Blasphemy: I do not like the Tobin 104T Mods on my Bozaks

[SiliconTi]

Well, I finally bit the bullet on the Tobin mods for my 302s. I had high hopes. I performed the mods even taking the time to tuck it all into the original cans so it looks stock at first glance. I checked everything 10 times before buttoning them up.

Ran some test listening - disappointed. The highs are way too muted. This may make them "balanced", but the tweeters are too "cold" now. Bass and mid are much cleaner.

If I did it again, I think I'd recap and add L-pads to the tweeters to better control them (they were very "hot" before the mod).

I hate to rip it all out, but now I need the EQ at 10K bumped a bit to make them sound right (to me). I dunno, maybe I'll create my own crossover for them.

Dang it.


EDIT:

OK, if you are looking for info on the Tobin mod, here is a summary of what over a year of trial, error, blood, sweat, and tears has resulted in. Feel free to look through the entire thread:

The Tobin mod does work.

Using an L-pad to attenuate the tweeters is a better (more flexible) option than the 7.5 Ohm resister.

Setting the Woofer to the end of the inductor, (the lug marked N-101 on my crossovers) and the mid should be connected to the center tap of the inductor (the lug marked N-102 on my crossovers).

Retrovert's flower-pot midrange backer is a great addition while you are in there.

PAY ATTENTION TO DETAIL: make sure it is all correct before you judge.

The amplifier used may make a difference as well, keep that in mind.

 

[Sandstrom]

I had the exact same experience. I felt that the highs went away after trying it out. Fortunately I had built it on a separate board and bypassed the original using only the existing inductors so it was easy to revert back.

 

[drbiggles]

Note: Are you sure you used the 104T schematic versus the 101T? They're both floating around out there.

Hey SiliconTi,

I had the same experience, only worse. Thankfully, I had AK member Retrovert in the background working with me for nearly two and a half weeks. Towards the end I was nearly in tears, on my knees with my head firmly planted in the backs of mine. I had my ipod touch rigged up to do sweeps, isolated drivers and pulled apart the crossover a multitude of times. I too thought the same thing. I simply did not like what Pat Tobin's design did to my crossover.

I got pissed off and knew that so many people's opinion couldn't be that far off. I tore the crossover to pieces, again. I made my own crossover board. I bought new terminal strips, used new wire and very carefully soldered everything back into place. Paying special attention to my connections. I'm talking laser, Nasa type attention to detail. Voila, all the drivers popped into play just as they were supposed to.

One thing I did was to toss Pat's schematic. I joined the Bozak users group on FaceBook and found this schematic that helped me build my new crossovers. I've got 6 crossovers now rebuilt and working as they should.

One thing you could try is to take the 7.5 ohm resistor out of the circuit. That's the attenuation resistor, leave the Zobel network in place. That might brighten things up.

Biggles

 

[Tom Brennan]

It's OK, you get to prefer Rudy Bozak's own voicing of his speaker over Tobin's. Sometimes mods become the thing to do not because they're superior but because they're, well, the thing to do. One way some enthusiasts show enthusiasm is by putzing around with things, and not always to sonic benefit.

 

[SiliconTi]

Thanks to all of you! I've never read anything bad about the Tobin mods.

Thanks Biggles! I'll pull the 7.5 Ohm resistor and retry.

 

[SiliconTi]

I checked every signal path ten or twelve times. I am sure they are correct, I just do not like it.

I'll play next week and devote some time to resolving this.

 

[mrphilco]

I recently finished restoring a pair of E-300 cabinets which had, and have, the B-302A system in each (B-199 woofer, B-209 midrange, two B-200X tweeters, and an N-10102 crossover in each cabinet). These speakers were purchased from Sandstrom two years ago. He put new caps in the crossovers before I bought the speakers.

I went against the advice of others and kept mine stock...and I love them as they are. Actually, I found the tweeters just a little too "hot" for my liking...and I did add L-pads to the tweeter circuits, turning each down to about 3/4 volume. Now they are pretty much perfect to my ears.

I'm buying a pair of Bozak Urban B-302As, and picking them up this weekend. They have the Tobin mod and B-200Y tweeters. I'll soon find out how the mod sounds to me. If I don't care for it, then they too will be changed to a stock type crossover - or, at the very least, eliminate the 7.5 ohm resistor as Biggles suggested.

 

[Retrovert]

I don't remember if you had the B-200X or B-200Y tweeters. This makes a difference. Biggles and I extensively discussed the attenuation from the Zobel and somewhere I have posted a description of how it works.

The Tobin modification is threefold:
(1) Downwards moves the crossover points for the midrange and woofer (inductor taps)
(2) Balances the hotter B-200Y tweeter to the other drivers (attenuator resistor)
(3) Flattens out an impedance rise at the upper end of the tweeters (Zobel)

Adding L-pads is tricky because it alters the resistance not the impedance. Remember, speakers have frequency-dependent resistance (aka impedance) which is not the same as pure resistance.

If you remove the attenuator you will restore the original volume levels. This will make the B-200Y too loud.

I would not remove the Zobel as it flattens the rise in impedance and results in a more natural sound.

If you are running with the original capacitors that is a good part of the problem. Replace all of them and the sound will be greatly improved.

 

[SiliconTi]

I did add L-pads to the tweeter circuits

What I should have done.

 

[SiliconTi]

OK, so I cut the lead on the 7.5 Ohm resister - better balance. Not what I was looking for, but I think it is because I was used to the "hot" 200y tweeters and liked it.

I'll run them and see if I like it.

I will say, that if I did it all over, I'd just recap them.

