Tweeter protection for active speakers

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frugal-phile™
Joined 2001
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wintermute said:
These guys http://www.speakerbits.com/net/catalogs/cat19.aspx (in Melbourne) have solen 33uF caps for about $30.... probably about the same as what you were looking at for 3 10Uf caps :(

That gives a good idea of what it takes to get them to Oz. I looked up the 33uF 250V and figured resale of $13 CAD each (CAD real close to AUD these days + postage to get them here --if i can amortize the post over a larger order that goes down), then post to Oz (guess $13 USD air for a pair)

We buy quite a few of the larger voltage for power supply caps. I can't imagine doing an active XO and then series an elco with the tweeter.

dave
 
Hi Aussie fellows!

If you are looking for high quality parts at very reasonable prices try www.ledeaudio.com. I have used Jaycar, Altronics, Farnell, RS Component and finally mainly ordering from Lede Audio. Dave at Lede Audio in Darwin can get you all sort of parts that not listed in his website.

Paul,

I would take Kuei Yang Wang's advice because his 3rd order suggestion was what I did. It saves my power amp's input cap and possibly the output protection cap in the XO and saves 2 opamps in the signal path. No DC will flow through to the power amp. If your power amps do not have too much DC offset (more than a few mAs), don't worry about your tweeter protection too much. Turn on your CD, preamp, XO and power amp in that sequence and turn of them in the opposite sequence you will be OK.

Regards,
Bill
 
Hi Paul,

I can’t see why no-one has recommended this excellent Australian design: http://www.altronics.com.au/index.asp?area=item&id=K5051 . It’s a really excellent little self-powered (it charges up a capacitor from the speaker signals) speaker protector, designed by David Tilbrook of ETI, and later Australian Electronics Monthly. He was the hi-fi design guru, and he produced some really excellent designs for amps, speakers and so on. It shouldn’t have any effect on sound quality after it’s charged up, and you set it to trip at any power up to 1500 watts! He recommends setting it based on when you hear your speakers beginning to sound strained. You need two, one for each speaker box (or one for each driver, with your active speakers, or with active crossovers), they are easy to build, and protect your speakers from either overpowering, or amplifier faults introducing DC. They are very small (65 x 65 x 30 mm), so you can put them in the speaker boxes. The ETI protectors are currently on sale at a cheap price, according to their website.

In the mid to late 1980’s there was a commercial equivalent of these, the Nexus speaker protector, which had a stereo boxed version, and a potentiometer to set the power, and it was highly recommended by Australian Hi-Fi Magazine, who also used to sell it. It was only due to mis-guided, uneducated, snobbish British hi-fi reviewers, who believe that you can’t have speaker wire, or anything else between the amp and speaker, too thin or it affects the sound (a laudable sentiment, but I’ll bet they’ve never seen how thin a PCB track is), that devices such as that were withdrawn from sale due to poor sales. The fact that resistance is directly related to the length of a wire, multiplied by its resistivity, would probably sail right over their stupid heads! Still, if they want their houses set on fire when an amplifier dies and sets fire to their speakers, I’m sure they’ll be happy thinking they know what they’re talking about! It’s something that can readily happen with modern direct coupled solid state amps. Good luck, is all I can say, because that’s what they’re surviving on. All it will take is to be out of a room, amplifier left on….

The other EA speaker protector sold by Altronics is also a good design, but needs to be powered, either by putting it in an amp and powering it from the power supply rails, or externally with a transformer, rectifiers, and so on. Personally, having built both protectors, I think the ETI self-powered one is the best and simplest, although the EA design can protect against amp clipping. It’s often hard trying to find space for the EA module inside an amp – it won’t fit in a Playmaster Pro Series 3 easily, for instance, without quite a bit of redesigning of the amp internal wiring.

Regards,
Don
 
Konnichiwa,

MosfetOwner said:
I can’t see why no-one has recommended this excellent Australian design: http://www.altronics.com.au/index.asp?area=item&id=K5051 .

I can. Here is why:

MosfetOwner said:
It’s a <snip> little self-powered (it charges up a capacitor from the speaker signals) speaker protector,

Self powered. As in, it draws irregular current from the driving amplifer in parallel to the intended load, the driver, thus dramatically increasing distortion.

MosfetOwner said:
It shouldn’t have any effect on sound quality after it’s charged up,

I'm worried about the bit before it's "charged up", plus it invariably must draw power constantly to remain "charged up".

Sayonara
 
Can't say I've ever noticed any difference in the sound, protector or not. The 'charges up a capacitor' bit was just my quick estimate - it's been a while since I built mine, so I'd have to dig out the circuit, and the original electronics article to tell you exactly how it works. It may not charge up, as it's based on a CMOS switch to switch the relay on and off, so draws virtually no current when not operated. As I said, it makes no difference to the sound that I can hear, and I've got some good amps and speakers available to me! I'm also still young enough (mid-40's) not to have lost all my high frequencies yet, although I'm sure that like most people, it's reducing at about 2kHz per decade.

Considering the non linear impedance that most speakers provide to an amp (anything between 4 and 80 ohms, depending on frequency, for a typical multi-driver moving coil speaker system, with varying degrees of capacitance, inductance and resistance), an extremely small amount of current loss makes very little difference. There's plenty of capacitance in typical speaker leads, as well, unless you attach the speakers directly to the amp - rather impractical, unless it's an active speaker system, which introduce other problems.
 
Assume, for a moment, that you are going to use a cap for tweeter protection, should you also bypass the large value one with a smaller, quality cap (say, a 33uf with a .1uf)? Will this provide any sonic improvement?

I'm going to be experimenting with a number of amps in my "soon to be" tri-amped system. Using an Aurum Cantus G2 as the tweeter, I'm just not confident that all the amps I've got will not produce DC on start-up. And I can't be sure that the stuff will be started in the right order, either (as I'm not the only person in the house).

I have been thinking of using some dome midranges that I've got lying around, instead of just going straight from the PHL 10" to the G2 (like AR2's speakers). Using a simple series x-over from the domes to the G2 would provide the protection needed. And the added bonus would be that I could get a smaller, better cap for the same price as the larger one required just for DC protection.

Any one have any thoughts on this?
 
Cloth,

I wrote a wiki on "making your system user friendly" which you might find helpful. I think the best way to deal with others using your system is make it so that there is only one way to turn it on - the safe way.

The most reliable way I found to get rid of thumps was actually to switch it all on/off at the mains with one switch. A lot of power switches tend to ark but I've not had this problem with mains GPO switches.

If you have to switch individually, someone will turn off something they don't think needs to be on while a power amp is running. There is no way to train family to do more than just turn it all on/off at the wall. Or add in a "power up kit" from Jaycar that will turn it all on/off when you turn on/off a master unit, which could be something which you can switch with a remote. Then you just sit there and turn it all on/off with remote, even your diy stuff if you have such components.

wiki:
http://www.diyaudio.com/wiki/index.php?page=Is+your+system+user+friendly?
 
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