and mid frequencies because the leading edge of a note is fast - if the highs are distorted much of the fine detailing in the bass and mid frequencies is lost. Also by improving on distortion linearly throughout the entire audio band the sound stage comes alive as you've never had before.
Another one of the Solo Ultra Linear secrets is its greater input linearity: usually a solid state amp cannot take much input signal before it is overdriven when it distorts badly and copious amounts of negative feedback have to be applied to correct it. What you end up with is restructured music that doesn't quite hit the spot. Some claim "no negative feedback" but if that were the case all you'd hear is distortion - it's a very misleading marketing trick that the Advertising Standards Authority should look into.
Like most headphone amps except for the ridiculously expensive, the Solo Ultra Linear is basically a pair of transistor assisted op-amps. But here we chose one of the very few op-amps which feature one of the best output stages ever designed! Featured in Wireless World in 1969 and authored by J L Linsley Hood it remains the most musical of output stages and is class-A. To these we add our proprietary open-loop bandwidth widening technique and the difference is staggering.
So how come all manufacturers don't do the same? They could if they were so seriously interested in you that they put in over 35 years research into understanding the true ways to really great audio, that Graham Slee has!
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
