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Thread: IMF ALS30

  1. #41
    Join Date: Feb 2013

    Location: W Lothian

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    I'm Grant.

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    Quote Originally Posted by RothwellAudio View Post
    What I said above refers to transistor amps only. Most valve amps have an output transformer which will block all DC. Some valve amps have output coupling caps, but they are quite rare. I think Croft used to do one and I think Graaf amps are designed that way.
    What was your amp?
    was a wad.. yup if memory serves it was a coupling cap
    Regards,
    Grant .... ؠ ......Don't be such a big girl's blouse

    I've said it before and I'll say it again: democracy simply-doesn't-work
    .... ..... ...... ...... ................... ..... ..... ..... ..... .....
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    Oh my god! There's nothing wrong with the bidet is there?

    “Nothing discloses real character like the use of power. It is easy for the weak to be gentle. Most people can bear adversity. But if you wish to know what a man really is, give him power. This is the supreme test. It is the glory of Lincoln that, having almost absolute power, he never abused it, except on the side of mercy".

    “You see these dictators on their pedestals, surrounded by the bayonets of their soldiers and the truncheons of their police ... yet in their hearts there is unspoken fear. They are afraid of words and thoughts: words spoken abroad, thoughts stirring at home -- all the more powerful because forbidden -- terrify them. A little mouse of thought appears in the room, and even the mightiest potentates are thrown into panic.”

    "You don't have free will. You have the appearance of free will.”

    “There's a war out there, old friend. A world war. And it's not about who's got the most bullets. It's about who controls the information. What we see and hear, how we work, what we think... it's all about the information!”


    ***SMILE, BE HAPPY***

  2. #42
    Join Date: Mar 2017

    Location: West Sūţsēaxe

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    I'm Edward.

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    Quote Originally Posted by RothwellAudio View Post
    Yes, it's perfectly possible for one channel to get fried. Either thrashing the amp so the power transistors overheat or running into a short circuit could do it. Leaving speaker cables unplugged from the speaker, dropping them on the floor so the red and black touch and still having the cables plugged into the amp (whilst switched on) could induce instant and terminal injury to the power transistors. They can die in a fraction of a second and put the total DC from the power supply across the output terminals. Then you plug the cables back into the speakers and ... oh dear

    Just as an aside, power amps can employ quite sophisticated circuitry to prevent this from happening and make the amp "bomb-proof". However, does it have an adverse effect on the sound quality? Many people believe so, so there are amps which can be quite robust as long as they're never shorted-out - but in danger of blowing up if they are.

    More likely power transistor failure.


    If using an unknown amp, switch it on first without speakers connected. Use a multimeter to measure the DC at the output terminals. Up to about 100mV is ok. Over a 100mV, looks dodgy. 40 volts? Switch it off!!!

    You could put a capacitor in series between the amp and speaker as a safety measure, but it would have to be such a huge capacitor that it isn't really practical.
    Thanks Andrew

    This actually I think completes the picture of the blown bass drivers of the IMF speakers.

    The seller mention that when he plugged in an amp it went bang/pop etc.

    The speakers came with some very dodgy cable which I threw out. Just retrieved them to take a pic and as can be seen the covering was brittle exposing the wires. Likely that when he plugged the amp in he disturbed the wire, creating a short, blowing the rh amp channel and then the bass drivers.

    He had the speakers for 18 years and one lapsed moment destroyed his pride and joy.

    Thanks for the tip on measuring a solid state amp output.

    On RCA outputs, to test say unknown items, what would I be looking for?

    Edward





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  3. #43
    Join Date: Feb 2013

    Location: W Lothian

    Posts: 99,005
    I'm Grant.

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    that speaker cable is one hell of a lapse
    Regards,
    Grant .... ؠ ......Don't be such a big girl's blouse

    I've said it before and I'll say it again: democracy simply-doesn't-work
    .... ..... ...... ...... ................... ..... ..... ..... ..... .....
    FIIO K7 BT, M11 PLUS, BTR7, KA5 - OPPO BDP-103D - PANASONIC UB450 - PANASONIC 4K ULTRA HD TV - PIXEL 6 - AVANTREE LR BLUETOOTH - 2* X600 SOUNDCORE - HEADPHONES INCLUDE, FIIO, NURAPHONES', FOCAL, OPPO, BOSE, CAMBRIDGE, BOWER & WILKINS, DEVIALET, MARSHALL, SONY, MITCHELL & JOHNSTON - 2*ZBOOK'S- MERCURY BD ROM, ROON, QOBUZ, TIDAL, PLEX, CYBERLINK, JRIVER - MULTI HDD'S -

    Oh my god! There's nothing wrong with the bidet is there?

