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Old 10th August 2002, 06:02 AM   #1
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Default Amplifier and speaker protection circuits

I've just read the other thread and it seems like some people are really concerned with protecting their amps. They put fuses on rails, fuses at the output, speaker connection delay, DC detecting circuits, relays on rails, relays on secondaries and relays on primaries.
I've installed those circuits only once in my first amp and never did it after. The only protection I'm using now in my amps is a single fuse at the transformers primary and inrush thermistor. Never had any problem.
I wonder what other people opinon is on that subject, especially Mr. Pass' who also doesn't seem to be too much scared about proper functioning of his amps. Alephs have only output current limiter and one fuse as far as I know and they have reputation of reliable products with trouble free operation.

Any comments?
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Old 10th August 2002, 06:16 AM   #2
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I wonder why would we go through all the trouble of using special caps, resistors, HEXFRED's, silver coated OFC wire, etc, etc, and then stick a fuse or a relay contact on the DC rail or speaker output. There should be no fuses or relays after the rectifiers, it just doesn't make good audio sense.

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Old 10th August 2002, 06:21 AM   #3
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My sentiment exactly.
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Old 10th August 2002, 06:54 AM   #4
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Hi.

My Kef Reference series crossovers are equiped with "inrush thermistor" only for HF and thats it.

But what is your opinion about this soft start circuit from LCAudio and can we use the same circuit in NorthAmerica with our 120V primary side.

LCAudio

Thanks in advance.

Trigon.
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Old 10th August 2002, 07:11 AM   #5
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Because there's a speaker on the other end and they tend to be very sensitive about faults at the amp output.

Nah, seriously, i would not sleep well if i didn't know there's SOMETHING protecting my speaker (and my amp) from a fault that can, and probably will happen, sooner or later. It's a power equipment we're talking about, don't forget it.
I'm using a relay based protection on my amp, and i just can't hear any coloration whatsoever, nor i can measure any difference (even the resistance of the contacts!). This works extremely well, and has already saved a woofer while testing the amp. I mean, if you use quality relays and stuff, why would the performance have to suffer? Same deal with fuses.
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Old 10th August 2002, 08:06 AM   #6
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Trigon,

The LC stuff should work fine in the US, but you can't use the "Earth Ground" in their schematic as the only ground for your amp. They can connect together at the plug, but the ground for the amp should be connected to the chassis. You should alway try to be aware of your homes ground wiring. It does no good to use good grounding practices in your amp and have a wall socket that doesn't have a copper ground back through the breaker box to earth.

Lisandro_P,

I have never done any listening tests on fuses or relay contacts, but I know they are not made with a thought of how they may effect the sound in an audio circuit (particularly high current signal paths). If you're not particular about the sound of wire, or resistors, or any of the other components in the signal path, than fuses or relay contacts shouldn't be a problem. But, if you went though the trouble of investigating which parts will sound the best, and paid for those premium components, and went to all the trouble of sourcing those parts, you have to at least think about what a fuse or contact will do to the sound when used in the signal path. If you say that you can't hear the difference, than I can't argue that point. It's a decision you have to make for yourself. It's a trade-off between safety (for the speakers) and the sound they emit. It is not a personal safety issue. You should definitely fuse the AC power to the amp.

But Always Have Fun,
Rodd Yamas***a
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Old 10th August 2002, 09:51 AM   #7
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Granted. Always, it's about everyones tastes. I'm happy with my relays

But again, why does the relay HAS to compromise the sound? I mean, there're VERY good quality relays, fuses and fuseholders out there, thats what i meant. There's no reason why an output protection to be the bottleneck of your beloved hifi amp, if you care enough about it. For example, i'm pretty sure the contacts on my relay are far better conductors than some cheezy cables i used (not on the signal path, of coz).
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Old 10th August 2002, 09:59 AM   #8
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As an Apogee user, the penalty for dc on the output of your amp
is the ruination of your beloved speakers, finito, no more.
You can't simply slap in another driver.
At the moment my current amps have no protection and I wince every time I power them up (not good for relaxed listening).
So in my case a fairly transparent protection system would be a godsend, and the slight loss in transparency would be compensated for by the more relaxed state of body and mind,
without the need for a herbal remedy
Jules
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Old 10th August 2002, 10:15 AM   #9
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Quote:
Originally posted by Lisandro_P
Granted. Always, it's about everyones tastes. I'm happy with my relays

But again, why does the relay HAS to compromise the sound? I mean, there're VERY good quality relays, fuses and fuseholders out there, thats what i meant. There's no reason why an output protection to be the bottleneck of your beloved hifi amp, if you care enough about it. For example, i'm pretty sure the contacts on my relay are far better conductors than some cheezy cables i used (not on the signal path, of coz).
I agree with this. I normally use a special output relay in the speaker line. It has dual contacts: a 100 amps (yes, 1-0-0) wolfram contact closed first, next the gold contact closes over the wolfram contact. Opening sequence is reverse of course.
In my experience, disaster rarely strikes at you own place. You know your amp, your speakers and you control what's going on. My problems always have occured when I leave my amp with a friend who does things I have never anticipated. This can range from defective speaker cables to preamps that give out hughe switch-on/off pulses.
So, I feel better with those relays. Y M M V.

Jan Didden
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Old 10th August 2002, 01:28 PM   #10
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I checked LC Audio site and Mains Filter seems to be interesting. What is 250V VDR in the schematic?
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