Bozak B4000 Symphony - Restoration - Seeking Advice

[MATT0404]

Bozak B4000 Symphony Speakers by Audio Database, on Flickr

I recently lugged these beasts into the house after working out a trade with a fellow AK'er. They sound quite nice as-is, but they appear to be all original, so I'd like to rebuild or make new crossovers incorporating the Tobin mod.

Driver arrangement consists of B199A woofers, B200A mid, and B200Y tweeters. The crossovers appear to be original.

I have a few questions before I begin gathering parts:

1. Is the Tobin 104T crossover plug and play for my application?
2. It appears I'm missing the bowls that cover the back of the midranges. I've read to use a Tupperware container, or something similar, and line the interior with batting. Should I be looking for a container with a certain volume? And what type of batting is appropriate?
3. How do I tell if my mids are wired in phase? Tracing the wires from the mid to the xo, the "1" terminal on the speaker is connected to the "1" terminal on the xo.

So, what am I missing? Anything else I should add to the list? I should mention that I've joined the Bozak FB group and I've gained a lot of knowledge and gotten a lot of great advice from the guys over there. I just don't find that medium the best format for documenting a restoration while having an organized discussion.

Here are some pics inside the cabs and one of the Tobin 104T:

 

[Drugolf]

Hey Matt. Agreed on the FB format being a little cumbersome for dialogue.

I don't think you have a lot to do. You can swap in and make the Tobin crossover and maybe get more out of these. Or just recap with same values and configuration. I recently re-did my Concert Grands, but for now just went back to the original specs in the crossover since I have the X version tweeter array. Your later version drivers are perfect for the Tobin.

I find it interesting that these and other stock factory models don't isloate the mids but we all want to now. I believe it's a flower pot actually that others have found to be the best choice. Looking at your internal lay-out it appears that cross piece along the tweeters might be in the way of that. The mids in my CG's were already isolated so I didn't have that to deal with.

 

[saltwater]

@drbiggles

Sorry man. Your just so good at this.

 

[MATT0404]

Hey Matt. Agreed on the FB format being a little cumbersome for dialogue.

I don't think you have a lot to do. You can swap in and make the Tobin crossover and maybe get more out of these. Or just recap with same values and configuration. I recently re-did my Concert Grands, but for now just went back to the original specs in the crossover since I have the X version tweeter array. Your later version drivers are perfect for the Tobin.

I find it interesting that these and other stock factory models don't isloate the mids but we all want to now. I believe it's a flower pot actually that others have found to be the best choice. Looking at your internal lay-out it appears that cross piece along the tweeters might be in the way of that. The mids in my CG's were already isolated so I didn't have that to deal with.

Thanks for your input. Are you saying that some Symphonies didn't come with the midrange cover on the back? I did notice that with my mids being off-center and sitting closer to the centerline of the baffle, that there's less real estate available to mount a cover.

Regarding the crossover, I wouldn't mind just performing a simple re-cap, but I'd like to remove, or replace the factory L pad, as well. Maybe that's the ticket, factory re-cap and replace L pad with new replacement. After reading through some threads, I'm a little concerned the 7.5 ohm resistor in the Tobin crossover would mute the mids too much for my liking.

@drbiggles

Sorry man. Your just so good at this.

Haha, I know! Patiently waiting...

 

[MATT0404]

One curious thing to note...while most of my tweeters have factory labels on them identifying them as B200Y, some of the mounting plates appear to have 200X casted into them. Does anyone know if this is common practice?

 

[drbiggles]

Making coffee, yo.

Xo biggles

 

[drbiggles]

Happy Good Morning!

