Bravo Audio Tube Amplifier - V2

I enjoyed the sound from the Bravo Audio v2 amp, while it was working.  Driving PSB M4U-2 headphones (with internal amp off), the sound was relatively open and uncolored.  I found the two LEDs annoying and would have preferred to see only the tube's warm glow as a pilot light.  Unfortunately for me, my unit started making static noises about 6 months in; the blue LED would flicker with the static.  Two months later, the unit is completely dead.  Only an occasional small pop comes out.  I guess you get what you pay for.

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Me: I am a 21 year old student living in a small town in India. I would like to call myself a music enthusiast, rather than an audiophile. I was inspired by music since childhood, and as the time passed, the passion of music grew in me, and that subsequently led me to join Head-Fi. Eventually, I found the pleasure of listening to music mainly by the HD600 and recently, by the seductive LCD2 headphones, and realized the true components of recorded music. I usually like to listen to Indian Classical Music along with Bollywood songs. My main listening genres include classical, vocal, instrumental, jazz and sometimes pop.  With time, my sonic preferences have very much grown. I avidly admire transparency, accuracy along with neutrality, and currently my favorite headphones are K702, HD800 & K812, which I mainly run from my trusty M-Stage HPA-2.

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Intro:  Bravo Audio is a popular Chinese brand specializing in the area of tube headphone amplifiers in economical price. Bravo was established in 2010.  Even though a relatively newer establishment in the field, Bravo managed to capture attention of the world by their amp offerings which had attractive price tag & appreciable performance. Back in 2010, tube/hybrid amps would be expensive, and out of reach of a humble Enthusiast. Bravo made well performing hybrid amps in an affordable price.  Bravo was the one who made hybrid amps in sub 100$ category. This made them a well known name across the Audiophile World. 
 

 
All of Bravo’s amps are hybrids, and are driven by Mosfet’s, and are pure class A. This ensures in mammoth output power, appreciable clear sound quality, but heat dissipation is high, and the amp physically gets hot even to touch comfortably. Bravo has been famous since its release of V1 (6922) & V2 (12AU7) amps, which were budget friendly, yet performing, which won ears of many enthusiasts. The V2 employs Shuguang 12AU7 tube. Both V1 & V2 are very similar in design, features & functions.
 
Specifications of V2:
 
Input Power: DC 24V 1.5A
 
Input Sensitivity: 100mV
 
Input Impedance: 100KOhm
 
Headphone Impedance: 20~600 Ohm
 
Frequency response: 10Hz-60 KHz +/- 0.25dB
 
Signal/Noise Ratio : >90dB      Gain: 30dB
  
THD: 0.016% (300 ohm) 0.45% (33 ohm)

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Let us see what the V2 amp has got for us,
 
Packaging and Accessories: The V2 amp arrives packed inside a general cardboard box, packed inside a removable foam packing. Packaging is generic, but nothing to complain about. But all the included accessories have a good quality and feel to them.
 
List of accessories in the box, which include the following: 
 
 Power Adapter: AC to DC 24V 1.5A power adapter EU/US/AU/UK is supplied as per specifications.
 
¼” Converter: A 1/8” to ¼” converter for headphones with 3.5mm Jack.

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Design and Build: The V2 has a very good overall build quality. Though it is enclosed in open acrylic sheets to save manufacturing costs, it gives out funky DIY looks. The V1 looks much different& funky, and stands out from the crowd. Even then, the open case is of good quality transparent fibre & metal supporting beams. The transparent sheets make us gaze through it and onto the well soldered circuit board. The V2 is fairly small in size The V1 is light in weight, & weights under 250 grams.
 

 
At the front we have volume knob, ¼” headphone output socket & a 3.5mm input socket. At the rear side of V2, we can observe the presence of power socket & on/off toggle switch. Volume knob rotation is smooth and knob has just the right size for fingers. ¼” jack is also a very sturdy, but is slightly tight. The ¼” socket employs clip mechanism, which may cause scratches/damage on the headphone jack. Power switch has a good switching feel and strength, and is very precise in its job.
 

 
Internals quality is certainly good. The V2 amp has no manual wirings; everything is fixed on the PCB. Soldering & joints are very well done. Volume pot is well known Alps branded, which a plus for both volume control & audio quality. Please do note that the Mosfets run very hot, be sure not to touch anywhere near them, otherwise burn injuries are guaranteed!
 

 
Since the V2 amp follows Tube/Mosfet Hybrid design, there is a 9 pin vacuum tube socket present, in which we may roll any compatible 12AU7 family tubes. The default one is 12AU7 from a Chinese brand called Shuguang, & does a great job in sound quality. There is a blue LED below the socket, which gives out a glow effect to the tube.
 

 
I observe a drawback in the power supply, it is not earthed. I am at a loss of understanding why Bravo did not include a third earthing pin or ground to make the amp safe. Since it is a DC supply, few ripples will be present in the final output. These either cause light electrocution/sock or audibly raise noise floor of the amp.  All Bravo amps use the same 24V 1.5A power brick, and are not grounded o earthed. So if you happen to find a better quality laptop power supply within this specification, then it is a plug in replacement or upgrade.
 

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Sound:  The V2 amp delivers ‘Clear’ sound as a typical entry level tube amp and goes in the line of Bravo’s ocean amp. Presentation is in such a way that, mids are little more intimate, with lows & highs sound tad more relaxed and laid back. 
 
Burn in: I could not notice any major improvement by burn in. But let’s say a playback of about 20 hours provides few minor audible improvements, Bass prior to break-in is quite muddy & loose, and eventually it becomes a little more accurate and clean, Mids will sound more open & slightly forward, airy and natural. Highs become slightly smoother; soundstage will open up by a margin.
 
