B&W 802 Series 80 repair

[The Monkey]

My parents have an old pair of B&W 802 Series 80 speakers. I've read that these are still considered pretty decent, but I'm concerned about the condition these are in. I'd like to replace parts like the binding posts and maybe parts of the crossovers. How difficult is this type of thing? Could an advanced beginner DIYer do it?

The speakers look like this (these aren't the actual speakers):

[The Monkey]

Hard to tell, actually. According to my Dad, at some point the speakers caused the amp to blow a fuse. Is that possible? I also think the right speaker cuts in and out. Finally, the binding posts are old and dirty, so actually getting them hooked up right now is difficult if not impossible. I'm not sure how the current posts ever worked in the first place to be honest.

[mypasswordis]

Yeah, if the binding posts still make good connections I'd just leave them. But if the crossovers have electrolytic caps, it'd be a good idea to replace them.

Edit: Nvm, do replace the binding posts. And caps if they're 'lytic. Should be pretty straightforward, depending on how easy it is to open up the cabinets.

[Dusty Chalk]

Obviously he needs to remove the crossovers and replace them with digital active crossovers and amps. Also the driver elements and the cabinets.

[nikongod]

Hard to tell, actually. According to my Dad, at some point the speakers caused the amp to blow a fuse. Is that possible? I also think the right speaker cuts in and out. Finally, the binding posts are old and dirty, so actually getting them hooked up right now is difficult if not impossible. I'm not sure how the current posts ever worked in the first place to be honest.

It is very possible for a speaker to blow an amp.

Check the web to see if you can find the "impedance VS frequency" response graph for the speakers your parents have. If it dips much below 4ohms anywhere some amps will go poof. If it dips below 2ohms many amps will go poof.

Regarding cutting in and out: I dont know. Id try to clean the binding posts first.

Obviously he needs to remove the crossovers and replace them with digital active crossovers and amps. Also the driver elements and the cabinets.

Solves ooh so many problems.

Replace the drivers & cabinets with horns? I like!

[The Monkey]

Yeah, if the binding posts still make good connections I'd just leave them. But if the crossovers have electrolytic caps, it'd be a good idea to replace them.

Edit: Nvm, do replace the binding posts. And caps if they're 'lytic. Should be pretty straightforward, depending on how easy it is to open up the cabinets.

I've read that replacing the caps on these is pretty easy. But you are, of course, correct; depends on getting them open.

It is very possible for a speaker to blow an amp.

Check the web to see if you can find the "impedance VS frequency" response graph for the speakers your parents have. If it dips much below 4ohms anywhere some amps will go poof. If it dips below 2ohms many amps will go poof.

Regarding cutting in and out: I dont know. Id try to clean the binding posts first.

Yeah, all of the contacts in the system could use a nice cleaning. Is that Caig Deoxit stuff worth it, or is it so much snake oil?

[mypasswordis]

Deoxit is awesome. I used it on my vintage receiver, brass rings on my Concept CE-H, lighting fixtures in the kitchen, etc. and it's very effective. Digital xovers ftw but that's a little involved.

[dsavitsk]

B&W is notorious for using really cheap caps in the crossovers, and there is a lot of room for improvement. Likely that even some solens, or something like them, will make a big difference.

I've read that replacing the caps on these is pretty easy. But you are, of course, correct; depends on getting them open.

You have to remove a driver and pull the crossover out that way. Then, desolder and replace. Mine were a pain, but then mine had smaller diameter drivers which gave less room for reaching into the cabinets. Not sure whether the matrix construction will block access, though.

Also, when my B&W's got old, some rubber o-rings started decomposing. I emailed a B&W rep who sent me a whole new set.

Edited October 27, 2010 by dsavitsk

[Uncle Erik]

I've read that replacing the caps on these is pretty easy. But you are, of course, correct; depends on getting them open.

Yeah, all of the contacts in the system could use a nice cleaning. Is that Caig Deoxit stuff worth it, or is it so much snake oil?

Deoxit works pretty well - I've cleaned up a lot of scratchy old pots and other stuff with it.