A few things to go over here, so let's hunker down and get to gettin'. I'll start with the crossover and any updates that are recommended. Please, anyone reading this, pay attention. Mr. Pat Tobin's "Mods" are essentially a swapping around of original factory settings, with the addition of a Zobel Network for the tweeters. Read that again, yup. It's using what Rudy Bozak already designed into the N10102 3-way crossover. But wait, I don't think I want a Zobel Biggles! I want factory !!! No, no you don't. See, the B200Y tweeters are upwards of 60 years old. They have an inherent impedance rise. What this translates to is a spikey response at approximately 9k, it'll make your ears ouchie. What the Zobel does is flatten out this impedance rise and give your tweeters a smooth response. So, what you're saying is that you want a spikey tweeter. Uh, I guess not Biggles. Oh wait! I hate Pat Tobin's 9 db attenuation circuit! Pat Tobin sucks. Hold on here Hondo, here's the scoop. The B200Y tweeter is 9db hotter than the earlier B200X tweeter. So, Rudy Bozak built in a 9db attenuation circuit into his crossovers to give them. All Pat Tobin did was use what Rudy had already implemented. Oh, yeah, it's like that. Now maybe you can see that Pat Tobin's 104T schematic is more friendly than what you thought it was. The Symphony and Concert Grand already crossed the woofer and mid over at 400Hz, so a portion of your update was already done at the factory. If you or anyone need information or help with a Bozak crossover refresh/update, please visit this thread here:

http://audiokarma.org/forums/index....like-the-tobin-104t-mods-on-my-bozaks.732688/

The B200x tweeter has a paper cone with a shiny chrome dust cap. Those need to be removed and replaced with the B200Y. They have different sensitivities, and the Zobel Network was not designed for the X tweeter. Or, you can remove 4 of the tweeters and use 4 B200Y tweeters per cabinet. This is what I'd do if they were mine. It will improve their pinpoint accuracy, and save you some coin. I can get you the wiring diagram for loading it with just 4 tweeters per. You could buy these from the factory loaded with 4 instead of 8.

Rebuild your crossover to the 104T schematic, the picture is above in another post. Omit the 7.5ohm resistor. In its place, install an 8ohm 15 watt l-pad with a 1" shaft. Use your multi-meter on the l-pad to find the variable 8ohm leg. Wire it in where the 7.5ohm resistor was supposed to go. Please thank AK member Retrovert for this solution, it is not mine.

I can see on your baffle where the original Bozak midrange covers were originally mounted. My speculation is that someone wanted to see the mids. So, the unscrewed the cover. It was lightly glued down and those things are about as brittle as using potato chips. Mr. Curious ended up cracking them into multiple pieces and tossing them. Ta da! No midrange covers. The original B800A midrange covers had a volume of 452 cubic inches. Just in case anyone wants to know. With modern acoustic testing equipment, we now know that tubes, spheres (or half rounds) and square boxes have nasty resonance issues. AK member Retrovert's solution of using a plastic flower pot is absolutely the best solution ever. It's none of those shapes, no resonance issues. They're inexpensive, easy to find and easy to install. The Rubbermaid solution is none of those, trust me on that one brother man. Line and cover the flower pot with 1" of 100% cotton upholstery batting. I bought 1/4" 100% cotton upholstery batting and used 4 layers. Bam, done. Use a cheap ass flexible caulking to seal the lip of the flower pot.

Rudy's wiring markings are non-intuitive. He used 1 and 2 to mark polarity. 1 is negative, 2 is positive. The orange wires are negative! As long as your mid follows 1 to 1 and 2 to 2, it's in phase and that's where you want it.

You're really close to getting this all wrapped up and ready to go. The only thing that puts a snag in the project are the X tweeters, those things need to go. You cannot complete this project with those in place.

Biggles

 

[MATT0404]

Happy Good Morning!

A few things to go over here, so let's hunker down and get to gettin'. I'll start with the crossover and any updates that are recommended. Please, anyone reading this, pay attention. Mr. Pat Tobin's "Mods" are essentially a swapping around of original factory settings, with the addition of a Zobel Network for the tweeters. Read that again, yup. It's using what Rudy Bozak already designed into the N10102 3-way crossover. But wait, I don't think I want a Zobel Biggles! I want factory !!! No, no you don't. See, the B200Y tweeters are upwards of 60 years old. They have an inherent impedance rise. What this translates to is a spikey response at approximately 9k, it'll make your ears ouchie. What the Zobel does is flatten out this impedance rise and give your tweeters a smooth response. So, what you're saying is that you want a spikey tweeter. Uh, I guess not Biggles. Oh wait! I hate Pat Tobin's 9 db attenuation circuit! Pat Tobin sucks. Hold on here Hondo, here's the scoop. The B200Y tweeter is 9db hotter than the earlier B200X tweeter. So, Rudy Bozak built in a 9db attenuation circuit into his crossovers to give them. All Pat Tobin did was use what Rudy had already implemented. Oh, yeah, it's like that. Now maybe you can see that Pat Tobin's 104T schematic is more friendly than what you thought it was. The Symphony and Concert Grand already crossed the woofer and mid over at 400Hz, so a portion of your update was already done at the factory. If you or anyone need information or help with a Bozak crossover refresh/update, please visit this thread here:

