Bozak/Tobin Crossover Mod Help

[guyhifi]

I have read numerous threads on the Tobin crossover mod, however the mod deals with the Bozak B200Y tweeters, not the B-200X paper cone tweeter. So, a few things...

1. Does anybody have a complete parts list (high quality parts) to build a complete 104T crossover from scratch? I do not want to upgrade the crossovers that I have for a few reasons, one of which I would like to do an A/B compare when complete.

2. Does anybody have step-by-step instructions on building the 104T crossover that will work in the Concert Grand speakers, while utilizing the B-200X paper cone tweeters? The reason for this is because the Y tweets are very difficult to obtain in excellent condition and at a price-point that I could afford. So for now I will retain the X tweeters which are in pristine-mint condition.

3. I see some 104T v2 parts lists on the internet which include resistors and such, but do not see resistors and such on the corresponding 104T schematic diagram???

4. Is it advisable to utilize an L-Pad for the X tweeters? I have read pros/cons on this and do not know where things stand today.

I am well experienced in building pre-amp and amp kits, and I am certain that I can put together a pair of crossovers, however my knowledge of the inner-working of crossovers and design is very limited, thus the reason I need step-by-step instructions and a complete parts list.

I have tried to contact Brodtek HiFi numerous times this past month to have a pair customized/built, but I have not been able to get a single response so I do not know what is up with that. I guess that is my queue to build the crossovers myself.

Here is what I have in each Concert Grand cabinet:

4 - 8 Ohm B-199 Woofers
2 - 16 Ohm B209B Midranges
8 - 8 Ohm B200X Tweeters

 

[drbiggles]

Good morning,

I don’t have the time available like I used to, so I can’t really go into detail about everything and why. Everything you need to know is searchable here and on the net.

Simply rebuild your original crossovers, you don’t need anything else. If you want Y tweeters, just to with a pair or a quad in each cabinet. Wire for an 8 ohm load. 8uf cap and 8 ohm l-pad is all you want for tweeter circuit. Toss Tobins circuit for tweeters.

Reasons for this are on the net. None of this is complicated, you got this.

Biggles

 

[guyhifi]

1. Looking at Pat Tobin's v2, his corresponding schematic does not utilize everything in his parts list (taking into account 2 crossover networks). Will there be left over parts when building these for the Concert Grands, and why?

2. What voltage should each of these parts be?

3. What are the specifics of all of the inductors, and in what gauge should I order them (Parts Express)?

4. Some of these specific values are not available from Parts Express, in which direction should I compensate?

5. Are there other parts that are not in the schematic that I will need to obtain? Again, I am building everything from scratch.

6. I am keeping and using the existing 200X tweeters, not the Y's.

 

[drbiggles]

1. No idea
2. As long as it the same or higher than the original voltage rating, it doesn’t matter.
3.18 gauge, values are on his schematic.
4.all values required were available on parts express about a month ago, they should be there.
5.No. All you need on the tweeter network is an 8uf cap. DO NOT BUILD Tobins tweeter network.

using your original crossover with original capacitors is dangerous. Those caps should have been replaced in the late 1960s. They’re off spec, and probably sound dull. You’ll over drive them trying to hear them, then you’ll blow them. It’s a bad practice.

Biggles

 

[twiiii]

Steve at Audio Classics has a bunch of Bozak drivers he wants to get rid of. Some are NIB. I would replace the 200 X as fast as I could. And especially the B-209 which are noted for their failures. The early grands the woofers were only rated at 18 watts RMS. The later 25 watts and the Bc were further designed so the voice coils would be damaged by bottoming out. The tobin mod will not work with the X tweeters. There is a big efficiency difference between the X and Y.

 

[guyhifi]

Thank you for the reply Biggles. I also wanted to clarify the N-101A (designed for the B-302A) that I purchased new sometime in the 1980's, it is not the N-10102 that is widely known.

It is interesting that this crossover uses only 4 components in total (as opposed to other N-101 variants), and that it is utilizing SEACOR capacitors. I am wondering if these original capacitors are still good by todays standards?

The reason I am not able to utilize these crossovers is that they crossover at 800 Hz, not 400, and utilize the 1.58 mH Inductor, not the 0.509 mH which is required for the B-310B Concert Grands which I have built.

This is why I am asking for a complete parts list, with part numbers if possible, so that I can place an order with Parts Express.

C1 - 5.0 mfd
C4 - 25.0 mfd
L1 - 0.509 mH
L3 - 1.58 mH

 

[guyhifi]

I have located the part numbers that I need, however I am not able to find new Air Core Inductors with the specific values that I need:

0.509 mH (driving 2 16-ohm midranges)
3.15 mH (driving 4 8-ohm woofers)

I have looked on eBay for used crossovers to use as parts but the cost of Bozak crossovers is too expensive these days.

Does anybody know of a source, or substitute values, that I can purchase new which will be within required parameters?

 

[twiiii]

Did you check Parts Express or Mid western Speaker? Parts express has a .5 Mh coil which is close enough, and you can use a 2 mh and a 1,0 in series to get to 3.0. The also have a 1.3 mh coil. There are books out there that will teach you how to wind your own speaker coils. being with in 5% of the desired value is close enough. Caps you want at least 100 to 200 volt rating. And here you place them in parallel to combine then to get the correct values. Like I said 5% error is about all you can hope for. And remember a Tobin mod will not work with the less efficient 200X tweeters. You think Bozak crossovers are expensive, Wail till you price new air coils and the correct capacitors.

 

[guyhifi]

Yes I have tried both, twiiii. I have read where some folks substitute value of the Air Core Inductors, however I am not sure which direction to go (up or down), and what effects it will on the drivers, as well as audibly.

Now that I have identified the exact capacitors that I need, the Inductors are my stopping point :-(

 

[Retrovert]

The difference between 3 mH and 3.15 mH can be addressed by (a) ignoring it, (b) series wiring a 3.0 mH and a 0.15 mH, or (c) unwinding turns from a higher-value inductor such as 3.3 mH.

Construct your capacitors using smaller values with bypassing as I have elsewhere described. Not only does this provide better performance, it permits exact values instead of using the standard values.

The X tweeters do not require attenuation. The Y tweeters are louder for the same power input than the X variety, hence attenuation. Do not, as Biggles correctly noted, use the Tobin attenuator or its high-frequency bypass. I have explained in detail why this is the wrong value and why it the crossover point shifts if the the tap is made variable. The explanation will never change as of "today" or any other day. The math doesn't lie. The X tweeters, furthermore, like all paper-cone tweeters of that vintage, have poorer reproduction as frequency increases. The aluminum-cone Y tweeters are superior, and the four-way super-tweeter easily solves the problem.

Mountains of explanations for all of your requests for information exist in other threads.