Graham Slee Solo SRG II Headphone Amplifier

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  • Top flight Headphone Amplifier from Graham Slee

Graham Slee Solo SRG II headphone amplifier

The latest edition of our flagship Solo headphone amplifier - the Studio Reference Green MK II puts a real life force behind the music.

The Solo SRG II headphone amplifier combines conventional negative feedback with line driver load sensing to exert greater control over your headphones where it is needed.

It therefore reduces or eliminates altogether the comb-filter effect most headphone impedance curves exhibit in the upper midrange and treble frequencies. It also ensures correct matching with the widest range of headphones and overcomes cable capacitance and inductance problems which could otherwise strip the music of its airy qualities and sound staging. The Solo SRG II headphone amplifier does everything better as well as giving a more weighty bass.

Looking back, What Hi-Fi? Sound and Vision said this about the Solo 2004 edition headphone amplifier...

"Verdict: If you are serious about headphones go and have a listen to the Solo - and be prepared to buy it there and then" [Graham Slee Solo, What Hi-Fi? Sound and Vision, October 2004 and The Ultimate Guide 2004]

Five years of serious development later - would five stars now be enough to appraise the Solo SRG II headphone amplifier?

The Solo SRG II headphone amplifier has two line level inputs and a front panel input selector with centre off. It is housed in a strong anodized aluminium eurocard style enclosure. The volume control also acts as sensitivity adjuster and therefore the full rotation can be used (see further explanation below). The Solo SRG II headphone amplifier is suitable for use with headphone impedances from 16 Ohms to 600 Ohms.

The "Green" Headphone Amplifier
We also made it energy saving! You can buy the Solo SRG II headphone amplifier with an energy efficient power supply complying with world carbon reduction targets for nearly 30% less than the PSU1 powered standard issue.

The Solo SRG II headphone amplifier is available with PSU1 power supply for those wanting a traditional (but more power hungry) linear power supply.

Headphone Matching, Suitability and Volume Control Settings
The Solo SRG II is designed to work, and self adjust, on two different input levels (in either switch position): 1] professional (unbalanced) 0dB: 775mV, where its output is to drive 600 Ohm headphones for certain studio applications, and 2] domestic -10dB (DIN): 250mV, where its output is to drive 32 Ohm headphones. In either mode of use it will return virtually identical output power as well as similar sound pressure levels with identical headphone sensitivities.

In typical usage however, it will be used with different headphone impedances in the range 16 - 600 Ohms, having quite different headphone sensitivities (SPL), and input levels between 250mV and 1V. This gives a number of permutations which could not be covered with a gain setting switch, and instead, the Solo SRG II uses a combination of IEC/DIN 61945 headphone output "matching system" with an accurate Alps volume control which is used over its entire range to accommodate such widely differing conditions of use.

As such the user may find the ideal volume control position required for his/her listening tastes considerably different to that of a hi-fi amplifier. The left-right track matching of the volume control is adjusted by Alps, its manufacturer, for best channel balance between its 9 o'clock and 3 o'clock settings and as such when set for zero volume some residual signal may be heard on one channel and not the other - this is normal and part of the volume control design.

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

Headphone Jack: 1/4 inch (6.35mm) A gauge (BPO B gauge to special order)

Power output
(rms, both channels fully driven) 32 Ohms: 27mW/channel; 600 Ohms: 23mW/channel

Distortion (THD plus noise, ref 1kHz): 0.02%

Frequency response (-3dB) 32 Ohms load: 27Hz - 35kHz; 600 Ohms load: 10Hz - 39kHz

Output noise (20Hz-20kHz, CCIR quasi-peak): -84dB

Input sensitivity (for specified power output) 32 Ohms: 250mV rms; 600 Ohms: 775mV rms

Channel balance: better than 1dB, "9 to 3 o'clock" positions

Crosstalk: Left to Right -57dB; Input to Input -68dB

Mute: Signal off mute, non-shorting

Output Stage: Bipolar class AB

Supply voltage: 24V DC

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

Price: £434.00 ex VAT/GST ("Green" £314.25 ex VAT/GST)

Graham Slee on the Solo SRG II headphone amplifier
The Solo SRG II returns to its roots. The original Solo prototype is revived in the new SRG II. After many years searching for the grail of high performance headphone reproduction we combined the original prototype with the SRG control loop, and found what we'd been looking for.

Most listeners play CDs or music from computer files which is OK, but there's one source we've found that will expose the limits of any amp - vinyl!

Vinyl suffers from a problem the others don't: Scratch! By that we mean fast rising edges that may be something other than what was intended. Often when listening to vinyl records there are glitches that are not very musical - in fact they can sound very artificial, upsetting the otherwise very realistic vinyl sound.

These glitches demand a high slew rate, but there are a never ending number of high slew rate solutions - you'd think it would be easy?