http://audiokarma.org/forums/index....like-the-tobin-104t-mods-on-my-bozaks.732688/

The B200x tweeter has a paper cone with a shiny chrome dust cap. Those need to be removed and replaced with the B200Y. They have different sensitivities, and the Zobel Network was not designed for the X tweeter. Or, you can remove 4 of the tweeters and use 4 B200Y tweeters per cabinet. This is what I'd do if they were mine. It will improve their pinpoint accuracy, and save you some coin. I can get you the wiring diagram for loading it with just 4 tweeters per. You could buy these from the factory loaded with 4 instead of 8.

Rebuild your crossover to the 104T schematic, the picture is above in another post. Omit the 7.5ohm resistor. In its place, install an 8ohm 15 watt l-pad with a 1" shaft. Use your multi-meter on the l-pad to find the variable 8ohm leg. Wire it in where the 7.5ohm resistor was supposed to go. Please thank AK member Retrovert for this solution, it is not mine.

I can see on your baffle where the original Bozak midrange covers were originally mounted. My speculation is that someone wanted to see the mids. So, the unscrewed the cover. It was lightly glued down and those things are about as brittle as using potato chips. Mr. Curious ended up cracking them into multiple pieces and tossing them. Ta da! No midrange covers. The original B800A midrange covers had a volume of 452 cubic inches. Just in case anyone wants to know. With modern acoustic testing equipment, we now know that tubes, spheres (or half rounds) and square boxes have nasty resonance issues. AK member Retrovert's solution of using a plastic flower pot is absolutely the best solution ever. It's none of those shapes, no resonance issues. They're inexpensive, easy to find and easy to install. The Rubbermaid solution is none of those, trust me on that one brother man. Line and cover the flower pot with 1" of 100% cotton upholstery batting. I bought 1/4" 100% cotton upholstery batting and used 4 layers. Bam, done. Use a cheap ass flexible caulking to seal the lip of the flower pot.

Rudy's wiring markings are non-intuitive. He used 1 and 2 to mark polarity. 1 is negative, 2 is positive. The orange wires are negative! As long as your mid follows 1 to 1 and 2 to 2, it's in phase and that's where you want it.

You're really close to getting this all wrapped up and ready to go. The only thing that puts a snag in the project are the X tweeters, those things need to go. You cannot complete this project with those in place.

Biggles

And just like that, all my questions answered. You, my man, deserve an award! Thank you.

I will double check the tweeters. I'm pretty sure when I shined a light through the grill fabric, I didn't see any shiny dust caps. I'll do a little more investigation to confirm/deny the presence of 200x tweeters.

The crossover work seems pretty straightforward to me now with the modification to omit the 7.5 ohm resistor and add an 8 ohm L pad in it's place. I'll follow up shortly with a Parts Express BOM to confirm I have all the bases covered.

 

[drbiggles]

You're welcome! And, buy 2 25uF Dayton 5%'s for the mids, not the 50uF. This will help a tad with lowering ESR. Load the rest of the crossover with Dayton 5% as well. I've tested them against the 1% and you're not getting enough value for the dollar vs the 1%. Bozaks love Dayton.

If you want to take this a step further, add .1uF and .01uF poly bypass caps to each capacitor in the network. This combination is also AK member Retrovert's work.

