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Fix it time for PC monitor speakers

Posted 16th December 2013 at 05:23 AM by fas42
Updated 22nd June 2014 at 06:35 AM by fas42

Bummer!! After mentioning that Brad's (bcarso) units were doing very nicely I swapped CDs while they were set to max. volume, doing a good job on a classical piece. Unfortunately, the new disk was heavily compressed pop, my mind was elsewhere, and I hit the volume control a second too late - everything's OK except the right speaker has dropped about 6dB in volume, ...

I suspect that some protection circuitry has tripped, but it's not resetting. Which means, unless anyone has a good idea otherwise, that I'll have to dive inside and sort things out. But, on the other side of the equation that may be an excellent thing to do, it will give me a chance to do some more adventuresome tweaking ...

Trouble is, I'm lazy ...
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  1. Old Comment
    fas42's Avatar
    Success!!! Sometimes, instincts work for one ... on a hunch, I fed the speakers ramped 100Hz tones up to, and past max volume levels - you could hear the circuitry spluttering trying to process the signal - and, it managed to reset the protective attenuation, that was frozen into being on! Right speaker is back up to normal levels - would be interesting to understand exactly what might have happened, but I'll leave that for another time ...
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    Posted 17th December 2013 at 01:27 AM by fas42 fas42 is online now
  2. Old Comment
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    That another time is coming up ... because I've been driving these speakers fairly hard on occasion, they're getting a bit rattly - on the inside, so to speak. In particular, the volume control which I normally set on maximum to minimise the grubbiness introduced by every pot, is getting very flakey - the vibration is causing the pot's internal contact areas to deteriorate badly, easily heard spluttering on strongly bassy material is the result.

    So, pull it apart and see what's there. Apart from a little battle because not enough screws were undone, no prob's - and very little inside. Key component is a basic stereo chip amp, TDA2007A, with a BA4560 dual opamp doing some buffering. Speaker drivers as usual are pretty decent, a good magnet assembly - these are the least of my worries ...

    First up, bypass as much of the usual weaknesses as possible: the connectors, switches, pots - all the really junky stuff; simplifying the circuitry, paring it down to only what's needed.

    The key problem is that the chip amp is single voltage supply, so cheap, electro decoupling caps are everywhere - this is why the unit sounds terrible on switch on, it takes an hour or two before these parts are vaguely working properly.

    And, power supplies: single 3,300uF - might try intelligently upping this by an order of magnitude, to give the beast vastly better energy reserves - and other bypassing strategies ...
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    Posted 16th March 2014 at 11:34 PM by fas42 fas42 is online now
    Updated 16th March 2014 at 11:41 PM by fas42
  3. Old Comment
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    Geez, I'm slow these days ... something creeping up, perhaps, . Finally, did the first round, all the usual suspects - fired up, from dead cold, straightaway, much bitier sound - more of the gutsy PA thing. Let it bed in with a bit of a local hero, Guy Sebastian , doing his take on the Memphis classics - recent recording, so plenty of upper mid-range bite.

    What's been lost, is much of that dead, midfi sound - tons of life and drive now, even in an extremely no-optimised state ...

    Now a bit of Rodrigo, imaging very nicely, guitar working well - and the setup is rough as guts at the moment, cables everywhere where they shouldn't be - a good sign ...
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    Posted 22nd March 2014 at 01:42 AM by fas42 fas42 is online now
    Updated 22nd March 2014 at 02:33 AM by fas42
  4. Old Comment
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    Whoa, whoa, whoa ... see below, ...

    (Bugger!! I've been caught in the usual audio trap, that of improving one aspect which then merely serves to show that another area also needs attention - the analogy is having a normal car, and you hot up the engine a bit, which very quickly makes you aware that the gearbox won't handle the extra power smoothly, and the suspension is suspect ...

    First signs were very promising, but it's not bedding down so far - the sound is more sensitive to everything, it's veering too much into that typical, hifi, edginess - I was pleased to unplug the power supply!

    So, a decision time possibly coming up ... do I persist in sorting out issues; or, say it's not worth it, the value isn't there in the bits - it's too complicated for the benefit gained, and just do something to dumb down the sound ... hmmmm ...

    I've been here many, many times before, with other setups ... but I may give this one a miss ...)

    Hold your horses, I say, I say, boy! The above is a good example of how easily it is to go astray - the sound was not working, and I was going all negative about it. Then I chanced to see that the transformer feed cable was looped from all the fiddling, in a bad place, and hidden from view. Aha, the guilty party?!! Yes, indeed - dress it correctly, and voila, the sound snapped into place!!

