Bozak B-302A Century Speaker Project!!

[hardbop33]

Greetings! Longtime lurker, haven't posted much at all on this site but have enjoyed reading dozens of posts!

I recently purchased a set of Bozak B-302A Century speakers after reading up on them, including several posts on AK. They date from 1966 if I am reading the date code on the back panel correctly.

I determined they only open from the front and learned the driver complement is as follow - B209B midrange; B200Y tweeter array; B199A woofer. I have read the midrange and tweeter in my speakers is desired over earlier models. The woofer is no slouch either.

I am going to try the Pat Tobin crossover mod to the N-10102 crossovers in my speakers.

I am posting to see if I am missing anything or need to order any additional parts.

I placed an order with Parts Express for the following -

Dayton Precision Audio Cap - 25uF (2)
Dayton Precision Audio Cap - 8.2uF (2)
Dayton Precision Audio Cap - 2.0uF (2)
Dayton 4 Ohm Resistor - (4)
L - Pads (for tweeter / mid range - (2)

Not sure if I will install the L-pads right away or at all but was intrigued about the possibility of dialing in the mid and upper frequencies to my tastes.

The drivers look to be in great shape, as is the interior insulation, including the curtain that hangs in the back of the cabinet.

Am I missing anything?

Thanks in advance for any help or suggestions!

Troy

 

[Sam Cogley]

Great pickup! Bozak built some truly fantastic drivers, including that 12" woofer. The only thing I don't like about the design is the "firing at your shins" tweeter position. I've seen pictures of several setups where the tweeters were dismounted and installed in a small wooden box that sits on top of the cabinet.

 

[Jeff W.]

Welcome!

Hello Troy,

Beautiful speakers! I hope you like them as well as I like my 1964 302a "Urbans". You are correct on the dating. Yours were made in 1966 and you do have the most desireable drivers with aluminum cones (mids and tweets).

Looking at your parts list I would suggest looking at my post #24 on page 2 of this thread: http://www.audiokarma.org/forums/showthread.php?t=361932&highlight=bozak. Actually I would read the entire thread, but my post points out that Pat Tobin now recommends (I spoke to him personally) a lower crossover point from the woofer to the midrange on the 302a and I have the schematic attached there. You'll also want to be aware of a jumper to change on your crossover and I think it is mentioned in that thread by "tensleep". Also, check the link in my post to the thread about 302a's on Steve Hoffman's web forums. There is a wealth of information there along with comments from Pat Tobin.

Other things I would recommend:

1. Enclosing your midrange (B-209B) to isolate it from the woofer's backwave. If yours don't open from the rear (mine do) it may be more difficult to accomplish, but can probably be done by accessing through the woofer hole. Bozak actually did this on its larger models.

2. If you are handy with woodworking you may want to build separate cabinets for the tweeters and mount them on top of the cabinet. I did this with mine and really like the results! It gets them up to ear level and creates a better sonic "picture" IMO. (like Sam mentions above)

If you study the two aforementioned threads I'm sure you'll be able to make good decisions based on what you want from the information within. Keep us up to date and I'll monitor to see if I can assist futher. Enjoy! :thmbsp:

 

[hardbop33]

Thanks for the response Jeff! I totally checked out your post!

I looked at the Tobin schematic you referred me to and noticed a couple of differences from the earlier version I used. The schematic you referred me to is dated this year and is called Bozak 104T Crossover. The schematic I was using is from 2006 and is called Bozak 101T Crossover.

The 104T Crossover uses a 50uF cap for the midrange, as opposed to a 25 uF cap in the 101T Crossover. Does this change in cap value help out in preventing doubling of the mids between the midrange and tweeters and/or raise the midrange crossover point?

The 104T also uses a 3.0mH inductor coil for the woofer, as opposed to a 1.6 mH in the 101T Crossover. Is the change in inductor coil what gets you the lower, preferred 400hz crossover point for the woofer?

It seems I missed a 7.5 resistor in the 101T schematic that is also in the 104T design. Oops!

So - it looks like I am ordered two more 25uF caps to get the 50uF value, a couple of 7.5 resistors, and a couple of new coils.

Am I correct in assuming the stock N-10102 crossover in my Bozaks have 1.6mH coils for the woofer? Any recommendations on the type of replacement coils to buy?

You may have inspired me to relocate the tweeters!

Thanks!

Troy

 

[Les Lammers]

Nice speakers and the Tobin mods make a big difference. The schematic on the Yahoo Bozak users group has the jumper. Tensleep may have a copy. I used Sprague 25 uf motor run caps after trying the Daytons. *I* like them better. YMMV.

I replaced the speaker terminals with moder ones and need to put the 'bowl' over the mid. The speakers do open from the rear. Just unscrew the back.

