Hello everyone,
Need some advice on a Bose companion 3. This weekend I've sort of finished a repair of a Bose companion 3 Series II (2.1 speaker) system. The set is from a friend of ours and hadn't been used for a while. It sat in the attic doing nothing but collecting moisture (and fungi 😏). So the thing was in a terrible state with lots of noise when switching on (if it even wanted to). So took it apart and started replacing all SMD electrolytic caps because some of them looked leaky. Found out that lots of them were actually leaking and / or in a bad shape anyway. Especially the 10uF ones were bad and needed to be replaced.
So after going through all of that it is now working again. But the amount of static / hiss this thing produces is beyond what I find acceptable. However, it might just be poor design. Since I've never had a BOSE on my bench, is it normal that this thing is so noisy? I wouldn't mind digging in a bit deeper but now feels like I'm chasing red herrings.
So far I did find the full service manuals, bulletins and schematics (although being the wrong revision of the board). It has a peculiar power supply and a tiny voltage regulator for all op-amps and bias voltages. My guess is that noise in the power supply would easily get into the amp and out the speakers (the hiss is present in all channels).
Need some advice on a Bose companion 3. This weekend I've sort of finished a repair of a Bose companion 3 Series II (2.1 speaker) system. The set is from a friend of ours and hadn't been used for a while. It sat in the attic doing nothing but collecting moisture (and fungi 😏). So the thing was in a terrible state with lots of noise when switching on (if it even wanted to). So took it apart and started replacing all SMD electrolytic caps because some of them looked leaky. Found out that lots of them were actually leaking and / or in a bad shape anyway. Especially the 10uF ones were bad and needed to be replaced.
So after going through all of that it is now working again. But the amount of static / hiss this thing produces is beyond what I find acceptable. However, it might just be poor design. Since I've never had a BOSE on my bench, is it normal that this thing is so noisy? I wouldn't mind digging in a bit deeper but now feels like I'm chasing red herrings.
So far I did find the full service manuals, bulletins and schematics (although being the wrong revision of the board). It has a peculiar power supply and a tiny voltage regulator for all op-amps and bias voltages. My guess is that noise in the power supply would easily get into the amp and out the speakers (the hiss is present in all channels).
Can you post the manual or schematic?
Is hiss acceptable with volume control at 0? I.e. does hiss originate in PA, or in earlier stages? Same in both channels?
Is hiss acceptable with volume control at 0? I.e. does hiss originate in PA, or in earlier stages? Same in both channels?
I found the circuit diagrams over here: elektrotanya. Might be slightly different from the circuit board that I have.
What I already did do:
1. Fed the unit from a bench power supply at 15V, no difference but this did rule out the power supply board from being defective.
2. The unit is always on but in stand-by just muted via a pin on the chip amp. Stand-by with the remote control makes it dead silent. Unmuted it hisses. Both muted and unmuted (but no inputs) it draws about .3 amps at 15V (so 4 to 5 watts).
3. To rule out the remote control: jumped the pins in the connector to directly redirect inputs to the pre-amps (so bypass remote). This didn't change a thing.
4. Removed one of the input SMD caps (C318 on the right channel just at the input of the chip amp). This stopped the hiss in that channel, so IMO this ruled out the chip from being defective.
5. Volume control does almost nothing to amount of hiss.
In conclusion: I'm fairly certain that it is the pre-amp and equalizers that are (just?) noisy.
What I already did do:
1. Fed the unit from a bench power supply at 15V, no difference but this did rule out the power supply board from being defective.
2. The unit is always on but in stand-by just muted via a pin on the chip amp. Stand-by with the remote control makes it dead silent. Unmuted it hisses. Both muted and unmuted (but no inputs) it draws about .3 amps at 15V (so 4 to 5 watts).
3. To rule out the remote control: jumped the pins in the connector to directly redirect inputs to the pre-amps (so bypass remote). This didn't change a thing.
4. Removed one of the input SMD caps (C318 on the right channel just at the input of the chip amp). This stopped the hiss in that channel, so IMO this ruled out the chip from being defective.
5. Volume control does almost nothing to amount of hiss.
In conclusion: I'm fairly certain that it is the pre-amp and equalizers that are (just?) noisy.
Hi Johan,
Do you have any clues about U301? Manufacturer, part number, etc?
I do believe your C318 experiment shows that the PA section is not a significant contributor to the noise. I suspect the hiss is inherent in the design but, with very little evidence, I suspect U401 and U590 may be the dominant problems.
You can probably conduct similar experiments to determine if the dominant noise originates in these two devices or if still earlier in the signal chain. Do you have a scope and audio generator?
Good luck!
Do you have any clues about U301? Manufacturer, part number, etc?
I do believe your C318 experiment shows that the PA section is not a significant contributor to the noise. I suspect the hiss is inherent in the design but, with very little evidence, I suspect U401 and U590 may be the dominant problems.
You can probably conduct similar experiments to determine if the dominant noise originates in these two devices or if still earlier in the signal chain. Do you have a scope and audio generator?
Good luck!
Hi BSST,
Yeah that hiss being part of the design sort of reflects all the bad reviews I found on Youtube. Actually found people complaining about hiss in similar brand new bose systems. But anyway, I might try to isolate those other chips U401 and U590, good call!
I do have a scope and signal generator so that's good. I did not really saw any major changes in noise levels but then again I did a poor job in probing around the signal path in the opamps. It was already kinda late that evening I was working on the thing.
If I do find anything I'll post it here, thank you again for the help!
Yeah that hiss being part of the design sort of reflects all the bad reviews I found on Youtube. Actually found people complaining about hiss in similar brand new bose systems. But anyway, I might try to isolate those other chips U401 and U590, good call!
I do have a scope and signal generator so that's good. I did not really saw any major changes in noise levels but then again I did a poor job in probing around the signal path in the opamps. It was already kinda late that evening I was working on the thing.
If I do find anything I'll post it here, thank you again for the help!
Just check with an external power supply, cut the traces at a convenient spot, so you can rework them if needed.
A transformer based supply would be nice if available, a battery eliminator from old radios works for most of this type of testing, as the current needed is less than 100 mA in most cases.
Bose quality is no good, the stuff is designed and built by Chinese contractors with a tight price limit, it is a bottom end Chevy posing as if it is a high end Cadillac.
I have no connections to any named entities above, the car companies were just a convenient example, even Audi / Volkswagen / Skoda share the same engine blocks, again no connection with them.
A transformer based supply would be nice if available, a battery eliminator from old radios works for most of this type of testing, as the current needed is less than 100 mA in most cases.
Bose quality is no good, the stuff is designed and built by Chinese contractors with a tight price limit, it is a bottom end Chevy posing as if it is a high end Cadillac.
I have no connections to any named entities above, the car companies were just a convenient example, even Audi / Volkswagen / Skoda share the same engine blocks, again no connection with them.
