(For more details and further sound impressions, check out my original review of the Porta Tube+.)
If you don't know GoVibe, it is Jaben's top-end brand, consisting of headphone amps, DAC's, and sometimes, cables. Today's review encapsulates the GoVibe Porta Tube+, a 24/96kHz USB DAC/headphone amp. 24/192kHz is achieved via upsampling. The DAC, a CIRRUS CS4398-CZZ. USB plug-play is its only stumbling block.
The main feature of the Porta Tube+ is the output valve, but I would like to draw attention to the fact that the GoVibe Porta Tube/+ is more impressive in that no matter which headphones are connected, whether low Ω headphones that drive down to 4Ω during heavy bass passages, or high Ω headphones like the DT880, that act very much like no load, but require more voltage, never stray farther than 1% performance from each other. Impressive performance to say the very least.
Of course, with a valve amp, there is overall more distortion than there is via a solid state amp, more phase errors, and oftentimes, a higher noise floor. The Porta Tube strikes each one of those except the last. Noise floor is extremely low even when very sensitive earphones such as the 1400$ FitEar ToGo 334 is plugged in, and equally as impressive via the Sleek Audio CT7, a dual-driver custom monitor.
There is no noise via any on-ear or over-ear headphone at any volume level in low gain. High gain is the realm of headphones, not earphones.
Now I suppose I should mention: gain is changed via internal jumper switches. While archaic, it has less impact on the sound because of fewer circuit connections in the amp. But, to change from low to high and visa versa, you must unscrew each of 8 screws, push the board out, then use long-nose pliers, or be handy with a small (-) screwdriver.
TMA's review goes further into that.
Low gain has good balance between channels for sensitive IEM earphones, while high gain will render too much volume for them to achieve balance. High gain is great for voltage hungry headphones, but I found even low gain more than enough for my 600Ω DT880, and the 64Ω K701. No problems at all.
Sound in a nutshell
While this amp is driven by a valve, and it posts higher distortion numbers than a solid state amp, it is bright, energetic, and easy to love. There is none of that bloom that pervades the signal of lesser valve amps, and no congestion at all.
Again, no matter which earphones/headphones you have plugged in, the Porta Tube acts very like there is nothing plugged in at all. Nothing obstructs the clarity of its signal, its rise time, and decay. That said, there is a bit of softness in the signal no matter the output device. It's a lovely cloud in both the high/low frequencies that demonstrates itself in a slight blending of L/R channels.
It is perfectly 'tubey', yet perfectly coherent in every phase.
The volume pot is silky smooth and balanced even at low frequencies, and unless you trip the high gain and attempt to blow your headphones at 90% volume, phase errors are nil. In other words, there is no phasing the Porta Tube/+.
As a DAC, it is competent, but I've found that USB battery powered DAC's perform less well as DACs than they do as line-input devices. The iPod touch drives signal better from its line out better than the USB-DAC does. If you up the quality of the input, say, to a AlgoRythm Solo, a CD player, or good pre-amp, it only gets better. But, the final output will remain within CD-quality benchmarks.
Whatever you think about that is whatever you think. I'm incredibly impressed. Admittedly, my experience with valve has stayed 100% in the living room with power amps, headphone amps, and one or two DACs (how does that work?), but I'm confident in saying that from a performance and sound perspective, the Porta Tube+ is one of the greats in this field, certainly at its price.
Final rating: 4/5
For more details and further sound impressions, check out my original review of the Porta Tube+.
Edited by shigzeo - 6/17/12 at 4:26am