I have read the similar posts and I am not exactly sue about the fix.
I bought the pcb's (pictures attached) through ebay and used them in my active speakers (posted in an other thread) However I am unable to get rid of the 50 hz hum on both of the speakers.
I have tried to relocate the transformer and using all shielded cabling and connecting the ground to large metal objects like the central heating system
(this helped a little though) and nothing so far cured the problem.
I have read in other thread that with an other chip amp people were successful with ripping off the ground lines and connecting them in star topology. This seems a little big harder for me to implement due to the way I mounted the pcb inside the speaker.
I sense that something is wrong around the rectifier bridge and this could be the switching noise of diodes.
Before diving into my speakers I have spare board I can try your recommendations (I don't have transformer, but I will be getting one this weekend hopefully)
PS: My active speaker is a relatively small one with a 4.5 inch woofer so the 50 hz hum is eating much of it's xmax and as I used passive line level XO the 50hz humm also hits to the directly coupled tweeter, probably killing it slowly.
I tried to attach hiüres pictures
Mertol
I bought the pcb's (pictures attached) through ebay and used them in my active speakers (posted in an other thread) However I am unable to get rid of the 50 hz hum on both of the speakers.
I have tried to relocate the transformer and using all shielded cabling and connecting the ground to large metal objects like the central heating system
(this helped a little though) and nothing so far cured the problem. I have read in other thread that with an other chip amp people were successful with ripping off the ground lines and connecting them in star topology. This seems a little big harder for me to implement due to the way I mounted the pcb inside the speaker.
I sense that something is wrong around the rectifier bridge and this could be the switching noise of diodes.
Before diving into my speakers I have spare board I can try your recommendations (I don't have transformer, but I will be getting one this weekend hopefully)
PS: My active speaker is a relatively small one with a 4.5 inch woofer so the 50 hz hum is eating much of it's xmax and as I used passive line level XO the 50hz humm also hits to the directly coupled tweeter, probably killing it slowly.
I tried to attach hiüres pictures
Mertol
Attachments
Hai mertol, if you mean didn't conect ground for the input power supply..that is the problem! you must conect them...from your picture's, I see that is voltage input 18-Gnd-18 V, right?? If you use EL trafo's, conect Center Tape (CT) to Ground,don't leave it.
you must use isolator on the LM1875 metal tab, there is conect to negative rail (-Vcc).
you must use isolator on the LM1875 metal tab, there is conect to negative rail (-Vcc).
This could be a solution to the problem but only if the heat sink is connected to the o volt . If this is the case im sure there would be magik smoke by now as the nagative supply rail would be a direct short to 0 volts . Then again if each rail is fused then there wil be a large dc offset on the output and the speaker will soon be destroyed
if you bought the board already assembled as in NEW LM1875 + NE5532 Audio Power Amplifier board --C56 | eBay, I would ask for a refund...
Thanks for all the responses, I will try to answer all the questions.
Madtechy : As the amplifiers are embedded into the speaker I can not take any more pictures. However humm was aparent even when the amplifiers were being tested outside the speaker enclosures. Cabling is very basic, inputs from the back of the speakers is carried to amplifier input with shielded cable. It's a stereo amplifier and there are 2x RCA's at the back of the speaker. At this moment line level passive XO is external.
(PS: I know the dangers of DC speakers with amplifiers)
It doesn't effect the sound too much but it's quite disturbing in silent passages or in low listening volumes.
Slicon ray : I installed a metal plate under the pcb (at the same size of the pcb and it's 3-4mm thick) It's used for grounding the pcb. And all grounds from rca inputs and shields are collected in str topology to a central ground. Also I installed a connector at the back of the speaker, connected to the central ground inside the cabinet. Using this connector I connected the ground to metal water pipe (decreased the humm greatly)
Michael Chua : Yes 1875T is connected to a big headsink, I run the system for 2-3 hours and only gets slightly warm. 1875T is isolated from the heatsink. Heatsink is not grounded or connected to anywhere. --- Should I connect it to ground? ---
AndrewT : I mounted the rca terminals at the back of the speaker. However humm was evident even before I built the speaker and everything was directly connected.
Carcass : Yes, I bought that board. Anything you know particular about this board?
johnr66 : After your post I did so and I realized the amount of hiss and humm decreases (but do not vanish)
Madtechy : As the amplifiers are embedded into the speaker I can not take any more pictures. However humm was aparent even when the amplifiers were being tested outside the speaker enclosures. Cabling is very basic, inputs from the back of the speakers is carried to amplifier input with shielded cable. It's a stereo amplifier and there are 2x RCA's at the back of the speaker. At this moment line level passive XO is external.
(PS: I know the dangers of DC speakers with amplifiers)
It doesn't effect the sound too much but it's quite disturbing in silent passages or in low listening volumes.
Slicon ray : I installed a metal plate under the pcb (at the same size of the pcb and it's 3-4mm thick) It's used for grounding the pcb. And all grounds from rca inputs and shields are collected in str topology to a central ground. Also I installed a connector at the back of the speaker, connected to the central ground inside the cabinet. Using this connector I connected the ground to metal water pipe (decreased the humm greatly)
Michael Chua : Yes 1875T is connected to a big headsink, I run the system for 2-3 hours and only gets slightly warm. 1875T is isolated from the heatsink. Heatsink is not grounded or connected to anywhere. --- Should I connect it to ground? ---
AndrewT : I mounted the rca terminals at the back of the speaker. However humm was evident even before I built the speaker and everything was directly connected.
Carcass : Yes, I bought that board. Anything you know particular about this board?
johnr66 : After your post I did so and I realized the amount of hiss and humm decreases (but do not vanish)
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.