I'll pursue the ground issue. I'm using a star ground and connecting all grounds (both from the amps and power supply) to that one point (small copper pcb). Is this ok? I'll try rearranging the ground wires so that they connect closer together on the star plane. Not a speaker issue because it happens on one particular amp channel even if I swap speakers.
Now get a scope.The audio ground sounds suspicious.blap0220 said:
Take all the wires off the copper clad board.
Solder tags onto the ends of each wire.
Bolt them all together.
You can now experiment with the order that they are joined.
I put a single channel together in the following order:-
safety disconnecting network, smoothing cap 0v, decoupling/power ground from amp, Zobel/speaker return, signal ground. Yes, the order does matter. You may find that a different order works for your assembly.
For a coupled two channel amp I suspect that the high current returns should be coupled together and the low current returns coupled but towards the clean end. Keep the unclean returns as far along the bolt from the signal returns. I build up two completely separate channels, each with their own audio ground and each then connects to the safety earth with it's own disconnecting network. I prefer the quietness and ease of assembly of monoblocks.
I prefer Leach's suggestion that the PCB signal ground go to the RCA input socket and from there to the audio ground.
Note, that any experimentation is almost impossible or at least very time consuming if any of the returns are soldered to any other component.
I'm experimenting with the bolted grounds now. Please view the attached picture to see how I have ordered them. I'm still getting the same exact fuzz with this configuration. Note that my input grounds run to the Amp circuit boards and then the ground from the amp circuits go to the star bolt. Is the configuration bad? Should I have noticed at least a little difference with the new grounding config? I feel like it's not a grounding issue anymore now since I hear the same exact fuzz sound.
Not Amp Circuit related (follows Power Supply Channel)
Not Caps or rectifier (Swapped)
Not Transformer (Swapped)
Grounding???
THANKS!!!
Not Amp Circuit related (follows Power Supply Channel)
Not Caps or rectifier (Swapped)
Not Transformer (Swapped)
Grounding???
THANKS!!!
Attachments
blap0220 said:
The first thing to realise is that there are currents all through the ground leads and these set up voltage differences. This is critical. If you think that ground = ground and everything the voltage is zero, then star grounding and other techniques don't make sense. But they do. It helps if you think of all ground leads as resistors with series coils....
Think of it this way. There is ground current flowing from the amp board to the star ground. This sets up a small voltage between the board ground connection and the star ground, right? OK. Now you connect the signal ground lead from the RCA input jack to the amp board ground. We now see immediately that there is a voltage on the RCA ground lead wrt the start ground (the current through the RCA ground lead is orders of magnitude smaller so there is almost no voltage difference between the two ends of the RCA ground lead).
Same thing happens at the other channel. So now you have a voltage difference between the two RCA ground connections. Depending how the two amp board grounds are run, and how the supplies connections are run, the voltage difference between the RCA grounds can appear 'added' to the signal connections at the amp board input. In addition, if you have connected the RCA grounds together at the chassis where they are mounted, this sets up a small ground current through the loop RCA ground - amp board - star ground - other amp board -other RCA ground back to first RCA ground. These things are the most common cause of ground loop problems.
Try connecting your RCA input ground leads directly to the star ground, NOT via the amp board. And isolate the RCA's from the chassis.
Jan Didden
your diagram shows the bolt with an arrow to chassis.blap0220 said:
I hope you have a disconnecting network between your audio ground and the chassis.
The safety earth MUST be bolted permanently (or welded but NOT soldered) to the chassis.
Janneman's description of the isolated RCA ground going direct to audio ground is the Leach suggestion that works for me.
Fig 26 shows the speaker return adjacent to the smoothing cap 0V connection. The current returning from the speaker goes straight to the caps across the faces of the joint.
The caps 0v connection in turn is adjacent to the transformer centre tap, once again the highest (unbalanced charging pulse) currents pass between the faces of the joint.
In both cases these high current flows do not travel along the signal ground wire or across the signal ground to speaker return coupled faces of the connections.
You can liken the contact face of the sig ground to speaker return as 0v with respect to any signal at the input and to any signal at the speaker terminal.