    “Nothing discloses real character like the use of power. It is easy for the weak to be gentle. Most people can bear adversity. But if you wish to know what a man really is, give him power. This is the supreme test. It is the glory of Lincoln that, having almost absolute power, he never abused it, except on the side of mercy".

    “You see these dictators on their pedestals, surrounded by the bayonets of their soldiers and the truncheons of their police ... yet in their hearts there is unspoken fear. They are afraid of words and thoughts: words spoken abroad, thoughts stirring at home -- all the more powerful because forbidden -- terrify them. A little mouse of thought appears in the room, and even the mightiest potentates are thrown into panic.”

    "You don't have free will. You have the appearance of free will.”

    “There's a war out there, old friend. A world war. And it's not about who's got the most bullets. It's about who controls the information. What we see and hear, how we work, what we think... it's all about the information!”


    ***SMILE, BE HAPPY***

  4. #44
    Join Date: Feb 2008

    Location: Middlesex, UK

    Posts: 4,481
    I'm Alex.

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    Quote Originally Posted by walpurgis View Post
    I've not built a half wave box, but I'd imagine the bass output may be rather prodigious and tricky to keep under control with no useful benefit in performance over a quater wave, the extra complexity and bulk would be unwelcome too. I'd bet money that IMF would have experimented with this though.

    A good quarter wave speaker can sound amazingly good through the bass. I've heard loads and built a few.

    Even small ones deliver excellent sound, here's some info on a development of the seventies Daline design: https://www.blackdahlia.com/html/tip_80.html

    The original used a 5" KEF B110 and went down to 30Hz believe it or not.
    I have original Dalines 3 unit version, KEF B110, KEF T15, Coles 4001G, and yes, even with the small B110 they go down really low, I would say lower than 30HZ. However, one can't have disco levels!

    The two unit version was B110 and T27.

    Daline.jpg
    Spendorman

  5. #45
    Join Date: Mar 2017

    Location: West Sūţsēaxe

    Posts: 2,015
    I'm Edward.

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    Quote Originally Posted by struth View Post
    that speaker cable is one hell of a lapse
    QED Qudos shite.

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    Current: [P20] Roon/Tidal > Custom PC> Chevron Paradox NDF16 > Phast Pre > Neuro. 686 > Tannoy Berkley (RFC tweaks)


  6. #46
    Join Date: Mar 2017

    Location: West Sūţsēaxe

    Posts: 2,015
    I'm Edward.

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    Quote Originally Posted by RothwellAudio View Post
    Yes, those speaker cables were in a very poor state and look like an accident waiting to happen - which it did

    RCA outputs? As in pre-amps etc? They're often DC blocked anyway but it wouldn't do any harm to measure the output for any DC. Any more than a few millivolts (ten?) would give me concern. Even so, it probably wouldn't cause catastrophic failure because whatever it's connected to will probably have DC blocking at its inputs.
    I was just thinking of how to check for correct operation and possibly have a source playing through it. So, for example, an old cassette player or CD player.

    As mentioned earlier I normally use a sacrificial amp or speaker to test things but easier just to use a multimeter.



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  7. #47
    Join Date: Jun 2015

    Location: London/Durham

    Posts: 6,869
    I'm Lawrence.

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    Quote Originally Posted by Edwardlon View Post
    QED Qudos shite.

    §
    I got some with an amp I bought, it was also cracking in places, I thought it must have been placed behind a radiator or something but may have been a design flaw in the choice of plastic.

    Sent from my BLN-L21 using Tapatalk

  8. #48
    Join Date: Apr 2012

    Location: N E Kent

    Posts: 51,624
    I'm Geoff.

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    As there were questions about amplifier failure, I thought this might clear things up: https://www.analogbros.com/tech/articles/goodgobad.html

  9. #49
    Join Date: Mar 2017

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    I'm Edward.

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    So after a bit of a lul I've managed to source some correct drivers for this project from the USA (thanks Grant) and today plugged them in. Mind you a bit of a faff bringing stuff in from abroad what with import duties and Parcelfarce seemingly having a monopoly on imports. But no damage thankfully.

    Immediately obvious that these speakers are something special. Full coherent sound across the range with great definition and punch. Played my usual array of test tracks and the IMF comes up trumps. No wilting around the edges and running away.

    As the speakers have the active lines to boost the bass I played tones through it. And yes they do go low. Good tight sound at 30hz and improves from there. Obviously not bass that rocks the walls (and anyway only two 6 inch drivers) but nice bass. On the other extreme I could get to circa 15khz but nothing beyond that. But I assume that is more a factor of my hearing and/or the aged caps.

    So now will ponder if I do a recap and wood restore. I think a recap will enhance the definition and open the sound up in a worthwhile way.

    Although the baffles have screws it looks like they are solidly glued down as well so may be an issue of getting to the crossovers easily. The crossovers can be seen from the bottom bass driver but can't be retrieved without removing the baffle.



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