AR915 Crossover Help

[AR surround]

I just acquired a pair of AR915 speakers in pretty good cosmetic shape.   The AR915 is similar to the AR91, but without midrange and tweeter switches and has fake veneer.   I opened them up to do an inventory of parts that I need for a recap and found some problems.  

The first photo is of the left speaker crossover.  It shows a 2 ohm resistor hanging in space as shown by the arrow.   It appears that another resistor (1 ohm) has been substituted in its place.   Anyone know if AR may have done this?   Or is it more likely that someone messed with the speaker in the aftermarket?  Note also that two of the caps are Mylars rather than Callins NPE's.

 

The second photo is of the right speaker crossover.   It also has a 2 ohm resistor hanging into space as shown by the arrow.   However, there is no 1 ohm resistor substituted as with the left speaker.    Also, there is only one Mylar cap in this unit.  I find this bizarre since the serial numbers are only 3 units apart.   Looking at the AR91 crossover schematic - included here for reference - it appears that dangling end of that 2 ohm resistor should connect to the terminal circled and marked "T" in the photo.   Can someone correct me if I am wrong?

Lastly, does anyone know how to remove that blob of glue in the middle covering the binding posts?   Soften it up with 91% isopropanol perhaps?

Thanks for the help.

 

[Stimpy]

Well that's bizarre!  It looks to me like someone definitely was in there, as I wouldn't think they left the factory like that.  It looks to be an easy fix.  Or, pick up a set of 91 / 92 crossovers on eBay.  They pop up fairly often.  Then you'd have level switches too!  And I'd try isopropanol on the glue also.

Good luck.

[ra.ra]

Concerning where those loose 2-ohm resistors were intended, I believe you are reading this correctly with regards to your terminal marked "T". Also, it appears that the 1-ohm resistor in the right x-o has been removed (along with some glue and masonite). All remaining components appear fully original to me, and although it's mildly irritating to the restoration purist, it's not unusual to find different caps (in your case, the 8uF mid cap) within a "pair" of AR speakers.

My understanding of the differences between the 915 and the 91 is pretty much the same as yours, but I think the 915 also had a square top cabinet profile (like the AR-92) and was also offered as an option in real wood veneer as well as vinyl.

Looking at the AR-91 schematic - - once you strip away the switches and their associated four resistors - - - what is curious to me is that your x-o's in the 915's have (or had) three resistors each while the schematic for the 91 only shows two (1-ohm for mid and 2-ohm for woofer). From what I see, the mystery 2-ohm resistor in the upper left appears to be in the mid circuit.

[DavidR]

Here's a crossover pic from my 91's. It might help as a wiring reference.

[ra.ra]

The crossover assembly drawing (not a schematic) for the AR-915 (and 915 veneer) is located in the Library under "special sections" for AR. It is identical to the one used in the AR-58s, and in fact, shows four coils, five caps, and only two resistors - - just like in David's pic once you remove the switches and their resistors. The assembly notes also state that all resistors should be kept at least 1/2" clear from the x-o panel.

If you are unable to locate it, I can post an image for you later.

[DavidR]

That goop on the backside of the binding posts looks like liquid nails. Ugghhhh. Butcher......... They disconnected your woofer zobel.

It also looks like some early style of mylar caps (the ones that say Mexico).

[AR surround]

2 hours ago, ra.ra said:

The crossover assembly drawing (not a schematic) for the AR-915 (and 915 veneer) is located in the Library under "special sections" for AR. It is identical to the one used in the AR-58s, and in fact, shows four coils, five caps, and only two resistors - - just like in David's pic once you remove the switches and their resistors. The assembly notes also state that all resistors should be kept at least 1/2" clear from the x-o panel.

If you are unable to locate it, I can post an image for you later.

Thanks ra.ra.   I found the drawing.  I didn't notice it earlier because the lead-in starts with AR58.   The connection points are clear.   Both crossovers in my AR915's have only two resistors; it's just that the left speaker has a third resistor sticking out in space and the right speaker has the second resistor disconnected.  

It should be an easy path to recap / reconnect everything now.  I just don't understand how these crossovers got so mucked up.

[ar_pro]

Here's the AR-58S blueprint which might be helpful.

Rotate the drawing 90 degrees counter-clockwise, and it will line up closely with your crossover board photo.

The AR-58S schematic in the Library reverses the placement of the 2 ohm resistor and 100 mfd capacitor in the woofer circuit.

[ra.ra]

Thanks, ar_pro, that's the correct drawing, and I may be seeing this incorrectly, but something still looks fishy to me. From the OP's pics, I still don't see the 2-ohm R in series with the 100uF C.......and, why are there three resistors in the x-o pics?