    A very good example of how the slightest aspect can be critical, and catch one out, no matter how many times before it's happened ...
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    Posted 23rd March 2014 at 04:27 AM by fas42 fas42 is online now
    Updated 23rd March 2014 at 05:51 AM by fas42
  5. Old Comment
    fas42's Avatar
    Might just mention that playing items like classical tracks is a doddle, it's only heavily compressed, very high energy material that taxes the miniscule power supplies - and brings problems to sharper focus. Just playing some Ravel, Live from the Proms, now - operatic voices doing nicely, good triangle, etc ...
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    Posted 26th March 2014 at 01:34 AM by fas42 fas42 is online now
  6. Old Comment
    fas42's Avatar
    Bizarrely, what's catching out the speaker driver construction - just thin punched metal, of course - is absolutely pure meditation music: Drift Away - Music for Relaxation. This is largely sequences of long, pure tones and harmonics - and guess what, at higher volumes all sorts of subtle resonances and vibrations are excited, and sustained - easy to hear little, subtle metallic buzzing things happening, which shouldn't be there. Plus, good for catching bass drivers out - some very deep tones there, flakey bass units and setups will make themselves obvious ...

    Edit: the more I listen to this set of discs the more impressed I am with their ability to unearth problems - in particular, interference issues. I've only had the album set for a short while, and they have the marvellous knack of sounding terribly dreary and nothing when the SQ is below par, and to completely transform when things are in alignment. The music happens very, very slowly so plenty of time to catch whether something is "happening", or not ...
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    Posted 26th March 2014 at 04:19 AM by fas42 fas42 is online now
    Updated 26th March 2014 at 05:46 AM by fas42
  7. Old Comment
    fas42's Avatar
    Well, I'm rather pleased - by dint of enough fiddling, and general fooling around I've worked out a pretty reasonable combination of temporary tweaks, fixes to lift these speakers to the point of decent disappearing - no actual further tweaking on the insides, just trying to create as electrically benign environment around everything as possible ...

    As usual, that old bugbear, static induced interference was a major offender - will have to work out some better arrangements to keep this at bay.

    Have got on now one of my fav' torture albums - Southern R&B, tons of very busy, upper midrange EQ - and it's going very nicely ...

    Edit: what I always look for, unconsciously mostly, is for a system to give me a good endorphin hit - and it's especially satisfying when it's not really expected, it comes as a bit of a surprise. This is what I got today, so quite chuffed at the moment ...
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    Posted 3rd April 2014 at 02:28 AM by fas42 fas42 is online now
    Updated 3rd April 2014 at 04:36 AM by fas42
  8. Old Comment
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    Some interesting behaviour occurring, timing is everything ...

    In the course of trying something, I fed near full level 15kHz sine waves into the speakers - the correct tone was certainly there, but very obvious were some pretty loud artifacts, way down in the midrange. Even more interesting, a particular "note" would appear at precisely a certain volume, above and below that setting that artifact disappeared.

    So, was this the speakers/amplifier, or the DAC/source misbehaving? Easy to test, pull the power on the speaker setup, and leave the player running at full volume - previous experience demonstrating that warm-up solved many things ...

    And, somewhat later, try powering up the speakers again - immediately, quite a bit better, and that peculiar level dependent artifact was gone. This demonstrates quite clearly that electronic misbehaviour in areas directly relating to the DAC can very much be part of poor sound ...
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    Posted 8th April 2014 at 06:01 AM by fas42 fas42 is online now
    Updated 8th April 2014 at 06:04 AM by fas42
  9. Old Comment
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    A thought - the chip amp powering these is a nothing thing, on just a rectangle of aluminium as a heat sink, only capable of a few watts per channel at reasonable distortion spec's, yet the subjective impact is far, far more than this would imply. Yesterday, running highly compressed, dense modern rock you could easily hear the limitations of the miniscule power supply doing its best, yet really only the major problem was that the sparkle of the cymbals, etc, was steadily lost and squashed as the volume was pushed - it was capable otherwise of clean, "deafening" volumes, that would start my ears ringing if I sat too close for a decent period.

