Folks:
I'm looking for some guidance on a speaker repair project. My daughter and I recently built a chipamp-based integrated amplifier for her (a father-daughter project which was great fun). After a couple of months of use, one of the channels on that amp blew (entirely my fault; I stupidly misread the BOM and used a couple 1/2W resistors, not 2W resistors). My daughter told me that when the amp released its magic smoke, she also saw smoke coming from the rear port on one of her PSB Alpha B1 loudspeakers. The amp has been repaired and I'm ready to tackle that speaker.
The blown speaker measures 0.2R across its terminals. The other speaker measures 3.8R across its terminals. My first question: how do I determine what to repair/replace in the blown speaker? Notably, I haven't tested the presumably good speaker yet. I don't have any test equipment other than a few multimeters.
My second question: regardless of whether the problem with the blown speaker lies somewhere in its tiny crossover, this seems like a good opportunity to upgrade both speakers' crossovers. A closed thread ( https://www.diyaudio.com/community/threads/psb-alpha-b1-internal-pic.137546/#post-4542271 ) provided the values of the caps and resistor used in the PSB Alpha B1; should I just install better quality equivalent-value parts?
Your advice is appreciated!
Regards,
Scott
I'm looking for some guidance on a speaker repair project. My daughter and I recently built a chipamp-based integrated amplifier for her (a father-daughter project which was great fun). After a couple of months of use, one of the channels on that amp blew (entirely my fault; I stupidly misread the BOM and used a couple 1/2W resistors, not 2W resistors). My daughter told me that when the amp released its magic smoke, she also saw smoke coming from the rear port on one of her PSB Alpha B1 loudspeakers. The amp has been repaired and I'm ready to tackle that speaker.
The blown speaker measures 0.2R across its terminals. The other speaker measures 3.8R across its terminals. My first question: how do I determine what to repair/replace in the blown speaker? Notably, I haven't tested the presumably good speaker yet. I don't have any test equipment other than a few multimeters.
My second question: regardless of whether the problem with the blown speaker lies somewhere in its tiny crossover, this seems like a good opportunity to upgrade both speakers' crossovers. A closed thread ( https://www.diyaudio.com/community/threads/psb-alpha-b1-internal-pic.137546/#post-4542271 ) provided the values of the caps and resistor used in the PSB Alpha B1; should I just install better quality equivalent-value parts?
Your advice is appreciated!
Regards,
Scott
Make me look. You should have done the work of digesting that thread.
Crossover is 1 ohm wirewound resistor, 5.6 uf e-cap, air coil inductor. None of those likely to go 0,3 ohms with DC on speaker terminals. When you open it, I suspect you will find the woofer is 0.3 ohms. 3.6 is more likely. Check your meter on the 1 ohm resistor, a bad battery can give stupid readings on resistance <10 ohms.
Only thing I would change in the crossover is electrolytic cap, for polyprophylene. With a blown woofer and a replacement probably random T/S values, you are not looking at a premium result. You could measure T/S values on the existing woofer. Takes some free software, A PC, a $100 onmi microphone, cables, mixer with phantom power, and a mike stand. You up for that? Some people avoid the mixer by buying a USB mike, but the variable delay in the PC makes timing measurements garbage.
About the diy amp. I build single supply speaker cap circuits so a $3 part protects the speaker. Only problem, the pcbs for IC amps from ali/ebay/amazon only contain the dual supply circuits.
Or you can buy a anake oil protection circuit with a relay only rated for AC voltage. Or build a real protection circuit for about $100. Or buy a $50 blown PA amp with a real protection circuit built in. I do the last, too.
Crossover is 1 ohm wirewound resistor, 5.6 uf e-cap, air coil inductor. None of those likely to go 0,3 ohms with DC on speaker terminals. When you open it, I suspect you will find the woofer is 0.3 ohms. 3.6 is more likely. Check your meter on the 1 ohm resistor, a bad battery can give stupid readings on resistance <10 ohms.
