Help with Bozak B-310 Concert Grands

[guyhifi]

Hi all,

My B-310B-based Concert Grands consist of 4 - B-199, 2 - 16Ohm B-209B, 8 - B-200X and N-101A Crossover (designed for the B-302).

I intended to eventually swap out all 16 200X's and replace with the Y's. But being they are very difficult to locate in pristine condition (or a price-point I can afford), as well as the issue of the Y's having an internal foam damper which desiccates over time, I have opted not to replace them. The 200X's that I have are pristine-mint condition.

The crossovers that I am using obviously does not maximize the bass/mid to full potential. The issue is the N-101A crossover network, which crosses over at 800, as opposed to 400. I have contemplated the Tobin mod, but know that his mod dealt with the Y tweeters, not the X's.

Brodtek offers a 104T (Tobin Mod) crossover which can also be custom made, but I am not sure what to request. He offers the L-Pad, but from my weak understanding I take it that the X tweeters should not utilize the L-Pad?

I stumbled across this in another thread as well: "I've seen it claimed that the B-200X was purportedly designed to roll off at that point, but that is obviously false. Bozak literature claimed (see Brown catalog from 1956, for example) that the B-200X had a response of 2,000 to 16,000 Hz and was "useful" to 20,000 Hz. So there was no intentional rolloff, at least not one publicly admitted. The early Bozak systems were perfectly balanced - woofer to midrange to tweeters - and everything in phase."

Aside from obtaining a super-tweet (which I may or may not do down the road), can any of you suggest a crossover mod that will yield best results for the low/mid while also dealing with the 200X Tweeters to maximize their potential?

 

[Nat]

There used to be a useful Bozak users group on Yahoo, but I have no idea if anything remains of it.
Adding a super tweeter can be easy and cheap, or it can be made complicated and expensive. Apart from the obvious cost advantage, the cheapo route has the merit of allowing you to experiment (and evaluate) without a lot of emotional freight. I don't have any classic Bozaks right now, but I've had a good deal of luck with some Fostex horn tweeters (fished out of a pair of Fisher speakers and clearly the same driver as the Radio Shack supertweeter) and a film cap, 2 mfd if memory serves, that produced about a 10k crossover. I use it firing forward with efficient speakers like Altec Valencias and pointing up with less efficient speakers. I even had it on the floor behind the speaker with a pair that was really inefficient. It wasn't perfect in any situation, I suppose, but it did add a nice airiness to systems that sounded slightly closed in. And my ears, and the rest of my system aren't exactly perfect either, though they are good enough to give me a lot of pleasure.
I've gone through several modern small speakers that don't need any help in the high end so I haven't used the supertweeters recently. But now I am using Dick Sequerra's Met 7s, which were always meant to be used with a supertweeter. Unfortunately the supertweeters he made to use with them - ribbons in a transmission line - will never be in my price range, so I'm thinking of digging the old ones up. Or maybe some Linnaeums or Pioneer ribbons...

 

[rider33]

I have Symphonies with the B800 mid and Y tweeters. When I first bought them I frolicked with super tweeters (home brew) which seemed to help but in the end I replaced the crossovers with Brodtek's. There are some strong opinions among the Bozak faithful on that, the gist of which is you can build better one's for a whole lot less. I, on the other hand, was just never going to get around to doing that so I popped for them. Once installed the speakers sounded MUCH better, more balanced, less boxy. The L-pad thing came along for the ride which, since this the speaker had a tweeter level adjustment to begin with, at least filled that hole but honestly, I leave it full-on all the time which effectively takes it out of the circuit. Since changing out the crossovers I dialed down & eventually disconnected the super tweeters, it just sounded better that way to me. Old Bozak's are never going to be the last word on treble, I have other speakers for that. They do have an amazing midrange tho and solid bass which I really enjoy. Whether you buy or build do get the right & updated crossover in there. 50+ year old caps can drift, a lot, and in doing so can significantly compromise what otherwise excellent drivers are capable of. I was sort of stunned at how much better they sounded actually.

 

[twiiii]

Tobin mod won't work with X tweeters it is designed to be used with the more efficient 200Y Tweeters. I would get rid of the mids and tweeters as fast as you can as the mids have desentagrated in some ways by now. and the X tweeters don't do much above 10 KHZ. What you really want is the B 209 BC mids and the 200 Z tweeters. The tweeters are flat above 18,000 HZ and don't really need any manipulation. I don't have the crossover schematic for Z tweeters. Go to Facebook and join the owners group. Somebody will have the info. Steve at Audio Classics has a bunch of new in box drivers and pre-owned bozaks drivers that you might get a great deal on. He even has some paneled Symphonies and 4000 Symphonies for sale at the moment.

 

[guyhifi]

Thanks again twiiii. Yes, as I have stated, I am fully aware that the Tobin Mod tweeter portion will not work with my 200X's. Also, I have the Aluminum B-209B 16-Ohm midranges, so there will not be a problem with going ahead with the rest of the mod. I will provision the mod to include the tweeter portion for later use, so that a couple of jumper wires will be all that is needed.

I have spoken with Steve a few times in the past, I bought my 4 B-209B's from him. I do not think I can swing the tweeters at this point and time due to finances.