    It also has that telling property of not changing its character as the volume drops - going from a reasonable max - some obvious soft clipping - down to the lowest that the digital volume would do, in its coarse decrements - the tonality of the sound doesn't significantly alter - the same intrinsic 'bite' of the recorded sound comes through ...
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    Posted 11th April 2014 at 10:44 PM by fas42 fas42 is online now
  10. Old Comment
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    Worth repeating, yet again, that the mediation music CDs are quite brilliant at pinpointing the SQ - one's subjective involvement with these lives and dies by the harmonic quality of very slowly building and decaying, pure and frequently very high frequency, tones, sound envelopes; if these are not exactly right the "music" is extremely forgettable, totally bland ...
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    Posted 19th April 2014 at 02:18 AM by fas42 fas42 is online now
  11. Old Comment
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    Audio never loses its ability to surprise - and enchant me ... I was inspired to try another bit of tweaking, because a classical piece, a no-name recording of Brahms Trios, made it clear that interference effects from other electricals plugged in were still a very significant factor. So, resorted to nothing more than a bit more of reorganising where the essentials were plugged into the mains - and, very nice benefits: a mid 80's DG recording of Prokofiev and Ravel violin and piano sonatas projects lovely tone and air - the big space around the instruments comes through beautifully ...
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    Posted 24th April 2014 at 12:59 AM by fas42 fas42 is online now
    Updated 24th April 2014 at 01:04 AM by fas42
  12. Old Comment
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    The current fad for fake, old style recording sound in some recent pop albums is quite testing on the SQ abilities of the system - there is absolutely no margin of error. Being a replica of something that happened naturally, back when they were actually trying to do decent recordings, this faux version has an extra layer of 'sludge', from the deliberate manipulation side effects. Very testing material ...
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    Posted 6th May 2014 at 02:28 AM by fas42 fas42 is online now
  13. Old Comment
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    Just tried an organ piece from YouTube on the little fellows, wasn't too bad considering all the usual fine tuning hadn't been done. I might have a go shortly at recording what it sounds like, when running in a decently stabilised tune - from nearby, and then the other end of the house. Either tape this piece, or something similarly grand - and post it ...
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    Posted 15th May 2014 at 12:00 PM by fas42 fas42 is online now
  14. Old Comment
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    Need a bit of time "space" to do the recording of this and/or Karl's piece reasonably well, too much going on at the moment, hope to get something decent done tomorrow ...
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    Posted 18th May 2014 at 01:08 AM by fas42 fas42 is online now
  15. Old Comment
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    Boy, do I hate software - have I mentioned that before, ! Anything infected with Microsoft crud becomes a monster at times, this sort of thing burnt me out on the industry years ago ...

    Did some recordings, quite reasonable, let's transfer to the Windows XP machine ... uh, oh, Windows Explorer goes into total meltdown because the file is too large, ends up completely deleting the destination directory, which had other files on it, because it lost the plot. So guess what - Bill Gates is one of my favourite people ... .
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    Posted 19th May 2014 at 01:54 AM by fas42 fas42 is online now
  16. Old Comment
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    And, I also hate websites - dropbox does things just enough in a slightly non-intuitive way, to really bug me - by the time I've worked out how to make dropbox do what I want, I'm in a really bad mood ...

    Anyway, here are a couple of fun files that I did while warming up the speakers - ran out of time to do the organ piece:

    Some gutsy saxophone playing done in the mid 50's, from CD:
    https://www.dropbox.com/sh/y918d183r.../SamButera.wav

    Scott Wurcer's selection of a 'prime' piece, ripped from a YouTube video:
    https://www.dropbox.com/sh/y918d183r...MachineGun.wav

    Both run at max volume, the Butera recorded in same room with mic about 3m away, pointing in the wrong direction; Hendrix from the other end of the house, as far away as I could get without going outside.
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    Posted 19th May 2014 at 08:00 AM by fas42 fas42 is online now
  17. Old Comment
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    'Tis truly amazing how people can say how digital interference is not a factor in SQ - my wife was working on the PC, at the same time as some classical music, designed to be very backgroundy was playing on it ... this was starting to bug me, a slow buildup of an irky unpleasantness about the sound was disturbing me. Finally, she stopped what she was doing, and shut down the editing program - aahhh, the relief! Soothing music again ...
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    Posted 21st May 2014 at 03:06 AM by fas42 fas42 is online now
  18. Old Comment
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    One of the recent YouTube videos mentioned in the music playing thread is very pointedly highlighting the speakers' problems in the 100 - 200Hz range - these seem to have got a bit worse lately, possibly from the capacitors getting old fast, or some side effect of fiddling. Using a ramped up and down tone at the particular frequencies, a buzzing artifact gets on board, and disappears, which differs per speaker - always another round of troubleshooting! Also, these sort of test signals make it easy to hear the DAC playing up when cold, all sorts of little peculiar sounds mixed in until it fully stabilises.
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    Posted 22nd May 2014 at 11:04 PM by fas42 fas42 is online now
  19. Old Comment
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    Having car troubles at the moment - don't we all! - so still haven't got the organ piece done, later this week hopefully ...
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    Posted 26th May 2014 at 12:48 AM by fas42 fas42 is online now
  20. Old Comment
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    Duuuhh ... still haven't done the organ piece, life conspires at the moment, unfortunately ...

    Anyway, a big sigh of relief - I had an album from the library, MPD Limited, 60's Oz pop, which was a very bad transfer, or the master was in poor shape. The sound was almost impossible, and I thought I might not be able to recover listenable quality ... so today I pulled out a lot more stops, essentially making the playback electrical environment even more benign than usual - and that did the trick, high 5's!!! The recording has lots of upper midrange, and reverb was used freely in the production; combine that with poor transfer quality, and it's a recipe for an audio headache! Absolutely minimal degradation in the playback chain is essential for such recordings to bear fruit, and I needed more rounds of effort than usual to get the inherent distortion under control ...
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    Posted 22nd June 2014 at 06:23 AM by fas42 fas42 is online now
 
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