Rebuild AA's or Upgrade?

[Deang]

Obviously if you have the skillsets then build them yourself. OTOH, on several occasions I have dealt with people who assured me they could do it, only to then force me into a running turtorial with them through email after they got the parts. Time consuming and frustrating.

"I think I agree with most of what you said. I'm glad to know that it is "observation" more than "criticism" because in my reading of your post, I thought it sounded like criticism".

O.K., a little critical maybe. You've often encouraged people to try the factory sound so they can hear what PK heard, and this is the reason you've always given for why you use(d) them -- when you yourself didn't listen to your Klipschorns the way he listened to his. I don't recall ever reading a single post by you on this subject where you said, "I don't really like the factory sound, I find the stock squawker setting too foward for my tastes so I run my Type A with the squawker attenuated an additional 3dB as compared to stock." So, you don't prefer the 'factory sound', and this creates a bit of a contradiction in your posts.

My understanding of what that intent is: is that you want to "improve" on factory spec. My understanding of Bob's intent is to "restore" crossovers to factory spec."

We have similar approaches and feelings on the subject. Bob also improves on factory spec when he chooses to use high quality capacitors that measure significantly better than the stock PIO's and Mylars. I believe the bass sounds tighter when DCR on the low pass inductor is a bit lower -- so I use a different part. Bob still puts zeners in his AA's where I make a call from build to build. I think we both have improvements over the original products. I'm pretty sure I spend more time on my builds and try to present a polished product and this is reflected in the cost compared to his builds.

"I don't think you are aware that I'm not listening to Khorns at all. I am listening to bone stock Heresy II's. So does this validate my statement about my interest in hearing what Mr. Paul heard?"

I wonder what involvement, if any, PK had with the Heresy II. At any rate, all I can really say here is that your comments about "factory sound", 'hearing what PK heard", etc., were all initially made when you were listening with your Klipschorns, after you dropped the ALKs and went back to the Type A -- which you then modifed by dropping the midrange output, and then later modified again with Bob's 4500Hz network and tweeter. Right?

"Dean, did my post sound communicate that I have dogmatic positions on network topology?"

Not at all. I didn't have what you said in mind at all when I made the statement.

About the only thing I would be "dogmatic" about would be the idea that if a person wants to compare high end crossovers to factory spec, that in order for that comparison to be meaningful, one must have experienced the sound of factory spec, or some approximation of it.

O.K., sure, if the goal is to compare -- but when a person says they have a big room, use a 200 watt power amp, and say they like to drive up the volume -- I think you're setting them up for disappointment by recommending one of the early networks. The K-400/401 needs some help at those power levels and none of those networks give any. Knowing that you're listening to the factory sound isn't going to deliver much comfort when the horn is shrieking and drilling a hole into your head.

[Guest " "]

DeanG

"Obviously if you have the skillsets then build them yourself. OTOH, on several occasions I have dealt with people who assured me they could do it, only to then force me into a running turtorial with them through email after they got the parts. Time consuming and frustrating."

Maybe some of us old timers who have been doing this since the early 70's can help out.

An email or PM is all it takes to reach me.

In one of my previous lives, I used to be a regional master trainer for a six state area. Tutorial services is one of the skill sets needed.

[Hardhead]

I really appreciate everyone's thoughts, they've helped a ton.

Two conclusions: I think I'm going to have the AA's in my '79's rebuilt, so I can get a baseline. My gut is telling me that I may be happy with just a rebuild, since I already like the sound of these speakers as is.

With my '84's though, I have the same dilemma Michael has: did we indeed make a mistake by putting AA's in speakers the K55 and K77 M drivers? If I like the sound of the AA's in my '79's, how can I get my M driven '84's to sound like the '79's?

Jeff

Jeff--

No one has answered your real question yet. As I noted above, I believe your K-55-M squawker and K-77-M tweeter are simply too loud (efficient) for the Type "AA" crossover. The way to find out for sure if that really is the problem is to swap the "-M" tweeter and squawker with the Alnico ones as I previously suggested. If that is, in fact, the problem, Al Klappenberger's ALK crossover networks have a way to adjust the volume of both the squawker and the tweeter to put their outputs in line with the woofer. You can kill two birds with one stone that way: get a fantastic crossover and fix the tweeter-squawker output problem.

[Daddy Dee]

Dean,

This is making me smile. How about, I also have a pair of stock Heresy (which Paul did design) with a stock xover with refreshed crossovers maybe approximating the sound Paul heard.

You are correct that I have done and undone various mods on Khorns and LaScalas. Among those seasons has been some considerable time listening to stock Khorns, or as close as fresh caps can approximate factory spec. I know what that sound is and IMO it is very good.

In my experience, that was a joyful discovery, and even better, it didn't cost much to discover. It is also something I wish I would have known when I started. It's the best advice I have to offer, IF someone wanted to improve the sound of vintage Heritage for about what it costs to take the family to dinner.

