HF driver protection

[Scorpion]

Ive seen some kind of HF protection on some passive crossovers that looks like a couple of car lamp bulbs (211-2) that light up as the HF driver is pushed. Is this just some kind of current limiter circuit? I want to put something similar in a Yamaha club4 monitor i have. Would i just put the bulb(s) in series with the driver? or parallel?

[bob p]

EV used to do this with their ST-350 and ST-350A horn supertweeters. EV speakers were very popular in the 70s because they were so efficient, and they were often used with underpowered amps as a result. The problem was that an underpowered amp would clip and send the tweeters a square wave. The ST-350 were famous for blowing out when that happened.

EV addressed the problem by designing a crossover that included a small incandescent lamp. When the crossover received too much HF energy the light bulb would come on, and get brighter as the amount of power to the tweeters increased. As I recall it wasn't a simple series current limiter, there was some switching involved, but I don't remember exactly how the crossover worked. I don't even remember the model number of the crossover, but that tech data has got to be out there somewhere in cyberspace...

[g1]

This is a very common form of tweeter protection. The bulb goes in series with the driver. You will have to figure out what wattage bulb to use to get the best protection.
As far as I know the bulb is preferred over the fuse as it's resistance increases the more the light is on, acting as a bit of a limiter.

[Bruce]

Yorkville used a bulb in some of their stuff check here in the " Obsolete service manuals" Pulse speakers Yorkville Sound: Obsolete Service Manuals , hope this helps !

[Scorpion]

That does help. The pulse speaker PDF on Page 2 ,M435c schematic shows the bulb couple to a fuse via a couple of caps, and also a resister/cap combo couple the bulb/fuse to the driver. I'm planning to skip all that and run 2 12w auto lamps paralleled , in series with the driver. Is this a bad idea?

[jrfrond]

Bulbs are common and provide a measure of compression. FYI- the bulbs are usually halogen. 24V/75W is very common.

If you just want overvoltage protection, there is a device called a "Resettable Polyswitch" that some manufacturers use. This device will not compress your HF signal to the driver. In-line fuses work also, but are highly-inaccurate due to their tolerances, and I've seen too many drivers cook BEFORE the fuse.

[g1]

I would suggest sticking with a single bulb. If you download the yorkville speaker component chart, they show the different wattage auto bulbs available, mostly under the older elite & pulse series. You will want to know what kind of wattage your horn is designed to handle, or start with a low wattage bulb and work your way up if they blow but are not being pushed hard.

[Bruce]

I've seen too many drivers cook BEFORE the fuse.

" What's that smell ? Well the fuse is still good ."

[chipprogr]

, in series with the driver. Is this a bad idea?

Yes its a bad idea. The lamps cannot simply go in series between the xover and driver. Look at any 6th or 12th order xover formula and notice what happens when you start to increase the speaker resistance, the xover frequency drops. Point is that where your suggesting placing the lamps , as they start to heat up, will add resistance to the circuit causing a frequency shift LOWER than the desired xover point. You might even get into mechanical failure range of the driver abecause they arent capable of handling the lower frequencies. Light bulb limiters are a great idea in my opinion and i have been a live sound company owner for many years. They do a great job for the horns ;however, they need to be placed before the high freqency portion of the xover as shown in the Yorkville Pulse schematic.

[Brad1]

I've got an Acme Low B4 bass cab that uses an 1156 12V bulb. The cab is rated at up to 1000W. (These are very good-sounding punchy cabs!). Here's a discussion from the their web site:

Acme Sound Ltd. Homepage (In the "faqs" section)

Q. Light bulb questions and whimsy

Is it ok to use a bulb marked 24V 21W instead of your regular 12V 21W bulbs?

David

A. Nope. The 24v bulb would have too high a resistance, and wouldn't allow enough current.

No wonder it didn’t sound so good!

David

Customer writes again:

At Bulbs Direct (no joke!) they show:

Volts: 12.8, Watts: 2.1, Base: BA15s
1156-GE, Osram Sylvania, Philips
$1.47

1156-Ushio, Eiko, & Others
$0.52

Is there likely to be any practical difference?

In Talkbass there was some discussion about a “ruggedised” bulb used by Harley – any thoughts?

David

A. I think they're all more or less equivalent. I like the green Sylvania packages, though.

I've heard of the Harley bulb, but I would hope vibration of the crossover should be low enough so it wouldn't make any difference. At any rate, I don't know if there's any difference, but I doubt if HD is in the bulb business. I've been using Eikos lately, and they seem fine.

Actually the 1156 is generally rated at 50 watts, not 2.1. In my tests, the bulb fails at about 23 volts and its resistance at that point is about 6-6.5 ohms. At this current, as you can calculate, the bulb is actually dissipating around 80 watts!


Just thought I'd throw that in.

Brad1

[chipprogr]

In my tests, the bulb fails at about 23 volts and its resistance at that point is about 6-6.5 ohms. At this current, as you can calculate, the bulb is actually dissipating around 80 watts!


Just thought I'd throw that in.

Brad1

Thnaks for that add Brad, i quoted part of your post to point out something. Like Enzo, i too have worked on amusment devices for years (pinball & arcade games). Doesnt matter how "secure" you think you have your coin box, given enough effor, the crooks WILL break in to it. Same applies here with the lightbulb limiter circuit. You will blow it up if you try to hard enough. They are general great protection superior only to using dedicated system processor that biamps the speaker, has sense wires coming back off the amps to the processor, and controls the thermal and excursion of the driver by directly controlling the amplifier.
Their tests of blowing the lamp did not include increased resistance of the driver as the temperature of the voice coil rises. Was the test a DC test or AC test and what frequency. A drivers voice coil is reactive and the impedance will shift depending on the frequency it sees, the bulb wont i believe because its purely resistive. So many variables here that the blanket statment they posted just isnt the complete story.

Thanks -Great discussion -Eric

[Scorpion]

The crossover i'm using is modelled (rev engineered) after the yamaha club where the HF driver is 16 Ohms and the LF driver is 8 Ohms (per the schematic). I have tried it with an 8 ohm HF diaphram and it sounds OK but not as good. But it didnt blow up. This was with a 300 watt solid state power amp.

Despite chipprogr's wise advise i want to stick a bulb inline with the HF driver and see what happens. It looks like,from the earlier discussion that less volts = less resistance. I have found a 6 volt, 50 watt tail light bulb that looks promising.

This is to amplify a digital Hammond organ. The power amp i'm using is a 120 watt peavey tube guitar head with the master volume mostly dialed out. This amp seems louder than the 300 watt power amp i used before.

Thanks for all the great info offered. Keep it coming if you have more.

[chipprogr]

The crossover i'm using is modelled (rev engineered) after the yamaha club where the HF driver is 16 Ohms and the LF driver is 8 Ohms (per the schematic). I have tried it with an 8 ohm HF diaphram and it sounds OK but not as good.

Hi Scorpion, whats happening here is that you probably have a 2 way crossover constructed for 2khz xover point. If you had a 16 ohm tweet, the woofer and tweeter would have the same frequency transistion point. Where you are changing to an 8 ohm tweeter, you have now changed the horns xover point to 4k and the woofer is at 2khz. Your missing alot of needed sound energy from 2k-4khz range and this is probably why it doesnt sound as good. This is where alot of the "meat" of many musical instruments' sound lies. Cut that out and it will have a scooped sound. Alot of the mid is gone. As your lighbulb adds resistance to the circuit, your tweeter will smear up and down in frequency range, like a slide whistle (only not so drastic).

Good Luck- Eric