If the arrangement as shown is not good enough then one has the option to swap around the order of the connections or even add extra connections interposed between any others.
I do not see what is dangerous about the fig26 posting.
The caps 0v connection in turn is adjacent to the transformer centre tap, once again the highest (unbalanced charging pulse) currents pass between the faces of the joint.
In both cases these high current flows do not travel along the signal ground wire or across the signal ground to speaker return coupled faces of the connections.
You can liken the contact face of the sig ground to speaker return as 0v with respect to any signal at the input and to any signal at the speaker terminal.
If the arrangement as shown is not good enough then one has the option to swap around the order of the connections or even add extra connections interposed between any others.
I do not see what is dangerous about the fig26 posting.
My P3A Layout
Hi All,
OK! I've gone crazy on my P3A trying to get rid of this buzz/distortion or whatever it is. I've attached my layout. Please review and critique for me.
This is what I've found so far though. It is in the power supply!
Instead of using 4 caps per power supply channel, I switched down to only 2 caps (4700uF) on the bad channel. IT WORKED! Buzz gone. BUT!!! The buzz went to the other channel!!!!!! WHY!?!?! So I tried the same thing (down to 2 Caps). But the other channel still buzzed.
I then thought it was all in the connections. So bought some good wire connectors for the rectifier and redid all the wiring. Still buzzed.
Then completely changed the power supply design to utilize each cap bank for either V+ or V-, and supply both amps off the same rails. Buzz kind of gone. Much better than before! BUT!! I feel like the sound isn't the same now that I'm supplying both channels off the same supply. I liked the sound better when the Power Supplies were separated. Is this just in my head?
Anyways, I wanted to try one other thing. I'm only using 18Guage wire between the rectifier and Caps. Is this too small? Maybe I should go to 14Guage?
I think this might be an oscillation/distortion issue. Not Grounding. It still happens when only one input is connected. And I totally disconnected the grounds from earth just to see if there was a loop. I tended to notice a little difference in the buzzing when I moved the cap banks around (closer to transformer and away from it). But it was still there.
Please any suggestions?
THANKS!
Hi All,
OK! I've gone crazy on my P3A trying to get rid of this buzz/distortion or whatever it is. I've attached my layout. Please review and critique for me.
This is what I've found so far though. It is in the power supply!
Instead of using 4 caps per power supply channel, I switched down to only 2 caps (4700uF) on the bad channel. IT WORKED! Buzz gone. BUT!!! The buzz went to the other channel!!!!!! WHY!?!?! So I tried the same thing (down to 2 Caps). But the other channel still buzzed.
I then thought it was all in the connections. So bought some good wire connectors for the rectifier and redid all the wiring. Still buzzed.
Then completely changed the power supply design to utilize each cap bank for either V+ or V-, and supply both amps off the same rails. Buzz kind of gone. Much better than before! BUT!! I feel like the sound isn't the same now that I'm supplying both channels off the same supply. I liked the sound better when the Power Supplies were separated. Is this just in my head?
Anyways, I wanted to try one other thing. I'm only using 18Guage wire between the rectifier and Caps. Is this too small? Maybe I should go to 14Guage?
I think this might be an oscillation/distortion issue. Not Grounding. It still happens when only one input is connected. And I totally disconnected the grounds from earth just to see if there was a loop. I tended to notice a little difference in the buzzing when I moved the cap banks around (closer to transformer and away from it). But it was still there.
Please any suggestions?
THANKS!
Attachments
Yes. The box in the middle is a ground plane. - I tried using just a bolt and bolting all the grounds to the chassis, but that didn't fix the problem.
Here's the link to the power supply I was trying to build.
http://sound.westhost.com/project04.htm
And here's the link to the new power supply (diagram 3) (Only one channel)
http://www.tnt-audio.com/clinica/ssps1_e.html
Which is better?
Here's the link to the power supply I was trying to build.
http://sound.westhost.com/project04.htm
And here's the link to the new power supply (diagram 3) (Only one channel)
http://www.tnt-audio.com/clinica/ssps1_e.html
Which is better?
Your layout looks fundamentally right to me.
