Hi all,
I own an RA-972 which I bought new some 16 years ago, and I like a lot still. However, for the past year or s I have been getting a pop from my speakers whenever I turn the amp on. The pop is present regardless of the input or records selections, and the position of the volume knob.
If anyone has any idea what may be causing this, I'd appreciate the help. I am definitly willing to take it apart and hunt down the issue, but I am not sure where to start.
thanks in advance!
I own an RA-972 which I bought new some 16 years ago, and I like a lot still. However, for the past year or s I have been getting a pop from my speakers whenever I turn the amp on. The pop is present regardless of the input or records selections, and the position of the volume knob.
If anyone has any idea what may be causing this, I'd appreciate the help. I am definitly willing to take it apart and hunt down the issue, but I am not sure where to start.
thanks in advance!
There is a basic service manual here: B&W Group North America Service & Support - Rotel Current Manuals & CAD Drawings
However, it does not detail circuit operation or adjusments.
In general terms, most amplifiers power up with a loud thump as the amplifier circuit voltages rise and settle at different rates and this causes a brief DC voltage spike to appear at the input of the amplifiers. Hence the pop or thump and this was normal on old 1960s-80s amplifiers yet there was never damage to speakers as people, now unused to the effect, worry about.
What should happen, is that a time delay of at least 1 second should occur before a speaker relay closes and connects the speakers. This should mute the pop and then allow normal operation. In this amplifier, the operation is under control of a microprocessor so it's not that simple to spot anything like a small electrolytic timing capacitor that provides the delays to relay closure whilst it charges up via a resistance.
I suspect C703 on first glance but I could well be wrong. This may inspire others to look though.
However, it does not detail circuit operation or adjusments.
In general terms, most amplifiers power up with a loud thump as the amplifier circuit voltages rise and settle at different rates and this causes a brief DC voltage spike to appear at the input of the amplifiers. Hence the pop or thump and this was normal on old 1960s-80s amplifiers yet there was never damage to speakers as people, now unused to the effect, worry about.
What should happen, is that a time delay of at least 1 second should occur before a speaker relay closes and connects the speakers. This should mute the pop and then allow normal operation. In this amplifier, the operation is under control of a microprocessor so it's not that simple to spot anything like a small electrolytic timing capacitor that provides the delays to relay closure whilst it charges up via a resistance.
I suspect C703 on first glance but I could well be wrong. This may inspire others to look though.
Hi Ian,
Thanks a lot for the reply. I have read similar elsewhere as well. The RA-972 schematic is not on the page you supplied here, however I have found one elsewhere. TO confirm, your suspicion is C703, as indicated in this section of the schematic:
Parts list indicates an electrolytic capacitor of 1uf:
CAP,ELEC.50V1UF
Cheers!
Thanks a lot for the reply. I have read similar elsewhere as well. The RA-972 schematic is not on the page you supplied here, however I have found one elsewhere. TO confirm, your suspicion is C703, as indicated in this section of the schematic:
An externally hosted image should be here but it was not working when we last tested it.
Parts list indicates an electrolytic capacitor of 1uf:
CAP,ELEC.50V1UF
Cheers!
Hi
The page I linked was the closest to the Rotel Manual listings I could find. The navigation isn't simple and permissions are required but all manuals, current and archives, are there for Rotel, Classe and B&W products. Using the scrolling menu on the left side select service manuals and the next page gives the logical options. You could also try this link: B&W Group North America Service & Support - Service Manuals
Anyway, the parts list disagrees with the schematic as 4.7 uF is shown for C703 there. I am not at all confident that part is the problem anyway. I would simply test in-circuit with an appropriate type of ESR meter first, but that's something you don't find in every DIY's kit of tools. You could read the actual marked value for interest and you could also estimate the delay in the speaker relays after the power is turned on. Note there is a soft-start and Transformer secondary relay too, presumably for standby mode. It's a heavily protected unit but you need to listen for the last click that turns on the speakers after the power relays have turned on.
In my RA1060 Rotel, the relays click like crazy but there is a 1.5 second delay before the speaker relay (either RY601 or RY602 on your amplifier, depending on the A or B set selection) closes and couples the speakers. If you don't have that order of delay, you may have found the reason for the noise but not yet identified the fault.
The page I linked was the closest to the Rotel Manual listings I could find. The navigation isn't simple and permissions are required but all manuals, current and archives, are there for Rotel, Classe and B&W products. Using the scrolling menu on the left side select service manuals and the next page gives the logical options. You could also try this link: B&W Group North America Service & Support - Service Manuals
Anyway, the parts list disagrees with the schematic as 4.7 uF is shown for C703 there. I am not at all confident that part is the problem anyway. I would simply test in-circuit with an appropriate type of ESR meter first, but that's something you don't find in every DIY's kit of tools. You could read the actual marked value for interest and you could also estimate the delay in the speaker relays after the power is turned on. Note there is a soft-start and Transformer secondary relay too, presumably for standby mode. It's a heavily protected unit but you need to listen for the last click that turns on the speakers after the power relays have turned on.