 

[mrphilco]

SiliconTi

They are your speakers; set them up stock or modify in a manner that suits you, not the crowd.

I really didn't want to add the L-pads to my E-300s but I didn't feel like tinkering around with the crossovers after spending the entire summer restoring the cabinets. I was junking a set of Pioneer CS-88 speakers at the same time anyway; so their L-pads (short shaft) went into another pair of speakers I have which had long shafts but only needed short shafts. The backs of my E-300s had been drilled and cut multiple times for various mods over the years. I filled the holes with Bondo in order to keep the original backs but I figured "hey, what's another hole in each back after all this?" So yes...I did it...and I am glad that I did.

Heresy? No, that's Klipsch. These are Bozaks.

I don't have my second pair of B-302As yet (illness prevented our making the trip to get them this past weekend), but from what you have said, it sounds like I'll be removing the 7.5 ohm resistors as well once I pick up my Urbans.

 

[Northwinds]

I know nothing about this mod but would it not it stand to reason that somethings have to break in? I know when a amp is rebuilt (or preamp) it takes time for things to settle in and sound right

 

[Retrovert]

I know nothing about this mod but would it not it stand to reason that somethings have to break in? I know when a amp is rebuilt (or preamp) it takes time for things to settle in and sound right

That's mostly the brain settling in to accepting the newer sound as normal.

No break-in time exists for a crossover and there is no proof this exists outside of the brain. Resistors and capacitors and inductors do not require use to settle to some final value. No capacitor manufacturer, at least any which does not exclusively deal in audiophile capacitors, has any application note, technical report, or published paper about this alleged phenomenon. If you call up, say, Cornell Dubilier's or Mallory's technical support it will deny this process exists. Some years ago I did this because I wanted to disprove the phenomenon. I called a number of major manufacturers and they all politely sighed about audiophiles and their beliefs. Some gave me an earful about how hard it is to prove the negative (i.e. that it does not exist).

I described the various purposes of the Tobin modification in posting #8.

The issue here is simple: some people like a tweeter that is disproportionately louder than the other drivers. That can be the result of: (a) personal preference, (b) age-related hearing loss (no disrespect to anyone, but this type of age-related hearing deficit is why convenience stores often play high-pitched whining drone sounds to drive away teenagers who still have the upper registers, but leave the older clientele unaffected), or (c) room acoustics.

I have friends who cannot hear past about 10 to 12 kHz. I can hear to 16 kHz on my computer speakers, which is where I ran the test. Given my advanced years that's pretty amazing. I have other friends who want to boost the midrange and treble to account for bathtub curve hearing loss. Ears do not always age well.

What we have here is personal preference or room characteristics, not a defect in the crossover, and it's easily accommodated by removing the attenuator. A variable bypass (L-Pad) can be used to obtain exactly the amount of attenuation that is desired for the person for their own tastes or for the room, or both.

People should adjust their speakers, tone controls, equalizers, etc. to make their listening experience enjoyable. As long as I don't have to hear the results from teenagers who push their bass up 120 dB and drop their midrange and treble 40 dB, it's all good.

 

[Retrovert]

OK, so I cut the lead on the 7.5 Ohm resister - better balance. Not what I was looking for, but I think it is because I was used to the "hot" 200y tweeters and liked it. ... I will say, that if I did it all over, I'd just recap them.

The Zobel is a good idea because it flattens the linearity and prevents a rise at the high end. No judgement on whether you like more highs (see above) by removing the attenuator, but I think you'd want those highs flatter and thus uniformly louder.

 

[SiliconTi]

I spent an hour or so with them last night. As my brain adjusted, I think they are OK now. Highs are still a touch weaker than I like from them, but the mods changed so much of the sound from the other drivers that I really need to give them some time. I do not think I'll end up going back to the stock configuration at this point.

 

[mrphilco]

Well...

I now have a pair of Bozak Urbans (B-302A) that have the Tobin mod, and...

I like it. I posted a separate thread about my experience with stock E-300s vs. Tobinized Urbans here.

 

[bshorey]

<snip>

I will say, that if I did it all over, I'd just recap them.

<snip>

I'm in the middle of this project myself. Inadvertently ordered up a set of stock replacement caps (the DMPC parts, not the PMPC 'audio' caps), then stumbled across the Tobin mods, so I ordered up a complete set of parts to perform those mods.

If anybody is interested in just recapping a pair of these, I have the pair of 8.2 uF and 25 uF caps sitting here unused. Yours for the cost of shipping (still in the unopened Parts Express envelope!). Part #'s Dayton Audio DMPC-8.2 and DMPC-25.

bs

 

[bshorey]

In addition to removing the resistor to brighten them up, you might also try raising them up a little bit. Those tweeters at shin level can't be ideal. I've also read where people have removed the tweeters and placed them in small enclosures on top of the original enclosure and had very good results.

bs

 

[drbiggles]

As soon as I get my vintage DIY B302A's done, I'm going to build new smaller cabinet to match for the tweeters. I've also ordered the 8 ohm L-Pads for my Symphony project and am going to remove the 7.5 ohm resistor and replace it with the l-pad. That way I can adjust it to how I like it. I like my tweeters louder and would like to see what the l-pad does for that.

Biggles

 

[bshorey]

If anybody is interested in just recapping a pair of these, I have the pair of 8.2 uF and 25 uF caps sitting here unused. Yours for the cost of shipping (still in the unopened Parts Express envelope!). Part #'s Dayton Audio DMPC-8.2 and DMPC-25.

Caps are spoken for.

bs