Someone has asked me to look at a pair of Wharfedales that play ok for a while then cut out. Once the amp has been turned off and on again they seem to start playing again but will cut out again later on. Have tried them with several amps ( some without protection circuits) and it is the same on all of them. I notice that the specs on the back of the amp show the tweeter size and in brackets it says "Protected". Does this mean that there is a protection circuit in the crossover which is triggering the cut-out, and if so, is there an easy remedy for this. I am not playing at excessive volumes etc. Thanks.
Only the tweeter appears to be protected. If it is overloaded it will cut out, but the bass driver should continue to play.
This is an old speaker and protection components can get oversensitive with age.
I can't find out anything about this precise model, so please post a photo of the complete speaker showing the drive units.
For us to study the protection system, you would need to remove the crossover circuit and post clear photos of it.
This is an old speaker and protection components can get oversensitive with age.
I can't find out anything about this precise model, so please post a photo of the complete speaker showing the drive units.
For us to study the protection system, you would need to remove the crossover circuit and post clear photos of it.
Thanks Galu. I can't seem to find the exact model on the 'net but here are some pix of the actual ones I have here.............. I'll get some pix when I look into the crossover too.
Check or simply replace the electrolytic capacitors in the crossover, see if the resistors are in proper condition.
If needed, use the next higher voltage rating (some values are in erratic supply at times).
Your problem seems heat related, and in a speaker, that is a bit unusual.
Check for corrosion in all wires and so on, maybe it was used and stored in a damp area, that gives peculiar results at times. Check the soldering as well for deterioration if you see any damage caused by damp conditions..
Another thing, sometimes the coils go out of center, Galu (or another speaker expert) will tell you how to check.
The cause usually is cone sag due to storage in poor conditions.
The coils will then heat up to the point the movement stops, and start working after cooling down.
It is a long shot, take the advice of the more experienced members.
If needed, use the next higher voltage rating (some values are in erratic supply at times).
Your problem seems heat related, and in a speaker, that is a bit unusual.
Check for corrosion in all wires and so on, maybe it was used and stored in a damp area, that gives peculiar results at times. Check the soldering as well for deterioration if you see any damage caused by damp conditions..
Another thing, sometimes the coils go out of center, Galu (or another speaker expert) will tell you how to check.
The cause usually is cone sag due to storage in poor conditions.
The coils will then heat up to the point the movement stops, and start working after cooling down.
It is a long shot, take the advice of the more experienced members.
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I'll be interested in seeing the condition of the internals.
I have learned that this particular Programme range was intended for commercial use, e.g., in association with a jukebox in a pub.
Such speakers can lead a challenging life. However, the pair photographed appear to be in good nick and may only have been used domestically.
Have you got any user history on them, Whelkie?
I have learned that this particular Programme range was intended for commercial use, e.g., in association with a jukebox in a pub.
Such speakers can lead a challenging life. However, the pair photographed appear to be in good nick and may only have been used domestically.
Have you got any user history on them, Whelkie?
You are not clear if the loudspeaker cuts out altogether or just the tweeter. It is possible the tweeter has gone short or open circuit from the usual 6 ohms DC, which could trip an amplifier.
The amp can trip with open circuit because the tweeter crossover then becomes undamped and resonant without a 6 ohm load.
Tweeters are often protected by a polyfuse or PTC component in the crossover behind the bass unit, as Galu says, which looks like a small ceramic disk cacpacitor in the typical 4uF, 0.2mH teeter circuit..
Google Loudspeaker Protection Polyfuse to find out more.
The amp can trip with open circuit because the tweeter crossover then becomes undamped and resonant without a 6 ohm load.
Tweeters are often protected by a polyfuse or PTC component in the crossover behind the bass unit, as Galu says, which looks like a small ceramic disk cacpacitor in the typical 4uF, 0.2mH teeter circuit..
Google Loudspeaker Protection Polyfuse to find out more.
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Yes, Steve. I'll (we'll) be looking out for a Positec protection device (or two) in the crossover.
After a prolonged period of overload, a Positec can fail to return to its normal low resistance value on removal of signal, and can stay high resistance.
However, from Whelkie's description, that doesn't seem to be what's going on here, as turning the amp off and on again restores function, if only temporarily.
After a prolonged period of overload, a Positec can fail to return to its normal low resistance value on removal of signal, and can stay high resistance.
However, from Whelkie's description, that doesn't seem to be what's going on here, as turning the amp off and on again restores function, if only temporarily.
Yes, it could be lots of things. A multimeter on the resistance scale can tell you a lot about drivers, when taken out of circuit.
You might be able to measure them in circuit in the particular case below, because I don't see a DC path for either driver.
I have dug up a picture of a Wharfedale Laser 90B which might be similar, though I would expect a polyfuse in front of the 0.05mH coil in this case.
p.s. The forum is more comfortable with small JPG images which are quick to load and use less storage on the server.
