ra.ra
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Posts posted by ra.ra
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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?
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WAF: the first time I encountered this acronym, I had no idea what the bleep it was, but like yourself, I was amused by the concept.
Apparently, there are two versions of the 1700 receiver: early and late - - - if you have capability for two sets of speakers, it sounds like you probably have the later version (with loudness control concentric with balance control), as discussed in link attached. Product info shown below appears to be for early version, so you may want to double check the specs and wiring configurations for multiple sets of speakers.
http://audiokarma.org/forums/index.php?threads/strange-mcintosh-1700.113441/
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Hi Patrick, and welcome to the CSP forum - - what a great first post! My first step into AR speakers (1970 or '71) was with the AR-4x, and even though the 4xa was a poorly marketed product, I think it is the slightly better speaker model with that 1-1/4" tweeter.
I can't help you much with the mix-and-match of various impedance speakers, but knowing that you have Mcintosh power, you're already in a pretty good starting position. I'm pretty sure that many Mac amps (and receivers?) can comfortably reach down into 2-ohm territory.
Your primary question about which larger speaker to acquire is not an easy one - - - as others have begun to mention, there are many variables to consider. The 2ax had various iterations, and so did the 3a. Basically, the 5 was mostly consistent except for minor woofer variations. Purchase cost will be one factor, but restoration costs will be a whole other ball of wax, dependent on condition of cabinets, grilles, drivers, badges, and crossovers. Some woofers have cloth surrounds, some have foam ......... etc., etc.
The decision is not simply a matter of how much LF bass to purchase. Evaluation of the tweeters and mids is also important - these aged drivers frequently exhibit diminished performance and can be expensive to replace. Also, there is the matter of physical size and visual appeal - - the 3a is only slightly larger than the 5 or 2ax and is considerably heavier, but it does have the unique wide face frame trim that the others do not. Additionally, many different wood veneers were offered for cabinet finish - - - is the WAF a consideration?
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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.
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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.
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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.
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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.
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Speaking of "the early years", I just found this thread which included a pic of the Mt. Auburn St. building. Am not sure exactly when the street address numbers were revised, but a 1930 map of Cambridge (attached) shows this building as 21 and 23 Mt. Auburn when it was the Boston Bookbinding Co. Inc. The building extends thru the middle of the block to Arrow Street, and I think there is a thread on this site (started by JKent?) about the Baruch-Lang speakers that mentions an Arrow Street address for Henry Kloss' pre-AR enterprise.
A very comprehensive book about the history of Cambridge has just recently been released, but I have not yet inspected it for any mention of these specific buildings or the loudspeaker industry in general. It was produced by the MIT Press, and I have long been an admirer of their publications. One of the co-authors is Charlie Sullivan, the "go-to" source regarding Cambridge history.
https://mitpress.mit.edu/books/building-old-cambridge
My personal feeling is that this project would best be served if kept to a single volume in the 150-page range, with both black/white and color images, and I would love to see the graphics reflect a contemporary look suggestive of upwardly mobile America of the 1950's and 60's. Someone has already mentioned including the "watershed" models, and I want to get in a request to not only discuss the "big boys" (AR-1, 3, 3a, 9's etc.), but to also be sure to cover the more modest models, particularly the hugely successful AR-4x. The entire "classic" lineup should be described within a timeline, marketing rationale, and matrix of features and attributes, including the oddballs (AR-1x) and ne'er-do-wells (AR-8).
AR's place within the larger loudspeaker industry is an important topic, and I would also love to see: 1) a "family tree" of industry personnel, beginning with Villchur and Kloss and then spreading into the principal AR staff as well as all of the offshoot speaker companies that had significant ties or origins with Acoustic Research. Also, it would be highly informative to include: 2) one or two maps to illustrate the concentration of highly-regarded audio companies in the immediate metro Boston region - - - perhaps Cambridge deserves one of its own (AR, KLH, Advent, a/d/s, etc.), but also a larger view of a portion of New England (AR - Norwood and Canton, EPI - Newburyport, Avid - Providence, Bose - Framingham, HH Scott - Maynard, and on and on) might be effective to communicate the impact of AR in being instrumental to the establishment of a burgeoning industry.
