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AR90 Crossover Recapping - Taming the UMR

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Many of you recall from my post titled "AR-9 / AR-90 Crossover Re-capping Adventure" that I had a heck of time trying to find the proper combination of the attenuation resistor switches to achieve acceptable results.   People probably thought I was crazy or losing my hearing.   The culprit was the 24uF Solen MKP 400V capacitor installed inline with the Upper Mid Range (UMR.)   It was all over the place depending on program material.  It sounded anywhere from great to shrill and exhibited the uncanny ability to drill down into a recording, extract whatever grain is there and put it front and center.  This cap seems to be incompatible in this particular circuit with this driver. 

Stimpy suggested adding a Dayton 0.1uF F&F bypass cap as a fix.   Doing so decreased the shrillness of the Solen, but also increased the grain to the point of rendering many recordings unlistenable.   My goal is not simply to obtain the best sound from the best source material, but also to get acceptable results from average recordings.    So this very unforgiving capacitor had to go.

I decided to try one other poly cap before going to an NPE as Carl, RoyC and others had suggested.   I had read that the Jantzen Cross Caps are considered comparatively smooth sounding, so I installed them in place of the Solen.   Although the improvement was a step change, I still wasn't quite where I wanted to be.   A 16 hour burn-in period using high volume pink noise made no difference.   So I installed Mundorf E-Caps (Plain) in matched pairs purchased from Sonic Craft:  http://www.soniccraft.com/index.php/mundorf-ecap-ac-c-23_318_358

Like magic, everything was now where I wanted it to be and has remained so after several days...no "it sounds different on Tuesday afternoon than it did Monday night;" no waiting for burn-in; no endless effing around with the attenuation switches.   Great recordings still sound great, average material is very listenable, and I perceive no loss of detail in going from the poly cap to the Mundorf.  Remarkably, the Mundorf sounds like it has more "air" and "depth."  I surmise that this perception is related to how the E-Cap integrates into the entire speaker system rather how it directly compares to the poly caps.

AR90-1.pngAR90-2.png

Notes:

1)  I confirmed with Carl that the E-Caps with their 70VDC/50VAC rating is a suitable replacement for the stock 100VAC Callins NPE.

2) The 24uF Solens were still installed in the AR9 surround speakers and got the 16 hours of pink noise burn in.  It still isn't acceptable but for some unknown reason has always sounded more tame in the AR9 than the AR90.

3) I use -4.5dB (estimated) attenuation with the E-Caps in the UMR.  I've always used -3dB going back to 1980.  The attenuation network is now set up so that I can go back to -3dB if desired.

The AR9's are next.  I may try the Cross Caps first just as an experiment before going to the E-Caps.

 

Woofer shunt.jpg

E-Caps installed.jpg

Resistor bank.jpg

UMR 6 ohm.jpg

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Nice write up John.

Why did you go with (2) 3 ohm resistors in series instead of (2) 12 ohm in parallel ?

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20 minutes ago, DavidR said:

Nice write up John.

Why did you go with (2) 3 ohm resistors in series instead of (2) 12 ohm in parallel ?

Because the vendor didn't have the 12 ohm Mills in stock.

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Awesome write up.  I love the chart, showing the changes and the audible results.  And pictures.  Everyone loves pictures!  Though, next time, pop-up's would be even better!   Nice work.   :)

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Great write up - thanks so much for the charts and pictures!!! Excellent engineering work!!!

I have the same problem with my AR-9s - that graininess that clearly is coming from the UMR.  So I am going to order the recommended parts and see if they work in my situation. 

Again - many, many thanks to both the author and all those who contributed.

Great forum!!! 

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Thanks so much for this excellent piece, with great detail explaining your approach. This is really useful information, and will be helpful to anyone considering this sort of restoration.

Very nice job!

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Thanks to all of you for your kind comments and for all of your help.   I could not have gotten through this without the input and advice of those of you who enthusiastically participate in this forum.

John

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Having achieved success with the AR90's, I finished the rework on my AR9's last week:

- Replaced the Solen 24uF cap in the UMR with Mundorf E-Caps.

- Replaced that 6 ohm resistor which is in series with the choke across the UMR.

- Replaced the resistors in the attenuation network.

I installed the same value attenuation resistors in the AR9's to yield the same results as with my AR90's:   -1.75dB and -2.5dB attenuation on the tweeter and -3dB and -4.5dB attenuation on the UMR.   If I were to do this over, I would change the AR9's UMR resistors to provide only -1.5dB and -3dB of attenuation.   The balance of the AR9 is very different than that of the AR90's.   So although I prefer -2.5dB attenuation on the AR90 tweeter, I like the AR9 tweeter set at 0dB.   With the UMR, I use -4.5dB attenuation on the AR90 but find even -3dB to be too much of a reduction for my taste with the AR9.

