Tried and true crossover upgrade: Tobin Mods for Bozak B302a

[Steven Ver]

Can't wait to find out just how they were formed. They sound as they were designed right now, so time to settle into different source material. I do appreciate all the information. Searching for better hearing by finding the perfect speaker to pair with my Bogen tube gear. They sound great on almost everything recorded before they were made, so I can switch between speakers pretty easily. I'll try to keep the crazy in check...it's only rock and roll

 

[Retrovert]

What happened to improve the sound? Don't keep us in suspense, here.

I read your post about the impedance being nominal 8 Ω. Was it a polarity reversal in one driver?

Or just a stiff surround which required playing to loosen up?

Some other issue?

 

[Steven Ver]

I found if I keep the volume down and play mostly vintage uncompressed material they sound ok. They may have needed some voice coil exercise....anyway, getting used to the sound and when a track distorts I change tunes. All the drivers are reading within their designed ranges...will recheck the crossovers. Have a great day!

 

[Steven Ver]

One thing I neglected to check before driving them with low tube power was, the actual reading at the terminals...both read 4.7 ohms....what? B302a cabs are supposed to be 8 ohm s speakers....sticker right above the terminals says so. Hooked them up to an old Pioneer AV receiver....now they sound like I expected them to when I got them....at least they have the upgraded drivers now...and I can listen to all music on them. Any ideas if that reading is typical? 4.7 ohms on both 8 ohm cabinets

 

[TudorTurtle]

Steven,
I might have guessed a DMM would read 6-ish Ohms for a 8 ohm nominal speaker. Did you include the crossover circuit, or just the driver? Either way the DMM is only reading a DC measurement, and music is AC. The actual ohms change with frequency, to test this you need a different tool, like a DATS from Parts Express.

https://www.parts-express.com/dayto...ss57OzokV3nlrVuT-lPEHvIaNi6EL44gaAuztEALw_wcB

Here's an example woofer Impedance curve in a bass reflex box (the second peak is due to the vent). This driver has an 8 ohm nominal rating, and typically, nominal rating is ohms @ 1000 Hz.

 

[Steven Ver]

I just applied my multi tester to the screws on the back of the speaker cabinets to check the impedance of the cabinet as seen by the amplifier. Still at a loss as to why these speakers are so distorted, maybe the crossovers have an issue. All the drivers seem to read properly and perform as they should before being wired into the cabinets. I could understand they might not sound amazing but they should at least sound ok. I have seen that tester, guess another $110 is about normal for this project...thanks for the info

 

[Steven Ver]

One thing I neglected to check before driving them with low tube power was, the actual reading at the terminals...both read 4.7 ohms....what? B302a cabs are supposed to be 8 ohm s speakers....sticker right above the terminals says so. Hooked them up to an old Pioneer AV receiver....now they sound like I expected them to when I got them....at least they have the upgraded drivers now...and I can listen to all music on them. Any ideas if that reading is typical? 4.7 ohms on both 8 ohm cabinets

...however they are still distorted no matter what amp I hook to them...

 

[Retrovert]

The only conclusion here is that the midranges are damaged.

This is a drop-in replacement for your existing paper-cones. So if the paper-cones sound great (for paper cones, of course) and the aluminum cones are horribly distorted, then your aluminum-cone drivers are DEFECTIVE.

I suggest you obtain a refund from the seller. eBay will side with you.

 

[Steven Ver]

Both configurations sound distorted so I ordered the speaker testing computer interface and will start over testing each driver old and new and checking the similarities, wiring, everything that can go wrong with my work and what I ordered online. Just noticed my original paper midrange read 4.4 and 4.3 ohms as they sit....marked 8 ohms and should be closer to 8 than that. Will keep after it for now... thanks!

 

[Steven Ver]

Well Bozak fans...I finally solved my distortion issue with my B302a provincials. It was a complete accident, as I picked up a homely thrift shop Sansui 8900ZDB gigantic receiver from 1980. Got it cleaned up and working...mostly (fm tuner dead)... and hooked it to the Bozaks. Tons of clean power was all the Bozaks wanted...the junk Pioneer home theater rig I was running was under powering them...has to be it. Sweet! NOW I get it....hearing the full range of frequencies now, just amazing! ...going to replay my whole collection of music now...see ya

 

[Steven Ver]

....Will have some early paper cone drivers for sale that were probably fine when I thought they weren't, now I have the aluminum cones on the mids and tweeters. Cheers!

 

[jdbglover]

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