Tobin Mods to Bozak 302A Urban speakers - definitely worth it!

I haven't seen too many comments on these forums about Bozak speakers. I recently acquired a pair of Bozak 302A Urban speakers from circa 1960. These are big, infinite baffle cabinet design speakers, 2 ft x 2 ft x 2 ft cubes, beautifully simple, "early 60s modernistic" styling, and the single prior owner kept them as new. Here's an image from the web of the 1960 ad brochure for Bozak's line, the 302As (with matching cabinet that I also have) are at top:

I wanted to sing the praises of these speakers a bit here and talk about some very simple mods that can be made to the older version of this speaker - which I acquired - to bring them into the big leagues. I'm so happy with these speakers after mods that I have stopped worrying about spending big dough to buy Tannoy Concentric Golds off eBay that I wouldn't even be able to listen to first. I still hope to pick up Tannoys someday, but now there's no hurry, and I can wait until I can find a pair at a garage or estate sale for $100 like Steve did! (I can dream, can't I?)

I WILL POST PHOTOS LATER TODAY of the speakers and the mods when I'm home. I'm NOT generally a guy who goes into making major mods to vintage gear - my MC30s and Marantz 7 are stock, stock, stock and will stay that way - but the Bozaks are a bit different. First off they are less expensive to begin with, even if stock, so resale value isn't a big deal. Second, the original Urbans I bought have some known major limitations that need to be addressed, but once they are, you get a world class speaker. So I took the plunge. Here's what I changed, working with my dad over the weekend:

1) First off, the older/original version of this speaker had all paper cones - each speaker had one 12" woofer (B199A), one 5" mid (B209), and two small (2 1/4" I believe) tweeters mounted side by side (B200X). The 12" paper woofer is one of the things Bozak was famous for. It is superb - more on that later. The paper mids weren't bad but not stellar either. The paper tweeters are frankly terrible.

Enter Pat Tobin, probably the greatest expert on Bozak speakers. His e-mail, in case anyone is interested, is [email protected] VERY approachable, nice person who is very willing to help anyone get their Bozaks singing. He was for example cited as "the" Bozak speaker expert in a recent Stereophile article about the Bozak flagship model, the Concert Grand B410 speakers (massive suckers, take most of a wall up!): Concert Grand article

Tobin has posted widely on many audiophile forums about the superiority of the slightly later aluminum tweets (B200Y) and mids (B209A) that Bozak developed, which are interchangeable in size with the older paper versions. I saw these posts in doing Web searches on Bozak speakers and then contacted him and after speaking was convinced this would be worth pursuing. So first thing I did was pick up a pair of Bozak 1970s 313s with whipped external cabinets - but which had pristine aluminum mids and tweets - and this weekend dad and I pirated those and installed them in the Urbans and took out the paper mids and tweets.

2) Second, a couple of crossover mods are optimal in improving the sound of the Urbans. First, the old Bozak N10102 crossover in the original Urbans has a huge cap box with 6 big paper caps. These are all out of spec and really unnecessary nowadays - there for a couple reasons originally that are no longer salient. 4 of the caps were for the midrange network, 2 for the tweets. Working in the cap box would have been a nightmare and I doubt worth the effort. Tobin agrees, and recommends eliminating this cap box and replacing the 4 mid paper caps with a single 25 uF Dayton Audio grade caps and the 2 paper tweeter caps with a single 8.2 uF cap. We did that. Much cleaner.

3) Finally, the biggest issue with going to the aluminum tweets is that they are much "hotter" than the original paper tweets, about 9dB louder. So to balance them with the rest of the cones a tweeter network mod is required, basically installing a 2.0 uF cap and some resistors (attenuation circuit). This mod also allows the tweets to extend above 10 kHz - in the original crossover, the highs roll off rapidly at 10kHz, a purposeful limitation within the crossover and not an inherent limitation of the aluminum tweeters. We used Tobin's instructions to make this modification as well.

4) So in summary, the circuit diagram below shows the entire modified speaker circuit, including Tobin's tweeter network mod WITH TWO SMALL ERRORS - first, the 8.2 uF cap in the tweeter network should obviously come BEFORE the attenuation mod. We wired things correctly, just didn't have a chance to redraw the incorrect diagram. Second, the numbers of the cones my dad put next to the speaker symbols are the older paper ones rather than the updated aluminum ones.

5) BEWARE! We also found some wiring mistakes FROM THE BOZAK FACTORY! Polarity was reversed on one of the speakers in the wires going from the back of speaker hookup terminals to the crossover network input! We fixed that. I'd suggest always checking Bozaks for stuff like this, apparently there were some issues.

6) Finally we also replaced the fiberglass baffling inside the cabinets with new fiberglass insulation material. The old stuff was crumbling to even gentle touch, a mess. Nice and clean now.