- Replaced the big 2500uF and 470uF Callins woofer caps with bundled Mundorf E-Caps.

These reworked AR9's are very nice and produce a really big sound.   The AR90's also produce a big sound, but the 9's are really over the top.

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19 minutes ago, harry398 said:

AR Surround

so its been a while.......how are the AR9's sounding?  still pleased?

 

would you do anything different?

 

Thanks.

Harry,

I'm extremely happy with the system.   If I were to do anything different, I might have experimented with the Jantzen Cross-Caps + a Dayton 0.10uF F&F bypass cap in the UMR 24uF spot.   As I had noted, the Jantzen Cross-Caps alone in that 24uF spot didn't cut the mustard, but I never tried them with a bypass cap.    I'm sticking with the Mundorf E-Caps + Dayton 0.01uF bypass cap in the 24uF spot.

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5 hours ago, harry398 said:

Is there a reason for juggling 0.1    And. 0.01?

It's what Carl said in the sixteenth post in this thread:

http://www.classicspeakerpages.net/IP.Board/index.php?/topic/9683-ar-9-mid-and-hf-cap-suggestions/

One can mess around with caps, bypass caps, etc. endlessly.   I stopped with the experimentation once I got my quiver of reference recordings to sound the way I wanted.

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yes, He responded after you did.  Thank you

 

I got my ar9's up and running.   they are really good.

However, I can hear they need caps.  I am preparing.....:D

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1 hour ago, harry398 said:

yes, He responded after you did.  Thank you

 

I got my ar9's up and running.   they are really good.

However, I can hear they need caps.  I am preparing.....:D

59ad716714202_AR90RECAPP_20170409_113655_HDR.thumb.jpg.d0d897f7c34e8f044860e2643ff38b0a.jpg

I went a little over board on my 90's.  But, why not?  I think the speakers are worth it.

 

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You've got a high likely hood of inductor cross-talk in a couple of spots due to their same orientation and close proximity to each other. One of the large coils in the left pic should be stood up on edge, In the right pic, stand the blue coil on edge. These changes should be beneficial to your speaker's performance. For more info. on inductor cross talk, visit Troels Graveson's web site. He has a nice chart there that shows recommended mounting of coils and distances.

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20 minutes ago, Carlspeak said:

You've got a high likely hood of inductor cross-talk in a couple of spots due to their same orientation and close proximity to each other. One of the large coils in the left pic should be stood up on edge, In the right pic, stand the blue coil on edge. These changes should be beneficial to your speaker's performance. For more info. on inductor cross talk, visit Troels Graveson's web site. He has a nice chart there that shows recommended mounting of coils and distances.

I did exactly that on both boards.  I stood up the left coil, of the large inductor pairs, and stood up the blue coil too.  I guess I need to update my picture?

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1 hour ago, Carlspeak said:

You've got a high likely hood of inductor cross-talk in a couple of spots due to their same orientation and close proximity to each other.

I keep seeing this discussed in various conversations and I have no reason to doubt it .......... but exactly how does cross-talk present itself in a measurable or perceivable manner; in what ways does re-orientation provide improved performance; and why was this concept not enforced by AR engineers when the crossovers for these loudspeakers were originally laid out for fabrication?    

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Here's a later crossover picture, with better coil orientation. 

59ad8e620f2f1_AR90UPDATED20170904_125418.thumb.jpg.c9c3733e2de4f57f6ed1b8b48494bada.jpg

I'm not sure either, what'll improve?  But it's easy to try, and what can it hurt?

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40 minutes ago, ra.ra said:

was this concept not enforced by AR engineers when the crossovers for these loudspeakers were originally laid out for fabrication?   

Good question! I've adhered to the idea that the coils should be oriented differently whenever I re-arrange a xo (to make room for bigger caps) or build from scratch but it never occurred to me to change a stock layout. Guess it couldn't hurt ;)

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1 hour ago, ra.ra said:

I keep seeing this discussed in various conversations and I have no reason to doubt it .......... but exactly how does cross-talk present itself in a measurable or perceivable manner; in what ways does re-orientation provide improved performance; and why was this concept not enforced by AR engineers when the crossovers for these loudspeakers were originally laid out for fabrication?    

http://www.troelsgravesen.dk/coils.htm 

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Doesn't the AR9 bass section, use 2 stacked coils?  That's listed as "never do this", according to the coil layout pictorials (#8)...!  Can (and should) those coils be separated and remounted?

59ada3e8134e7_AR9wGyFX5s.thumb.jpg.5bade0c0df013b58cac038d37336cadf.jpg

 

 

 

 

 

 

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As you can see in Troels stacked experiments, mH values changed noticeably. I'd be much more concerned if the AR9 had stacked coils in the mid or HF circuits where your hearing is much more sensitive to.

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