Bozak N-101 xover for B-302a questions

[Retrovert]

Thanks Retrovert. I had already read that post but need go over it again as I always pick up more things on multiple readings. In my parts order was two 8 ohm 15 watt L-Pads. I forgot to order the .1 and .01 caps even though they were in my wishlist. Doh! I plan to do the flower pot mod. Fortunately my Urbans are in very good factory original condition.

The Bozak upgrade packages is more than merely adding components; it is adoption of a lifestyle.

The omission provides you with an opportunity. Try adding the bypass capacitors to a single crossover, then perform an A/B comparison using a mono signal so both speakers are identical. You should be able to hear a difference. It is subtle but nice. Then try the flowerpot, again mono for an A/B comparison. That difference is obvious. So obvious it makes me shake my head at the pernicious effect that trivial cost savings have upon audio. Midrange distortion is the worst place for signal corruption. Woofer inaccuracy is very hard to hear, particularly at the low end. But midrange? That's home.

You might also consider upgrading the tweeters, as I suggested in the above-referenced thread. I know everyone wants to keep things original, but the B-200Y is not able to compete with the SEAS (as Biggles discovered after his upgrade experiments, nicely documented), or some other tweeter technology (AMT, as I've also suggested, or electrostatics, as I own).

Another option I've suggested to improve the high end is retaining the B-200Y but cutting off at 10 kHz via a second-order band-pass made by adding an inductor to the tweeter capacitor, much like a midrange) and transitioning to a supertweeter. This removes the spikey behavior and distortion and should provide a smooth response to 20 kHz. Definitely add an inductor to limit that supertweeter to about 25 kHz to avoid destruction from ultrasonics. Yes, such ultrasonics, particularly oscillations, do exist in many amplifiers and will cook a tweeter able to reproduce such signals. The phase shift at the high end will not be significant as tweeters are shifting all over the place anyway, particularly based upon a lack of time alignment in the cabinet. In brief, the acoustic center of the tweeter should be aligned with that of the woofer and midrange so that the emitted sound for a given time slice all arrives at the same point. The Dahlquist DQ-10 was famouse for performing such alignment.

Do let us know how you feel about the upgrades. Others (see the thread and some others) have reported great clarity from the midrange cover. Huge improvement for a trivial amount of expense and labor.

 

[gawgaboy]

Thanks retrovert.

Been looking at the flowerpots on line at Lowes and Home Depot. What size, diameter, pot is normally used?

I see drbiggles post with a pic of the pot in this thread. http://audiokarma.org/forums/index....aks-and-tell-me-what-to.771019/#post-10554590

 

[drbiggles]

They are 8" pots. Iam sitting in a parking lot waiting for an ak member to buy my Scott tube integrated. Iam a busy guy.

Biggles

 

[gawgaboy]

Thanks. Much obliged.

 

[Retrovert]

Been looking at the flowerpots on line at Lowes and Home Depot. What size, diameter, pot is normally used?

I see Biggles has given you the size even though he is busily exchanging vintage HiFi for etchings of dead political figures. You see how Bozak is a lifestyle, not a speaker?

The Home Depot flower pots here are made by Teku, I think. I used Akro-Mills from a garden center across the river. I'm not sure what brand Biggles used. The difference between them is in wall thickness and lip construction, so you may need to trim varying amounts to fit.

Don't forget to line the flowerpot outside and inside and to make sure the holes are closed up. You should be able to purchase a small amount of cotton batting from either a fabric store, upholstery supply store, and even an re-upholstery store.

 

[gawgaboy]

https://www.lowes.com/pd/Bloem-8-7-in-x-6-8-in-Honey-Dew-Resin-Self-Watering-Planter/1000174849

My color choices are Honey Dew, Calypso, Passion Fruit, and Union Red. Maybe I can do an acoustics analysis of which color is best for specific genres of music. LOL.

Edit: Home Depot has a lot more color options but alas I don't want to drive all the way to it when Lowes is much closer and the acoustical merits of the different colors is yet unknown.

 

[drbiggles]

I used orangish, reminded me of the 70s decor. Its how i roll, yo.

Amp sold! A great day indeed, no back to work.

Biggles

 

[gawgaboy]

First one done in the standard factory B-302a xover. Will see what it sounds like tomorrow.

 

[gawgaboy]

Tobin mod.

 

[gawgaboy]

The 2uf cap / 25 ohm R tweet later Bozak xover recapped lost some tweet sparkle vs the old factory xover without the B-200Y attenuation. I decided to go straight to the Tobin mod xover for the second speaker for an A/B comparison rather than do the same 2uf/25 ohm on it.

