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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. shabtronic
    Hi there folks
    I'm a bit late to the bravo audio party - but hey I did finally manage to make it!
    I got the Bravo V1 - with Russian tube about 3 days ago - and it's blown my mind - sounds so damn good. I'm using Senn's HD419 with the open vent mod and it sounds amazing - monster bass that is detailed and tight without killing the tops. Even my crappy AC97 motherboard sound card sounds musical with the damn thing - it is amazing.
    Until today I switched on my little wonder amp - and bam - started pulsing - a 1 second cycle - the pulse is the LEDs starting from dim then growing bright (both LEDs) over a 1 sec period then starting again, repeating forever!. I did attempt to read every message on this post - and I found a few with the pulse issue - but no solution or reason for it. Because it's xmas time and sending it back from UK to HK is a no no, I suspected it was the power supply - I have no clue about electronics - so I jumped in and tried a 27V 2A switched power supply I had (creative labs speaker PS), using that it goes thru it's pulse cycle 7 times - then eventually works - sounds good again. Yaaay!
    Does anybody know the impact of using a 27v supply on the thing - or even how to fix the pulsing - it seems like some sort of feedback loop (I'm guessing wildly here !!) that gets stuck. But before this happend it was amazing and I really want the thing to work again!
    many thanks
  2. Cirric
    Shabby, I know your pain! My first V3 (same electrical design) did the same thing but with a little different pulse. A low quick 3 burst pulse in about a quarter of a second that lasted about 1 second before repeating. Removed the top plex ond tryed turning rhe 2 tube bias pots. (Factory said to try this.) Did not fix the problem. Did the same as you, reading through the posts. Bought some new parts but never put them in (nerve problems in my hands.) Finally bough a second unit which sounded great until it developed the same trouble as the first unit. I resorted to using a Fiio E6 until the Bravo is repaired. But I miss that tube sound! I will continue to follow this thread hoping for a fix. Good luck!!
  3. shabtronic
    Hi Cirric
    Yeah - the damn thing it's killing me - that sound is so good !
    I've contacted the Seller in HK and they suggested trying a  new tube - I don't think its that. I contacted Bravo Audio but have not heard back from them yet. With the 27v it does work after a few pulse cycles - but I'm reluctant to use it - it feels like it's "rigged to blow" lol. I'm not going to get another unit - because it feels like cheap power + cheap components - and if my mains is dirty or whatever caused the problem - it's just going to happen again. I'd like to find out what the cause is (cheap caps? cheap PS) and fix it at the root.
    The sound so good - it feels like I've just set sail on a lifelong quest to fix the thing :p
  4. Didhefocus

    My V3 didn't pulse but after about a year it started shutting down when it warmed up after a minute or so. It turned out to be the LED under the tube. I just piggy-backed another LED underneath so I'm not sure if it was a bad LED or just a bad solder joint.
    About the 27 volt power, while 3 volts difference isn't much It could put extra stress on tightly spec'd components such as capacitors rated at 25volts. During my modding I made sure all capacitor voltage ratings were a little higher than stock. 
  5. shabtronic
    Hi Didhefocus
    yes I looked at that first 25V cap - I guess that's a power smoothing function or something (I have no idea really just guessing!)
    Thx for the info on the LED. That's one of the thing I was thinking of doing - just upgrade all the components and hope it makes the thing more robust! But I have no idea about electronics or how the thing works really so I guess doing that could break its wonderful sound?
  6. Didhefocus
    I was impressed with the sound with no mods at first but when I read about the crosstalk distortion and was able to identify it I couldn't NOT hear it. It then sounded terrible to me until I changed the output MOSFETs from IRF630 to IRL510. If you do only 1 mod, do this one, you won't regret it!
    The 2 LEDs are part of the power circuit but only the red one is critical, I wouldn't change it unless it goes bad.
  7. shabtronic
    Interesting! thx for the info - it's great to see a healthy mod vibe with this device.
    Mine sounds really nice out of the box - I have the electroharmonix tube 6922EH - and it sounds wonderful. I write DSP software and all that jazz so I know a little about sound - and what the device sounds like it's doing is: a lowpass filter at 10-12khz, some compression and some some sigmoid type distortion (to recreate the highs lost from the LPF) - that's what it sounds like - it's probably not doing that but some other analytical voodoo magic that the tubes do!
  8. Mike12345678

