I've never experienced a tube amp before - so all I can do (for now) is compare this to my E11 (portable) and E9 (desktop) setup.
For all three amps I am using the same source (iPod Touch G4 via LOD). I'm comparing using a set of DT880 Pros (250 ohm), and I'll also briefly comment on my Alessandro MS1i & Brainwavz B2.
The Porta Tube measures approx 115mm x 73mm x 28mm. Add another 13mm for the volume pot. It weighs approx 315g. Comparatively my E11 is a fairly diminutive 92 x 54 x13mm and 65g.
The Porta Tube has a 3.5 mm input socket, and dual 3.5mm and 6.3mm headphone out sockets. It also has a power on/off switch, and an adjustable volume pot. It operates off an internal rechargable battery which is good for around 10 hours portable use. It is recharged via the included wall-wart. You can power the Porta Tube off the mains, and listen at the same time - so it would be good for desktop use. It also comes with 4 small rubber footings prefitted - again good for use in a desktop setting. The top is vented, and you can just catch a glimpse of the tube when in operation. The Porta Tube does generate a bit of heat when operating - but nothing excessive. It's warm to the touch - but definitely not hot.
It came with a plug, an adaptor, cord for connection to a suitable DAP, and a nice velour case.
I hope to add to this section - if I can actually find any information. Unfortunately nothing was included with the box (it was a demo unit), and I cannot find a website. I have asked Jaben for more information, and will edit this review if I discover anything.
Aesthetically the unit is really quite sleek, and looks extremely well built. The pot is a little loose (it's adjustable by a small grub screw - so I will get that fixed), but apart from the little bit of slack, it has an extremely nice smooth motion. Whilst I couldn't see myself using the GVPT in a really portable situation (ie on the move), I could see myself taking it with me to work, or to a cafe, or anywhere else I just wanted to chill out. It looks fantastic on a desktop - sleek and unobtrusive.
Once I charged it, I connected my headphones, and had my first listen. First impression, and hasn't changed after the 10 hours or so I've been using it - very clear, very balanced - warm and eneveloping - and very smooth. This has been my first listen to a tube based amp, and I really like it. With the 250 ohm DT880's, I'm only at about 1/4 on the volume pot - so this little amp looks to have a serious amount of driving power. I asked my wife (she has the better ears) to listen with no music playing, then raised the volume to 100%. She confirms what I hear - or more precisely didn't hear. Even at maximum volume, the amp is completely 'black' - no hiss, no noise.
To give you an idea of how good this unit is (to my inexperienced ears), from first listen - instead of critically trying different genre's and testing strengths and weaknesses, I ended up 'lost' in Eric Clapton's "Unplugged" ablbum, and from there to Nils Lofgren's "Acoustic Live". Over two hours elapsed, and I was just sitting there with a silly grin on my face - totally enjoying the music. Almost three days later I'm finally sitting down to put together some impressions - then I can get back to simply listening again.
(Photo - you can just see the tube through the grill)
Sound Quality & Comparisons
Having never heard a tube amp before, I didn't know what to expect. I'm not very good at describing in audiophile terms - so I'll simply tell you what I'm hearing.
First, it appears really detailed - I am hearing everything, and it is really clear.
I'm also finding that instruments are well separated - I am able to listen to everything, and that's what makes it so engaging I think.
Mid-range (especially vocals and acoustic instruments) are really smooth and an absolute pleasure to listen to.
Bass has a nice kick and is quite punchy. No sign of boominess or hollowness.
Highs are not overly prominent - maybe rolled off a little, but this still has sparkle for me - so it's a really nice overall tone.
Staging is intimate (close) rather than expansive
If I had to sum up in a few words I'd say smooth, warm, rich but sweet - definitely not dark.
OK - onto comparisons:
Classical - Julia Fischer and the Russian Philharmonic (Tchaikovsky's Concerto for violin in D, Op. 35: I. Allegro moderato)
GVPT - warm and enveloping - the timbre of the violin sounds really perfect
E11 - overall warmth is still very good - just lacking the clarity and sweetness I was getting from the GVPT. For the first time to me the E11 sounds a little 'dark' in comparison.
E9 - closer to the GVPT overall - but again doesn't sound quite as sweet. Clarity is good though. Still very enjoyable.
Jazz - Diana Krall (Love Me Like A Man)
With all three amps, this track was actually quite closely matched. The main difference was a little more sparkle with the GVPT, and also a shade more clarity. But all 3 (because of their warmth) make Jazz shine. No clear standout winner here - all very enjoyable.
Blues - Joe Bonamassa (Another Kinda Love - live)
Bass line is good with all three amps. All 3 are very similar once again - with the E11 and E9 being slightly drier in the vocals. The main difference with the GVPT is a sense of smoothness and richness.
Classic Rock - Eric Clapton (Layla)
This one was easier to spot - all three sound great, but the GVPT has the edge with clarity, and just sounds more engaging. It somehow just pulls me in.
All 3 amps are really close. There is no doubt that the E9 and GVPT have the edge with pure power. Overall difference is mainly clarity (minor difference in favour of the GVPT) but also sweetness, and richness of tone. Especially with acoustics - I find myself lost a little more with the GVPT. It's hard to describe - perhaps best to say that the GVPT just provides a little more 'body' and 'timbre'. It's also quite lifelike.
Sadly I recently sold off my SRH840's, SE425's and AD700's - to make way for the DT880's and SRH940's. Unfortunatelly the 940's are in transit - so all I have left is the Brainwavz B2 IEM's and my Alessandro MS1is'
The B2's are extremely easy to drive - and to be honest, the GVPT really supplies too much power. I had to have the volume down so low that I was in danger of channel imbalance on the pot. When I got it right, it makes the B2's really sweet. Takes a little edge off the highs - which is nice, while still retaining a great mid-range. If the GVBT had a gain switch - it would be easier.
MS1is - I have a couple of mods done with these already - quarter modded Senn pads & vented 4 joles to add a little more bass impact. They're still pretty bright compared to my Beyers. The GVPT really goes well with the MS1i's though. The brightness is still there, but it's somehow more palatable, and very engaging. I'm looking forward to hearing these again with the GVPT - after I eventually woody them. In the meantime a really good match - especially for rock and blues.
Based on the sound and form factor - I really enjoy this little amp. The GVPT does everything right for my ears - very musical, sweet and engaging. It has a really good synergy with both the Alessandros and also the Beyers.
NOTE - I haven't shown the price is in this review. I was able to secure a special package deal with some headphones.