Bozak B305 Urban

[RMBRadley]

I became the proud owner of a pair of Bozak B305 Urban speakers today from an estate sale. It appears that these were bought and installed in 1963 and had not moved again until today. The cabinets have a few minor scratches, but some light 0000 steel wool and some linseed oil and they will look like new. The grill cloth looks as good as I have ever seen on a vintage speaker like this. I popped open the cabinet and the inside was pristine with the cellulose curtains hanging nicely intact. The have the B209A AL-cone midrange and the N10102 crossover. Each cabinet has 2 B207A 12" coaxial woofers.

I am excited to get to work on the crossovers and I am torn on whether to do the Tobin upgrades, or just to refresh the capacitor banks. I am also going to remove the mids and look at the dry rot situation for the foam dampening ring.

I hooked them up to a 50WPC Yamaha CR820 and they sounded great at low levels till slowly turning up volume started to get some buzzy harshness from the mids, so I'm thinking the foam ring needs to be scraped off and see if that quiets them down.

Any comments off B305 owners on the difference in the amount of work for doing the caps in the existing Xover o point the mods?

Also anyone have success in scraping the mid frames and eliminating the fuzziness?

As i make decisions on which way to go I will post updates and photos as things progress.

 

[Lucky Pierre]

Excellent find. My journey in this hobby has been drifting to big, old, efficient speakers and low power tube amps.

I am looking forward to watching your progress.

 

[RMBRadley]

I have removed the midrange drivers and sure enough the foam ring designed to damp cone ringing was as hard as a rock and crumbling. I removed the ring and repacked with some soft foam weather-stripping that I cut to match the space. The buzzy harshness is completely gone! One problem solved for about $5.00. I am still trying to find the best info on the crossover refresh. I would like to incorporate the improvements from the Tobin mods, but the B305 is not mentioned much. My hang up is lowing the woofer to mid crossover to 400hz, which seems to make sense, but it seems I would have to have a 6.6mH inductor coil to lower the woofer cut off to 400hz. The big coil on the current crossover are either 1.6 or 3.3mH's. Hoping to get on the Bozak Facebook page to access their expertise before ordering parts.

 

[drbiggles]

Hay, yeah get on the FB and get yourself some details. ... I edited my original text here. You've got the 16ohm mid. Tobins work on the mid section don't work. Tobins tweeter leg of the schematic isn't being used much any longer. It's much nicer being able to tune the tweeter level to your taste.

Biggles

 

[drbiggles]

Make sure you put your 8" flower pot over the mid to protect it from the woofer's backwaves. Lined and covered with 100% upholstery cotton.
And, congratulations!!!!!! Have fun and enjoy yourself!

 

[twiiii]

Rather than a Tobin Mod why not a pre-owned Rane program Equalizer, But 90 percent of the time the Graphic tone controls on my C-34V do all I that need. I added Celestion super tweeters to my Concert Grands and to my center low boy B-4005 for added highs above 12 KHZ. Something a Tobin Mod can't do. But I would replace all the caps in the crossover first before doing anything. You realize your speakers are 16 ohm!!!! So your Yamaha is down rated to around 30 watts. But that should be enough for an average listener. But I would want at least 120 to 150 watts per channel on an SS direct coupled amp rated at 8 ohms.

Personnally I would bi-amp using an electronic crossover to get rid of the coil in series with the woofers and rewire the woofers in parallel, You will get a tighter less ringing woofer sound that way. I would lower the crossover down 300 HZ with a second ordered filters and between the frequency change and wiring the woofers in parallel, 4 ohms, you will get a much cleaner more realistic bass sound and because the polarity of the midrange is already reversed you don't have to worry about phasing issues when changing from a 6 db slope to a 12 db per octave slope which will protect the midrange better than the 6 db slope. Especially when playing harp, Classical Organ, and classical piano recordings. Dynamics will seem to improve, too.

 

[RMBRadley]

Make sure you put your 8" flower pot over the mid to protect it from the woofer's backwaves. Lined and covered with 100% upholstery cotton.
And, congratulations!!!!!! Have fun and enjoy yourself!

The midrange has very little clearance at the top cabinet edge, and the mid cabinet cross brace has less than 1/4 inch at the cross brace (See top left of photo), so it looks like some serious surgery on the planter/enclosure would be needed to get a good fit with a seal. I don't want to get into moving or modifying the brace. Will have to get creative!

