I have been trying some electrolytics in this "protection" duty.
I have not reached final conclusions but first impressions are good.
Using 4 polar electrolytics, a parallel pair of series connected caps gives a net capacitance equal to one electro.
One series pair are connected neg to neg
The other series pair are connected plus to plus.
These are then paralleled and and a further 1uF MKT added across the whole lot.
I have tried 101uF and 23uF and 11uF so far.
These were all on a dual polarity supplied ClassAB, so no charging pulse on start up.
I will also be trying a series pair of non polar electrolytics. I have 220uF to give a net 111uF assembled, but untested.
I have not reached final conclusions but first impressions are good.
Using 4 polar electrolytics, a parallel pair of series connected caps gives a net capacitance equal to one electro.
One series pair are connected neg to neg
The other series pair are connected plus to plus.
These are then paralleled and and a further 1uF MKT added across the whole lot.
I have tried 101uF and 23uF and 11uF so far.
These were all on a dual polarity supplied ClassAB, so no charging pulse on start up.
I will also be trying a series pair of non polar electrolytics. I have 220uF to give a net 111uF assembled, but untested.
Last edited:
Alrighty, here's how things stand! (I lost interest for a while, and changed jobs)
Anyway!
I added a 15uF capacitor between the tweeter and tweeter amplifier, which creates a filter at about 1300Hz, so, should give some protection.
I also added a 1uF capacitor between the tweeter preamp, and amplifier stages, as well as a 10uF between the woofer preamp/amp.
As for the 50Hz hum/buzz from one amp, and the "snap, crackle and pop" from the other amp?
You'll love this....
I realised that the amplifiers ground was floating with respect to the earth ground, when it was tied to ground, the hum went away.
It seems that the 6.5mm input socket has a star washer between the back of the plate (that the amplifier is mounted to) and the socket...
Apparently, they were relying on this, in contact with a powder coated panel, to provide the earth to the audio circuit?!!? a small amount of aluminium was exposed, where the teeth of the washer had cut through it, but this is hardly acceptable, and I wonder if its the cause of so many tweeters in these failing!
The amplifier with the constant hum had no nut holding the socket to the panel at all, while the snap, crackle, pop amp, the nut was loose, causing this to happen as the connection made and broke!
Wire wheeled the inside of the panel back to raw aluminium, and all the hum is gone!
Anyway!
I added a 15uF capacitor between the tweeter and tweeter amplifier, which creates a filter at about 1300Hz, so, should give some protection.
I also added a 1uF capacitor between the tweeter preamp, and amplifier stages, as well as a 10uF between the woofer preamp/amp.
As for the 50Hz hum/buzz from one amp, and the "snap, crackle and pop" from the other amp?
You'll love this....
I realised that the amplifiers ground was floating with respect to the earth ground, when it was tied to ground, the hum went away.
It seems that the 6.5mm input socket has a star washer between the back of the plate (that the amplifier is mounted to) and the socket...
Apparently, they were relying on this, in contact with a powder coated panel, to provide the earth to the audio circuit?!!? a small amount of aluminium was exposed, where the teeth of the washer had cut through it, but this is hardly acceptable, and I wonder if its the cause of so many tweeters in these failing!
The amplifier with the constant hum had no nut holding the socket to the panel at all, while the snap, crackle, pop amp, the nut was loose, causing this to happen as the connection made and broke!
Wire wheeled the inside of the panel back to raw aluminium, and all the hum is gone!
TERRIBLE "design" .
Worst is that it uses no Zobels anywhere , *maybe* that´s why they added that 47pF in series with 20K in all feedback loops .... but that does not bring stability.
I bet the amp oscillated, clearly that´s a tweeter killer, and one of the tweeters shorted, killing the amp and bringing the -rail to the output.
The other *maybe* just tore to pieces but opened, so amp survived.
Add a Zobel to each speaker out.
Worst is that it uses no Zobels anywhere , *maybe* that´s why they added that 47pF in series with 20K in all feedback loops .... but that does not bring stability.
I bet the amp oscillated, clearly that´s a tweeter killer, and one of the tweeters shorted, killing the amp and bringing the -rail to the output.
The other *maybe* just tore to pieces but opened, so amp survived.
Add a Zobel to each speaker out.
so, what values for the zobel network?
anyone have any ideas? why would I actually even need one anyway?
anyone have any ideas? why would I actually even need one anyway?
Thanks a lot for all the info on these B300 units, and especially for the schematics.
I have two broken units and they seem to exhibit similar issues to what you describe, TheyDntWntMusic. One has a hum, the other plays but has scratchiness and distortion. Both units heat up very quickly. Some of the LM3886 chips specifically get hot to the touch. The one that now plays (badly) was initially giving me very loud noises until I replaced one of the two big filter caps that had failed.
Can you give me some tips on what would cause the LM3886 chips to heat up? They get hot whether or not I have the speaker connector plugged into the board. I'm trying to narrow it down. I've completely removed one of the LM3886 chips (IC2) from the board that hums. It still hums. I've also tried jumpering the ground wire to the outside conductor of the big phono jack.