The big problem with most of these solutions is the slew rate is enhanced - it isn't natural. With other solutions like FET inputs, the slew rate isn't symmetrical. In all these cases the bass gets compromised because the treble is so false or smeared. What the customer (and indeed us) wants first and foremost is the right tonal balance and enhanced slew rate or FET asymmetrical slew rate can never do that - it's a fact that's been cleverly hidden by the proponents of enhanced slew rate and FET amplifiers for over 30 years now.

In a meeting with an old colleague involved with touring band amplifiers several years ago we discussed the merits of FET and bipolar solid state solutions and were both of the persuasion that bipolar gave a more natural bass.

Little did either of us realise but over 30 years ago an AES (Audio Engineering Society) presentation concluded exactly the same, and they produced real evidence rather than what I and that colleagues ears told us.

Apart from the prototype Solo and the SRGI and now the SRGII, all previous Solo headphone amplifiers have featured enhanced slew rate or FET input stages - even so they sounded good enough to warrant some great rave reviews, and the Solo has gathered a great following being one of the best selling "grown-ups" headphone amplifiers in the world. But it is only human to try to push the boundaries as far as they will go and our followers have been urging us to go the extra mile.

So after all the advances we've made with the Solo over the last 9-10 years we decided to optimise them for the old prototype's input stage (as well as its line driver output stage), and wow, what a surprise! The Solo SRGII happened.

Op-amps can be of a number of varieties but fast op-amps fall into the categories of real slew rate and enhanced slew rate. Real slew rate can go as high as 20V/uS whereas enhanced slew rate can be anything up to 3000V/uS. The problem with enhanced slew rate is that the performance is forced, but after all, they are designed for video - for the eye to see and not for the ear to hear. Unless reigned back to something more akin to a natural slew rate, enhanced slew rate op-amps distort on "scratch" or any fast rising signal, and once they do, the life of the music is completely lost. Now, if you have to throttle-back to some more natural slew rate, the enhanced slew rate op-amp looks to be wasteful? Some may argue that there is something else in them that makes them sound musical... sorry, we don't agree and neither did the AES or my colleague in live touring band sound.

So now we discovered that fact shouldn't we reject the op-amp and use discrete transistors in our flagship headphone amp? Why? People falsely believe op-amps are cheap. All semiconductors are cheap! Millions are used around the world every day of the year - they're bound to be cheap! Transistors are a few pence if not one pence each so why do discrete amps cost so much? Hype maybe? Op-amps cost considerably more and are thermally optimised whereas transistors spread out all over a board are not. Therefore it makes sense to use the best audio op-amp there is in a flagship amp like the Solo.

But it's not what you do but the way that you do it. There's a lot more to a product than the semiconductors - discrete or op-amp. That's what gets the results!

Available with standard 'Green' power supply or upgraded 'PSU 1'

We endeavour to despatch same day for orders placed up to 2pm on available stock items (items with stock message "Usually dispatched within 24 hours"). Please remember to check with us first for a physical stock check if next day delivery is important to you. Any items with stock message "Usually dispatched within 72 hours" are items that we do not hold in stock but order in from the importer or manufacturer as soon as a customer order is recieved. Occasionally these may be delayed beyond 72 hours due to importer/manufacturer stock levels but we will inform you as soon as we can if this is the case.

UK ORDERS:  We despatch the bulk of our UK mainland items on a 24 hour service – Free of Charge.  Non Mainland locations - Isle of Man, Isle of Wight, the Scilly Isles, the Scottish highlands and Islands, the Channel Islands and Northern Ireland may take a day or so longer and are not Free of Charge. Smaller items are delivered using Royal Mail recorded delivery or special delivery. Larger items are delivered using a courier service such as Interlink Express, DPD, UPS or DHL. 

INTERNATIONAL ORDERS: We offer competitive rates which can be confirmed by email. Please just ask – we will need a full delivery address and telephone number. Smaller items are delivered using Royal Mail Small Packets Airmail with International Tracked and/or Signed depending on value of item and availability of the service. Larger International shipments are sent by insured and tracked services using DPD, DHL or UPS. If there are any delays due to specific customs regulations, etc, you will be contacted by Turntableworld or by the courier with a request for any further information required. Customs duties do not apply for shipments into any EU country (for a full list please refer to the EU Country List). Customs duties can apply for countries outside of the EU. Customers in these countries are responsible for all taxes and duties incurred when the items enter their country.

COLLECT IN STORE OR HOME INSTALL:At the request of the manufacturer some items cannot be supplied by mail order but you can click and buy them and then elect to collect them from our store or arrange a home install (if applicable). Applicable items clearly state that they are Collect in store or home install. Once ordered you will receive a message prompting you to contact us by phone or email to arrange for us to deliver and install or to reserve and collect from our store at your convenience, you will also be advised of the delivery time / stock availability as not all Home install / collect in store items are held in stock. 

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