I always thought the AR-915 was basically an international version of the AR-91, and I began to suspect that maybe the midrange in the 915 was a slightly different driver that required an extra bit of resistance. But nope, the assembly drawing for the 915 shows the mid p/n as the 032 driver, exact same as the 91. I'm sure this will get figured out, but I'm still a little perplexed. 

[JKent]

Here's a 91 xo, labeled. Also an "after" pic.

 

[ar_pro]

What a rat's nest, right?

The 2 ohm resistor should connect to the 100mf at the red dot on the blueprint.

[ra.ra]

1 hour ago, ar_pro said:

The 2 ohm resistor should connect to the 100mf at the red dot on the blueprint.

 

That's one of the same connections I was looking at. Attached is a great pic of an AR-58s x-o (courtesy of Roger Weld), which looks just like the 915 assembly drawing.

[DavidR]

Both 2 ohm resistors appear to be connected to the 100uF cap. So the other end/lead of the resistor needs to go to the negative terminal.

[AR surround]

I recapped one AR915 which is now in service as the center channel speaker between the AR9 fronts.    The AR915 sounds superior to my last center channel speaker, an AR48s.   Having drivers essentially matched to the AR9's along with the larger size of the AR915 obviously has helped.   The details:

- 100uF woofer shunt cap (lower right in photo) is an assembly of four 24uF Solen MKP's plus a 4uF Dayton DMPC plus a 0.10uF Dayton F&F bypass.   The Solens were first employed as the 24uF UMR series caps in my AR9's and AR90's but proved incompatible.   Had they not been sitting around in the parts bin, I would have gone with a Bennic 100uF NPE.

- 40uF spot is a Dayton DMPC plus 0.01uF Dayton F&F bypass.

- 24uF midrange spot is 22uF+2.2uF Jantzen CrossCap combo originally tried in an AR90 plus a 0.01uF Dayton F&F bypass.

- The other two caps (4uF and 8uF) are Dayton 1% PMPCs plus 0.01uF Dayton F&F bypasses.

- The midrange is attenuated -3dB by using a 2 ohm resistor (lower left corner) in series with the 24uF cap bundle.  Deciding to install this resistor right off the bat was an educated guess based on a lot of trial and error on the AR9 and AR90 recapping efforts.

 

[DavidR]

Good job getting that goop off of the terminal posts. You sure made good use of the evil solen caps. Looks good and will last a long time. Happy listening.

[ra.ra]

I will always applaud the resourceful use of available parts-at-hand, but nevertheless, it must be asked: exactly why were the Solen caps previously deemed to be "incompatible"?......and why are they now purported to be "evil"? And while there is no evidence to suggest that these speakers are now performing with anything other than spectacular results, I do have to question the wisdom of taking a well-designed, inexpensive, five-capacitor crossover and replacing it with an expensive, fifteen-capacitor version. (Yep....15....count 'em!)

My challenge is only based in the lack of KISS methodology applied to this solution. As originally designed, the AR-915 (and 91 and 58s and....) was a terrific loudspeaker even with the original dirt cheap Callins or Temple caps, so I'd be curious to know what the expected level of "improvement" is due to this excessive re-cap effort? 

https://en.wikipedia.org/wiki/KISS_principle

[Carlspeak]

OEM Callins and Temple caps are cr&p. They age terribly and drift way out of spec. 

I have a pair of 100uF Solen caps F.S. PM me if there's any interest.

[AR surround]

32 minutes ago, ra.ra said:

I will always applaud the resourceful use of available parts-at-hand, but nevertheless, it must be asked: exactly why were the Solen caps previously deemed to be "incompatible"?......and why are they now purported to be "evil"? And while there is no evidence to suggest that these speakers are now performing with anything other than spectacular results, I do have to question the wisdom of taking a well-designed, inexpensive, five-capacitor crossover and replacing it with an expensive, fifteen-capacitor version. (Yep....15....count 'em!)

My challenge is only based in the lack of KISS methodology applied to this solution. As originally designed, the AR-915 (and 91 and 58s and....) was a terrific loudspeaker even with the original dirt cheap Callins or Temple caps, so I'd be curious to know what the expected level of "improvement" is due to this excessive re-cap effort? 

https://en.wikipedia.org/wiki/KISS_principle

If you intended to get me riled up ra.ra, I congratulate you on your excellent work.     I installed those 24uF Solens in both my AR9's and AR90's UMR circuits.  If  you want to see where this is all written up, see the thread, AR90 Crossover Recapping - Taming the UMR:

http://www.classicspeakerpages.net/IP.Board/index.php?/topic/9406-ar90-crossover-recapping-taming-the-umr/

I had a bone to pick with those four Solens for which I paid something like $50 for the lot.   So they were either going to make themselves useful ganged together as the woofer shunt cap in this AR915 or find themselves subjected to capacitor "burn-in" over my fire pit!!!