You might be able to measure them in circuit in the particular case below, because I don't see a DC path for either driver.
I have dug up a picture of a Wharfedale Laser 90B which might be similar, though I would expect a polyfuse in front of the 0.05mH coil in this case.
p.s. The forum is more comfortable with small JPG images which are quick to load and use less storage on the server.
Thanks for all the replies. Sorry for the GIANT images - they are what the owner sent me before I collected them. AFAIK they have only been used in a domestic setting although they may have had a long-run of cable to them previously. I'll get the crossovers out and post a (smaller) image of them later. Both speakers cut-out after a loud half-second hum/buzz and, as I say, will only fire-up again by turning the amp off and back on again
Whelkie, does the Programme 50 have those two green terminals above the red and black ones as seen on the Programme 20 image I posted earlier?
I wonder what their intended use could be?
I wonder what their intended use could be?
Here are some pix of one of the crossovers. Sadly, it seems they are glued to the cabinet quite firmly, so if anyone has any tips for safely removing them to inspect the soldering etc. it would be much appreciated............. Sorry if the photos have come out large again
Yes Galu, it does have the two green terminals but they are not connected to anything - just a couple of lugs inside.
I've just spotted your edit, Steve.
However, Whelkie says "Have tried them with several amps ( some without protection circuits) and it is the same on all of them".
The Positec protection device is the small mustard coloured disc at top left. Can you measure its resistance just for interest's sake?
There's nothing remarkable regarding the crossover. Looks like a ferrite cored inductor in series with the woofer and a second order capacitor/inductor filter for the tweeter. Also an attenuating resistor in series with the tweeter as will be the Positec.
Next thing is to measure the DC resistance of the woofers and tweeters.
P.S. Is it not strange that both speakers are giving trouble?
And to be clear - both speakers are completely cutting out - no sound at all?
Next thing is to measure the DC resistance of the woofers and tweeters.
P.S. Is it not strange that both speakers are giving trouble?
And to be clear - both speakers are completely cutting out - no sound at all?
It is a simple 3.18 mH bass coil and second order tweeter here. The tweeter has a level adjust resistor and a polyswitch.
Hard to see how a failed polyswitch would trip an amp. They usually go high resistance under overdrive.
Also look for that which is broken or dry jointed in the crossover or terminals. Or shorting. Is the crossover glued down?
The green terminals are possibly an unused or unconnected 100V line connection which is a feature of some of the speakers in the series.
The 50 has polyswitches on the tweeter according to this too:
https://docs.rs-online.com/4cb5/0900766b80bdcd92.pdf
Hard to see how a failed polyswitch would trip an amp. They usually go high resistance under overdrive.
Also look for that which is broken or dry jointed in the crossover or terminals. Or shorting. Is the crossover glued down?
The green terminals are possibly an unused or unconnected 100V line connection which is a feature of some of the speakers in the series.
The 50 has polyswitches on the tweeter according to this too:
https://docs.rs-online.com/4cb5/0900766b80bdcd92.pdf
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Could be the watts are mismatched, but this is a head scratcher !
Same problem, both speakers, even with different amplifiers.
Please post a photo of the polyfuse devices.
Steve, you mean mains driven / transformer driven PA speakers?
The terminals are removed, no transformer is seen. It means somebody has modified them?
Oh boy, one more mess to sort out, then...
Can you drive the big speakers directly, bypassing all the circuits in the cabinets, use low volume, tell us what happens?
Ignore the tweeters for the time being.
Same problem, both speakers, even with different amplifiers.
Please post a photo of the polyfuse devices.
Steve, you mean mains driven / transformer driven PA speakers?
The terminals are removed, no transformer is seen. It means somebody has modified them?
Oh boy, one more mess to sort out, then...
Can you drive the big speakers directly, bypassing all the circuits in the cabinets, use low volume, tell us what happens?
Ignore the tweeters for the time being.
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Yes, both speakers are cutting out. I am using an old Pioneer SX600L to test them which I think doesn't have a protection circuit, but I could be totally wrong about that, in which case it would shed a new light on things.
I'll try to measure the resistance of the positecs and drivers tomorrow when I have more time, and see what we get.
I'll try to measure the resistance of the positecs and drivers tomorrow when I have more time, and see what we get.
This particular speaker doesn't seem to use a professional transformer option, Naresh
You will have to take the tweeter out of circuit to test it since it is shorted by a coil.
The bass resistance can be tested in circuit or at the terminals for about 6 ohms.
The old 1.5V battery test often tells you something if you don't have a meter. You should get a crackle from a working driver.
You will have to take the tweeter out of circuit to test it since it is shorted by a coil.
The bass resistance can be tested in circuit or at the terminals for about 6 ohms.
The old 1.5V battery test often tells you something if you don't have a meter. You should get a crackle from a working driver.