*I* think an L-pad will be a wasted effort.

Enjoy them. :thmbsp:

I am driving mine with a Musical Fidelity A-1 integrated ( 36 watts Class A ) and they sound quite good.

Read this thread too: http://audiokarma.org/forums/showthread.php?t=363572&highlight=murderous

 

[Les Lammers]

Thanks for the response Jeff! I totally checked out your post!

I looked at the Tobin schematic you referred me to and noticed a couple of differences from the earlier version I used. The schematic you referred me to is dated this year and is called Bozak 104T Crossover. The schematic I was using is from 2006 and is called Bozak 101T Crossover.

The 104T Crossover uses a 50uF cap for the midrange, as opposed to a 25 uF cap in the 101T Crossover. Does this change in cap value help out in preventing doubling of the mids between the midrange and tweeters and/or raise the midrange crossover point?

The 104T also uses a 3.0mH inductor coil for the woofer, as opposed to a 1.6 mH in the 101T Crossover. Is the change in inductor coil what gets you the lower, preferred 400hz crossover point for the woofer?

It seems I missed a 7.5 resistor in the 101T schematic that is also in the 104T design. Oops!

So - it looks like I am ordered two more 25uF caps to get the 50uF value, a couple of 7.5 resistors, and a couple of new coils.

Am I correct in assuming the stock N-10102 crossover in my Bozaks have 1.6mH coils for the woofer? Any recommendations on the type of replacement coils to buy?

You may have inspired me to relocate the tweeters!

Thanks!

Troy

Troy,

I was considering replacing the coils with some from North Creek music but Tensleep talked me out of it. What I should have done, IMHO, is used Mills resistors. I may change them soon.

*I* hear no reason to relocate the tweeters but I have a *live* room. Again, YMMV. Do the xover mods first and then change things in small steps.

 

[Jeff W.]

Hi Troy,

My pleasure!

The 104T Crossover uses a 50uF cap for the midrange, as opposed to a 25 uF cap in the 101T Crossover. Does this change in cap value help out in preventing doubling of the mids between the midrange and tweeters and/or raise the midrange crossover point? The 104T also uses a 3.0mH inductor coil for the woofer, as opposed to a 1.6 mH in the 101T Crossover. Is the change in inductor coil what gets you the lower, preferred 400hz crossover point for the woofer?

I believe (no expert) the 50uf cap, combined with the raising of the inductor value on the woofer from 1.6mH to 3.0mH, is what lowers the original crossover point from 800Hz to 400hz from woofer to midrange. the adjustment that prevents the doubling between the mid and tweeters is the jumper modification on the factory crossover.

Am I correct in assuming the stock N-10102 crossover in my Bozaks have 1.6mH coils for the woofer? Any recommendations on the type of replacement coils to buy?

Yes, this is correct. Pat advised that the replacement inductor needed to be an air core (like the original) and made from 18ga. wire. I ran this one by him from Parts Express: #255-274 made by Jantzen and he gave it his blessing.

You may have inspired me to relocate the tweeters!

I think Les has given some practical advice in general and specifically. That is, you may want to take things a step at a time and judge for yourself. I started off with B-300's so I had to start off building my own crossovers from scratch. You already have the factory crossover so you already have the 1.6mH inductors to try. Perhaps do the 101T configuration first (cheapest), listen for a while and make a decision if you want to lower from 800Hz to 400hz. This way you haven't spent the $ on new inductors and extra caps. If you then want to try the 104T (400Hz) you haven't wasted any $ because you just buy 2 more 25uf caps and the replacement inductors. Nothing will go unused that you purchased for the 101T. By the same token, you could try the tweeters positioned as they are and you may like it just fine. If you want to move them later there's nothing to stop you.

I, like Les, replaced the binding posts on mine with modern ones that have provision for heavier gauge wire and tighten by hand. This makes connecting much easier and makes a better connection. I used part #091-1245 from Parts Express and am satisfied with them. I don't use the separate solder tab provided. I solder my wires directly to the end of the mounting post.

What I should have done, IMHO, is used Mills resistors

I used the Mills resistors for the 4.0 value (part #005-4 from P.E.)

*I* think an L-pad will be a wasted effort.

Pat Tobin advises against any attenuators as well.

I hope all this helps you make some informed decisions. We'll be looking forward to hearing about your progress!

 

[Les Lammers]

Parts Express was out of Mills when I did the mod. :tears: Bozak made some excellent drivers, If these were labeled Altec or JBL they would be much more expensive.

Where did the 104T schematic come from? Is it a Pat Tobin design?

The backs of the speakers are removable and the xover is screwed to the bottom of the cabinet.

Mid range 'bowl': I am going to use aerosol rubber automotive undercoating on the inside of them.

 

[Jeff W.]