Edit: Well, never mind part of this blurb - - I had the chance today to look at the new Cambridge history book I was praising, and despite its back-breaking heft of 900+ pages, there is only scant mention of any of these buildings, and none of the writing pertains to the subject at hand.
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That's a fine-looking pair of vintage components. Not to derail this thread about the Sixteen integrated amp, but I'm curious about the volume control on the Eighteen tuner - - does this thing have some sort of pre-amp included in the circuitry?
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Hey, that's a great looking amplifier, and I suspect a fairly rare beast. Very simple, spartan appearance, and it's very unusual to see a two-step loudness switch. More knowledgeable KLH fans may be able to date or comment on this product, but what's curious to me is that the rear labeling suggests a date prior to the use of zip codes in addresses (1963), at a time when tube amplifiers (HH Scott, e.g.) were still popular in home audio. Rear views attached.
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That's an amusing story and a great-looking pair of speakers. I like the old Rectilinears, too, but I've never had a pair of the big boys like the III's. That's a lot of screws to remove the baffle board, but pretty easy to get at all the innards once you've done that. I know it's typical for these smaller drivers to be held in place with only silicone adhesive, but are those T-nuts and machine screws used for fastening the woofers? Thanks for posting.
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Agreed, the Howard's products can work very well for cabinets that do not require further treatment. And the 1966 dates on yours make perfect sense when compared to the dates and serial numbers noted on my schematic sketch.
Thx for the additional tweeter pics, and as suspected, the magnet seems to confirm this hybrid. What you have is indeed the AR-4x tweeter, but with the added metal cage and (partial) fiberglass damping associated with the earlier AR-4 tweeter. Yes, this is associated with the 20uF capacitor, and your wax cap block, like mine, has no identifying labels, which is where RoyC bailed me out.
Pic attached shows front and rear of 3.5" AR-4 tweeter on left; and 2.5" AR-4x tweeter on right. Note the difference in magnet diameters.
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Sounds like you're well on your way already. Looking forward to future progress reports.
Re: grille cloth, it is very typical for the original cloth to have some degree of discoloring, but just one word of caution - - if you have removed it from the grille frame, and then subject it to moisture, subsequent shrinkage is most likely to occur upon drying, which might make it very difficult to re-stretch and staple over the original frame. Other members have various methods for cleaning the linen, but link attached shows my experience:
Re: cabinets, great to hear that the veneer is in good condition, and re-finishing of the walnut is fairly forgiving for even the weekend hobbyist. Within limits, the veneer successfully accepts efforts to lighten or darken or modify the coloration.
Am still unclear about your "bypass" remarks. Your wiring sketch looks correct, and appears to keep the control in the tweeter circuit as intended. IMO, you want the potentiometer in the circuit for two reasons: [a] it is beneficial to have the variable control for tweeter output to respond to speaker placement and specific room acoustics; and even at full tweeter output, the pot provides a bit of necessary resistance.
Great project - - - take your time, document carefully, and report back when you can.
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Hi Coleman,
RoyC helped me confirm the accuracy of that crossover schematic, and although it's not a bad sketch, it was sort of stupid the way I drew that 24uF cap - - - it looks more complicated than it should. Instead, I should've sketched it so that the 24 cap is simply connected in parallel across the woofer terminals. In fact, I think that is how I built it, with the 24 cap attached to the woofer magnet instead of to the cabinet bottom (back). Either method of installation is fine - - an important thing to note, which both of our sketches show with a dot - - is to ensure the three-point connection where the coil, the 24 cap, and the woofer common wire are joined.
Your sketch looks just fine. The only thing I did not understand is the comment "Bypass to 1".