As you have pointed out, this advice and path is not for everyone. I am not saying that it is. It was what worked for me, that's all. It might be helpful to think of my advice as the minority report.

and, oh yeh, did I mention it's o.k. if we simply disagree?

[Deang]

I didn't really see any of this as disagreement as me just feeling like some things needed to be clarified.

Tried to call you about an hour ago.

[colterphoto1]

I hardly think removal of the zeners reduces the network to 'lite' status. Most remove them and purists don't want them. I still use them and the decision on whether to use them or not is done on a case by case basis. People using the older K-77 who really lean on the volume or those using older power amps with strong turn on/off transients might need them -- but the AA sure isn't less of a network if you don't use them. I also don't think it makes much sense to advocate their use in the AA but not in the Type A -- a network that dumps substanially more energy in the tweeter than the AA.

Question- how does that network of two zeners work and what should happen should that that circuitry kick in? Wouldn't it make a dead short against the amp- which could damage much more than a tweeter diaphram?

I have an engineer friend who thinks they should be taken out of ALL networks. Thoughts?

[BEC]

The zeners do absolutely nothing until the voltage across them rises to about 10.2 volts peak to peak (sum of positive and negative peaks). At that point the zeners start to conduct and shunt power away from the tweeter. At full conduction, they would still not be a short to the amp because there is a capacitor between the amp and the zeners. PWK used the zeners because they are much faster acting than a fuse and reset automatically when the over power condition goes away.

Bob Crites

[Al Klappenberger]

Bob is right. The zeners do nothing at all until the voltage across them gets to high, then they litterally chop the signal off top and bottom. Eventually, if you push them hard enough, you will get a square wave that is no higher than their breakdown voltage.

They do not short out the amp becasue 20 Khz is not high enough to be beyond the influence of the AA tweeter filter. If you could put in a signal at about 40 or 50 Khz, that might look like a short circuit to the amp as then start to come into action. At normal tweeter frequency it isn't a problem. The problem with 10Watt Zeners is they are very expensive. If you already have them, use them! They will not hear anyhting from them if you keep the volume within reason.

Al K.

[Guest " "]

The zeners really won't help protect the tweeters from continuous power above their continuous power rating of 5 watts. 6 watts continuous will blow the tweeter.

It will only help with peak power protection as it is set to turn on at 1/4th the peak power rating of 50watts (10ms).

[colterphoto1]

so don't throw those old AL's away, right?

I have AL's on my LSI's now. Use electronic crossover for the low/mid point, will the zener stage offer any real protection for tweeters or should I go three way and bypass the AL altogether?

M

[Deang]

Are these the same LaScalas you had the AA's in, or a different set? I've heard you voice concern about running the AA with your later model LaScalas, but I've never heard you say that you didn't like the sound. So, do the mids sound too hot to you?

As far as I'm concerned you only need tweeter protection if you're running the old round magnet K-77 or love to sit around watching your clipping meters light up from your high powered amp. If you decide to triamp, and you might still want a cap between the amp and tweeters to protect them from DC.

Old post from Dennis (DJK) might be of interest:

The urban legend about 'clipping distortion' damaging your speakers is just that, a legend.

As with all legends there is some basis in fact.

Over 25 years ago I contributed to a JBL 'tech note' titled: Danger, low power. It was written to try and slow the rash of tweeter failures we were seeing (I ran a service center).

The only portion of that note that I consider valid today is the caution about the use of tape lifters in RWD and FF with the volume up.

Speakers die from two root causes:

heat

mechanical damage

With the advent of what PWK called 'the stove' (an amplifier of 100W or more power), the K77s started to die.

The type A network became the AA with the 18dB slope and the zener diode protectors.

The main form of death was mechanical failure, the tweeter lead out wire broke.

The zener diodes limited the clean signal to 2W and turned everthing into a 4W square wave at high power.

That's right, the protection ciruit deliberately converted clean signal into square waves before feeding the tweeter.

In 1982 the elliptical filter was added, and the zeners dropped (they were actually quite expensive). The elliptical filter was basically the 18dB Chebychev with a zero added at the resonant frequency of the tweeter.

The interesting thing was that EV up-graded the voice-coil assembly during this time period and the network changes may not have been appropriate (the new network sounded sibilant on female vocals and had time/energy storage issues, see the Heyser review of the Klipschorn in Audio).

EV had changed the lead-out wire to a flat BeCu lead, the same as their top-of-the-line DH1 compression driver.

The lead-out wire no longer broke from flexing, but the coil came apart.

EV had changed from a long-cure thermo-set adhesive to a quick-cure UV-set adhesive.

The UV-set adhesive became soft under heat and the coil windings came apart.

The newest coils have the flat lead-out wire and the green thermo-set adhesive. These are very reliable.

Woofers die from clipping too, usually mechanical damage.

It is an amplifier design issue, and caused by the feedback loop being clipped. It can cause rail-to-rail pulses in the 1hz~4hz region. This in turn causes so much cone motion that someting has to give, the coil hits the magnet, the spider hits the top plate, the spider or cone tear, etc.