In my RA1060 Rotel, the relays click like crazy but there is a 1.5 second delay before the speaker relay (either RY601 or RY602 on your amplifier, depending on the A or B set selection) closes and couples the speakers. If you don't have that order of delay, you may have found the reason for the noise but not yet identified the fault.
Hi Ian,
OK, thanks for the info. I don't have an ESR meter, but I could easily get one...
Yeah, I had another look at the schematic (and found it at your link, thanks 😉 ), and the parts values differ, weird... Anyhow, I'll just take a look at it as you suggest.
Regarding the clicks on startup, I think there are three. Two which come at almost the same time (instantly on power up), then the third which come a second or two afterwards.
With the first clicks, the LED on the volume knob comes on and the speakers pop, with the third the source selection LED comes on. I don't know if this is helpful information....
Could it be possible that the two click which sound on startup are the A and B relays closing and coupling the speakers too early? This would mean a problem in two areas, or? I get the pop if I am connected to either set of outputs.
OK, thanks for the info. I don't have an ESR meter, but I could easily get one...
Yeah, I had another look at the schematic (and found it at your link, thanks 😉 ), and the parts values differ, weird... Anyhow, I'll just take a look at it as you suggest.
Regarding the clicks on startup, I think there are three. Two which come at almost the same time (instantly on power up), then the third which come a second or two afterwards.
With the first clicks, the LED on the volume knob comes on and the speakers pop, with the third the source selection LED comes on. I don't know if this is helpful information....
Could it be possible that the two click which sound on startup are the A and B relays closing and coupling the speakers too early? This would mean a problem in two areas, or? I get the pop if I am connected to either set of outputs.
Think - the power relays must close first to power the amplifier or nothing happens. Now, does the pop occur before or after the last click? If after, the delay is too short. If before, that cannot be the corresponding speaker relay if the speakers are connected correctly for the selected speakers.
Locate the speaker relay(s) and listen there. Of course, you can't have a pop when they are still open (i.e. no click, no power to the relay coil). Otherwise something very strange is occurring. Again, the last click should be at least 1 second (as you say) after the initial power relays (2) click in. Measure for 24V across the corresponding output relay's coil if you can't be certain by listening.
Take care with exposed voltages but small amplifiers are fairly safe provided mains wiring is shrouded correctly. If you have clip leads that could attach to the meter probes and any leads protruding from the board, use them, as this will help ensure you don't cause shorts and damage when testing.
By appropriate type of ESR meter, I mean one that operates at very low voltage so as not to turn on any semiconductor junctions in the circuit and spoil the measurement. These are not common and tend to be expensive. For the number of times they may be used, just not worth the expense. It is simplest to just remove and measure capacitance value with a basic meter or just replace, regardless.
As a further comment, in older amplifiers (16 years is not that old) replacing all electrolytic caps is often effective at solving many problems. They are not everlasting and lose electrolyte by vapour or even liquid leakage, like batteries. Rather than waste time and money deciding whether a half-failed cap is ok in the application, it is often better to just replace everything (in stages) and give the whole amplifier a new lease of life. You have said that the pop has been slowly increasing and that is a sign of slow failure, which is probably consistent with this.
Locate the speaker relay(s) and listen there. Of course, you can't have a pop when they are still open (i.e. no click, no power to the relay coil). Otherwise something very strange is occurring. Again, the last click should be at least 1 second (as you say) after the initial power relays (2) click in. Measure for 24V across the corresponding output relay's coil if you can't be certain by listening.
Take care with exposed voltages but small amplifiers are fairly safe provided mains wiring is shrouded correctly. If you have clip leads that could attach to the meter probes and any leads protruding from the board, use them, as this will help ensure you don't cause shorts and damage when testing.
By appropriate type of ESR meter, I mean one that operates at very low voltage so as not to turn on any semiconductor junctions in the circuit and spoil the measurement. These are not common and tend to be expensive. For the number of times they may be used, just not worth the expense. It is simplest to just remove and measure capacitance value with a basic meter or just replace, regardless.
As a further comment, in older amplifiers (16 years is not that old) replacing all electrolytic caps is often effective at solving many problems. They are not everlasting and lose electrolyte by vapour or even liquid leakage, like batteries. Rather than waste time and money deciding whether a half-failed cap is ok in the application, it is often better to just replace everything (in stages) and give the whole amplifier a new lease of life. You have said that the pop has been slowly increasing and that is a sign of slow failure, which is probably consistent with this.
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