The Jantzen Cross Caps while also somewhat problematic for me in the AR9 and AR90, seem to be OK in the AR915 24uF spot with the Dayton F&F bypass cap and 2 ohm attenuation resistor installed.

If you want to know why I used Dayton F&F bypass caps (at under a buck a piece), take a look at the May 29th post from DavidR in this thread, Latest Acquisition - AR91s:

http://www.classicspeakerpages.net/IP.Board/index.php?/topic/8163-latest-aquisition-ar91s/&page=2

So that is the saga of how I ended up using 15 caps and an extra resistor in my AR915.

 

[ra.ra]

Carl, I am well aware of the reputation of these black/red caps, and I automatically replace them in all of my projects when I find them - - this is by no means any sort endorsement or testimonial on their behalf, and I agree with your overall assessment - - but I believe you have completely missed my point. I was trying to say that, without the benefit of decades of hindsight regarding these caps and their aging characteristics, the engineers at AR found them suitable to deliver the designed performance for various speaker models, and it can be expected that those speakers performed exceedingly well for their owners for the ensuing years. My challenge was simply about the number and expense of replacement components implemented here in this project.

And to AR surround - - I do appreciate your humorous comment about "burn in" - - that gave me a chuckle , but no, my primary intent was not to rankle anyone, and again I commend you for putting those costly large Solen caps to use somewhere. However, I did expect that some feathers might get ruffled with my skepticism, but I think you already know that I have shown interest and tried to provide useful assistance with your project in earlier posts.

I have most likely read your previous threads, but perhaps I'll go back for another look. However, I'll be fully prepared to have my eyes glaze over yet again as I read about more hand-wrenching, hair-pulling, and teeth-gnashing over the selection of overpriced replacement capacitors for vintage speakers that originally used inexpensive, plain-Jane components - - - all the while providing very satisfactory results until, of course, the aging process compromised the original specs.

My question here is all about the added complexities and costs of "upgrades" weighed against the anticipated expectations and of course, the subsequent performance results. As an aside, I've got no particular allegiance to French manufacturers, but I have used Solen caps in some vintage AR's with excellent success. That said, I have no interest in any 100uF poly caps, Solen or otherwise, for any of my modest applications, but thanks anyway.

[RoyC]

Ra.ra, only those who have read lots of audio forum fluff, and have calibrated hearing, can hear those Solen/Dayton differences...and as a bonus they don't require any actual technical knowledge about electronics.

I have read your posts, AR surround, and don't at all mind riling you up.

To quote Paul Simon..."a man hears what he wants to hear and disregards the rest". 

Roy

[JKent]

13 minutes ago, RoyC said:

To quote Paul Simon..."a man hears what he wants to hear and disregards the rest".

Is that what's meant by psychoacoustics? 

[DavidR]

3 hours ago, ra.ra said:

I will always applaud the resourceful use of available parts-at-hand, but nevertheless, it must be asked: exactly why were the Solen caps previously deemed to be "incompatible"?....

AR Surround had tried the Solens in the UMR series cap for AR9 and 90. They are now being used in a parallel cap position where frequencies are shunted to ground.

There are some people who think all amps sound the same, not just caps.

[AR surround]

1 hour ago, RoyC said:

Ra.ra, only those who have read lots of audio forum fluff, and have calibrated hearing, can hear those Solen/Dayton differences...and as a bonus they don't require any actual technical knowledge about electronics....

Roy

I tried Solen caps only in the 24uF UMR spot in the AR90 and AR9, so I have no evidence that substituting a 25uF Dayton PMPC would have yielded different audible results.   I wish I had read the audio forum fluff, or remembered the PM from Bret back in 2007 bemoaning the use of Solen caps in his AR10pi's, before I bought the Solens.

I do know that the 22uF + 2.2uF combo of Jantzen Cross-Caps sounded substantially better than the single Solen.   However, I only achieved excellent results when I heeded Carl and Roy's suggestion of trying a NPE and switched to Mundorf E-Caps.  

I suspect that the Jantzen Cross-Caps sound fine in the 24uF spot on the AR915 Midrange because the crossover differs from that of the AR9 and AR90.  Or perhaps it is because I added the Dayton F&F bypass.   Or it could be as simple as the height of the midrange dome in the AR915 sits lower than that of the AR9 and AR90 and fires vertically off-axis for a seated person.

 

 

 

[DavidR]

I always like to recall this quote from Ken Kantor (from AK website)

<<< for some reason it won't copy and paste>>>

LATER

[DavidR]