The verdict. The tweets are better with the Tobin mod. Both have a fuller more balanced sound but the Tobin mod is better to my ears. I am going to add the L-Pads to the Tobin so I can add just a wee bit of the unattenuated tweet sparkle.

All in all a positive improvement with either version of the B-302a xovers.

 

[gawgaboy]

Oh. Forgot. Flower pot mod is next.

 

[Retrovert]

The Tobin mod for the tweeters has two components: impedance compensation and attenuation for balance.

The impedance compensation is very much needed to tame the rise in tweeter impedance with frequency.

The tweeter attenuation is either too much or too little which is why I've suggested an L-Pad. I have elsewhere speculated that Tobin wanted a solution requiring no tweaking or hole drilling.

So the two may be separately implemented.

 

[Retrovert]

The flower pot nicely cleans up the midrange. You'll like that improvement. Let us know what you think about it. Again, A/B comparison. Do one, test in mono, then do the other because the benefit is clear.

 

[Billa]

Well I might have to say nevermind. I found a thread I haven't seen before that has all the Bozak crossover schematics and it answers most of my questions regarding the capacitor listings and the schematics, as well as the N25 network.

Hi
Can you pls point me to the thread you mention in your post? I'm the proud new owner of stock b302a's and am just beginning my upgrade journey!

 

[gawgaboy]

Hi
Can you pls point me to the thread you mention in your post? I'm the proud new owner of stock b302a's and am just beginning my upgrade journey!

I'll look for it. Been awhile since then.

 

[Retrovert]

I'll look for it. Been awhile since then.

Just to follow up and save you some time.

@Billa also asked me for the same information in a PM

I located the relevant postings and sent him clickable links to the relevant threads (the SiliconiTi and Steve Smiley threads) and specific postings, and I think he now has all the information he needs for the rebuild. So no need for you to spend time on searches, as the heavy lifting has already been done.

I'm going to put this together into a FAQ and post it to save effort for future Bozak newcomers.

 

[mitchalee]

Except in rare cases I try to keep to the original sound of all my loudspeakers and avoid improving them. This is because I have over 100 sets from Apogee to Warfedale. Once in a while I will replace rather than repair a driver. Even then I am careful to match the original specs but will compromise on a much better made model even if the sound does marginally "improve".

You see, since I have so many speakers I am not looking for any of them to be the last word or the best they can be. Instead my purpose is to have fun listening to their unadulterated character, "flaws" and all. For instance, I have a system that consists of a factory original Dyna PAS Preamp, Dyna Stereo 70, and A25 loudspeakers. I have another based around the KLH Model 6. And another on the Design Acoustics D-12, the Polk Monitor 7, the Mirage SM-3, the Apogee Stage, the Bose 901 Series 1 and Series 6, a very clean pair of Theil C3.5 that I rebuilt almost from the ground up. That was expensive! Anyway, I think you get my point: These are vintages, like fine wine, and I do not dilute them to make them better. I like their character or "distortion" if you hear it that way. To me it's character!

My 2 Bozak systems are a set of Tempos with the big woofer in the too small cabinet hooked to a Pioneer 518 with a Denon 103 through a fine Schiit preamp to a Kenwood 9600 monster receiver. The other is a factory original B-302 paired with a B-300 I upgraded with matching original mid and crossover. I just copied the wiring and, well, everything from the 302 to the 300, so it is now a 302. That's the great thing about Rudy! He's the gift that keeps on giving drilling the mid hole for me, but it was a bear getting the wooden square off the hole. Of course, once it was off Rudy had been so nice as to have the bolts and nuts in place, so the tweeter just glides on into its place easy peasy! Wonderful designer! Love you, Rudy!

Oh and my B302 are two tone. One is blonde and the other brunette. Drives my wife CRAZY!

I know Rudy preferred solid state, but I run these off of a Cayin A50 valve amp. Or sometimes a Sabaj A5 Class D Ice Power box I got from Amazon on closeout for a mere $110. And it is one SWEET 35 watt amp. Smooth, clear, transparent as they come, especially with strings. Though as has been indicated string are not a Bozak strong point because of the somewhat hard mid tones. But, then, brass and reeds are fantastic!!! And if I want strings I'll get out my 75 lb. sand-filled Warfedale W70, the acoustic suspension 2-way version. Or my AR2a. Or the Theil. Or, hell, why not the Apogee with the 375 watt Carver? . . . (which makes even YouTube and Prime music streams a fun swim)

I admit it. I am the Septuagenarian Rebel Without A Cause who lives for variety, not perfection. Hey, variety is the spice . . . no, make that, the Ghost Pepper of Life!

Cheers!
Mitch