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Bravo Audio S1 Class A Deluxe Headphone Amplifier with Op-amp

  1. YoYo JoKeR
    Bravo Audio S1: Perfect Solution for a Beginner's Desktop Amp
    Written by YoYo JoKeR
    Published Apr 26, 2015
    Pros - Clear Sonic Presentation, Rolling Capability, Driving Power, Great Match for Planar Magnetic Cans, Value
    Cons - Heat Emission, Open Case

    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.

    Intro:  Bravo Audio is a popular Chinese brand specializing in the area of Tube Headphone Amplifiers. 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 & V2 amps, which were budget friendly, yet performing, which won ears of many enthusiasts. The S1 is the lone solid state counterpart of these amps, and hence subsequently will sound most accurate, neutral and cleanest of all Bravo amps. The S1 amp is also the smallest & most reliable amp from Bravo.
    Specifications of S1:
    Input Power: DC 24V 1.5A
    Input Sensitivity: 480mV
    Input Impedance: 100KOhm
    Headphone Impedance: 20~600 Ohm
    Frequency response: 50Hz-20 KHz +/- 1.5dB
    Signal/Noise Ratio : 68dB      Gain: 16.21dB
    THD: 0.060% (5mW) 0.12% (30mW)
    Noise: 600uV

    Let us see what the S1 amp has got for us,
    Packaging and Accessories: The S1 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.

    Design and Build: The S1 has a very good overall build quality. Its design is decently practical. Though it is enclosed in open acrylic sheets to save manufacturing costs, and also for funky DIY looks. The S1 looks much different& funky, and stands out from the crowd. It looks more of a DIY-amp. Even then, the open case is of good quality transparent fiber & metal supporting beams. The transparent sheets make us gaze through it and onto the well soldered circuit board. The S1 is fairly small in size (smallest & most compact of all Bravo’s amps, with V3 being the largest in size). The S1 is light in weight, & weighs under 250 grams.
    At the front we have volume knob, ¼” headphone output socket & an on/off toggle switch At the rear side of S1, we can observe the presence of power socket & an 3.5mm input socket. 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, if not very good. The S1 amp has no manual wirings inside; 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 (IRF630N) run very hot, be sure not to touch anywhere near them, otherwise burn injuries are guaranteed!
    Since the S1 amp follows Op-amp/Mosfet design, there is a DIP8 op-amp socket present, in which we may roll any compatible dual audio op-amps. The default one is TL072ACP from Texas Instruments, & does a great job in sound quality. There also a red LED besides the op-amp socket.
    I also 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 or 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.

    Sound:  The S1 has a very clean, clear yet airy sonic character. ‘Clear& Enjoyable’ is the key word. I find it fairly accurate.  Presentation is in such a way that, mids are little more intimate, with lows & highs sound tad more relaxed and laid back. Surprisingly, stock op-amp is pretty great and does not necessarily need to be changed/upgraded. 
    Burn in: I could not notice any major sonic improvements or changes 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, and eventually it becomes 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. Also, the noise floor further went down towards complete silence.
    Op-Amp rolling:  One can roll enormous number of 8 pin dual op-amps or single channels ones on adapters. After much testing on vast number of op-amps like, 2134NA, 4562NA, 6171,6172, 2111KP, 49720HA/NA, 49860NA, 49990MA, OPA209/627 /827, I could conclude, the stock one (TL072ACP) is indeed very good at its job, is optimal for the existing circuit parameters. But after intensive testing & attentive listening, I found the 4562NA also to be a be great match, both for circuitry as well as for headphones by sound quality.
    The gain is fixed at 16.21dB, which is still quite high and certainly not recommended for IEM’s. This amp is extremely powerful and can drive any dynamic/Planar 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.  This incredible power brings out the best out of a matching headphone. But there is a firm 'pop' to be heard when amp is switched on with headphones plugged in (with default op-amp). But with replacement (4562NA) op-amps this pop disappears. Also, power distribution across the volume pot eases up a lot, becomes more even. Noise floor is audibly almost silent with demanding cans (yet i could detect a very faint hiss at max volume on the pot. There is absolutely no channel imbalance, thanks to the alps pot.
    Lows: are accurate, tight and refined; have a great impact & extension. Depth is good enough.
    Mids: Neutral & clean, but sounds a little ‘far away’ and is not intimate or forward.
    Highs: Very clear with desirable amount of sparks. They are airy with good amount of space sensation.
    Soundstage: feels airy, natural and nearly-circular. Width is very good, & depth is decent enough for imaging. Instrument separation & detailing is pretty good.
    The S1 sounded good in all genres I tried, and hence I conclude, The S1 is decently transparent, detailed but also slightly forgiving to poor recordings. Hence I can say the S1 is an all rounder. It does not compromise anything too much to affect any of its characters. 
    Another thing to mention, since S1 had ample of output power, I decided to try it on the LCD-2, after the 4562NA. Unbelievably, the combo worked like a charm. I didn't expect a 70$ typical amp to make LCD-2 sound so good. Even I had tried the Little Dot 1+, Bravo Ocean to be double sure. Yep, S1 drives the LCD-2 great. First thing LCD-2 looks in an amp is clarity & transparency, and second but important thing is: power. The S1 has both of these traits, which ultimately led to a great match between the two. I would recommend this amp for Planar magnetics.