1. I'd make sure though that your speaker return wire is positioned closer to the cable connecting the earth 'box' to your filter capacitor bank 0V point than the amplifier return line. This is to ensure that modulation of the amplifer 0V line by spreaker return currents is minimized.
2. Double check that your speaker connector ground terninals are not connected to ground on the chassis (to check this, disconnect the ground line to the terminal and then measure to chassis
3. someone already mentioned about checking your input connections for th e same problem - re-check.
4. It is also possible that you have your input ground and signal wires swapped wrt your source equipment. If you do this, you will get a buzzing sound (usually on both channels). However, if you remove the input source (both channels) from your amp, the problem will go away temporarily.
5. Another check you can make is to remove th e connection to the inputs at the PCB - if the problem goes, you have an input wiring problem.
6. I am not familiar with your circuit, but one trick used in a lot of designs is to isolate the front end ground of the amp with a low value (typically 10-100 Ohms) resistor. If your amp uses this trick, check that resistor value is correct.
7. One final check I thought of: Check that one of your caps is not making a connection to chassis ground - eithe r short or partial. You can do this by lifting all the caps clear of the chassis - if th e problem goes, you have found it.
Good luck.
1. I'd make sure though that your speaker return wire is positioned closer to the cable connecting the earth 'box' to your filter capacitor bank 0V point than the amplifier return line. This is to ensure that modulation of the amplifer 0V line by spreaker return currents is minimized.
2. Double check that your speaker connector ground terninals are not connected to ground on the chassis (to check this, disconnect the ground line to the terminal and then measure to chassis
3. someone already mentioned about checking your input connections for th e same problem - re-check.
4. It is also possible that you have your input ground and signal wires swapped wrt your source equipment. If you do this, you will get a buzzing sound (usually on both channels). However, if you remove the input source (both channels) from your amp, the problem will go away temporarily.
5. Another check you can make is to remove th e connection to the inputs at the PCB - if the problem goes, you have an input wiring problem.
6. I am not familiar with your circuit, but one trick used in a lot of designs is to isolate the front end ground of the amp with a low value (typically 10-100 Ohms) resistor. If your amp uses this trick, check that resistor value is correct.
7. One final check I thought of: Check that one of your caps is not making a connection to chassis ground - eithe r short or partial. You can do this by lifting all the caps clear of the chassis - if th e problem goes, you have found it.
Good luck.
Hi,
keep the safety earth connected to chassis. This must never be removed.
Disconnect the audio ground from chassis.
Test the system with the audio ground "floating".
Check it is isolated from the chassis.
Check that the mains transformer centre tap is directly connected to the power ground (0v) of the smoothing bank by the shortest possible route.
Check that the speaker return and Zobel return (or Thiele network return) are directly connected to the PCB power and decoupling ground.
Check that the RCA ground and input signal ground and NFB ground are directly connected.
Now experiment with how these three grounds (signal=clean, output /PCB=dirty, Power/0v=impulsive HF garbage) are interconnected using short, thick wire.
Once you have these operating well, then experiment with a disconnecting network to connect the audio ground to the safety earth. Prior to making this safety connection, you must ensure that mains is well earthed and well insulated. The audio ground is floating and must remain isolated from ALL risk of mains contact. BE VERY CAREFUL.
keep the safety earth connected to chassis. This must never be removed.
Disconnect the audio ground from chassis.
Test the system with the audio ground "floating".
Check it is isolated from the chassis.
Check that the mains transformer centre tap is directly connected to the power ground (0v) of the smoothing bank by the shortest possible route.
Check that the speaker return and Zobel return (or Thiele network return) are directly connected to the PCB power and decoupling ground.
Check that the RCA ground and input signal ground and NFB ground are directly connected.
Now experiment with how these three grounds (signal=clean, output /PCB=dirty, Power/0v=impulsive HF garbage) are interconnected using short, thick wire.
Once you have these operating well, then experiment with a disconnecting network to connect the audio ground to the safety earth. Prior to making this safety connection, you must ensure that mains is well earthed and well insulated. The audio ground is floating and must remain isolated from ALL risk of mains contact. BE VERY CAREFUL.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.