Purpose of a HET in a Speaker Crossover?

[Deleted member 133]

Folks,

Hoping some of you electronics engineers / speaker experts out there can answer the following question for me: what's the purpose of having a HET (Hall Effect Transducer) in a speaker's passive crossover?

Quite some time ago, a tech who refurbished a pair of Koss CM/1020 speakers (circa 1978-84) sent me a wiring diagram that he had made of the original (pre-refurbished) crossover. I've attached it below. I've since shared it with a dozen or so folks looking to do their own refurbs and everyone found it very helpful. Well the other day someone else did as well and after he'd used it he got back to me and said that he noticed that the value of the HET shown on the diagram is 5ohm / 10W and that the left lead is connected to the green wire above it.

Up until now I'd never really noticed, to be honest. But now I'm a bit puzzled. Puzzled in that a HET would carry the same type of specification as a resistor. Which then got me back to my original question: what's it doing there?

I can find lots of info on Hall Effect Sensors - and their applications - but not on HETs and how they could be used in a passive speaker crossover. Does HET mean something else in this case?

I do have Koss-original schematics for the CM/1030 speaker and there are no HETs shown on those. Why would Koss have used one on the CM/1020 and not the CM/1030?

Could it be that the tech who prepared the CM/1020 diagram made a mistake? That it's really just a resistor? I'd have to take my own CM/1020s apart to check their crossovers to be sure - but I'd prefer not to since there's always a risk of damage when doing so.

Anyhow, any insight would be appreciated.

Jeff

 

[yromj]

After looking at the diagram, I have a couple of questions:

(1) It appears to me that the HET is connected with a single wire to the Orange lead, not the Green. What am I missing?

(2) How was the value of the HET determined? I don't see it listed on the diagram.

Typically when devices are connected with a single wire, you think of a capacitor, since the direction of current flow depends on whether the capacitor is charging or discharging. I'm looking forward to seeing an explanation of this.

John

 

[MakeMineVinyl]

A Hall Effect transducer detects magnetism. To do anything, it would have to be located near some source of magnetism. I could possibly see somehow if it were located near one of the inductors in the crossover, it could somehow sense the external magnetic field generated by the audio passing through the inductor, and in turn do something useful. Just what that might be, I have no idea.

Are you sure that it really is a Hall Effect transducer? A more complete picture of exactly how this mystery component is being used would help.

 

[Deleted member 133]

I've asked the guy who most-recently contacted me to take a picture of his board, and one of the HET in particular. Hopefully that will help solve the puzzle. I too have my doubts that it's a HET, but if it is I'm even more puzzled by what it could possibly be doing there.

John,

As mentioned in the OP, the fellow told me that the other end of the HET, as shown on the schematic, is attached to the green wire (just above it on the schematic) based on his actual board. The value / rating is as reported to me, by him.

Jeff

 

[yromj]

My guess is that it's going to be a "proprietary" name such as "High End Transistor" or something like that because it's connecting the two "high range" drivers in this case. (Sorry Jeff, I thought you were saying it was ONLY connected to the green wire.) That could mean that it is in fact a resistor between the two drivers or even a transistor allowing current flow in one direction.

John

 

[Deleted member 133]

My guess is that it's going to be a "proprietary" name such as "High End Transistor" or something like that because it's connecting the two "high range" drivers in this case. (Sorry Jeff, I thought you were saying it was ONLY connected to the green wire.) That could mean that it is in fact a resistor between the two drivers or even a transistor allowing current flow in one direction.

John

Yeah, I'm starting to think that HET stands for something else.

As for it being a transistor of some sorts... even if the two ends / leads were shown connected on the schematic, I thought that transistors all had three leads? (And do transistors need a power source to operate, or is the voltage differentials in such a passive crossover circuit sufficient? (I really am way out of my depth here - having barely made it by with a "C" in 2nd year "circuits and signals" that was mandatory for even us budding mech engineers. But that was almost 35 years ago!)

Jeff

 

[MakeMineVinyl]

I would seriously doubt that it is a transistor because it just doesn't make sense in a crossover type circuit. Yes, transistors have three leads. The mystery device might be some negative or positive temperature coefficient thermistor used as a protection device. Some crossovers actually used light bulbs as positive temperature coefficient limiters in-line with the tweeters to limit the maximum power delivered to them.

Could be some proprietary device containing audiophile approved silicon which has been blessed by virgins. :scared-eek:

 

[Barney]

^^
rammisframmis, you remind me of soundhound with his humor.

 

[MakeMineVinyl]

^^
rammisframmis, you remind me of soundhound with his humor.

Never heard of him, but he sounds unpleasant.

 

[Towen7]

Welcome to the Audio Annex rammisframmis!

 

[yromj]

Yeah, I wasn't thinking about transistors having 3 leads.

More importantly it's great to see someone like rammisframmis hanging out around here. We can always use someone with some electrical knowledge, not to mention a good smart ass. Welcome to the fray!!

John

 

[Barney]

^^
rammisframmis, you remind me of soundhound with his humor.

Never heard of him, but he sounds unpleasant.

Soundhound sold his peepee to audiophiles for big bucks. He hasn't been around for years though.

 

[jamhead]

Huh. I don't remember Soundhound.

 

[Deleted member 133]

Ok I think the mystery has been solved ... about the HET, not Soundhound's reincarnation.

To summarize the issue ... As I said in my OP, the posted schematic was made a while back by a tech who sent me a copy. The guy I've been in touch with recently was asking about the values of a couple of caps, because the ones on his were obscured by epoxy. I sent him the old schematic and he came back to me to say that, FYI, the "HET's" other end is connected to the green wire and it has an indicated value and rating of 5 ohms / 10 watts. Which led me to noticing the "HET" for the first time and wondering what the heck it is.

Well he sent me a photo of that section of the board and the "HET" looks to be identical to a resistor (bottom left corner of photo below). I have no idea why the tech who made the schematic some years ago called it a HET, since, from the photo, there is no such marking on it.

Anyhow I'll update the schematic before I pass it on to anyone else.

Jeff

 

[MakeMineVinyl]

Yep, that's a garden variety power resistor.

OTOH I guess if we wanted to get technical and speculate, wire wound resistors like this do have some degree of inductance. HET could in some universe mean that that inductance was tailored to make a handy R-L device in one package which shapes the response somehow.....

OTOH, OTOH, its probably just a garden variety power resistor.

 

[Rope]

Yeah, I wasn't thinking about transistors having 3 leads.

More importantly it's great to see someone like rammisframmis hanging out around here. We can always use someone with some electrical knowledge, not to mention a good smart ass, welcome to the fray!!

John

Well, I can sit on an ice cream cone and tell its flavor.

Rope