Recapping the crossovers won't be too bad once you get them out of the cabinets. Be thankful there's no power supply.

[The Monkey]

There's no power supply, true, but there is some protection circuit that has a battery in it--the speakers have small LEDs on the front. I think that's probably kaput at this point and have read elsewhere that it makes sense to just disconnect it.

[The Monkey]

Just fyi, this site seems helpful for B&W, Rotel, and Classe:

B&W Group North America Service & Support Homepage

[The Monkey]

I found this on the above website. Does it make sense to you wise ones?

http://www.bwgroup-support.com/downloads/techmanuals/bw/802-TM.pdf

[mypasswordis]

Hm, I'm actually learning this now, so please correct me if I'm wrong. When I have time I'm going to derive the transfer functions for the various order Butterworths and draw Bode diagrams but I'm busy right now. 4th order Butterworth, high pass on the tweeter, band pass on the mid, and low pass on the woofers, the diodes just before the drivers in conjunction with the cap to ground form a half wave rectifier with a zener diode shunt regulator to power the protection circuit which has got some Sziklai pair thingy going on?

Edited October 28, 2010 by mypasswordis

[Emooze]

I'd say MPI is right. Neat little protection circuit too.

[kevin gilmore]

protection circuit similar to QUAD... They don't usually break.

Top midrange/tweeter box turns. And so does the wire inside.

Known issues relating to the wires shorting inside the turn tube.

This might trigger the protection circuit.

[The Monkey]

If the wires shorted in that way, would they possibly blow the fuse on the amp?

[kevin gilmore]

Looking at the schematic, depending on where the short is, and whether or not

the protection circuit is working right, it sure could cause some trouble.

I think there are only 2 wires to the midrange/tweeter, if those are shorted

it would definitely blow the fuse when the protection circuit releases the relay.

Edited October 28, 2010 by kevin gilmore

[The Monkey]

I suspect that's at least one thing that could be going on. In terms of the crossovers, considering my relative lack of DIY skill, should I just pick the exact same values for the caps but maybe go with a different brand, if indeed they should be replaced at all?

[kevin gilmore]

Make sure you get non-polarized caps for all the crossover parts.

And obviously do both speakers at the same time otherwise its going

to sound different.

[The Monkey]

Saw this B&W answer in one of the FAQs at the support site:

We usually find that customers who alter crossover components are not fully satisfied with the results. They find that some aspects are improved, but others made worse. A classic case of this is when a polypropylene or other very low-loss type substitutes an electrolytic capacitor. We all know that polypropylene capacitors can sound inherently better, but the change in internal losses changes the response of the filter, which is designed assuming the losses of the electrolytic component. What usually happens when the low loss component is fitted is that the corners of the roll-off are sharpened, giving a peak in the combined response that can make the sound unpleasant in various ways depending on the crossover frequency. One way of getting round this is to wire a small resistor in series with the capacitor to approximate the original losses. I say approximate because the loss factor is a frequency dependent resistance. The actual value you need depends on the original capacitor loss factor and its capacitance value. The larger the value, the lower the resistance for a given loss factor. The formula for the equivalent resistance is:

R = d / 2

[Nebby]

It means you should replace the old caps with the same type and size. They're warning against audiophile "tweaking" of the components.

[The Monkey]

Got it. Thanks.

[mypasswordis]

Basically they admit to using cheap electrolytic caps and say that they tune the values with the losses in mind. So if you want to replace the caps with better caps, you have to compensate somehow. But yeah, if you're just going to replace them with same value same type capacitors, make sure the electrolytics are nonpolar or they're going to blow.

[Nebby]

make sure the electrolytics are nonpolar or they're going to blow.

Very good point and one that's worth repeating yet again

[Pars]

Another point that they touch on is if you are replacing a lossy cap with a good cap plus a series resistance of 0.8 ohms (their example) to compensate, why bother? I guess you would have to try it, or better if someone was able to analyze the FR, phase etc. changes that you brought about with your tweaks. And of course, listening.