SO HOW DO THEY SOUND? In a word, unbelievable! The 12" paper bass cones Bozak made were amazing. I'm still learning and have a lot of speakers to hear, but the transient response on these woofers is amazing. Plus I'm coming from much smaller speakers with 8" woofers, so to me the visceral impact is simply amazing with the Bozaks, drums sound like drums and bass like bass, and it's not bloated or rounded off bass - you hear the growl and twang of string bass on jazz recordings, and it sounds different than the round fatness of the electric bass on a disc like Steve's BOB JAMES IN HI-FI - just as it should be! The aluminum mids are to die for - you listen to ELLA AND LOUIS and they are standing there in your listening room (particularly when these are paired with MC30s!). I am hearing vocal nuances I have never heard. And the aluminum tweets are a HUGE improvement over the paper versions, which hissed and spat in response to anything in the 5-10 kHz range. With the aluminums, it's smooth as silk and Tobin's crossover mod allows you to get extension above 10 kHz. I haven't done any test tone testing yet but I'm guessing they go all the way up to 20 kHz as modern speakers do.

The only remaining weakness I can see with these speakers is the tweeter placement. Tweets are placed in front of the bass cone as you can see from this brochure (it's the 207A woofer/tweet combo:



...and the bass cone is mounted down low in the cabinet. This places the tweets only about a foot off the floor, below the midrange cone. No good. Next project which will be easy will be to dismount the tweets from the woofer bracket and build a very small enclosure for them to sit on top of the Urbans. We'll run the tweeter wires through the back of the cabinet and up on top. This will get all the cones properly oriented and at that point we'll be done. Make no mistake even with this flaw the highs are gorgeous, but clearly this needs to be addressed based on my listening tests (sitting on floor versus in usual chair - highs better when I'm on the floor).

So anyway, wanted to share this for a few reasons:

1) Bozaks are fantastic speakers, don't let anyone tell you otherwise. Maybe one of the best bargains in vintage speakers. Altogether I paid about $500-700 for these speakers, including buying the upgraded aluminum cones and all the crossover mod parts - PLUS I also got the matching audio component cabinet Bozak made to go with them. I can't be exact about price because I bought these as part of a larger sale where I acquired an entire single prior owner vintage system for a lump sum. Bozak was notorious for not publishing speaker sensitivities but I'm guessing based on where I have to put my volume knob on the preamp, as well as the era of manufacture and use of paper and very thin aluminum cones that they are in the 94-96 dB/watt range. Great for vintage tubes.

2) Bozak Urbans will likely require some work to get them up to snuff. If you plug them in as is, stock, you'll be disappointed, especially with the older all-paper cone versions. Very boxy, dull sound with terrible highs. The contrast after the modifications is amazing, they become world class speakers. I don't think you need to worry much about resale if you do these mods - in fact, I'm guessing the value of mine has not been hurt and may actually have gone up with the "Tobin mods." But I could care less because I'm not selling! The combo of the paper 12" woofer and the aluminum mids and tweets is to die for.

3) Even with the mods, these speakers still have a wonderful, "vintage" sound - and it's primarily the amazing midrange cones that provide this. So don't worry about making them into something they shouldn't be, I view this as bringing out their best. They sing with all kinds of music but I have to say, they sound most magical with well-recorded material from the 1950s-60s.

4) Anyone who can read a circuit diagram and solder can make these modifications! Totally simple with Tobin's help/guidance. I'm the poster child for "if I can do this, anyone can do it!" And if you're still gun shy about doing the mods, Tobin will make the crossover mods for you for $60 if you send them to him. A really, really great guy who in my book has great ears - what he said the mods would do to the sound is exactly what I'm hearing.

5) Finally: if you buy the slightly later Urbans that already have the aluminum mids and tweets, beware: you will STILL need to make the crossover mods Tobin recommends because Bozak did something weird to the tweeter network on that later model - generating a really off-putting "hump" at 5-10 kHz which sounds harsh and fake, plus the highs still roll off sharply at 10 kHz. Good news is that the later N10102A crossover in these later Urbans can be modified just exactly as the older N10102s can - they end up looking and sounding just the same as you will rip out the crappy sounding stock tweeter network.

Happy to field questions/comments - and I'm hoping there are at least some other Bozak fans out there.

 

Shoot! I had just convinced myself that these (mine are a disassembled conglomeration of parts) were too big and resolved to sell them! Now I'll have to try them instead! Thanks a lot!!! ;-)
Pete

 

Pete - insert evil laugh here! Seriously though, it is most definitely worth taking on this project given the sonic gains. I was frankly quite skeptical that it would work out this well sonically, but figured just doing the project I would learn a ton about speakers, crossovers, etc - which I have. Worth the hassle for that alone. The great sounding results were a huge, wonderful layer of icing on the cake!

