Inherited 6 La Scalas - Need some assistance please

[Klipschguy]

The exact year I do not know but it seems like a bunch of AAs from the 70s are ferrous (some I have checked first hand, some as reported by members of this forum). My brother’s 1950s Khorns use brass machine screws in the 500-5000 crossovers, so the impact of ferrous metal was well known to Mr. Klipsch. I would be interested in what Jim has to say as his available resources far exceed my own. 
 

BTW, 001 posted a link to the AA ferrous screw thread, but it doesn’t seem to be there now. 
 

Respectfully,

 

Andy

[Travis In Austin]

1 minute ago, Klipschguy said:

BTW, 001 posted a link to the AA ferrous screw thread, but it doesn’t seem to be there anymore. 

I think he copied and pasted from it instead of a instead of putting a link, I’m sure it’s still there

[Klipschguy]

Yes - a technical error (I did not think otherwise) 

[Travis In Austin]

There it is.

 

But I’m recalling discussions about this issue from the early to mid 2000’s. 

[Klipschguy]

Not that one (but thanks for posting). 
 

The title is: AA Network sounds better with…

 

Not sure how to link it. 

[Klipschguy]

AA Network Sounds better with…

 

 

….figured it out

[Travis In Austin]

This was back when @Deang was a buck fifty. 

 

Dean was right, acoustically, you tweak the tweet, all things being equal, the perception of the bass will change.

 

It also explains why some would prefer the ferrous screw.

 

So I learned about 5 new things today. 
 

@Ed Wolinski between the AA Networks sounds better with limited in the post previous to this, and the one I linked in this post you will know everything you want to know about what the screw metal can change things. 
 

If you can find nylon that would be best, then brass, then stainless you know isn’t magnetic at all, then aluminum. 
 

Has anyone tried just removing the screw and giving a listen? It that produces the preferred sound than I say duct tape is your friend.

[OO1]

great discussion .

[DizRotus]

The back story regarding your acquisition would be interesting, as well as your plans for them.

[Ed Wolinski]

You guys are amazing. Just to see, I am going to do the test as described above with various non-magnetic crews, the original magnetic screw and a piece of duct tape. I will report the results if I can discern any aural enhancement/detraction. 

[Ed Wolinski]

4 hours ago, DizRotus said:

The back story regarding your acquisition would be interesting, as well as your plans for them.

The back story is quite lengthy. Short version: they were originally bought by me, (I still have the warranty cards) in the late 70's/early 80s. A lot of music went thru those cabs. I distinctly remember doing the house mix for 3 Dog Night in 1981. I measured 111 dB SPL at a Biamp 1642 mixing console (that I desperately need a transformer for & cant find any donors); the board placement was 70 feet from the speakers...backed out all of the limits and protection....The La Scalas took the abuse but I DID blow 3 JBL 2220's...). EDIT (I neglected this part): Many years went by and I lost them due to a job change. More years went by and I found all of them banished to a basement. I inquired about getting them and they are now back in my possession!!! Plans? First, I need to get them cleaned out and the 15's inspected. I have found that I need to replace 2 tweet diaphragms (will order from JEM), and plan on recapping the AA crossovers. On the LSI's, I an thinking of polishing up the exterior skeleton aluminum trim. The fiberglass mat looks ok; might do a quick coat of clear.  On the other 4, a light sand and repaint with a highly recommended good grade of paint (paint brand yet to be found out, any thoughts?) is on the things-to-do list. Once I get the LSI's sorted out I will probably put them on the market. The other 4? Not sure. Might sell 2 of the 4 if someone makes me an offer I cannot refuse, def keeping 2 for sure. 

Edited January 20, 2023 by Ed Wolinski
added info

[DizRotus]

Thanks Ed. They have an interesting history.  

 

Michael Colter @colterphoto1 might be some help regarding the needed transformer.  He rarely haunts these forums anymore, but a PM to him might get his attention.  Good luck.

[Edgar]

13 hours ago, Travis In Austin said:

If you have a multimeter that measures inductance you can check them yourself (which I highly recommend) to see. I can’t speak to what this equates to in the amount of change in XO frequency, and whether it is up or down. @Deang or @Edgar can address that.

There is more to the problem than just the change in inductance caused by the ferrous mounting screw. You are effectively changing an air-core inductor into an iron-core inductor. That increases the inductance, but the iron core is subject to hysteresis and saturation when the current through the inductor is high. Hysteresis causes asymmetry in the waveform while saturation causes the inductance to change near the peaks in the waveform; both of those count as distortion. This is the reason that audiophiles prefer air-core inductors.

[Klipschguy]

True, Edgar. However, if feeding a Khorn speaker system, the amplifier power it would take to saturate the inductor in the tweeter leg of a AA network…well one would not want to be in the same room!  Of course you did say “when the current is high.”

 

I guess the ideal solution is to buy an air core .34mH inductor if saturation proves problematic! 😉

[Edgar]

1 hour ago, Klipschguy said:

However, if feeding a Khorn speaker system, the amplifier power it would take to saturate the inductor in the tweeter leg of a AA network…well one would not want to be in the same room!  Of course you did say “when the current is high.”

True. Just pointing-out the potential pitfalls of using a ferrous bolt to secure an air-core inductor, in the generic case. In the specific case that you describe, the biggest problem would probably be the change in inductance.

[DeanG Crossovers]

On 1/20/2023 at 9:56 AM, DizRotus said:

Thanks Ed. They have an interesting history.  

 

Michael Colter @colterphoto1 might be some help regarding the needed transformer.  He rarely haunts these forums anymore, but a PM to him might get his attention.  Good luck.

I didn’t see a reference to an autoformer or “transformer” issue - I stock these parts. 

[DeanG Crossovers]

The schematic shows 245uH. A plot revealed that it moves the crossover point down, which would potentially put the diaphragm in distress and induce distortion. It also moves the target frequency for the EQ that brings the peak down in the K-77. 
 

It doesn’t matter if Klipsch missed these, or if it sounds better to one set of ears. It’s wrong, and should be fixed. 

[Klipschguy]

6 hours ago, Deang said:

The schematic shows 245uH. A plot revealed that it moves the crossover point down, which would potentially put the diaphragm in distress and induce distortion. It also moves the target frequency for the EQ that brings the peak down in the K-77. 
 

It doesn’t matter if Klipsch missed these, or if it sounds better to one set of ears. It’s wrong, and should be fixed. 

Hi Dean, 

 

I respectfully disagree. I am convinced Mr. Paul Klipsch did it on purpose; he was way too bright to let such a widespread defect occur for almost the entire life of the AA network. You agreed back in 2005, but that was a long time ago (BEC was trying to set you straight). Perhaps in time I will come around to your way of thinking. Thank you for taking time to share your thoughts; the exchange of thoughts and ideas makes us all better as we pursue audio excellence. 

 

Cheers,

 

Andy

P.S. The K77 is perfectly safe with the .34mH of inductance in the AA except for cases of EXTREME abuse.

 

[DeanG Crossovers]

So I was wrong once and you have evidence? 🙂

[Travis In Austin]

3 hours ago, Klipschguy said:

Hi Dean, 

 

I respectfully disagree. I am convinced Mr. Paul Klipsch did it on purpose; he was way too bright to let such a widespread defect occur for almost the entire life of the AA network.

 

 

You can know for sure, Ask The Historian he would know for sure, he was around at that time and it is his initials JRH approving that schematic.