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Old 21st January 2012, 04:40 PM   #1221
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by tvrgeek View Post
I was surprised at Cordell's measurements of switch and relay contacts. I did hot think it was that bad. It does not say much for the consumer amps assembled with wire-wrap now does it?
I was unsurprised.

Quote:
Originally Posted by tvrgeek View Post
What relay spec is suitable for output protection and still be very high quality?
Non I care to to use.

I work on the principle that the speaker protection is there to protect the speaker from a defective amplifier. I therefore use crowbar circuits on the principle that when they actually engage the amp is already broken.

Just in case this is actually not the case and the protection circuit was triggered by DC on the CD (there are some such) I first mute the Amp which has a relay that pulls much faster than the big output crowbar.

So far I have not had any amp fail that had this arrangement and take a speaker out and I am not aware of any Amp that was taken out by the protection circuit engaging in error, from multi-killerwatt 20" borg cube Pro-Amp's I build in the 80's (they used Fets for mutes and industrial triacs for crowbar) to more modest domestic Amp's.

On the other hand in my Pro-Day's I had multiple times speakers taken out by amp's blowing up when the relay did not release cleanly and instead arced and welded shut...

Ciao T
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Old 21st January 2012, 04:45 PM   #1222
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Quote:
Originally Posted by scott wurcer View Post
That leads to confusion too, SPL is dealt with like voltage (mV/PA for instance). If you want real confusion photodiodes are A/W.
I am confused already on questions how acceleration of air movement is related to electrical power applied to the speaker, how SPL is related to loudness, and audibility of reproduction errors to SPL.
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Old 21st January 2012, 04:54 PM   #1223
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Quote:
Originally Posted by ThorstenL View Post
Hi,



Thank you, but no. These Mozzies are worse than those in West Africa! Probably carry Malaria too (sure killed a lot of Gulag inmates).

Ciao T
My point was, subconscious competence to kill that flying beasts without paying attention. Just by sound localized in 3-D around head and body. Now, calculate precision that subconscious mind uses to localize sound sources when they are dangerous, or annoying...
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Old 21st January 2012, 04:59 PM   #1224
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by Wavebourn View Post
My point was, subconscious competence to kill that flying beasts without paying attention. Just by sound localized in 3-D around head and body. Now, calculate precision that subconscious mind uses to localize sound sources when they are dangerous, or annoying...
Sure. Sounds like fun.

Would you mind if I decline any actual empirical research on the subject and leave that part to you...

I already did my stint in west africa.

Ciao T
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Old 21st January 2012, 05:59 PM   #1225
a.wayne is offline a.wayne  United States
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Whoooa, you guys been hitting the sauce early today i see......
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Old 21st January 2012, 06:01 PM   #1226
Pano is offline Pano  United States
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Old 21st January 2012, 09:33 PM   #1227
tvrgeek is offline tvrgeek  United States
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Hmmm, If I sense DC, then I really should put the relay in the AC and that way it stays clear of the audio. It would let me put in a remote trigger to. Then rely on the fuses to protect the amp. It does not solve a turn on delay mute though.

That leads me to another question. I have seen the speaker fuses put inside the feedback loop. The DH-200 does so. If the fuse blows, does that not remove the feedback and do potentially not very good things to the amp, or do things just bounce off the rails a bit and do no damage as the output current is zip?
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Old 21st January 2012, 09:53 PM   #1228
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Quote:
Originally Posted by tvrgeek View Post
Hmmm, If I sense DC, then I really should put the relay in the AC and that way it stays clear of the audio. It would let me put in a remote trigger to. Then rely on the fuses to protect the amp.
Err, aren't DC protection circuits in amplifiers to protect the speakers not the amp ?

Once there is a fault that is putting DC on the speaker output something major has usually already blown, (shorted output transistor etc) and its too late for the amp. Let the fuse blow to prevent a fire or complete meltdown of the amp...

The important thing is to get the DC disconnected from the speakers ASAP, (within milliseconds) and that can only be done by disconnecting the output of the amp from the speakers.

If you just switch off the AC (before or after the mains transformer) there will be enough storage in the filter capacitors to maintain DC output long enough to potentially do serious damage to the woofers, and it may prevent the fuse from blowing as well - thus subjecting the speakers to second and subsequent blasts of DC if the owner switches the amp off and on again a few times.

With a conventional DC protection system with the relay on the output the speakers are disconnected quickly enough to avoid damage and the fault current is allowed to continue long enough to blow the fuse thus preventing any further DC spikes if the equipment is turned off and on. (Albeit at the expense of probably blowing up more components in the output stage)

Good amps are relatively cheap, good speakers can be very expensive. (Not to mention the sentimental attachment if they're DIY) I know which of the two I'd rather be protecting in the event of catastrophic failure
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Last edited by DBMandrake; 21st January 2012 at 10:00 PM.
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Old 21st January 2012, 10:18 PM   #1229
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Tvr, learn electronics design engineering, and it will all become understandable. '-)
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Old 21st January 2012, 10:49 PM   #1230
tvrgeek is offline tvrgeek  United States
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Appreciating this is yet another very complex problem, and neither easy nor cheap to do well. Going on the assumption a DC fault is inductive of blowing half the outputs or a driver already, then the crowbar approach makes sense. Thinking out loud here, I could then assume a triac would be sufficient to protect the speakers and eventually blow the rail fuses if an output was shorted. To keep it from stewing in it's own juices, I still should take down the AC. Fifty percent solution maybe. An external fault like a shorted cable would still likely take the amp out. I can vouch for a fuse not protecting the amp anyway. (Waiting on my mosfets from England).

Then I address the turn on delay with just a decent relay on the output. But now I need to protect it from arcing, so I need to mute the input until it has closed. Round and round it goes. I can see the advantage in just buying an amp and assuming the designer did everything perfectly. Hard to worry about what you don't know to worry about.

Going by my rule that I am too cheap to follow, speakers should cost several times the amp or the next best investment would still be speakers. Well, I buy my amps cheap used, and build my speakers, so maybe not "several times".
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