Tube rolling:  One can roll enormous number of 9 pin 12AU7 or equivalents. After much testing a few tubes from different, I could conclude, the stock 12AU7 is indeed very good at its job, is optimal for the existing circuit parameters. But tubes like Mullard or RCA brands also do provide a more pleasing sound. Replacement of stock tube is not absolutely necessary.
 
The gain is fixed at 30dB, which is on higher side and is certainly not recommended for IEM’s. This amp is extremely powerful and can drive any dynamic magnetic cans to insane loudness with just 40% of the volume used, which is at 11 o’clock. Anything above 12 o’clock is unbearably loud.  
 
Lows: are fairly accurate, are slightly on ‘looser’ side; but have a good impact. Depth is decent.
 
Mids: Forward & intimate, are smooth and feel natural.
 
Highs:  Spacious, but not detailed.
 
Soundstage: decently airy & spacious. For anyone who is looking for a good soundstage definition in entry level tube amp, V2 is a satisfactory performer.  But one should not expect sonic qualities like detail retrieval, accuracy or good imaging from this amp, owing to its economic cost & the V2 is one of the cheapest available tube amp today.
  
Overall, final sound deliverance is decently satisfactory for an entry level tube amp.

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Comparison: Bravo’s own V1 amp can be compared with V2, owing their vastly similar design & functions. Also, the price different is mere 10$.
 
Bravo V1: Same functions, features & design, and sonically is slightly inferior by sound. The V2 is more neutral, provides a much cleaner sound output with good soundstage definitions, when compared to the V1. The added bonus here is The V2 costs 10$ less than V1.
 
Verdict: The V2 edges out the V1 with overall better finer accuracy & neutrality in sound, finer power distribution.

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Conclusion:  Sonically, Bravo’s V2 amp performed well & has pleased me for a tube amp available around 70$. The V2 is a good performer owing to its 12AU7 architecture. This would a friendly amp for any enthusiast looking for a decent low cost tube amp.
 
Pros: 
 
1) Build Quality: even though it is open by case, the V2 has a very good interior build. No compromise to be seen anywhere in exterior too. Circuitry is also neat & well built.
 
2) Rolling Capability: Enthusiasts can roll great number of tubes to alter the final sonic signature.
 
3) Driving Power: The V2 amp has a sheer output power. It definitely can comfortably drive any set of high impedance cans.
 
4) Sound Quality: Is satisfactory considering its price, & performs upto expectations. 
 
4) Value:  Considering the above points, the V2 amp will have a solid price/performance ratio. There is no such tube amp which can perform better than Bravo V2 under 70$.
 
 
Cons:
 
1) Heat emission:  Actually not really a con, it is quite normal for a hybrid mosfet driven amp. But during operation, the V2 amp gets very hot; it becomes very difficult for a user to touch the surface of amp more than 2 seconds. The mosfet heatsinks, which are exposed & are very hot.
 
2) Power Supply: The default power supply is not grounded, hence a fair change of light electrocution and audibly higher noise floor. Thus one needs to earth it by connecting the input cable to a grounded source (like PC, which will be earthed)

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The Bravo V2 is an attractive and inexpensive "pseudo-tube/hybrid" amp that is easily accessible to beginner DIYers if modifications are desired (which they definitely are as I will expand on later). 
 
I'll review both the stock unit as well as modified amp although the star rating is for the stock unit. The modded unit would be a 3.5 - 4 star rating.
 
Build/Design
 
The V2 is a small desktop amp (8 x 8 x 3.5 cm approximately) with exposed sides and a clear plexiglass top and bottom plate. It is very attractive and easy to access for mods, but that's where the build/design strengths end. The PCB is very cheap and the stock components are very cheap. For example, the amp is powered by 24V but the power cap is only rated at 25V, leaving little room for overvoltage protection. Replacing this cap with a 35V cap is good preventative measure. The is also a sound popping sound upon power ON, which can be fixed with an induction coil and relocation of the switch; I'm no electrical engineer, but this is bad circuit design I would think.
 
The blue LED is obnoxious in my opinion and is an eye-sore. You can either short it to turn it off or replace it with another LED of your choice.
 
Also, this is what many consider a pseudo-tube amp since the tube itself does very little of the amplification and is largely used a pre-amp stage for coloring/warming the sound. Other hybrids utilize the tubes a bit more and pure tube amps run crazy high voltages.
 
Sound
 
The stock unit does not sound very good. The highs are muffled and there is noticeable distortion. Bass heavy songs sounded OK, but everything else sounded muffled and harsh with none of the warmth you might expect from the tube preamp. Replacing the stock tube will help the sound, but the real fix is to replaced the stock IRF630 voltage regulator with a IRF510 or IRL530 regulator instead. This extends the highs and also seemed to reduce distortion. The heat generated form these upgraded regulators however is higher, so it may be wise to upgrade the LM317's to LM317A's as a preventative measure. After switching to an IRF510, the heat sink measured 70-75C after 30 minutes of operation (I used an IR laser thermometer). Replacing the output caps with 25V/2200uF caps are said o improve the lower frequencies, but that's debatable depending on who you ask.
 
Value
 
At under 70USD, this is a great way to get your feet wet when it comes to DIY audio devices. If however, you want bargain sound under 100USD without doing any mods, go with a solid state amp like the Schiit Magni or a FiiO E-Series amp. 
 
In closing, I think this is a nice introductory amp although the sound quality was never stellar even with a full suite of modifications. As I mentioned earlier, this is a great DIYer's amp although the cheap PCB is terrible for desoldering. It would be great if this amp was offered as a kit for home assembly (that way, you only need to solder once and include any upgraded components the first time around), which would further drive down cost.