speaker overload protection

[David Deratany]

I would like to do something to protect my altecs from being damaged from accidential exposure to excessive power levels. However remote a possibility it may be, I worry that one of my pets might accidently turn on the receiver or up the volume too far by stepping on the remote control.

Can anyone give me some ideas? Since I do play them at high levels sometimes, a variable device might be more practical; either that or something I can disengage for those times and then reset.

[Todd W. White]

You need a pair of compressor/limiters.

Altec's later (and REALLY good) models are -

1612A (verrry nice)
1712A (extremely nice!)

Properly set up, this is THE way to go!

Todd W. White, Owner & Webmaster
Altec Lansing's (unofficial) Homepage

[Fitts]

I use quick acting fuses, a quater amp for the HF horns and 1 amp for the woofers. I change the fuses when I want serious volume which is not too often. If you don't like changing fuses you could mount the fuse across the back of a switch. That way when the switch is on you get full power and when off you get protection.

[Earl K]

Hi dderat
You might want to consider researching the protection circuitry that was built into the Model 14 passive crossover. It appears to be a good way to go . You can read about it by going to Lansing Heritage Library and clicking on the Model 14 info . My belief is that the core design philosophy of this circuit was in fact a small light bulb in series with the signal /& maybe a varistor as well . The sonic results of adding a bulb in series is a form of "soft compresson" as excess watts are converted to light . Its' been used by a few manufacturers , including I believe Urei in their large monitors . The only way to determine a value for the bulb, that I know of , is by trial & error . ie Get it "lit" when the music is approaching loud . Apparently, 12 volt car bulbs are a good place to start . My morning thought for the day .

regards <. Earl K

[David Deratany]

I see, something like a DPDT switch with fuses across the terminals in one position but
not in the other. One switch could do both hf andlf, as only one of each pair of leads
would need to be fused. Too easy! I like it. I suppose if I find myself going through
too many fuses in the "normal" course of listening, I could experiment with increased
values.

Thanks Dave

[[email protected]]

Hi Dave
Still enjoying those 511's? Looks like it if you're worried about exceeding power on the drivers! Commercial pro-sound crossovers by Eminence under their name (and as Dayton for half the price) all use 211-S bayonet light bulbs as overload protection (two bulbs in parallel). I have to believe if this is what the pro-sound market uses for driver protection it must be optimum. Earl K has the right idea here. I'd search the WWW for some design hints on this approach.

[David Deratany]

The 511/902A combinations are glorious, especially with new GPA aluminums, and tube powered.

I hooked up one of them and one internal 604b horn, switched off the lf, and compared. Once I balanced the output of the two, they were surprisingly close, at least to my ears. Others' results may vary. I had become annoyed with the b's, as I was getting some occasional slight muddiness in the 500 hz range. This went away when I set the b's horns at the level that sounded best with the 511/902's. I had had it too low all this time.

I also popped in 1200 hz crossover modules into the 1631A's.

Bottom line, the 604b's are incredible; but the 511/902s are better. I will keep them forever.

Now, as for the speaker protection, since I am biamping, the passive crossover suggestions aren't an option, but I do appreciate the suggestions. I just "bought now" an Altec 1712A compressor/limiter on Ebay, for not a lot of money. I will need one more, as they are mono. Hint, hint, out there.

[[email protected]]

Dave:
I understand what you're saying, but I think the point is that the power dissipation of the lamps due to their resistivity is going to be proportional to the voltage, so a parallel pair on perf board in series with the driver will give you variable protection and relatively low losses at low power due to the parallel resistors (lamps).

[David Deratany]

I now understand what you are getting at. It does seem quite uncomplicated. That would be one bulb on one lead of each driver pair and not one on each of both leads? How does one make sure too much power won't get thru. Do the bulbs just cut it down, or can there be set a level where no further signal can get through. The whole point for me, at least, is to prevent damage in a worst case scenario.

Since I have a 1712A coming in, I will of course try it. If it looks like I'm not going to be able to pick up another right away, and/or I don't like it, I will try the approach mentioned here. Less usually is more, and I am concerned about needless additions into the signal path.

[cclark65]

I bought a pack of bulbs that were specifically designated as horn driver bulbs. I got 12 of them for about 10 bucks or so. It is my understanding that you hook them up in series with one side of the driver. (I don't think it really matters which side, but I always use the positive terminal.) When the levels are low, and the bulb isn't lit up, the resistance is near zero, so the signal goes through with no problems. As the light gets warm due to higher power levels, the resistance in the filament will go up, therefore creating less of a signal getting through the circuit. The extra current is turned into heat and light by the bulb, and the more power that the bulb absorbs, the brighter it will light up, and the less power it will let get to your driver. After the high levels, the signal goes down, and the resistance in the bulb also goes down, resulting in more power getting to the driver again. I believe it is basically a crude form of limiting, but is very simple, and it works.