Biggles

 

[twiiii]

There is a special version of the tobin mod I believe for the original 4000 Symphony. As it is a totally a different speaker using a 105 crossover from the later versions that used the B-209b or Bc midrange and the 104 crossover. There an additional resistor in the 105 network to balance the mid the N-104 doesn't have, and the 105 doesn't have an additional capacitor in the tweeter network the 104 has. So I would remove the tweeter volume control and leave the crossover as original and only replace the caps with identical values. I owned 4000's for over 6 years, and the later versions and Concert Grands have a totally different harder more forward sound has been my experience. My current 4005's are even further away in sound from the original Symphony. I know the Tobin mod is supposed to bring this harness under control, but the few times I have heard it I think it goes to far the other way for balancing the tweeters to the midrange and does nothing about balancing the mid to the woofers, and is why he made folks change the coil tap on the midrange. I much prefer the N-105 crossover. I bi amped all my large Bozaks over the years and prefer the sound. The bass has more truthfulness. but you have to be care ful keeping the balance so you don't compromise the synergy between the B-800 A and the B-199's. My current tri ampedGrands and bi amped center front 4005 have added super tweeters, so a Tobin mod is of no concern for me. You definitely need to find a pair of bowls stuffed with acoustic material to cover the mids in order to keep from further compromising your Symphony pair. I pre fer SS direct coupled amps for Bozak woofers in Grands and Symphony, In my case ver the years, Crown Dc 150 A, 300A, Mac 7100, 7200, 207 and MC 2002. My 275's, 240's, 2100's, 2200's borrowing 2255's, 7150's and my MC 60's operating full range or bi-amped just didn't cut the mustard, though the 60's and 275's had a very special upper bass and lower midrange sound balance SS stuff never captured.

Now that I have a spare room it would be fun to have a MX-110Z, 240, and an unmodified pair of 4000 Contemporaries again. Maybe with my TD 125 and Dynavector, with my MVP 861 disc player. Then I'd have a place for a SME 15A, with an upgraded Dynavector and a MCD 500 in my current system.

MX-110, MC 240,MCD500, pair of Symphonies, SME 15A and Dynavector, ouch. $$$$$$. $27,000. A used MA 6200, Symphonies , my 861 and a feed from my MP 100 and my MR-78 would be much cheaper. $3000 possibly.

Enjoy your Symphony pair. Just because the tweeters have the stamped X on them means they are X tweeters, you will have to confirm that. Shine bright flashlight through the grill cloth and see if you have tweeters with the silver center cap. If you don't you have 200 X chassis with a 200y cone. No problemo! I have seen quite a few Bozaks with 200X frames that were 200 Y's. But it pays to be careful.

There is a big squabble among Bozak owners about polarity of the mids. I suggest you read articles written about that by Bob Betts who was lead engineer working with Rudy for quite a period of time. Just Google BOB Betts Bozak and his site will pop up.

 

[Sam Cogley]

Don't throw out tweeters just because they say B200X. Look at the cones. Bozak apparently ordered a huge supply of tweeter frames from their foundry, and a lot of early and mid-1960s B200Ys have frames with "B200X" cast into them.

 

[drbiggles]

Here is the N-105 Crossover that's stated to be used for the B-4000 Symphony.

 

[MATT0404]

You're welcome! And, buy 2 25uF Dayton 5%'s for the mids, not the 50uF. This will help a tad with lowering ESR. Load the rest of the crossover with Dayton 5% as well. I've tested them against the 1% and you're not getting enough value for the dollar vs the 1%. Bozaks love Dayton.

If you want to take this a step further, add .1uF and .01uF poly bypass caps to each capacitor in the network. This combination is also AK member Retrovert's work.

Biggles

Just to clarify, do the bypass caps go on all caps in the crossover, or just the big 25uF's? Is there any reason not to reuse the factory inductors if they test well?

