[MikeC]

Hi

Does anyone have any experience with Rod Elliotts Loudspeaker Protection and Muting Project (Project 33)? Any opinions on it are welcome.

I am considering this as tweeter protection in an active set-up, as an alternative to very large blocking caps. Rod also sells a PCB for a simplified but apparently equally effective version, which would make implementation fairly easy. Circuit sensitivity can be altered by changing capacitor values, so a tweeter protection implementation will use smaller caps than standard, and be more sensitive. A switch in circuit should have less sonic influence than 100uF of capacitance - right?

Also, does anyone have any suggestion as to a suitable relay or manufacturer? It should have good mechanical integrity, little or no contact bounce on activation, and high conductivity material employed for the contacts (my guess). Rating should probably be around 4A or higher.

Thanks for any advice.

Mike

[MikeC]

I was hoping for some reply or comment on this message. Either everyone is ignoring me or no-one wants to help. I promise I'm not always obnoxious.

Let me clarify. It would be used for a low power AKSA driving my tweeter in an active configuration. Caps would work, but will effectively be part of the crossover unless sized to move the knee far enough down the frequency range, hence very large values.

If anyone has any comments on this type of protection circuit, or suitable relays to use, please do chip in.

thanks

Mike

PS, for the Aussies, if this lack of comment is tri-nations related - you got Rathbone, we got the trophy. I think thats fair.

[Malcolm Fear]

You state that either everyone is ignoring you, or no one wants to help.

I try to help wherever I can, and I try to ignore no-one. There are a few other explanations.

I know nothing about the subject.

You are trying to introduce something else into the signal path. Most AKSAphiles like the simplicity of the circuits. I have recently soldered my speaker leads directly to the speaker lugs, the other end directly soldered to the AKSA power boards. The best connector is no connector. It makes a huge difference.

[kyrill]

I was hoping for some reply or comment on this message. Either everyone is ignoring me or no-one wants to help. I promise I'm not always obnoxious. ...

Hi Mike

None of the above reasons did me not replying you.

SIlence is a good answer to the grammar of yr first question if you do not have experience with your R. Elliot examples and the second question I could not answer, because of lack of exp with speakers relay "an sich"

I am sorry "for the silence"
and O yes, I agree word to word with the philosophy of  Malcolm.

[MikeC]

Hi Kyrill and Malcolm

         

Please accept my apology if I offended you; no offense was intended. I was hoping someone would have been able to help, and accept it if no-one has experience of this. I guess I will have to suck it and see.

I agree with Malcolms philosophy, but in this case, I think it is necessary to insert protection of one form or another. I am not worried about power protection, but rather damaging the tweeter through over-excursion due to the switch off DC surge. Passive crossover tweeters are inherently protected by the series cap in the crossover, active crossover tweeters are directly connected to the amp, so are at greater risk.

Thanks for the response though. Even if it didn't answer my question, at least I know I'm not being ignored.  

Cheers

Mike

[kyrill]

Hi Mike

I have triamping as well  jsut because I want to get rid of the components in the speaker filter. And having heard the difference there is no way back.
My amps are Hugh's amps and I just trust his babies. And in the very worst case, a tweeter is not that expensive is it? I have an expensive (relatively to other speakers) ribbon tweeter, but the ribbon is replacable.

The listening quality of relays is a rather new subject. I have not met yet a review on the web or in my memory that compared different  relays for their listening properties.

So you are stepping  on relatively new territory

[AKSA]

Mike,

Some years back now, when I was developing amplifiers pre-AKSA days, I looked very closely at this problem.

I tried the usual protection system on the voltage amplifier drive;  a transistor which cuts base drive when signal excursion is too high.  Self uses this approach;  others use shorting transistors on the output stage.

I found that both these regimes, which comprise about 80% of the protection racket, conferred considerable sonic coloration.  I persevered for some time, about six months, but could not remove the effect.  Basically, it compressed the sound, making it sound less dynamic and adding 'constriction' which was quite apparent.

As late as the end of last year when I was developing the ultimate form of the AKSA (which was unsuccessful, incidentally, and which I codenamed Utopia) I tried again with an output stage variant developed by a Californian audio designer, an elderly friend of a pal of mine called Robert Jones, a brilliant ophthalmologist in Newport.  This system too showed early promise, but required very careful calibration, and eventually because of the variability of the semiconductors used I decided to shelve it for the moment.  I still think it has promise, but haven't the time just now to complete the design, which adds considerably to the complexity and introduces another 12 or so components.