104T is Pat Tobin's latest recommendation

Hi Les,

Yes, I spoke w/Pat directly and he sent me the schematic you see posted in the other thread. He asked me to post it. He recommends this for the 302a now and especially if the tweeters are liberated from in front of the woofer. He has mentioned elsewhere (I think in the Hoffman forum thread that was started by "DrJ") that this crossover point was optional on the 302a directly from Bozak, but was not advertised. This way you can take more advantage of the wonderful B-209B! Too bad about the resistors. Man, that kind of thing always happens! I think it happens every time I go to Lowes or Home Depot. There's always one thing you need for your project that is not in stock!

I agree with you, the drivers are top notch. I just love finding equipment like this! What a bargain! The gentleman fom Stereophile that did the Vintage equipment review of the Bozak Concert Grands several years ago commented in "DrJ"'s thread on the Tobin Modified B-302A. He said that with the crossover mod and the tweeters mounted on top he felt it was competition for speakers costing several thousand dollars available currently. To see his exact comments check the link in the "tensleep" thread to the Hoffman forum I provided. Sorry I can't do it here now as I am in-flight and can only open one browser with my netbook.

To isolate the mid you might have a tough time fitting the "bowl". There is barely any room above the B-209* and not much below. "Bold Eagle" commented about doing this over on the Audio Asylum forum. He recommended a tube like you see used on mids in so many other speakers to isolate midranges. I used a section of plastic tubing that is 1/8" thick. I capped one end with 3/8" Polycarbonate (Lexan) and made a flange for mounting it out of the 3/8" polycarbonate as well. Ideally you'll need a tube with a 7" inside diameter. "Bold Eagle" recommended that the inside should be completely filled with dampening material such as fiberglass or "acoustuff". This is what I've seen in many speakers that have an isolation tube for the midrange. Just some food for thought.

Enjoy the music !

 

[hardbop33]

Moving forward - slowly!

Waiting on replacement caps and such from Parts Express and thought I would disconnect the crossover from the speaker and remove the old caps.

The following was the capacitor compliment - 10 MFD; 2 MFD; 5 MFD; 5 MFD; and 15 MFD. Big and crusty! There was also a resistor (I think) with 25Ohms 10% - not sure what that means - 2.5?

Although I was advised to perform these mods gradually, to observe sonic differences, I am going forward with the tweeter reinstallation on the top of the cabinet. It just makes sense to me and won't be difficult (and will be reversible!)

Here is a pic of the naked woofer - front and back - magent is huge!

Researching prebuilt boxes that might work to house the tweeters - my carpentry skills are suspect.

I will try the stock Bozak coil inductors first, although I went ahead and ordered new inductors to get the 400hz crossover. I am interested in hearing the difference.

Thanks for all the posts - its keeping me motivated!

P.S. Anyone ever mount a bottom plate and casters to these speakers so you could move them around easier?

Troy

 

[Illusions]

Great looking Speakers
Interesting Design

 

[tensleep]

Excellent thread, Troy, and congratulations on your Bozaks. I have a spare pair of crossovers, so I will probably build them with the 104T schematic. I may get back into mine before the year is out. You are gonna love the improvements from reworking the crossovers. Keep the updates coming!

 

[jessdw]

This may be a question for the DIY forum, but since we're talking about it... Do these tweeters (B200Y) require an enclosure of any specific volume? I know there are calculations to determine the appropriate volume for a given driver based on the specifications of said driver, but these are just tweeters right? Also I'm guessing their box should be sealed? I'm just trying to get the technical details nailed down so I can design something my wife will let me leave on top of the speakers. It might actually have to function as a base for a lamp...

*EDIT - While I was lying in bed I remembered that in the 302a configuration the tweeters are just suspended out in open space. I guess that's my answer. I think the only thing I need to emulate is the toe-in angle.

 

[hardbop33]

Getting ready to install the caps and resistors - any tips?

This will be the first time I have worked on a crossover or soldered in caps or resistors. When I solder it is usually for a tonearm or turntable.

Would love to see any in progress pics of others who have modified this crossover.

Any instructions would be most welcome. I have the schematic and the crossover layout seems logical but I love to screw things up!

Thanks!

Troy

 

[Jeff W.]

Jess,

I see you basically answered your own question about cabinet volume the tweeters. The tweeters are completely sealed in their housing, so cabinet size is not a factor. Do whatever looks good/works for you.

Troy,

I know there are some progress photos of the factory crossovers being converted to the Tobin layout on this Steve Hoffman Forums thread: http://www.stevehoffman.tv/forums/showthread.php?t=75950 , however you'll need to join the forum to see them. There's a lot of great information there and I search this forum often.

