Loudspeaker protection kit

[Vivek]

Hi,
I would like to ask all Indians on the forum where I can get a loudspeaker protection kit. Does anyone know if Vegakit sells such kits?

Vivek

[navin]

i think there are such kits on lamington road in mumbai. normally all you need todo is protect the tweeter. what amp -speaker combo are u using?

tweeters usually blow if your amp is a bit too small for your needs. you push the amp a bit to hard it overloads and clips. creates all sorts of HF noise which the XO directs towards the tweeter and wham.

i find all protection ckts change the sound in a way i dont like. in a pro - pa enviroment they are useful but for audiophile use i doubt it.

woofers usualy complain so you get a chance to turn the volume down.

[Vivek]

Hi Navin,
I made an amp published in Electronics For You in 1991. It has also appeared in their Electronics Projects No.13. It is a 70 W amp designed by C Sanjay. You might have seen the article.
The amp has fuses in series with the outputs to protect the speaker in case of DC appearing at the speakers. But I do not know how reliable it will be.
The speakers are DIY with Peerless drivers. Naturally, I do not want my efforts to go up in smoke. What do you suggest?

Vivek

[navin]

fuses? that is odd. there are better methods. however i have not seen the design you are talking about so i cant tell what would suit the design best. the easiest is a DC blocking cap. however that affects sounds quality most. there are other current managing/sensing circuits that can also work. most fuses are not fast enough to protect the speaker.

[tcpip]

Navin,

Is it possible that this protection circuit that Vivek refers to uses fuses only for DC protection? I would have thought that a speaker can handle a few seconds of DC, in which case the fuse might be good enough? Can't speak from experience...

I'd have thought that a proper speaker protection circuit would protect against transients, turn-on "thumps", etc. I've seen some; they use relays. Randy Slone's book has one. I've wondered about the sonic effects of a fat relay in the poweramp output path, but I haven't yet built one so can't say from experience. In any case, I would have thought that if the amp is really high-powered, a speaker protection circuit would be advisable. (Really high powered = 200W/ch or more). Randy Slone's take on this is that it is reasonable to expect that some goof-up somewhere will expose your speaker to some sort of transient or DC at least once in its life, even in the home.

Tarun

[navin]

Most protection ckts have a sonic character. the digital ones are a bit beter. i have seen some that actually work well. Perraux uses one that is quite nice.

[tcpip]

Originally posted by navin
Most protection ckts have a sonic character. the digital ones are a bit beter.

What is a digital protection ckt? You mean something which has sensors triggering a microcontroller? I guess such things can have more complex analyses and responses, no? Are there any designs/kits for DIY? These PIC and Atmel microcontrollers are quite incredible... both from their processing power and inexpensive price points of view. If I wasn't fiddling with audio, I'd be fiddling with those, I guess.

Incidentally, you're the only person I know of in Bombay who talks of Jordan full range drivers. I have a pair in small boxes. They are probably the best speaker drivers I've heard, which is not saying much because I've not heard much.

Tarun

[navin]

you got a pair. are they for sale? actually the smallest application i got needs 5. eventually it'd need 20. 4 per channel. 5 channel.

i see some new amps with these ckcts. cant claim to know much but the mags say that their effects are less audible.

[tcpip]

Originally posted by navin
you got a pair. are they for sale? actually the smallest application i got needs 5. eventually it'd need 20. 4 per channel. 5 channel.

I'm totally in love with the drivers myself. And I paid a big markup for them (I paid full courier charges for the pair from the UK to India, which came to UKP 50+.) So you wouldn't like to buy them from me... Anyone who travels as much as you do can probably pick them up from the UK and avoid the exorbitant courier charges, I presume. If you don't mind the price and you don't mind the fact that I'll be removing them from enclosures where they're mounted (in effect they're "used" units), then you can have them, I guess. Email me.

I have made the small single-driver bookshelf speakers using those JX92s, and this has encouraged me to try building something bigger to fill in the lows and highs. I'll add a tweeter and a large bass unit to each of these, someday. Maybe even try open baffle for the JX92s, instead of ported box. But currently, no time or budget to build that augmented system, so the little JX92 boxes are lying unused.

When are you making your full-range based speakers? Can I come listen? I'll be real quiet.

Tarun

[tcpip]

Originally posted by navin
tweeters usually blow if your amp is a bit too small for your needs. you push the amp a bit to hard it overloads and clips. creates all sorts of HF noise which the XO directs towards the tweeter and wham.

i find all protection ckts change the sound in a way i dont like. in a pro - pa enviroment they are useful but for audiophile use i doubt it.

Do you know of this lovely approach to clipping which one of Randy Slone's amps has?

Randy claims that one of the main reasons tube amps sound more pleasant than SS (solid state, not single sided) at high volumes is because they do "soft clipping", i.e. when they clip, the waveform does not have sharply-sliced-off tops and bottoms. They have rounded corners. In frequency terms, this "soft clipping" will introduce less high-order harmonics than the sharply sliced off waveforms of SS amps. And he goes on to say that we often drive our amps to points where they are occasionally clipping, but we don't realise it, so we just ascribe the final sound to the "characteristics" of the amp, where actually it's clipping-induced distortion.

So, to address this problem, he designed a totally symmetrical amp topology, with MOSFET output stages, and then introduced some protection circuitry which actually mimics the soft clipping. The protection circuitry part is very simple, and uses (probably) four transistors to control the biasing of the OPS driver transistors. But to get that rounded waveform from a SS amp... it's quite something else. And like all Randy Slone amps, this one has distortion and transient characteristics which are super hi-fi anyway.

I was reminded of this because of your post about clippings, high-order harmonics, and tweeter blowups. I guess this soft clipping will not only give the amp a more euphonic sound when over-driven, it'll also help protect the tweeter, won't it? Simply because it'll generate much less higher order harmonics?

Tarun