    Hi, first post so "Hello" , anyway-the reason i registered, i received my Bravo Audio V2 in the post today set it up and started listening to some music, after about 10 minutes the blue LED started to flicker, odd i thought, so i paused the music and there was audible interference that was in time to the flickering, the noise was the same volume irrespective of the volume position, i decided to leave it turned on but with no input, eventually the Blue LED went out completely and the interference disappeared, i am currently still listening to it and it sounds great.
    Thing is do you think it's alright? I'm not worried about the light not glowing, but is it, or will it cause a problem in the future?
    Any thoughts gratefully appreciated.
  9. Didhefocus

    Welcome to the forum Mike,
    I'm sorry you are having problems with your Bravo so soon!
    Mine would stop playing completely but would work again after a cool-down period. It's curious that on yours, the blue LED would be out but the amp is still working. You should check the bias since the voltage regulator is controlled by the LED circuit. You may be overdriving the tube which can shorten its life. Check earlier in this thread or the one I started on the V3 for info on checking the bias.
    Installing a new LED fixed mine and it even warmed up much faster from then on (15 seconds vs 45).
  10. Didhefocus

    Here's the V3 schematic.
  11. Didhefocus
    Sorry but I forgot that you have a V2 when I commented last. The V2 doesn't have bias adjustment pots like the V1 or V3 so I'm not familiar with that bias circuit.
  12. Mike12345678
    Hi, no problems, i may contact the seller and pose the question, i've ordered another tube anyway (a Mullard) so if this blows, and depending on time span i may  ask for a replacement.
    Still, not massively expensive if it all goes pear-shaped.
  13. Cirric
    Hi, I ordered and have the IRL510s on hand. If I can do the mods this will be the first one. As I stated earlier, I now have two V3s, and will mod both. Thanks!
  14. shabtronic
    Here's what I've tried to fix the pulsing issue so far:
    1)    New LED across the Red LED points
    2)    New LED across the Blue LED points
    3)    resoldered all the under side points - just in case of dry joints
    4)    Messed around with bias pots 
    no joy - still pulses and does not work with the original PS, works with 27v PS but still pulses.
    I did notice with 27V PS the pulsing is faster(1.5x), usually 7 times before it becomes stable and works again - so maybe 
    it's a cap charging thing? (I had look at the schematics post on this thread - but it's all hieroglyphics to me and I don't
    understand the ciruit one bit)
    I don't have any meters or whatnot - but the original PS is still working I guess - because it still sparks
    like a demon when plugged into amp if amp left switch is on (probably a bad idea?).
    I have left amp on pulsing with original PS for 5-10 mins and nothing gets hot - tube is cold, all heatsinks are 
    cold also - it just pulses merrily away!
    I checked out component parts on ebay uk and got this so far
    Nichion 6800uf 35v     £4
    2xPanasonic 1000uf 35v     £2.49
    2xIRF630         £2.60 (I'll skip the IRL510 mod for the moment - I like the dark sound it produces with the IRF630)
    10x2N3906         £0.99
    5xLM317T        £1.98
    total:            £12.06
    Tube    12AX7/ECC83
            12AX7 tung sol        £16.25
            ElecHar            £14.95
            JJ ECC83S 12AX7        £8.99
            Mullard            £20-200!!!!
    so at the cheapest it's gonna cost £21 to fix
    Looks like I'll be soldering over xmas!!
    I will put the components in one at time and will post when/if I find out what component/s is the issue, so any body else with the
    pulse can fix it!
    many thanks for your help folks
  15. shabtronic
    So I finally got a meter and some components.
    I replaced the main caps with some of higher quality and higher voltage - didn't fix the issue.
    I put off replacing the mosfets till later (no static gear).
    but Eventually I found a old 20v laptop PS.
    It is the power supply that causes this for me - I measured on the original 24v PS and the output  was a CRAZY 29-35v - fluctuating wildly!! hard to tell because the meter was going crazy (just a cheap meter), my creative labs power supply registered a solid 26.9v. 
    I tried the amp with a known working 20v supply (switching laptop PS) and it worked just fine - no pulsing at all, a little distorted tho with breakup - I guess the lower voltage does that!
    I'm guessing the cheap ass PS you get with the V1 is really sensitive to mains fluctuations or whatevere.t.c... and borked itself somehow! Wondering what caused this?
    mains issues?
    It's probably worthwhile getting a RCD and/or a Linear power supply instead.
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