If you can work with and solder fine gauge wire you should not have any trouble with the crossovers. You may just have to turn up the heat a bit on your iron or wait a little longer for the contacts you are trying to join to heat up if your soldering iron is not adjustable.

 

[hardbop33]

Inductor Coil Wiring Question

This may be a silly question. I am going to attempt to replace the inductor coil for the woofer with a 3.0 18 gauge coil recommended in a prior post. If I recall from my earlier reading this mod goes toward lowering the crossover point to 400hz for the woofer. I think

My question is that the stock inductor coil - the ginormous one - has three wire leads, whereas the new coil only has one. The three leads of the stock coil for the woofer go to a) the number 2 position on the Amplifier terminal strip, b) N-101 position on Terminal B, and c) N-102/N-104 on Terminal B.

I am tempted to forgo the lowering of the woofer crossover point from 800hz to 400hz until I get my head around this.

That means I will only use one 25uf cap instead of two, yes?

 

[hardbop33]

Schematic / Soldering Question

I checked out Tobin Mods thread on Steve Hoffman forums started by DrJ several years ago.

http://www.stevehoffman.tv/forums/showthread.php?t=75950&highlight=bozak+crossover

It looks like he performed most of the mods I want to attempt.

I am no expert at reading schematics but I think I understand it. DrJ posts a nice picture of a hand drawn schematic which I plan to follow.

DrJ also posts a photo of the crossover with the new caps and resistors installed and it looks like he did not follow his own schematic. May be I am seeing things.

In the schematic the 8.2uf cap comes BEFORE the 2.0 cap in following the wiring from the speaker back to the amplifier. In the photo it looks like the 2.0uf cap was installed before the 8.2uf cap. I bought virtually identical Dayton caps so I am assuming cap value based on the physical size of the caps.

Are the photo and the schematic the same? If not, do I follow the schematic and solder in the 8.2uf cap before the 2.0uf cap?

One other question (I promise and then its soldering and hopefully speaker magic!), in the schematic it looks like the 7.5 resistor is bridged across the 1 and 2 wires. In the photo it looks like the 7.5 resistor is installed differently.

Clearly I am easily confused! Someone please tell me what to do. If the photo is spot on then I will due it just like the photo. If I happen to wire anything incorrectly will I fry anything?

Thanks!

Troy

 

[Jeff W.]

I'm gonna be brief Troy as it is late and I've just got back from being out of town. DrJ's handwritten schematic does have mistakes in the order of the capacitors in the tweeter circuit (he mentions it in his text). Look for schematics that are not hand drawn. Somewhere you'll find one marked "Bozak 101T Crossover, Pat Tobin and 09-21-06" at the bottom. This is Pat Tobin's shcematic for the 800Hz crossover. The one marked "104T" that I posted is also directly from Pat and is for the 400Hz crossover point. Both of these have all the components in the correct order. I'll look at DrJ's pictures tomorrow and see what you are talking about. One thing is certain: the schematics are correct that are from Pat Tobin. The 7.5 ohm resistor does bridge the tweeter leads (1 & 2) and connects between the two 4.0 resistors on the "common" (1) side.

The 3.0 inductor you bought should have two leads. If you are doing the 800Hz crossover point you will only use one 25uf capacitor per speaker and use the 1.6 inductor not the 3.0. See the "101T" schematic mentioned above. I hope this helps. When I have some more time I'll check into it more carefully if you haven't found the answers or still have questions.

 

[Jeff W.]

Troy,

I see what you mean by the 7.5 ohm resistor not being connected according to the schematic in DrJ's thread on the Hoffman site. That's a good observation. It looks incorrect to me as well if you are referring to the photo in his post #9. In his hand drawn schematic he has put the 8.2uf cap on the wrong side!

Tensleep has a picture of the 800Hz crossover schematic in his thread that is from Pat Tobin here: http://www.audiokarma.org/forums/showthread.php?t=361932&highlight=bozak in post #11. This is the one to follow for the 800Hz point. Don't forget about changing the jumper too!

I'm not sure about the three leads on your old coil. This is not typical of inductors that you buy off the shelf. I know your new one should have two (as I had mentioned). Maybe Tensleep could chime in here as he reworked his factory crossover with the Tobin mods.

 

[hardbop33]

Crossover Saga - Stage 1

Here are some pics of my poor attempt to follow the 101T crossover schematic.

The sound quality I achieved for my efforts was awful. The bass was bloated and weak, the tweeters okay, and the midrange absolutely missing! Nada for the midrange - scary.

Thanks for your responses Jeff. They will help me keep trying! I had a though of using alligator clips to temporarily hold caps and resistors and wires in place while I experiment. Anyone tried that before?

I believe the 7.5 resistor is the one straped to the 25uf cap - above the 4 resistor.

I am going to open a nice bottle of red wine, get some jazz spinning, and will figure this thing out!