Only thing I would change in the crossover is electrolytic cap, for polyprophylene. With a blown woofer and a replacement probably random T/S values, you are not looking at a premium result. You could measure T/S values on the existing woofer. Takes some free software, A PC, a $100 onmi microphone, cables, mixer with phantom power, and a mike stand. You up for that? Some people avoid the mixer by buying a USB mike, but the variable delay in the PC makes timing measurements garbage.
About the diy amp. I build single supply speaker cap circuits so a $3 part protects the speaker. Only problem, the pcbs for IC amps from ali/ebay/amazon only contain the dual supply circuits.
Or you can buy a anake oil protection circuit with a relay only rated for AC voltage. Or build a real protection circuit for about $100. Or buy a $50 blown PA amp with a real protection circuit built in. I do the last, too.
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The amp sent full DC of one rail to the speaker, which melted the voice coil, then probaply the fuse blew.
The tweeter is in series with a capacitor, which blocks DC. So there is a very good chance the tweeter is OK. Carefully move the cone of the 0.2R woofer, it will make ugly noises. You need to replace this woofer. The coil in series with the woofer may have gotten hot, but is usualy many times stronger than the voice coil. So it may have changed in colour a bit, but measure and perform OK.
That is as far as my online diagnosis can go.
The tweeter is in series with a capacitor, which blocks DC. So there is a very good chance the tweeter is OK. Carefully move the cone of the 0.2R woofer, it will make ugly noises. You need to replace this woofer. The coil in series with the woofer may have gotten hot, but is usualy many times stronger than the voice coil. So it may have changed in colour a bit, but measure and perform OK.
That is as far as my online diagnosis can go.
Firstly looking at the link the front and rear baffles are plastic on the model shown.
Be gentle when undoing or tightening the screws that hold the woofer. Once you have removed the woofer driver make a note or take images of where the connecting wires go.
Remove one wire form the woofer connections at the back of the drive unit and then measure with you ohm meter do you now a measure value 3.8 - 6 ohms ?
If so it indicates that the voice coil is still intact and still connected via the terminals. If you measure a short it will be time for a replacement driver. You may also be able to smell something, this will be the smell of cooked electronics related to your daughter observation about seeing smoke.
You now have the crossover components and the tweeter to measure. Can you see the crossover through the woofer cut-out does any of the components look cooked?
With the woofer still disconnected what impedance reading do you now measure on the rear cabinet speaker terminals, if the short has gone away this again indicates that woofer is to blame.
If needed repeat for the tweeter, gently remove (do not crush dome) take images and measure. Post back what results you obtain.
I am sure other will know what suitable replacement drivers to use, possibly check the Parts Express website for help or related posts.
Be gentle when undoing or tightening the screws that hold the woofer. Once you have removed the woofer driver make a note or take images of where the connecting wires go.
Remove one wire form the woofer connections at the back of the drive unit and then measure with you ohm meter do you now a measure value 3.8 - 6 ohms ?
If so it indicates that the voice coil is still intact and still connected via the terminals. If you measure a short it will be time for a replacement driver. You may also be able to smell something, this will be the smell of cooked electronics related to your daughter observation about seeing smoke.
You now have the crossover components and the tweeter to measure. Can you see the crossover through the woofer cut-out does any of the components look cooked?
With the woofer still disconnected what impedance reading do you now measure on the rear cabinet speaker terminals, if the short has gone away this again indicates that woofer is to blame.
If needed repeat for the tweeter, gently remove (do not crush dome) take images and measure. Post back what results you obtain.
I am sure other will know what suitable replacement drivers to use, possibly check the Parts Express website for help or related posts.
Frankly, I wouldn't bother. 6" woofer 2 way in plastic case? Salvation Army Clarksville throws away dozens of speakers like this after they have sat on the shelf for 2 or 3 months. The e-caps in the CD/casette/radio go bad, they throw that part away immediately and put the speakers on the shelf out back. 2 months they go half price. I got a couple of 3 way 6"+2"+1"+ for $5 the pair, and they sound pretty decent. Use them on the HDTV. You buy a pair of used speakers that sounds bad, throw them away and try again. Random T/S woofer replacement, you are not going to do much better.
