Since no reviews of these amps have been posted at the website, I have tried to write something more complete that may assist people contemplating one of these units to be a bit more informed in their decisions.
Here are a bunch of caveats:
1. I am not an audiophile – but I have read enough crap on the internet to be able to sound like one. So don’t trust my judgement or my words.
2. My room, my associated equipment, my ears. Not much hi-end here. Room is 14x14x9 carpeted BR with a bunch of junk in it. Current equipment: Sources: Sony CPD CE245 and Pioneer HDD/DVD recorderDVR-460H (both used as transport only); Motorola Satellite receiver routed through Pioneer. DAC: GF TubeDAC-09 (Straight DAC); GF TubeDAC-09 (preamp); Amplifiers: Shuguang I-12; Shuguang I-25; Harman Kardon 3490 (used as power amp). Speakers: Definitive Technology DR-7 floorstanders; GF LS3/5A. Interconnects: various generic RCA (and 1 GF brand), generic USB, generic optical and digital audio. Speaker wire: 1 GF, 1 generic ‘Mammoth super flex oxygen free copper’. Beauty eh!? Cut to about 7’ long. Power cords: GF power cords for the Schuguangs and the DAC, original cords for everything else. Everything plugged into a GF power conditioner. My ears: pretty ancient, can’t hear treble like I used to...
3. Preferences: The way I like my music may not be the way you like yours. How do you like your steak prepared?
4. And to add to the complexity: I am not a skilled listener; I am in the beginning phases of training my ears and my brain. This limits what I am able to hear, and flaws that may be obvious to others may not be noticed by me.
I have been unable to discern differences in sound between GF interconnects and the cheap generics. The GFs look much better, though.
I have been unable to discern audible differences between the butch GF power cord and the original power cord supplied with the DAC. I have not tried swapping GF and stock power cords on the Amps.
I have been unable to discern audible differences between the GF and Mammoth speaker cables.
HK 3490 receiver vs. Shuguang Tube amps: the HK benefitted significantly from using a TubeDAC-09 as preamp, bypassing the built-in HK preamp. A veil was lifted. From what I read on the ‘net, this should be audio nirvana: the sweetness of a tube preamp with the low distortion, dynamics, power and bass control of 120 WPC SS power. No nirvana noted: the HK is able to play loud with power to spare, but there is a lack of refinement in comparison to the tube amps. The HK adds artefacts to the sound. The HK lacks refinement and precision. The HK makes an absolute mess of classical and baroque music. On the plus side: the HK runs cool and quiet. My younger son prefers the HK to the tube amps, because the HK is louder.
I-12 vs. I-25. The amps share their looks, the single RCA inputs, and the built-in MP3 player that plays at such a low level that it is virtually useless for serious listening. The sound quality of the MP3 is not bad, the quantity is. The smaller I-12 has a headphone jack that the I-25 does not have. I have swapped speakers between the two amps, and the amps sound different from each other with each speaker. The amps are neatly packed in foam in a double cardboard box. The tubes are inserted into the amp, and held in place neatly by the foam packaging.
Value: The I-12 has 12 WCP of EL84 power. The 4 EL84s are generic Shuguang tubes. I have not upgraded the tubes, and there are many possible upgrades, including the Psvanes. The I-25 has 25 WPC through 4 EL34 Shuguang black bottle Treasure Tubes. My estimated replacement costs for the 4 EL84s is about $40, the 4 EL34 about $280. For the $240 difference you could replace the I-12’s EL84s and two 12AX7s and have an amp that should sound better than stock and keep the spare tubes. The only problem is that once you add $240 to the price of the I-12 it is actually more expensive than the I-25 for half the WPC.
Build quality: identical for the two amps. Both are heavy, solid, thick aluminum face plate. Both are smaller than the HK, but weigh 2 – 3 times as much. These amps are more expensively built than your Denons, HKs, etc. All parts to fit together well. The I-25 is only a little bigger than the I-12, but considerably heavier. Switches, volume control, binding posts all have a high quality feel to them. The only problem I have encountered with the amps is with the headphone jack of the I-12. (I should mention that Ian Grant is determined to resolve this issue!) Sometimes it mutes the speaker outputs, and sometime it does not. In addition, the channels on the headphone jack are reversed. None of this is a big deal to me, because I use the RCA tube outputs on a TubeDAC-09 preamp for cans.