Then I reconsidered the problem.  Protection circuits are interesting;  they protect themselves first, and the circuit they are designed to protect, last.  They should be designed to take account of the SOAR curves of the output devices, and this makes them quite complex.  There is constant debate about their effectiveness in the designer world, but I don't like them, and so I investigated the failure mode of the AKSA.

First up, the tweeter and midrange are capacitively coupled.  DC cannot damage them;  only oscillation.  To my knowledge, no AKSA has ever destroyed a tweeter or midrange by oscillation, and from my own work on the CRO and various loads, I know that this kind of failure is so rare as to be almost unthinkable.  That leaves the woofer.

The woofer can be destroyed by DC, and in fact during development of the N+ I did destroy a woofer in just this way.  Not nice, but entirely my fault;  I went beyond the limits, the amp went into DC, and the voice coil was deep fried.  I keep the driver to show people how the speaker is designed;  it's a Vifa M18 used in the AKSonics, a beautiful driver.

I found that in almost every case, one device fails before the other, but the 100R fuse resistors maintain a working potential to the offset control circuits in the amplifier even after the fuse is broken.  This enables the other, good output device to hold offset to safe levels;  in the meantime the sound is terrible, the fuse resistor begins overheating, smoke and smell is created and the amp is switched off in short order - after all, people are listening to it, so ordinarily realize immediately.

On a commercial product, lack of protection is more of a problem, particularly if used with very expensive speakers.  However, when low cost, low parts count and DIY is concerned, if the amplifier fails in a reasonably benign fashion, protection may be eschewed.

Those who favor active systems will realize that the tweeter and midrange are indeed DC connected, and thus vulnerable where woofers are more robust.  In this case, protection is perhaps a good idea, but a blocking cap is normally used.  Incidentally, don't be squeamish about a blocking cap;  there is one on the input, one in the feedback loop, and one relaying the music to the top end of the output stage.  As if that were not enough, there are also blocking caps in the power supply, which actually serve as earth return for the music signal at the speaker, so the amp is redolent in capacitors passing audio signals, and thus one more, a quality metallized polypropylene, should do no damage providing the quality is up to the mark.

Lastly, a good protection system is indeed the Rod Elliott circuit, which senses DC at the output and then switches off a relay, disconnecting the speaker.  However, this can introduce degradation in the music signal, as the contacts of a relay deteriorate over time, and are clearly audible when corroded.  Nonetheless, if you use gold/rhodium plated relay switch contacts there should be no discernible problem within about five years.

Hope this puts it into the 'AKSA' perspective,

Cheers,

Hugh

[EchiDna]

my $0.02 worth...

ESP (Rod Elliot) also has his own forum where your question might be better answered by the designer himself.

cheers,

[MikeC]

I asked for a response, but Hugh, what a response.  I will send you an e-mail to discuss some technical issues. However, now that you brought it up - the Utopia????????

If there is any confusion, I am not advocating modifying the output stage at all; I would add either a capacitor or relay between the output and the speaker terminals. I am quite happy at the moment with passive speakers, just looking to protect the tweeter when I go active.


EchiDna

I am aware of the ESP forum. I might not have worded as well as I might have, but I was looking for comments in relation to the AKSA. I don't think there is a better place than this to ask. Thanks anyway.


Kyrill

So you are driving your tweeters directly with nothing between the output stage and the tweeter with no problems. Is it a Raven by any chance (replaceable ribbon). If you are comfortable, then I am reassured. It just seems that a tweeter is a very expensive fuse.  


Cheers

Mike

[kyrill]

Mike
The tweeter is an offspring from Raven The story is that the original designers were contracted in designing the Arum Cantus
I have the G3 (bought for 275 US $ ) from Zalytron (New York)
not bought in

http://www.e-speakers.com/products/tweeters.html

[andyr]

Mike,

Sorry for not replying earlier.  The heading on your topic was vague enough to suggest that I wasn't interested in/couldn't add value to your topic ... so I ignored it.

However, now that I've read your post ... I can indeed add value (if you had used a topic heading like "protecting tweeters in an active setup", I would've immediately responded!!).

Aksas have no power-on "thump" (well, mine doesn't) so you don't have a need for any muting/soft-start circuit!

Trust me ... I had the same issue when going 3-way active with my Maggie IIIas.  I don't think you can get a more fragile tweeter than the Maggie ribbon - they even give it it's own fuse (which doesn't always do the job of protecting it!).

In the end, I guess I switched on for the first time with a fair degree of trepidation but have had absolutely no problems for the last 2 years - provided, of course, you switch on your active crossover BEFORE switching on the amps ... or you leave the crossover permanently switched on, as I do.

Go to it, ma man!

Regards,

Andy