 

Welcome to the ALNICO club. I was scouring the Earth for Bozaks until I stumbled upon a good price for a Pair of 12" Tannoy Monitor Golds. I have been in Hi Fi bliss ever since.

The aluminum Bozak tweeter is a classic. It sounds like you have a lot of fun listening ahead of you. I hope you have some tubes and vinyl to go with them!

 

Yep, got tubes (MC30s and a Marantz 7) AND vinyl (Nottingham Space Deck and Arm with Shure V15VxMR). But CDs also sound great!

 

That's a formula for hog heaven! With that system, they are great placeholders until you find Tannoys.

 

kt66brooklyn - Out of curiosity, have you compared the Bozaks and Tannoys extensively, sound wise? I'm not really sure that I need anything else at this point, these things are amazing (though I certainly wouldn't pass on a bargain priced pair of Tannoys)!

 

OK here's the photos.

First two photos are of the original N10102 crossover - with the huge capacitor box with the 6 old paper caps (notice this is the one where the wires coming in from the speaker hookup terminals into the crossover were reversed - we corrected this). Third photo is what the original paper 200X tweets look like. Easy to tell apart from the later aluminum ones: paper ones have the silver dust covers, aluminum are painted solid black.

 

Next up is the modified N10102 crossover (which Tobin calls the N10102T), as well as a picture of the inside of the cabinet after the new fiberglass insulation material was added:

 

Finally I have some shots of the "finished product": a grille off shot showing the black aluminum B200Y tweets mounted in front of the B199A 12" paper woofer, as well as the B209A aluminum mids; a grille on shot (love the gold flecks, so early 60s!); a shot of the top of the cabinet which has laminated formica (very, very practical and handy - both speakers plus the equipment cabinet, not pictured because I'm using it for storage on the other side of the room, have formica tops); and a "this is what my system now looks like" shot. System has evolved rapidly over the past few weeks as I sell off stuff that I don't really like anymore and find my keeper gear.

 

I'm not sure what happened to my last reply, so here is another.....

The big difference between the Tannoys and the Bozaks is imaging. Tannoys, when properly implemented, create a great and very modern sound stage. It is incredibly addictive.

Another difference is that the earlier Bozaks tended to have very quiet treble, particularly compared to Tannoys. The later aluminum tweeters alleviate this for the most part.

The Bozaks are in much better cabinets than any of the reasonably priced Tannoys came in. To hear Tannoys at their best, you have to build your own cabinets.

Otherwise, they both have great woofer cones, and the mids and highs are both excellent. The Tannoys have the edge in the mid range. They are a bit more clear.

 

Wow that is remarkable about the Tannoy mids being better...the Bozak aluminum mids I have are unbelievable, really (have you heard those?). The older paper mids I would have a much easier time believing are inferior to the Tannoys, those were only so so. Oh well - never heard Tannoys yet, sadly, so will have to defer my own judgement on that until I get lucky!

The imaging part puzzles me a bit too...with the upgraded cones and crossover mod I'm getting fantastic imaging. Again this is a big, big difference compared to the stock paper cones and stock crossover. Last night listening to Grant Green's TALKIN' ABOUT CD, I could visualize exactly where his amp would have been sitting...eerie, never have had that type of imaging before with other speakers. Same thing with drums - exact placement of all the parts of the kit.

I think very few people have heard these speakers do what they are capable of doing. That has been Tobin's mission all along - to let people know how good these speakers can be with just a little bit of attention. That's why I hope my post inspires some folks who may have given up on their Bozaks to put a little time in to making these simple upgrades.

 

Imaging is great with the Bozaks. The Tannoys are just that much more magical. I should iimagine that the mids jump out more after mods are completed. I think there was a little bit of hash caused by old crossover components in the Bozaks I have heard. I think I like having only one big crossover point in the Tannoys.

I probably won't pass up a pair of Bozaks if I stumble upon a good deal. They are truly great.

 

Thanks for your input/impressions on all this, kt66brooklyn!

 

Just by way of update, I have now moved the dual tweeters in each speaker from their suboptimal, nearly on the floor location to a separate little enclosure we built and place up on top of the main cabinets. I'll post photos later today.

I have the tweeter pairs oriented vertically now, rather than horizontally, to avoid problems with "lobing" cancellation at the optimal seating position. Neat thing about having them up there in separate boxes is that I can now also experiment and align the tweeter and midrange drivers optimally - in the stock Bozak design the tweets were way too far forward. Now I am able to place the tweeters back from the baffle just a bit to get them at the same distance from my listening point as the mids, for better time alignment.

Anyway, BIG difference in the high end with these speakers now that I have moved the tweeters and placed them properly. They still have magic midrange and phenomenal bass, but quite honestly now I would say the highs rival those of my Zingalis (the only area where the Zingalis were winning out before). These Bozaks just keep getting better!