Your speakers look great, and this two-capacitor version of the AR-4x (with the AR-4 woofer) is somewhat rare, and they all tend to fall in that ± 28K to 42K range of serial numbers. In fact, yours might be even more peculiar than most because of that tweeter, which looks more like the AR-4 tweet (3.5" cone) than the AR-4x tweeter (2.5" cone).
Can you please help confirm more about this tweeter? Could you post a pic of the entire crossover to confirm the tweeter cap value (20uF, I presume?), and also include close-up pics of the tweeter, especially the backside? And measure the diameter of tweeter magnet? Since these speakers tend to suggest the production line transition between the AR-4 and the AR-4x models, I have a suspicion that your tweeters may be the 2.5" tweeter used in the 4x, but with the protective screen and partial fiberglass damping found on the 3.5" tweeter of the AR-4.
You have a very interesting pair of speakers. I hope the cabinets and grilles are in good shape as well. I suspect you'll be installing new caps, but you'd be well-advised to also to re-furbish the control pots or replace them (with A-P pots from other AR's or L-pads) and perhaps also apply a light coat of Roy's butyl dope to the woofer surrounds if they feel stiff. Your particular version of 4x shows up very infrequently, and one of the few identifications I've seen of this specimen is from a document sent to me by JKent a few years ago, as shown below.
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Fantastic collection, thx for sharing.
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One other thing......beware the 1" shaft version will be longer than desired. Shaft length of 3/8" much preferred. Pic attached from RoyC or JKent shows installation.
http://www.parts-express.com/speaker-l-pad-attenuator-15w-mono-3-8-shaft-8-ohm--260-248
http://www.parts-express.com/speaker-l-pad-attenuator-15w-mono-1-shaft-8-ohm--260-250
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Thx for the additional pics of the mahogany AR-3, Tom. It makes me curious why this gorgeous veneer finish seems relatively rare, given that the mahogany option was between $6 to $10 less in price (per cabinet) compared with the oiled walnut, per the 1971 catalog.
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If you read up some more and look at additional images, you'll find a few variations of this speaker model, but there is nothing obvious to suggest that any part of yours are not original.
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Yes, your images are viewable, and it appears that all drivers are original. I am no expert on the 10-pi, but according to the various drivers pictured in the AR-3a restoration manual, all of your drivers are from an early version (Mk. I ???): woofer (A.4); midrange (A.13) and tweeter (A.21).
I may be mistaken, but I always thought that little (Varec) button was simply a magnet to keep the wooden door closed, and if you view this attached thread, you'll see a pair of 10-pi's with the ID sticker inside the door flap like yours. You've got yourself some very nice speakers there.
http://www.classicspeakerpages.net/IP.Board/index.php?/topic/1520-ar10pi-crossover-schematics/
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Hey Glenn, those turned out just gorgeous and the new grilles look great. You (and Roy) did spectacular work with that restoration project. Your results look just like this random pic I keep on file. Congrats.
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Great job on those speakers, Glenn, and your grilles and frames look terrific. Nice to see the AR-12 (and badge) in a horizontal orientation.
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What is the preferred method for trimming the overhang on the veneer patch? Utility knife? Razor sharp chisel? Sanding block? Sledge hammer?
And, is that ordinary yellow wood glue used to secure the patch? Thanks.
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Hey Glenn, you got another great find there. Gorgeous speakers and great pics. Can I suggest maybe providing some temporary protection on those tweeters while you work on the cabinets? Looking forward to watching your progress. Carry on.
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The pair of speaker crossovers shown here (with #5 coils, however) had the same situation regarding mis-matched capacitors, and even though the can-type caps often still measure reasonably well, it is a good idea to replace both 20 uF caps at the same time. You can always parallel multiple smaller caps to achieve this value, or simply replace with a single good quality cap of the same value. And if you want to ensure the best HF performance from the tweeters in your restored speakers, while you are inside, you should also inspect, and then decide whether to clean or replace the pot controls.
AR915 Crossover Help
in Acoustic Research
Posted
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.