Incidentally, I'm confused as to how and why to test the rectifier DC rail as AC instead of DC? When I do that I get only about 40mV. When I test as DC I get about 15.8V. I also did check the frequency of the DC current and it's pulsed at 120Hz.
Ah, well, I've just checked the frequency going to the subwoofer, and it's exactly 120Hz. Seems like it's leaking current directly to the subwoofer somewhere, but only when it's attached to an AC power source...
What you are hearing is hum, that only comes from the AC line.
If Edison had his way we wouldn't have hum
Last edited:
A full wave rectifier (fwb) produces voltage every 180° or for every positive and negative voltage swing, whereas a half wave rectifier only coverts half or once every 360° or only on the positive or negative swing e.g. 120Hz or 60Hz modulated AC riding on this pulsed DC. Without the Ground reference this is nothing more than AC.
Fwb's are normally used when hum minimized and clean power are required. Half wave is used in cases where they don't matter, like in lighting. Because the fwb converts each cycle twice the time on charge constant helps reduce the deep well that occurs with a half wave using the same value of capacitance.
Basic electronics 101
Last edited:
Thanks, I know how the rectifier works, and was merely pointing out that the hum was not due to some other component in the mix creating an oscillation since it was at exactly 120hz.
I've got the 22,000uf cap on order, and will see if that solves the issue.
Success! I replaced the 22,000uf 25V cap with a new one, and the humming is gone!
I second the thanks -- now it is near the end of 2014 and this thread is still very useful for us still using these great Boston Acoustics Digital BA735s. They must have sold millions of these great sounding speakers. Mine are now plugged into the fourth PC since that old Gateway went to PC heaven many years ago.
Cheers,
- - Mike
Hi, its 2015 and hopefully this thread will still be useful to me.
I was helping my uncle with some computer problems and one of the problems was the dreaded hum from BA735s. I recognized the quality of the speakers and thought I could try to salvage them.
Well my search for help lead me to this thread. I'm really hoping the 12VC power supply I ordered from this link: 12 Volt DC - 3.5 Amp Power Supply will solve my problems.
However, I noticed the voltage on the original power supply is listed at 12V A/C 1500mA and the power supply from the link above is rated at 3.5.
Is this going to cause a problem? I really don't want to blow these speakers out.
I was helping my uncle with some computer problems and one of the problems was the dreaded hum from BA735s. I recognized the quality of the speakers and thought I could try to salvage them.
Well my search for help lead me to this thread. I'm really hoping the 12VC power supply I ordered from this link: 12 Volt DC - 3.5 Amp Power Supply will solve my problems.
However, I noticed the voltage on the original power supply is listed at 12V A/C 1500mA and the power supply from the link above is rated at 3.5.
Is this going to cause a problem? I really don't want to blow these speakers out.
If it is regulated it should not be an issue. The text on the site doesn't say though. Just measure the voltage when it is not plugged into the amp. If it measures 12V you should be fine.
If it is unregulated then it will probably provide higher than 12V at anything less than the rated 3.5 Amps.
Tony.
If it is unregulated then it will probably provide higher than 12V at anything less than the rated 3.5 Amps.
Tony.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.