Amplifier and speaker protection circuits

[Peter Daniel]

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?

 

[roddyama]

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.

Rodd Yamas***a

 

[Peter Daniel]

My sentiment exactly.

 

[trigon]

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.

 

[Lisandro_P]

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.

 

[roddyama]

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

 

[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).

 

[Jules]

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

 

[jan.didden]

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

 

[Peter Daniel]

I checked LC Audio site and Mains Filter seems to be interesting. What is 250V VDR in the schematic?

 

[trwh]

VDR stands for "Voltage Dependent Resistor". These components exhibit a large resistance until the voltage accross them rises above a certain threshold value, when their resistance falls rapidly.

VDRs can be connected across the mains like this to absorb any large spikes, helping provide a cleaner supply. Normally they have a quoted maximum AC line voltage, so here 250V is presumably intended for use with a 220-240V supply.

Hope this helps,
TRWH.

 

[AudioFreak]

Essentially a Varistor I assume.

 

[trwh]

I think its always best to have protection circuits than to leave them out on sonic grounds. There's nothing quite like a blown pair of $500 speakers to really ruin any listening!

If you want to save your precious speakers from any large DC voltages on the output of your monster DIY amp; a relay-based protection circuit is ideal. The contacts of a high current relay will exhibit negligable resistance (far less than any sensible speaker cables).

Thanks,
TRWH.

 

[Peter Daniel]

I guess that we all can agree that if there are differences in sound with different binding posts there must be a difference with a relay too. And it doesn't have to do anything with a resistance but rather with a kind of materials used.

My initial concern was why Alephs, being commercial products, don't have DC protection circuits. Presumably there was no complains about it from a field.

 

[Peter Daniel]

Trigon,

LC Audio soft start circuit is based on 220V operation. You can see IN and OUT connections on the board. Being pretty dedicated module with digital dalay it might not work properly with 110V. As alway in cases like that, the best is to contact the manufacturer and ask them directly.

 

[roddyama]

Essentially a Varistor I assume.

In the US they're called "MOV", Metal Oxide Varistors.

I guess that we all can agree that if there are differences in sound with different binding posts there must be a difference with a relay too. And it doesn't have to do anything with a resistance but rather with a kind of materials used.

It would be good if they could come up with something remotely close to binding post construction. Many relays have steel in the conduction path, contacts horribly mis-aligned, low contact pressures, plus a NO (if it's fail-safe) coil generating rf inside your amp. Granted, this is not the best case, but it is not the worst case either. It is quite typical. In 15 years of providing dynamometer controls, I have never put or even seen a relay used in a feedback signal path. It is detrimental to signal integrity.

I sympathize with the ribbon and panel speaker users. I guess you have to do something to protect your investment. If there are relays out there that are known to have been designed with audio in mind, I for one would be interested.

Fuses, that's another story.

My thought and experiences,
Rodd Yamas***a

 

[Peter Daniel]

One solution is bi-amping. Tweeter/mid amp doesn't really need DC protection, because of the usual series cap with a driver. Then you only need protection for woofer amp and there the relay doesn't do as much damage.

 

[trigon]

Trigon,

LC Audio soft start circuit is based on 220V operation. You can see IN and OUT connections on the board. Being pretty dedicated module with digital delay it might not work properly with 110V. As always in cases like that, the best is to contact the manufacturer and ask them directly.

Hi Peter.

You are absolutely right, I have noticed the same thing and will check with manufacturer if they have any options for 120V for us. I will let you know as soon as I find out something more.

Yes, VDR stands for "Voltage Dependent Resistor" or varistor if you wish.

Thanks.

Trigon.

 

[fcel]

BOSOZ Pre-Amp turn on muting

Since you guys are talking about amp and speaker protection, I would like to ask my question here regarding to my BOSOZ.

Currently, I always turn on my BOSOZ first before I turn on the power amp. If I do that in reverse, my speaker woofer would almost seem to depart from the enclosure.

In the original article by Nelson Pass, he stated that he'll leave the "turn-on muting circuit" as an exercise for the reader. I was wondering if anybody know of such a circuit. I presumed it has to be something really simple. What I want is the output to be muted (or equivalent) for one second at turn on.

I have a "DC protection and Turn on Muting" kit from Vellerman (model #4700) and I'm thinking of installing it on my BOSOZ. I would really hate to install this kit and introduce another signal path if there is another easier and simplier way of doing it.

Any help or suggestion would be very much appreciated.

 

[cocolino]

Regarding relays in the signal output of power amps I can say something and in contrary to some others here, I do have the opinion that relays in no way are equal to a piece of cable or a good plug connection.
Once there was a problem with my buddys active speaker system I did for him. Certain frequency ranges did not work anymore after the volume felt below a particular value. I investigated everything again and again and couldn`t find a fault. The thing almost drove me nuts. After a while the idea came up, to take a look at the amps output relays more closely (for each amp output there were 2 to 3 relays paralleled!!). While doing this I was aware that by tipping on of the relais group in question the signal came back again sometimes. I desoldered the relays from the boards and measured them with a milliohmmeter - everything seemed to be okay.
I changed all the 16 relays though and since the system works again.
What can be the conclusion from this:
Everybody is talking about high current in regard to output relais in power amps and what about the small ones??
High current isn`t the problem for an appriote relay, whereas in my opinion small current is, particular when the contacts beginning to corrode already (or/and are worn due to contact bounce). This is a sneaking process.
The reason why the above speakers worked at higher volumes is (now) easy to explain because it caused more current flow which was able to beat through the contamination (oxides, dirt) of the contacts whereas the smaller currents were not.

Here a small calculation helping to figure what currents are involved with a high dynamic range system as audio.
A dynamic range of 100dB (and audio gear even exceeds this not to mention our ears which are much more capable) means signal relations from 1:100000.
Assumed we have 5W mean power delivered to a 88dB/W 8 Ohms speaker (which is already pretty loud) there is about 0,8A of current flow. A signal 100dB below this levels create only 8µA (µ, not milli) through the speaker and the relais.
And now imagine there is some vibration involved also to that relay passing through this tiny signals.
When vibrations compromises sigal quality even in eletronic parts as condensators and chokes what influence than must this have on a susceptibly mechanical part as a relay???
Are there any investigations with measurements about relays in respect to small signal qualitiy in audio?? This would be very interesting.