Tried and true crossover upgrade: Tobin Mods for Bozak B302a

A little Forever Gold Van Morrison - I have to check out the world-famous midrange on the vocals, you know!

Edit: Oh
My
Goodness!

My Bozaks are slaying Van Morrison!
 
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As a Tobin convert, it does my heart good to hear of another pair of 302A's "liberated". Did you end up changing the jumper from the midrange inductor? I'm just curious, because I did the Tobin mod and changed that jumper without ever hearing it the other way.
 
As a Tobin convert, it does my heart good to hear of another pair of 302A's "liberated". Did you end up changing the jumper from the midrange inductor? I'm just curious, because I did the Tobin mod and changed that jumper without ever hearing it the other way.

I changed the jumper without an audition as well, so I cannot shed any light on leaving the jumper in the original position.
 
Latest Tobin Crossover

Hello fellow Bozak fans. I have to thank "Tensleep" and "DrJ" (over at Steve Hoffman's forums) for the inspiration to try a set of B-302a's. I spotted a pair of "Urbans" on the Cincinnati craigslist and did some research, out of curiosity, and found this thread and DrJ's on the Hoffman forums. Needless to say, I bought them ($150.00). Mine were only B-300's, so they did not have the B-209b midrange, but the cabinets and drivers were in excellent condition. I'd venture to say I was probably the first person to open the back since they left the Bozak factory. My set is from 1964 and so they did come with the 200Y (aluminum) tweeters. I found a pair of B-209B's at Audio Classics in NY and purchased them ($130.00 incl. ship)

Since I had no original crossover to work with (the B-300 only uses a single cap for the tweeters) I set out to scratch build a set incorporating the Tobin modifications. This led me to contact Pat Tobin directly. I wanted to find out specifics about the inductors that should be used and about the crossover point from woofer to midrange. There was some discussion of this over on the Hoffman site. "DrJ" experimented with a 400Hz crossover point, which Pat pointed out was an option on the B-302a, and was used for all of the other offerings in the Bozak lineup. The standard crossover piont on the B-302a was 800Hz.

Pat was extremely helpful/generous to me and so my thanks to him as well. He sent me a copy of his latest schematic and asked if I would post it here as he now recommends the 400Hz crossover point for the B-302a. "DrJ" found that he prefered this point on his B-302a's having compared the two. Pat will perform any of the crossover modifications/upgrades for you for a modest price. If you have interest I would encourage you to contact him: audio.consultant@verizon.net. I have no affiliation with Pat other than being the recipient of his generous assistance.

I built my crossovers using the 400Hz point and also liberated the tweeters from in front of the woofer having scratch built two custom cabinets for them to sit on top of the main cabinets to bring them to "ear level". "DrJ" did this with excellent results and it has been recommended (by several people) in order to position them "properly". If you want to know more please see DrJ's thread on the Hoffman Forums: http://www.stevehoffman.tv/forums/ar...75950-p-1.html. This is a link to the same thread that "jessdw" was kind enough to provide in post #8 of this thread.

I've been listening to the finished product for about one week now and I'm just loving these speakers :music:. I think they are going to be holding their position for the foreseeable future. They are keeping me up late because I just don't want to stop listening! Please see a few pics below and Pat Tobin's latest schematic for reference.
 

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Beautiful work Jeff! I have been kicking around designs for a separate tweeter enclosure like the one you built. I think you really nailed it. Do you have any process pictures from building them?
 
Thanks very much Jess. I don't have any "in progress/process" photos. However I'd be happy to give you some dimensions if you would like them and any assistance with building a set.

I made the cabinets from 1/2" MDF and veneered them with walnut to match the original cabinets. The grill frames are made from solid walnut. The original walnut veneer on my Bozaks were stained. I found that "Colonial Maple" from Minwax over my walnut veneer matched the color of the original cabinets perfectly. If your cabinets are walnut and have an orangeish patina to them I'd recommend this color stain as a starting point for matching.

I guess I kind of ended up with a mini Bose 901 look to them! I always did like the shape of those speakers. The original idea was to duplicate the angle of the tweeters as mounted in front of the woofer, so that is what really dictated the shape of the enclosure. Please let me know if you'd like more info. Thanks again.
 
Wow, I haven't visited this thread in some time. Jeff, your tweeter cabinets are super cool! I really like the way that they turned out and I can only imagine how much better the tweeters sound higher up. I was lucky that mine were mounted high in the baffle when I got my Bozaks. However, having the tweeters closer together and above the midrange is probably better that mine, where the tweeters flank the mid.

I have been working on an old Honda motor bike and my Lincoln Continental lately, so not much to report on the Bozak front, other than my wife loves to rock them! Jeff, I think I'll build up my spare crossovers to the 104T schematic this fall/winter and give that a whirl.
 
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Hey Tensleep, Nice to see you back with a post here in your thread. Thanks for your kind words. I am really enjoying the Bozaks. This thread is a large part of the reason I bought mine and took on the project. Thanks for putting all your information and impressions of the B-302a's here.

I reallly like your Barzilay furniture/speaker cabinets. Super sweet stuff there. I like the mid-century modern look! The Urbans have it too, but the Barzilay's have just that little bit of extra style. The grilles make it!

