Are the diodes in AA crossovers necessary?

[Al Klappenberger]

Bob,

I read that dope from hope blurb on the AA before. I don't beleive a word of it!

Al K.

[BEC]

What counts is the end result acoustically. I think PWK did a rather elegant job on the AA. If you look at the voltage output of that crossover and think about how the K-55V and K-77 work, I think you can see he got what he was after.

Bob

[Al Klappenberger]

Bob,

I agree, to a point. From a manufacturing standpoint, except for the zeners PWK was forced to add, it does what it has to do with a minimum of parts. The thing to realize is that he did it using very old techniques, constant-K sections using a slide rule. I started that way too. In fact, I still have the slide rule (somewhere!). Time has moved on and design techniques have improved. When the AA was in production (around 1975 or so) is when I got my first computer and wrote the first filter analysis program. The computer was a Heathkit H8. It had an 8080CPU running at 5 MHz. It was capable of analyzing a filter like the AA at a rate of about 1 frequency point every two seconds. The output was tabulated and printed on a roll of paper through a Teletype terminal. Now, my Pentium III 450 will do 1000 points in a fraction of a second and display it graphically. I can see changes made to a single part by pressing the up or down arrow key in real time to do optimization. In PWK's day, optimization had to be done on the bench using very crude equipment. PWK did the best he could considering the equipment of the day and the fact that he had no experience with filters at microwave frequency where requirements are far more stringent. You are forced to learn how to do much better designs at high frequency. Those better methods apply just as well at audio. These days there is no reason to keep doing it poorly.

AL K.

[kzr750r1]

Thanks for talking about this guys. I have a old pair of AA and noticed this circuit but wondered why it was there where I don't see them on other cross overs.

Strange as I have one tweeter testing open and the other not.

With the diods in place what else would have blown out this tweeter?

[Al Klappenberger]

kzr..

I had a tweeter actually fail years ago. Nothing blew it, it just turned into an open circuit. At the time, I exchanged it through Klipsch. These days I would have just opened it up and looked for a bad solder joint!

Al K.

[BEC]

Thanks for talking about this guys. I have a old pair of AA and noticed this circuit but wondered why it was there where I don't see them on other cross overs.

Strange as I have one tweeter testing open and the other not.

With the diods in place what else would have blown out this tweeter?

Most of the several hundred K-77 diaphragms I have replaced had nothing visible wrong with them. Just that the voice coil was open somewhere. I think they often just fail from old age.

Bob