This is mainly a solid state problem, tube amps do not have the extended power bandwidth (for the most part) to cause the same damage, and the feedback loops are different.

Raw power (volume) seldom damages speakers, I have seen a Klipschorn driven to 250W peaks with a 1A inline fast-blow fuse.

Another interesting (and valid) viewpoint on this subject:

http://www.rane.com/pdf/note128.pdf

[colterphoto1]

I have three pairs LS.

One pair is the LSBR's that are my main LR in Hearth Room HT, these had AL's and now sport BEC's AA's. THey have 55M and 77M's. These are the ones that exhibited the 'phase problem' warning from the Yamaha receiver after the AA's were installed (the wiring to the receiver stayed precisely the same)

Two pair are my garage LSI's that I use for outdoor playback, sometimes at low levels with just the unaltered AL networks. When I use them for PA, I have stereo 3way electronic EQ and plenty of amp channels. I had intended to triamp subs, LS W bins, and LS Mid/Hi, so the AL would still be in force for the upper bins. Reworking these would be expensive since there are 4 of the AL networks.

suggestions?

M

[BEC]

The zeners really won't help protect the tweeters from continuous power above their continuous power rating of 5 watts.   6 watts continuous will blow the tweeter.

 It will only help with peak power protection as it is set to turn on at 1/4th  the peak power rating of 50watts (10ms).

 

SF,

Please explain this. I have no idea what you are talking about.

Bob Crites

[Guest " "]

BEC

Looks like these zeners are designed ofr peak power protection rather than continous power protection.

EV's data for the voice coil in the T-35 has it rated at 5 watts continuous and 50 watts peak.

The Zener's look like they come on line at 12.5 watts. (on line calculator using the 10.x volts)

12.5 watts is 1/4 of 50 watts.

If you put 6 watts (1 watt more than the rated 5 watts continuous) of continous program material thru the tweeter, the tweeter it will blow, since the protection arrangement with the zeners do not add any value til you hit peaks of 12.5 watts.

Tweeters still blow reguardless of having zener diodes.

[colterphoto1]

I have a lot of trouble believeing that PWK would design and build something that did not work. Something must be wrong with the above arguement. Let's work it out guys.

Is the point that the tweeter isn't going to get CONTINUOUS power of any type (short of a dead DC signal) , being a tweeter?

And if indeed 5 watts are the tops for these, they sure don't make very good PA tweeters. If I were tri-amping I'd want to use like a Crown DC60 for a bank of 4 of the little guys. That also doens't sound right.

M

[BEC]

SF,

The zeners begin to conduct when the peak voltage either positive of negative reaches about 5.8 volts. .707 X 5.8 = 4.1 VRMS. 4.1 X 4.1 = 16.8. 16.8 / 8 ohms = 2.1 watts.

As power continues to increase, the average voltage would approach peak voltage at the maximum the zeners could dissipate which is 20 watts. At that point there would be 5.8 VRMS applied to the tweeters or about 4.2 watts. To get that amount of power to the tweeters should require about 1000 watts into the speaker.

For any reasonable application of power, the zeners can be considered to limit the power to the tweeter to 2 watts.

Bob Crites

[Daddy Dee]

Dean,

Missed your call. Thanks for the voice mail.

[Guest " "]

voltage E or V =

volts V (5.8)

current I =

amperes, amps A (.725)

resistance R =

ohms O (8)

power P =

watts W (4.205)

Your match adds up for continuos power.

I'm not sure how much total system power it would take to send 50 watts peak into the tweeter for the 10ms peak that would blow them. Too many factors. The 6db per octave of out of band material. Leaking caps. The intended cutoff. etc. But if you assume 80% of music is not HF, an amp that can produce a 350 watt peak could send a 70 watt peak into the HF section, zener captures 20, 50 goes to the tweeter.

Since tweeters are blowing, some version of this senerio is happening.

A fast blow fuse would protect the tweeters beyond the 20 watt limit of the zeners.

[BEC]

SF,

You are missing something here. Any peaks above two watts voltage equivalent will simply be shunted through the zeners to ground. The tweeters will never see it. That would continue until the zeners burn up at something over 20 watts. It would take around 1000 watts into the speaker to get 20 watts to the tweeter circuit.

Bob

[Guest " "]

BEC

I don't know about that Bob. The fact of the matter is that tweeters blow before the zeners do. We only need 50 watts peak at 10 ms to blow the tweeter.

20 watts of music above the tweeters cutoff frequency would send it right into the tweeter circut.

I addition, since the AA is a gentle slope xover, some of the lower bands would overlap into the tweeter circut as well.

Evidence is the fact that these tweeters do in fact blow.

I have a few AA's in which the owners put fuses inline with the tweeter since the tweeters kept blowing. Zeners tested out fine. Once the fuses when in fuse blew before the tweeters did.