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Bravo Audio - funny looking little tube amps

Discussion in 'Headphone Amps (full-size)' started by ear8dmg, Sep 9, 2009.
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  1. money4me247 Contributor
    thanks for your quick response. besides what you've said about the volume, are there any other potential issues or inadequacies based on the specs? I am just primarily worried about sound quality.
    I've also read somewhere that you should have the output impedance of the amp 1/8 of the headphones, but from my experience a 4ohm impedance headphone amp must be truly rare as I haven't found anything like that.
  2. HOWIE13
    Isn't 92.5dB relatively low sensitivity for these types of headphones?
  3. mhamel
    I buy and sell some tubes, and before I really got into it, I invested in a good tester.   After looking at the options for vintage testers, the costs/challenges to get them rebuilt and keep them properly calibrated, I went with a modern digital tester.  http://www.maximatcher.com/maxipreamp.html   There are others out there at lower and higher price points as well.   There are some eBay sellers that are very good about testing/matching, but there are others that I also think are full of crap.   I've seen where someone posts photos of the test results of the tubes he/she sells, and they use the same photo in every ad.   Every tube shows exactly the same result?  Not a chance.    
    That's not to say that vintage testers aren't good.  For someone with the knowledge, time and experience to keep them in top shape, they can be very accurate.  In addition, sellers like Brent Jesse have curve tracers that let them plot the response curves of the tube and compare it to the manufacturer's data sheet, giving an even more accurate result on how the tube performs compared to spec.   There's a lot of time involved, that's a big part of why he's expensive.
    When I sell a tube, I test it after a brief warm up, then again after at least an hour or two to see how it has stabilized.  I record the results, then listen to it through both my tester, which is ultra-sensitive to any sort of tube noise, and within an amp.  Finally, it gets tested again after being fully warmed up to make sure the results are consistent.  Every tube gets a label with the exact results that come out of the tester, and I'm happy to explain them, how those results compare to the published data sheets, etc.
    With the Bravo amps, since there's only a single tube involved, it's easier than having to find matched pairs or quads, but you do want to make sure the tube's triode sections are as well balanced as you can find.  It's also helpful to look for a tube that's been tested for gain between the sections as well.
  4. HOWIE13
    Thanks for the advice about the Maximatcher. I'll look into that. It would be nice to think that all sellers are as thorough as you are!
  5. MaN227
    its interesting how long these have held interest
  6. mhamel
    If you'd like a decent modern tester without completely breaking the bank, check out the Tube Imp.
  7. HOWIE13
    Brilliant-it's ordered!
    Thanks again.
  8. Evshrug
    More tube sources is always a boon.

    I'm not 100% sure cryo treating provides a benefit (although superconductors usually need to be kept extremely cold before they start to super-conduct, so it seems it MAY have some legitimacy though I suspect the molecular "alignment" gets scattered a bit more every time the tube heats up, that's basic physics), but I figure they're at least decent samples of tubes.

    2x What Mike said.

    To elaborate:
    The bravo amps are just too loud for many sensitive headphones, you have to keep the volume turned down really really low to keep from damaging your hearing. When potentiometers (volume knobs) are turned down that much, they create a channel imbalance which will either sound like one earcup is louder OR just off and unnatural (good manufacturers go to great lengths to match the drivers in their top headphones). The other problem, LOUD enough doesn't always equal GOOD. Headphones need a good supply of current to have the dynamic range to supply high-energy notes like low bass and complex music passages with lots going on... It tightens up music and allows them to play smoothly. I hate the song, but Kanye West's "Gold Digger" percussion is a great example of (poor mastering and) a sound that will easily distort if the headphone drivers can't handle the excursion or if they don't get enough current to prevent clipping.

    There are many factors influencing that, but to look at it that simply is a myth. What do you think even happens when you don't have a lot of headphone impedance to dampen the amp output impedance?

    Exacerbated by that designer of the O2, the real situation where having good headphone:amp dampening is important is when the headphone doesn't have a flat impedance curve... Check Inner Fidelity's impedance curve measurement for your headphone before you start obsessing about amp output impedance. For example, Sennheiser's HD headphones often have spikes in their imp curves (so bass would be boosted and hazed over), while the AKG Q701 and Beyerdynamic DT880 (and pretty much my entire headphone collection, even the V-MODA M-100) all have relatively flat imp curves and barely change at all. Many home theater receivers have headphone output impedances over 100 or 120 ohms, but plug your headphones into them... do they sound like crap?
  9. money4me247 Contributor
    Response is in BOLD.
    In Put PowerDC24V
    Input Sensitivity100mV
    Input Impedance100KOhm
    Out-Put Impedance20~600 Ohm
    Frequency response10Hz-60KHz +/- 0.25dB
    Signal/Noise Ratio>90dB
    Dynamic range84.6dBA(300 ohm) 89.8dBA(33 ohm)
    THD0.016%(300 ohm) 0.45%(33 ohm)I
    MD + Noise:0.045(300 ohm) 0.42(33ohm)
    Dimension79mm (D) X 130mm (W) X 44mm (H)
    InputStereo RCA x1, Stereo 3.5mm x1
    OutputStereo 6.35mm x1

  10. HOWIE13
    I would agree in that I have never been persuaded by the eight times rule. The bass is meant to become somewhat uncontrolled, but I have never noticed that.
    For Classical Music and Jazz the V3 volume knob is no problem for me driving even sensitive headphones. Maybe it's because Classical music is less compressed, with wider dynamics and generally lower output. I find the useful knob range is from about '20 to' to just over the '12 o'clock' position. 
  11. UmustBKidn
    So cryo-preservation of human beings is real science?

  12. DefQon
    Cryo tubes is bigger marketing bs scam than cryo cables.
    Anyway that's not the point.
    High gain on the Bravo amps with variable sensitivity headphones? Easily fixable. Of course given the craptastic and improper components used for this particular basic class A circuit. Swap the 10K pot for a 50 or 100K (if your source can accept it). The stock pot has to go, volume doesn't go up step by step in terms of db but one little turn after 11'O clock on the dial and you go from small volume to loud.
  13. HOWIE13
    I've never noticed a particularly sensitive point whilst turning the V3 volume knob. Have just tried again now and volume increase is smooth and I can't detect that particular problem.
    I wonder if the source input voltage might make a difference? Maybe a faulty unit? 
  14. DefQon
    I'm referring to the v1. Haven't pulled a v3 apart before.
  15. money4me247 Contributor
    interesting stuff. i've ever noticed an issue finding the appropriate volume as I can adjust the volume on my laptop & my music player after turning the knob.
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