    Comparison: There is one such Solid State amp which can put real good competition with Bravo’s S1. It’s name is SMSL sApII which is priced & available at 65$ shipped on ebay.
    SApII: It is also a hybrid design amp, and has a socket for op-amp. It has undeniably better build quality (both interior and exterior) & has fully enclosed case. By output power, I feel sApII is on weaker side when compared to the S1. The S1 is about 30% more strong in driving force. The sApII also has lower output impedance & hence the ability to drive IEM’s. But for headphones, Ultimately sound quality & Driving force of S1 prevails.
    Verdict: The sApII & S1 are both great amps but with different areas of proficiency. sApII cn drive IEM's & has fully finished casing & absence of hot mosfets. The S1 will have upper hand when it comes to clarity, output power & in controlling planar magnetic cans. In rest of the criteria’s. If output power is a factor (for demanding headphones), it is better to go with S1. If output power is not a factor (IEM's, easy to drive headphone), then sApII is the best choice for standalone amp in this price point.
    The S1 amp also has a very appreciable control for the planar magnetic cans. Just make sure to plug in a 4562NA which are easily available at a low price.

    Conclusion:  I feel the S1 is a very capable unique solid state amp in its price range. Build quality is good, sonic presentation is really appreciable; S1 is very powerful & can drive almost any cans except IEM’s & its sonic character can be tailored to meet one’s taste by op-amp rolling. The S1 sounds way better than any desktop amps in that price range one would come across in this price point; It also has a lot of output power as bonus for Planar's. At 70$, The S1 amp is hard to beat.
    Special mention is S1's ability to drive and control planar magnetic cans like LCD-2, at this price point, its appreciable trait.
    1) Build Quality: even though it is open by case, the S1 has a very good interior build. No compromise to be seen anywhere in exterior too. Circuitry is also neat & well built.
    2) Sound quality: Sound presentation here is clean & clear but yet is detailed, spacious, which is very much like-able for a attentive listen.
    3) Rolling Capability: Enthusiasts can roll great number of op-amps to alter & fine tune the final sonic character.
    4) Driving Power: The S1 amp has a sheer output power. It definitely can comfortably drive any set of cans from 20-600 ohms. Also with drives Planar's with authority. Great job!
    5) Value: The S1 is one of the two stand-alone & solid-state desktop amps in their price point (other one being sApII) which offer truly amazing price/performance ratio, considering its ability to control and drive LCD-2's.
    1) Heat emission:  Actually not really a con, it is quite normal for a hybrid mosfet driven amp. But during operation, the S1 amp gets very hot, it becomes very difficult for a user to touch the surface of amp more than 2 seconds. It is 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)


    1. GearMe
      Interesting -- a solid state amp from Bravo with rollable Op-Amps. The SNR (68dB) spec really caught me by surprise. The rest of their Hybrid Amps are all >90dB.
      One would think the Hybrid Amps might be a little noisier because of the tube...not the other way around.
      GearMe, Apr 26, 2015