Be sure to read the datasheet on any replacement woofer. My 3rd woofer replacement project, I bought a 10" woofer that fit a 9.5" hole. I cannot downsize a hole in plywood from 10" to 9.5", not on a 100 W PA speaker. I re-bought a PE random woofer of right diameter that was light on the deep bass but not particularly distorted. My local unemployed housepainter solved the problem by stealing the leftover from me.
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Sounds like the woofer is burned/shorted.
If you want to repair it I would suggest first checking with PSB to see if they will sell you one.
It might be pricey, but keep in mind replacement with third party woofers can be a big challenge.
There are physical fit issues, as all 5 1/4" woofers are not the same size for the cut out, mounting holes and depth, so finding a drop-in replacement may be difficult or impossible.
Then there are the electrical issues of matching to the crossover.
And if you do manage to find a suitable third party replacement you will need two, which increases the cost.
Good luck.
If you want to repair it I would suggest first checking with PSB to see if they will sell you one.
It might be pricey, but keep in mind replacement with third party woofers can be a big challenge.
There are physical fit issues, as all 5 1/4" woofers are not the same size for the cut out, mounting holes and depth, so finding a drop-in replacement may be difficult or impossible.
Then there are the electrical issues of matching to the crossover.
And if you do manage to find a suitable third party replacement you will need two, which increases the cost.
Good luck.
Folks:
Thanks for the counsel!
@indianajo You're quite right -- I should have installed a speaker protection board in the integrated amp. At the time we built the amp, the Store's speaker protection board was the obvious choice. Unfortunately, it was too large to fit. I didn't see another kit or pre-built alternative I liked, so we went bareback. Yes, that was dumb. Subsequent to our completing the project, esteemed member Prasi posted the gerbers for an updated version of the Store's speaker protection board; Prasi's version uses solid state relays instead of the mechanical version and is much smaller. I had boards made and it just fit in the amplifier (see the board mounted on the rear panel connected to yellow wires in the photo below). This problem shouldn't reoccur.
@Turbowatch2, @raymondj and @techtool Many thanks! I'll start noodling in the busted speaker first and, if things go well, migrate to the other.
Regards,
Scott
Thanks for the counsel!
@indianajo You're quite right -- I should have installed a speaker protection board in the integrated amp. At the time we built the amp, the Store's speaker protection board was the obvious choice. Unfortunately, it was too large to fit. I didn't see another kit or pre-built alternative I liked, so we went bareback. Yes, that was dumb. Subsequent to our completing the project, esteemed member Prasi posted the gerbers for an updated version of the Store's speaker protection board; Prasi's version uses solid state relays instead of the mechanical version and is much smaller. I had boards made and it just fit in the amplifier (see the board mounted on the rear panel connected to yellow wires in the photo below). This problem shouldn't reoccur.
@Turbowatch2, @raymondj and @techtool Many thanks! I'll start noodling in the busted speaker first and, if things go well, migrate to the other.
Regards,
Scott
Attachments
Before buying anything, check on eBay etc. for a replacement part and how much the speakers value may be. That might be surprising.
Often you can use such a mishap to get your kid a sonic update for less than the repair might cost. These speakers are nothing high end, they are from the "doesn't hurt the ears too much" class. Often you can pick up very good speaker for incredible cheap, even close to you. Just use the available online markets. Good speakers have gone out of fashion.
Often you can use such a mishap to get your kid a sonic update for less than the repair might cost. These speakers are nothing high end, they are from the "doesn't hurt the ears too much" class. Often you can pick up very good speaker for incredible cheap, even close to you. Just use the available online markets. Good speakers have gone out of fashion.
Yup, I checked with PSB and the woofer is no longer available. While I could certainly go hunting for a single Alpha B1, my daughter would be thrilled to get a new set of speakers. I made the mistake that caused the speaker to fail and I'll be happy to pony up enough to get her a decent pair of replacement speakers. It's the least I can do.
Regards.
Regards.