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801 Repair Guidance Thread

feynman

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I have picked up a lovely pair of B&W 801 Series 80, built mid-1981. The cabinets and grills are in great condition.

They have some audible electrical issues, and I want to restore them to their original glory (no upgrades/mods, yet). Some general wisdom seems to be to bypass those attenuators, which I won't use anyway, and modernize the crossovers...but I just want them back to stock.


Each speaker has three circuit boards, one in the hf/mid housing with selectable attenuation, and two crossover modules in the bass enclosure.

Starting with the easiest to access (the upper housing), I verified that the "Flat" HF path is dead...both resistors on each speaker are dead, and they even look like it. The other resistors are roughly correct for their listed values, though they fluctuate a bit outside of tolerances. I'd think it might be best just to replace everything while I'm in there?

I don't know how to properly test the capacitors/inductors.

I have obtained the schematics, and the circuit boards are easy to access, with plenty of space between components. The circuits appear to be pretty simple.


I don't know much, but I can follow instructions.

A quick search for a specific resistor on mouser told me quickly that I don't know enough about what I'm doing.

Help?

Thank you.

-mitch



Attenuator Schematic and photo:

attenuator_schem.jpeg


AttenuatorResistors.png

attenuator_ctrl.jpeg



Upper PCB

top_pcb.jpg




Lower PCB

bottom_pcb.jpg



---


full.jpg
 
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fordiebianco

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sergeauckland

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Firstly, nice 'speakers!
As to the environmental controls, the HF control needs to stay, as it provides the correct attenuation for the tweeter. You could bypass the MF control, as that's what position A does, but for originality, I would keep them as they are, just replace any resistors that are out of tolerance. Resistors of 5 watts rating are fine.

In the main crossover, inductors are extremely unlikely to be faulty, you can test them for DC continuity, and if they're fine for that, then you can safely assume they're OK, unless they show clear signs of having been abused, such as melted plastic formers. The overload protection would protect the crossover and drivers from abuse, unless of course some cretin bypassed that! There has been a lot on the web about how much better they sound with the protection disabled...utter idiots!

As to capacitors, I'm pretty sure that the values on the capacitors would have been selected on-test as the 801s I've worked on had small capacitors in parallel with the larger ones to make up the capacitance shown on the circuit diagram. If you get capacitors from a suitable source, (Falcon Acoustics here in the UK for example), they select capacitors to 1% tolerance, so you can make up the correct values fairly easily. Note that the bipolar electrolytics should be replaced like for like. Don't be tempted to 'upgrade' to plastic film capacitors, as firstly they won't physically fit, and secondly they will have different ESR properties, so won't be the same as the originals. The only capacitor I wasn't able to get is the 1000uF in series with the bass unit, as I couldn't find non-polar capacitors of that size.

Unless you have a capacitance bridge, you won't be able to measure the capacitors, but they're worth replacing after all these years as the cost is trivial unless you pay the 'audiophool' tax for special grade caps. Normal commercial grade, but selected for value as Falcon do is fine.

You may want to check that the relay in the protection circuit works, the service manual describes how to test it. You'll need a decent soldering iron, as the PC board the caps are mounted on has quite large lands, but apart from that, refurbishing the crossovers isn't beyond a reasonably competent DIYer.

Oh and one more thing, I recommend rotating the bass unit by 180° to give the suspension a reset, as I can't imagine anyone has ever done it, and the bass cone is quite heavy, so rotating it will help centre the suspension.

Good luck and have fun.

S.
 

Doodski

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Some general wisdom seems to be to bypass those attenuators, which I won't use anyway, and modernize the crossovers...but I just want them back to stock.
Why bypass the attenuators... They can be very handy. :D If me I would keep them in circuit.
 
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feynman

feynman

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Why bypass the attenuators... They can be very handy. :D if me I would keep them in circuit.

I won't...just pointing out that people say lots of things...but I just want these back to their original design.
 

JeffS7444

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LCR meter can be used to check inductors and capacitors, but a faulty capacitor can nevertheless appear to be on-spec when measured in this manner, which is why products like Capacitor Wizard exist.

I wonder how those speakers might perform if triamplified! Might be possible to do without making any permanent alterations.
 

Doodski

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LCR meter can be used to check inductors and capacitors, but a faulty capacitor can nevertheless appear to be on-spec when measured in this manner, which is why products like Capacitor Wizard exist.

I wonder how those speakers might perform if triamplified! Might be possible to do without making any permanent alterations.
These soak up the amp power very well. The woofers are prone to damage to the voice coil former if over driven loud and very hard with lotsa bass added. I know because I've done it. Otherwise they should respond to tri'amp'd very well. :D
 

sq225917

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What's the TT Serge? I imagine you're a Technics, Garrard or EMT man.
 

sergeauckland

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What's the TT Serge? I imagine you're a Technics, Garrard or EMT man.
EMT 948 and AEG TRS9000 are my main two, with a GL75 in my office system. I had a 401 a few years ago.
I've never had a Technics, wouldn't mind a SP10 sometime.

Edit.. Sorry misunderstood your post. I was joking about the turntable, as Feynman is doing a fairly detailed renovation of his 801s, I wondered if he might want a turntable as an 'easy' project if ever bored with the 801s.
S
 
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sergeauckland

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LCR meter can be used to check inductors and capacitors, but a faulty capacitor can nevertheless appear to be on-spec when measured in this manner, which is why products like Capacitor Wizard exist.

I wonder how those speakers might perform if triamplified! Might be possible to do without making any permanent alterations.
Mine are great. The only 'permanent' change is to add two more pairs of sockets to the back panel. The original crossovers are stored safely, and the environmental controls bypassed but still there. It wouldn't be too hard to put them back as passive if ever I had the inclination to do so.

S
 

sq225917

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Oh I knew you weren't selling... ;)

I'm just interested in what's good enough to be in residence at Serge towers,
 

JaMmy

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I have a pair of these 801s from 1984 and they sound great... But. Recently one of the woofers has developed a 'buzz' which occurs only on very low bass notes, such as extended low organ notes. I cannot see anything physical that is amiss and it is not an issue of the housing or physical attachment of the woofer to the enclosure. Visually the perfect woofer and the one with the fault appear to be the same. Any bright ideas about what this might be?
 

JaMmy

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BTW, I should add that following Sergeauckland's guide on Audio Forums, I'm in the middle of converting these to tri-amping, using the LR crossover and amps designed by Rod Elliott at ESP
 

sq225917

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Put the original xo back in place, to eliminate whether its physical or electrical first. Then and only then start checking driver.
 

JaMmy

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The original XO is still in place. Doesn't 'sound' electrical.
 

sergeauckland

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I have a pair of these 801s from 1984 and they sound great... But. Recently one of the woofers has developed a 'buzz' which occurs only on very low bass notes, such as extended low organ notes. I cannot see anything physical that is amiss and it is not an issue of the housing or physical attachment of the woofer to the enclosure. Visually the perfect woofer and the one with the fault appear to be the same. Any bright ideas about what this might be?
Those bass cones are quite heavy, and after 30+ years, they may have sagged slightly on the suspension. The cure is very simple, just unscrew them and turn the driver 180° and put it back. Whilst you have it out (note, it's quite heavy), you may like to check that the suspension looks undamaged before you put it back.

Do both 'speakers even if only one is rubbing.

You should repeat this in 30 years' time.

S.
 
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