Let us know when you do a comparison of the two crossovers. It would be nice to hear your observations between the two.

Working on two vehicles eh? That does sound a bit more involved than some crossover work. Are you doing some restoration work, general repairs or both? Good luck with them.
 
Working on two vehicles eh? That does sound a bit more involved than some crossover work. Are you doing some restoration work, general repairs or both? Good luck with them.

A little bit of both. The Lincoln is big, heavy, powerful, comfortable, and capable of 24 mpg on the highway. But, parts and repairs are terribly expensive.

The Honda CX500C is small, light, decently powered, exposed and capable of 40+ mpg on the highway. Parts and repairs are reasonably cheap.

They both will be around for at least 12 months. I may give them both up at that time, but for now, they are my main drivers. I have a Dakota truck that is a great backup - speakers that won't fit into the Continental trunk will definitely fit the Dakota!

I need to get the vehicles out of the shop before the weather gets bad. I can keep the doors closed and throw a little heat into the shop for winter work on audio gear. I have three sets of speakers - the Bozaks, Infinity Column II, and a pair of Cryslers - to work on this winter. If funds and Santa are good, I have a big pair of Klipsch KP301 that I would like to tackle - crossover and diaphragm upgrades. Oh, and a vintage University mono cabinet.

For me, I am really considering the Ultimate Murderous Bozaks - triamplified with an active crossover and matched Alesis RA-100 amplifiers. I have space in the Barzilay console to rack everything. I may get really fancy and figure out a switching system for going between the Ultimate Murderous Bozaks and the Murderous Bozaks, powered by my CR-1020. One can dream, right?
 
Good luck with the vehicles! I hope all goes smoothly.

Wow, tri-amped Bozaks, I'll be interested to hear about the results! Give us a post when you get back to this project and all the rest. Sounds like you are like so many of us here with projects backed up for the foreseeable future!
 
Got the Continental lined out - man, this is one fine car! I am seeking the RA-100 as we speak....
 
Hello gentlemen.
I bought a pair of Concerto Grosso's (305's) about 2 months ago.
Beautiful large speaker cabinets!
These are currently in the stock configuration, but I plan on upgrading the caps and doing the Tobin treatment on them.

Is there a parts list somewhere that can tell me what value capacitors I need to buy?

I've looked around on the Yahoo Group and I see lots of photos but no parts list or step by step.

Can anyone help?
 
Here's a pic:
C75CEC21-33E9-43A3-AAB0-2482B4889329-7311-000005CC353B6F84.jpg
 
Those are some fine speakers you have there, and they look fantastic in your room. Congratulations! Going from memory, the Tobin mod for the 305 should be the same as the 302. I will go back through my thread and put together a parts list. If you would, please take off the back of one cabinet and get some pictures of the crossover, especially the part number, so that I can be sure it is the same crossover.
 
No need to go back through your thread if the part numbers are there.
I can do it.
Here's a pic of the crossover:
F1B3FF9A-BAD5-40F2-8132-3DD25380C728-10943-000007B08CF07825.jpg
 
That looks just like mine - it is the N10102 Crossover, as expected. It should rebuild just the same as mine with the Tobin modification. There is a schematic further back in this thread. I can create a simple enough parts list. I used inexpensive Dayton parts from Parts Express. Madisound is supposed to be a bit less expensive, plus they have some different brands of capacitors. What is your rebuild budget like?

25uF capacitor qty of 2
8.2uF capacitor qty of 2
2uF capacitor qty of 2
4 ohm power resistor qty of 4
7.5 ohm power resistor qty of 2

This is the rough list. Brands, quality, etc. are all subjective. However, I do suggest that you go with the poly film capacitors, whatever the brand - they don't deteriorate over time. Others continue to use electrolytic capacitors with success - you will have to suite yourself.

I will look up the parts that I got from Parts Express to give you something to go by.
 
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Thank you!
I haven't really set a budget, as capacitors are usually pretty cheap.
Dayton's I would think would be fine, although I have seen some people using other brands. Not quite sure what to use.
 
Is that 8.2uF capacitor qty of 2, or 0.82uF?
I didn't see any Solen 8.2's on Madisound, only 0.82uf.
 
This is the list of caps/resistors that I am about to order:
(2) Dayton Audio PMPC-2.0 2.0uF 250V Precision Audio Capacitor
(2) Dayton Audio PMPC-8.2 8.2uF 250V Precision Audio Capacitor
(2) Dayton Audio DMPC-25 25uF 250V Polypropylene Capacitor
(4) Dayton Audio DNR-4.0 4 Ohm 10W Precision Audio Grade Resistor
(2) Dayton Audio DNR-7.5 7.5 Ohm 10W Precision Audio Grade Resistor

Does this jive with Tobin's recommendations?
These are going to be replacing the original bits in some dual woofer 305's. Is
this the correct units?

Also, does it matter that my 302's are 16 ohm and not 8 like a Symphony?
 
No, it won't matter and that looks like the same list that I had - well, I don't think I got the precision Daytons. Yours looks like an even better list!
 
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