There is a special version of the tobin mod I believe for the original 4000 Symphony. As it is a totally a different speaker using a 105 crossover from the later versions that used the B-209b or Bc midrange and the 104 crossover. There an additional resistor in the 105 network to balance the mid the N-104 doesn't have, and the 105 doesn't have an additional capacitor in the tweeter network the 104 has. So I would remove the tweeter volume control and leave the crossover as original and only replace the caps with identical values. I owned 4000's for over 6 years, and the later versions and Concert Grands have a totally different harder more forward sound has been my experience. My current 4005's are even further away in sound from the original Symphony. I know the Tobin mod is supposed to bring this harness under control, but the few times I have heard it I think it goes to far the other way for balancing the tweeters to the midrange and does nothing about balancing the mid to the woofers, and is why he made folks change the coil tap on the midrange. I much prefer the N-105 crossover. I bi amped all my large Bozaks over the years and prefer the sound. The bass has more truthfulness. but you have to be care ful keeping the balance so you don't compromise the synergy between the B-800 A and the B-199's. My current tri ampedGrands and bi amped center front 4005 have added super tweeters, so a Tobin mod is of no concern for me. You definitely need to find a pair of bowls stuffed with acoustic material to cover the mids in order to keep from further compromising your Symphony pair. I pre fer SS direct coupled amps for Bozak woofers in Grands and Symphony, In my case ver the years, Crown Dc 150 A, 300A, Mac 7100, 7200, 207 and MC 2002. My 275's, 240's, 2100's, 2200's borrowing 2255's, 7150's and my MC 60's operating full range or bi-amped just didn't cut the mustard, though the 60's and 275's had a very special upper bass and lower midrange sound balance SS stuff never captured.

Now that I have a spare room it would be fun to have a MX-110Z, 240, and an unmodified pair of 4000 Contemporaries again. Maybe with my TD 125 and Dynavector, with my MVP 861 disc player. Then I'd have a place for a SME 15A, with an upgraded Dynavector and a MCD 500 in my current system.

MX-110, MC 240,MCD500, pair of Symphonies, SME 15A and Dynavector, ouch. $$$$$$. $27,000. A used MA 6200, Symphonies , my 861 and a feed from my MP 100 and my MR-78 would be much cheaper. $3000 possibly.

Enjoy your Symphony pair. Just because the tweeters have the stamped X on them means they are X tweeters, you will have to confirm that. Shine bright flashlight through the grill cloth and see if you have tweeters with the silver center cap. If you don't you have 200 X chassis with a 200y cone. No problemo! I have seen quite a few Bozaks with 200X frames that were 200 Y's. But it pays to be careful.

There is a big squabble among Bozak owners about polarity of the mids. I suggest you read articles written about that by Bob Betts who was lead engineer working with Rudy for quite a period of time. Just Google BOB Betts Bozak and his site will pop up.

Thanks for all the info! I have a few tube amps I could try with the Bozaks, but right now they're sounding pretty good with a Yamaha A-S1000. I'll read up on the Bob Betts site.

Don't throw out tweeters just because they say B200X. Look at the cones. Bozak apparently ordered a huge supply of tweeter frames from their foundry, and a lot of early and mid-1960s B200Ys have frames with "B200X" cast into them.

Confirmed no shiny dust caps!

 

[drbiggles]

Hey man,

Yeah, bypass caps go on all the capacitors. You won't necessarily hear a difference right off the top. But some hours down the road the chance of you getting listeners fatigue is greatly reduced, if not altogether gone. Remember, 2x25uF caps for each midrange circuit on the crossover, you need a total of 50uF. Absolutely keep the original Bozak inductors. That's all I use out of the original crossovers.

No shiny dust caps! Situation handled, move on.

Bozaks are very revealing speakers. They respond to high quality amplification, sources and media. Try everything you have and see what you think. Rudy preferred solid state amps.

Biggles

 

[Retrovert]

I don't think you have a lot to do. You can swap in and make the Tobin crossover and maybe get more out of these. Or just recap with same values and configuration. I recently re-did my Concert Grands, but for now just went back to the original specs in the crossover since I have the X version tweeter array. Your later version drivers are perfect for the Tobin.

The only Tobin modification that is not needed with a B-200X is the attenuator for the tweeters, since the Y tweeters are louder than the X. That attenuator should be an L-Pad, anyway, as I've elsewhere described, so there's no reason to not use the Tobin modifications. The B-200X, like other tweeters, has a rise in impedance with frequency so the Zobel is still required. If the B-200X tweeters are perfectly balanced with no attenuation than nothing has been lost, aside from the minor cost of including the L-Pad.