 

[RMBRadley]

Rather than a Tobin Mod why not a Rane program Equalizer, But 90 percent of the time the Graphic tone controls on my C-34V do all I that need. I also have a MQ 112 I use when dubbing recordings in addition to my 3BX and model 119 DBX limiter expanders. I added Celestion super tweeters to my Concert Grands and to my low boy B-4005's for added highs above 12 KHZ. Something a Tobin Mod can't do. But I would replace all the caps first before doing anything. You realize your speakers are 16 ohm!!!! So your Yamaha is down rated to around 30 watts. But that should be enough for an average listener. But I would want at least 120 to 150 watts per channel on an SS direct coupled amp rated at 8 ohms.

Personnally I would bi-amp using an electronic crossover to get rid of the coil in series with the woofers and rewire the woofers in parallel, You will get a tighter less ringing woofer sound that way. I would lower the crossover down 300 HZ and between the frequency change and wiring the woofers in parallel, 4 ohms, you will get a View attachment 3299933much cleaner more realistic bass sound. Especially when playing harp, Classical Organ, and classical piano recordings.

I have a 300WPC @8ohm (so 150 @16ohms) Perreaux amp with an APT Holman pre waiting to take these over when the crossovers are up to it. The Yamaha was an easy hook up to do in the garage for the initial listen and checking the drivers. I really like the variable loudness controls on the old Yamaha's for tailoring the sound to the listening level. Sounded great with the Yamaha, but I am sure will improve with more power! Will wait to get on the Bozak FB group to get the best options on the crossover ironed out. I have lusted after Concert Grands as an end game speaker for quite a while, these B305's will give me a small taste of that "Bozak" sound. Yours look amazing.

 

[twiiii]

Yes 305 are of the same family but unless properly placed in a room are quite midrange and lower highs predominant. So thats why some folks think Tobin is the answer. If you pull them out from a wall you loose the bass below 60 hz quite rapidly, which some prefer. I don't. Leave them against the wall and move your listening position for the smoothest most resonant free sound. My Grands exhibit a nasty 50 HZ and 160 hz humps. My moving my chair I can get rid of the 50 HZ hump, but a little electronic voicing is necessary to calm the 160 HZ bulge and a little encouragement is needed to extend the bass and high treble just a bit. 4 db at 25 HZ and 4 db at 18,000 HZ. Parametric EQ's work best with speakers as you can center a filter exactly where you need it to be focused. Of course it helps if you have the right test equipment. And preferably you want to sit between the Critcal distance and 1.6 times that distance. Whats critical distance? Thats where the the near field or direct field of the speaker is equal in intensity to the reverberant field.

 

[DesertRatt]

Gotta love those Concert Grands!

 

[drbiggles]

The midrange has very little clearance at the top cabinet edge, and the mid cabinet cross brace has less than 1/4 inch at the cross brace (See top left of photo), so it looks like some serious surgery on the planter/enclosure would be needed to get a good fit with a seal. I don't want to get into moving or modifying the brace. Will have to get creative!

I've had to do some serious modifying, it happens. Sometimes you can find a pot that has a plastic that's bendy. You can snip here, snip there, bend it, screw into place. Then, use latex caulk to seal yer goofs. You'll do fine.

Biggles

 

[Steve Smiley]

The midrange has very little clearance at the top cabinet edge, and the mid cabinet cross brace has less than 1/4 inch at the cross brace (See top left of photo), so it looks like some serious surgery on the planter/enclosure would be needed to get a good fit with a seal. I don't want to get into moving or modifying the brace. Will have to get creative!

The flower pot mod is worth any modifications you can muster. With minimal effort, you could trim the top section of the mounting plate for the brace off (even with the top of the 2” x 4”) and then, with careful measuring, drive two black screws from the front baffle to resecure it. This is the kind of thing I love a Multi-tool for. And the black-headed screws will look fine from the front. Then I think you would have good space for the pot.

Smiley

 

[RMBRadley]

When I open them back up to do the crossovers I will figure something out to get the mids isolated. Seems silly not to do it. Just finished about 2 hours of listening in the garage with the door open. They seem to sound as good 40 feet away as they do at 15, quieter, but the same cohesiveness top to bottom. We are having some friends over for pizza on the patio tonight and I am going to pull them out on to the driveway for background music, but I will take the opportunity to feed them some more power. I'll drag out my Denon AVR5600 (with 140WPC @8ohms) and a turntable and see how that goes!

 

[RMBRadley]

Moved out and they sound smooth outside. Looking forward to an evening of casual listening.

 

[Steve Smiley]

Moved out and they sound smooth outside. Looking forward to an evening of casual listening.

Sounds like a great evening! Enjoy!