Sound quality: first the bad – the headphone outputs in the I-12 are quite noisy even when it works as well as it can. There is a noticeable amount of hum that is not increased by turning up the volume on the amp. I can adequately deal with the hum in the headphone output by turning the volume of the amp to `noon` and lowering the volume on my cans. But if I turn up the volume on the amp beyond `noon` other noises start to appear – not sure how to describe these noises... Variable frequency wobbling hiss?
Sound quality: The good: the sound through the speakers. Both amps are very well-behaved and sort out the input signals nicely. Both amps are very quiet, just a faint hum with full output is noticeable when you are very close to the speakers. So no worries about sounds that I should not be hearing – there are none. This is important to me. I live out of town, and my listening environment is very quiet. And anything that intrudes as noise on my music is a real annoyance to me. Both amps present a bigger 3D soundstage though the tube output than the SS output of the TubeDAC-09. I have the inner edges of the speakers at about 5` from each other, my ears are about 6` from the tweeters (and at ear level). The soundstage presentation depends a lot on the recording of a particular disc. At times the soundstage has been too wide for my little brain to comprehend, and I have needed to move away from the speakers to make the music more manageable for me to comprehend. There was never a gap in the centre, the music has just been too spread out for my brain to comfortably put it together – and there are times when I just do not want to work that hard. (This is challenge only with classical and baroque. Modern music may have detail, but to me that detail is more ornamental than meaningful, so it does not require much effort to integrate.) Anyway – any lack in soundstage width has nothing to do with these amps. Soundstage height is less huge. Depth is impressive. All of this is probably also affected by my listening room. Imaging is absolutely stable with both amps. With a decent quality recording each instrument and voice is in its own place in a 3D sound image, and stays there – unless the performer moves (e.g. Opera), or the recording engineer plays tricks (e.g. classic rock studio recordings.) Anyway, I used to listen to classical and baroque music almost exclusively through cans because the sound coming from various Yamaha and HK receivers through the DefTech speakers was so confused and muddled. Now I prefer listening through the speakers because of superior soundstage and dynamics. I had expected the tube amps to sound sweet with acoustic instruments and voice, and they do. An additional pleasant surprise is who they smooth out electronic instruments. In my set-up I can hear a lot more detail with a bit more volume with each amp.
How the amps differ: This is where things get difficult for me. The I-12 sounds ‘lighter’ and leaner to me than the I-25, but the I-25 is no less agile. Initially the I-12 seemed to have more sparkling treble than the I-25, and also more base, but this changed as the I-25’s tubes burned in more. The I-25 changed its character much more than the I-12 during burn in. I am not sure that the amps are completely done burning in, but I think their characters are now fairly clear: The I-25 is everything that the I-12 is and more: more and better controlled bass, more mids, and more treble. More detail, more ‘density’, more everything. That would be my A/B comparison. In terms of extended listening, I find the I-12 to be an absolute joy. It works great with the TubeDAC-09 and both sets of speakers in producing a musical and organized soundscape. Yesterday I enjoyed every minute of a 14 hour listening session with it. The I-25`s sound changed a lot since it first arrived. At first there was not much sound at all, and what was there did not really sound like music. It took about 20 hours for bass to introduce itself, and welcome though it was, it was uncontrolled at first. It was a lot of fun to hear the amp get better and better - probably mostly the tubes that kept improving.
Bach Brandenburg concerto 6, 3rd movement test: I-12: lots of viola notes in left channel, backed up by orchestra. I-25: 2 distinct violas playing their lines in left channel, backed up by orchestra. Variables: I-12 was hooked up with GF interconnects to GF speakers; I-25 hooked up to DefTechs through cheap generic RCAs. I-25 wins this test!
Final notes: Grant Fidelity ships their products free of additional charge in North America, I believe. Ian and Rachel kindly arranged to open up their showroom on a Sunday when I had a chance to be in Calgary on a Sunday, and meeting them allowed me to have confidence in them and their company. Over the last year I have made several purchases from them, and the orders have always shipped immediately, and been packaged very well. Ian and Rachel are committed to customer support. In dealing with Ian and Rachel I feel treated like a person rather than a credit card number, and that is very reassuring.