Moving the midrange-woofer crossover point also does not depend upon tweeter choice.

Every Bozak owner of a B-199 + B-209 + B-200 combination may benefit from the Tobin modifications.

I find it interesting that these and other stock factory models don't isloate the mids but we all want to now.

Woofer modulation of the midrange, and the reverse to a lesser extent, causes distortion so that is why we want to remove it. This issue was likely known to Bozak, but the non-inclusion was very likely a cost-savings issue because only a single, and notably the most expensive, Bozak model included the midrange covers..

In any a competitive marketplace any feature which a significant portion of purchasers cannot differentiate from the competition will be removed to lower costs and be competitive. I'm not surprised by this omission. It is no different than Bozak switching to cored inductors and using aluminum wiring when copper wire became significantly more expensive.

The point is that we may now fix these cost-driven decisions at minimal cost.

I believe it's a flower pot actually that others have found to be the best choice. Looking at your internal lay-out it appears that cross piece along the tweeters might be in the way of that. The mids in my CG's were already isolated so I didn't have that to deal with.

Yes, the CG were the only model to use midrange bells.

I described the flower pot modification here:

http://audiokarma.org/forums/index....mods-on-my-bozaks.732688/page-9#post-10917938
​

 

[Retrovert]

Just to clarify, do the bypass caps go on all caps in the crossover, or just the big 25uF's?

Yeah, bypass caps go on all the capacitors. You won't necessarily hear a difference right off the top. But some hours down the road the chance of you getting listeners fatigue is greatly reduced, if not altogether gone.

Biggles is correct.

As I've elsewhere described, the reason bypass capacitors work is the internal structure of capacitors creates a path for charge to cycle in and out of. The larger the capacitance, the longer the path and the slower charge moves in and out. This can interfere with reproduction of higher frequencies. The smaller bypass capacitors I suggested, 0.1 uF and 0.01 uF can more rapidly respond to higher frequency changes than the larger capacitors.

You can often hear this as an A/B comparison, as the bypassed crossover sounds more lively and responsive. It is a difficult difference to describe, but it is often audible. The long term listening effect is to reduce a lot of inaccuracy which, as Biggles noted, translates into listener fatique.

 

[Retrovert]

Also, if you have the B-209A midrange you should consider replacing with the B, Bc, or C variants. The short-lived A has resonance issues which resulted in a redesign of the surround, which was why the B-209B was created. The A required a latex-foam damping ring which has long since shrunk and fails to do its job. Nobody knows how to rebuild that ring. Without it the driver, like any aluminum cone, will ring and this causes distortion.

The thread to which I above linked also has details on the B-209A issue, I believe. If not, it has elsewhere been slice and diced to pieces.

 

[Retrovert]

Confirmed no shiny dust caps!

Congratulations on your B-200Y winnage. Good call on that one, Twiii and Sam.

The Tobin modification for the tweeter impedance rise and attenuation (use the L-Pad as I described in the aformentioned thread) will greatly improve the sound, particularly at low volume levels. The attenuator is sized for moderate-high levels and it simply is too much. Some prefer very little attenuation, even at high volume. It all depends upon your room, your hearing, the music being played, and your personal taste.

 

[MATT0404]

Congratulations on your B-200Y winnage. Good call on that one, Twiii and Sam.

The Tobin modification for the tweeter impedance rise and attenuation (use the L-Pad as I described in the aformentioned thread) will greatly improve the sound, particularly at low volume levels. The attenuator is sized for moderate-high levels and it simply is too much. Some prefer very little attenuation, even at high volume. It all depends upon your room, your hearing, the music being played, and your personal taste.

Thanks for chiming in and contributing to this thread!

My to-do list is pretty short:

1. Tobin 104T with addition of L-Pad for attenuation
2. Flower pot cover for B200A mids
3. After taking care of sonics, re-cover grills with new fabric

How's this look for my order from PE?

 

[Drugolf]

Looks good to me. Need any wire? I had to replace most of mine as I had a broken section somewhere along the line and replaced it all. Went with the Audyn Caps for the bypass. Got extras of those while at it for other efforts. Too bad PE doesn't have flower pots!