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
. 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.