I have two broken units and they seem to exhibit similar issues to what you describe, TheyDntWntMusic. One has a hum, the other plays but has scratchiness and distortion. Both units heat up very quickly. Some of the LM3886 chips specifically get hot to the touch. The one that now plays (badly) was initially giving me very loud noises until I replaced one of the two big filter caps that had failed.
Can you give me some tips on what would cause the LM3886 chips to heat up? They get hot whether or not I have the speaker connector plugged into the board. I'm trying to narrow it down. I've completely removed one of the LM3886 chips (IC2) from the board that hums. It still hums. I've also tried jumpering the ground wire to the outside conductor of the big phono jack.
Two heating up causes.
a.)
the Quiescent current times the supply voltage = power, when there is no output.
b.)
oscillation consumes current and gives more power to be dissipated.
Have you measured the output offset and the output hum+noise?
Have to fitted the minimum of four (4) decoupling capacitors, two on the supply pins and two more nearby?
Have you fitted the Output Zobel, near the output and Zobel ground?
Have you fitted the RF filter?
Have you fitted the DC blocking capacitor, that also limits sub bass frequency response?
a.)
the Quiescent current times the supply voltage = power, when there is no output.
b.)
oscillation consumes current and gives more power to be dissipated.
Have you measured the output offset and the output hum+noise?
Have to fitted the minimum of four (4) decoupling capacitors, two on the supply pins and two more nearby?
Have you fitted the Output Zobel, near the output and Zobel ground?
Have you fitted the RF filter?
Have you fitted the DC blocking capacitor, that also limits sub bass frequency response?
I have not done any of those things, but I do have a working B300 unit which is using this same design.
I understand there are some flaws in the design, but I'd like to try to troubleshoot what part of the circuit has failed relative to my working example before I try to attempt an improvement of the design.
Can you tell me what is the best way to measure output offset and the hum+noise? I have an oscilloscope, but I was wary of connecting it because I don't fully understand how to avoid the potential problems when using an oscilloscope and DUT that are both powered from AC mains.
I understand there are some flaws in the design, but I'd like to try to troubleshoot what part of the circuit has failed relative to my working example before I try to attempt an improvement of the design.
Can you tell me what is the best way to measure output offset and the hum+noise? I have an oscilloscope, but I was wary of connecting it because I don't fully understand how to avoid the potential problems when using an oscilloscope and DUT that are both powered from AC mains.
Use your DMM set to voltmeter.
Set to 600Vac and measure the output voltage.
Set to 1000Vdc and measure the output voltage.
If both readings are much lower than 10% of full scale then switch to next lower Vac and Vdc and measure the output voltages.
If both readings are much lower than 10% of the 200V full scale, then switch to next lower Vac and Vdc and measure the output voltages.
etc.....
Set to 600Vac and measure the output voltage.
Set to 1000Vdc and measure the output voltage.
If both readings are much lower than 10% of full scale then switch to next lower Vac and Vdc and measure the output voltages.
If both readings are much lower than 10% of the 200V full scale, then switch to next lower Vac and Vdc and measure the output voltages.
etc.....
The amplifier chips get hot if you power the unit up without the input board connected to the amplifier board 😉 I figured that much out! lol
Thy, Your posts and my questions are a few years apart, not sure if you get this one. Any how I found and dragged out of a bin 2 x B300 speakers, I took them home, powered them up and the base drivers worked and the tweets were dead.
I finally got around to buying 2 new tweeters and fitted them, I them powered on the first one and it worked with a slight hiss at no volume, when i powered the second one up it squealed and burnt out the new tweeter in about 5 seconds flat.
Obviously I was annoyed as i just killed 120 bucks for the tweeter. I have orderred 2 diaphragms to replace the dead tweeter and have a spare expecting during my journey to fix this I may need another.
I found this thread and it seems like I am reading the solutions to the problems these speakers have, the problem solving to me has now become more of a desire than the speaker as i want to beat this issue for my own personal knowledge and satisfaction.
I notice you are in Australia, is there a possibility I can discuss a few questions sometime re the B300?
I finally got around to buying 2 new tweeters and fitted them, I them powered on the first one and it worked with a slight hiss at no volume, when i powered the second one up it squealed and burnt out the new tweeter in about 5 seconds flat.
Obviously I was annoyed as i just killed 120 bucks for the tweeter. I have orderred 2 diaphragms to replace the dead tweeter and have a spare expecting during my journey to fix this I may need another.
I found this thread and it seems like I am reading the solutions to the problems these speakers have, the problem solving to me has now become more of a desire than the speaker as i want to beat this issue for my own personal knowledge and satisfaction.
I notice you are in Australia, is there a possibility I can discuss a few questions sometime re the B300?
Personally, after a round of dead tweeters (which were slightly less expensive than yours), I inserted a capacitor in series to to the tweeter on whichever side the crossover wasn't on.
It was just a guess; but, the tweeter harm expenditure vanished immediately, and never returned.
It was just a guess; but, the tweeter harm expenditure vanished immediately, and never returned.
- Status
- Not open for further replies.