 

Cool. Everyone I knew with them tipped them up, but that didn't solve the cancelation problem. Alligning tweeters front to back makes a big difference.

 

Great thread on Bozak's...I have been a fan for a while. I too have been in contact with Pat and he is a wonderful guy, who likes to share is knowledge...which is rare with a lot of experts. Not very rare with "experts" though!!!

I also have a pair of B-302-A Urbans and luckily stumbled across the matching equipment cabinet by accident. I was buying a pair of Wharfedale W-60's (also a wonderful speaker) from someone and saw a big mass under a tarp. When I inquired about the mass, the reply was that it was a Bozak equipment cabinet, and the seller was worried about how he was going to get rid of it since it was to large to ship via non truck frieght methods.

The cabinet was nearly new and I scored it for $60.00. My B-302-A's came from the original owner who bought them from Macy's in 1967 when they used to sell hi-fi.

I also own a pair of B-313's, and had a pair of B-312's and also run a 1954 B-305 in a mono system. The B-312/B-313 speakers are basically an attempt at competing with AR and KLH in terms of size. The do not go down as far as the B-302-A...but I only have one recording (with synth bass) that actually showed the limitation s of the B-312/B-313. The B-312 is the equivilent to the B-300 two way speaker.

A few months back I purchased a pair of Triangle Celius speakers, and they have been running in the main system. They do lots of things the Bozak's cannot, but the Bozak's have a magic that the Triangles just cannot do. Luckily since we moved into a new home I have the space to have both systems hooked up, and I finally have the space to utilize the Bozak equipment cabinet...which is important since the speakers are located in my fiancee's studio!!! WAF is very high.

I am curious to try your separate tweeter box design. That sounds really promising!!!

 

Good way of putting it...definite magic there!

Yes it does..and I suspect the suboptimal tweeter placement problem on the stock Bozaks was part of tne reason that your Tannoys, with their more optimal tweeter placement, had better imaging - better time alignment.

Man, it would be neat to eventually get lucky and get a pair of Tannoys for a reasonable price so I can do some head to head comparisons with the modded Bozaks.

 

Here's the pic with the separate tweeter enclosure:

 

Paper cones they ain't...

Howdy fellow Bozak fans. I have just shipped P Tobin my XO's and look forward to his ideas.
I'd like to suggest removing the feet and planting the 302A's more firmly on Mother Earth, it makes things a touch tighter and (in my case) user friendly for my bedroom setup. Wonderful old speakers that I have been enjoying since the mid 60's when times were a little easier going and laid back.
BTW, there are a pair on EBay, if you are interested and live on the left coast give them a spin, you will enjoy the ride. Nice forum... Thanks.
PS. Look closely, the cones are made of wool (seriously).

 

Actually yes you are right - I even knew that, just for some reason continue to call/think of them as paper!

 

Very interesting write-up, excellent work! When did Bozak cease to exist as a company? My understanding is Bozak was a company in CT, my home state. Stereophile actually did a review on a pair of Bozaks a while ago, but I do not recall if it was for the same model.

 

I think the write up you are speaking of was about their flagship speaker model, the Concert Grand...massive, huge speakers. I'd love to hear a pair of those some day.

RE: Bozak production history, yes, the original manuals for my circa 1960 302A Urbans list the company as being based in Norwalk, CT. I found this blurb on by searching Google, at AudioReview.com, posted by one Brian Levy in 2001:

"Actually, Bozak exists no more. That is THE real Bozak company. R.T. Bozak production was one of the longer runs of the vintage speaker designed systems until Rudy's death. The company ceased operations in about 1992 and sold all assets including the inventory, manufacturing equipment, intellectual property and rights to the product model names to N.E.A.R. which produced the R.T. Bozak products on custom order until all the NOS inventory was sold. It also used the designs developed by Rudy in metal cone technology to produce its own line of speakers. N.E.A.R. did not make it and was absorbed by Bogen International which still produces a N.E.A.R. outdorr line of sepakers based upon Rudy's metal cone technology. A tribute to Rudy's little round metal outdoor speaker that shows up on eBay from time to time. N.E.A.R. made a mistake in that it did not purchase the "Bozak" name with the other assets. It was sold to the current Bozak company whose products bear no lineage to those wonderful R.T. Bozak products we love."

 

Tony I was checking out the picture of the fiberglass insulation in the cabinet. I assume the back panel was also covered to enclose the hole in the middle of picture ?
I have a pair of 1973 B301A Tempos, love them, need to build a bigger enclosure they are only 2 cubic feet. I also have a pair of 1983 DMS 5500, they have a dome tweeter with the 6 inch mid. 3.5 cubic feet plus, Again I hope to build bigger boxes some day. I agree 100% with you on the amazing aluminum mids and the woofers go with out saying. I have ran many other speakers up against these guys. They sent a pair of Rogers AS6's packing last. Before that some KEF's.

 

Absolutely