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Any issues not using ground lead on potentiometer?

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  • tomzarbo
    replied
    Re: Any issues not using ground lead on potentiometer?

    Okay, I think we may be getting somewhere...

    I soldered two 5.1k resistors to the center terminal of the sub pot, and then the other ends of the resistors to the outer two terminals on the sub pot. If I understand correctly this simulates a 10k pot.

    Well, that did a lot to eliminate some noise. Grounding the metal body of the subwoofer pot to the negative side of the 12v input from the power supply did the rest. It's pretty quiet now, I can live with this for sure. You can hear the whining sound faintly if you put your head right in front of the subwoofer, but when music is playing at any real volume, it all but disappears. I think this will work.

    Funny, I was just about to post that adding the resistors didn't work -- I was typing it on the computer... then I saw that I had written down 5k on the little diagram I made. By mistake I soldered two 500k resistors, which did basically nothing at all. Thank God I caught that.

    So right now, it looks like a solution will be to order up a few 10k pots and ground the sub pot to the 12v negative on the amp board.

    PE sells two 10k pots. This one:

    http://www.parts-express.com/10k-ohm...meter--023-530

    and this one:

    http://www.parts-express.com/10k-aud...shaft--023-610

    I'll order a few of both and see which works better/quieter.

    Any ideas on the best way to solder to the back of a pot body? Sand, flux, and lots of heat?

    Thanks so much for the good advice. As soon as I get the parts I'll try the new pot on the board mounted on the alum panel and hopefully I'll be in business.

    TomZ

    Leave a comment:


  • craigk
    replied
    Re: Any issues not using ground lead on potentiometer?

    Originally posted by 1100xxben View Post
    I would ohm everything out first. If you already have connection between your input power ground and the ground side of your potentiometer for example, then all you'd be doing with the additional star grounding is creating a ground loop, which is not a good idea.
    this is not correct. when two or more devices are connected to a common ground through different paths, a ground loop occurs. Currents flow through these multiple paths and develop voltages which can cause damage, noise or 50Hz/60Hz hum in audio or video equipment. To prevent ground loops, all signal grounds need to go to one common point and when two grounding points cannot be avoided, one side must isolate the signal and grounds from the other. all grounds will being going to one common point with star grounding and there is not chance for a loop to occur.

    Leave a comment:


  • 1100xxben
    replied
    Re: Any issues not using ground lead on potentiometer?

    I would ohm everything out first. If you already have connection between your input power ground and the ground side of your potentiometer for example, then all you'd be doing with the additional star grounding is creating a ground loop, which is not a good idea.

    Leave a comment:


  • craigk
    replied
    Re: Any issues not using ground lead on potentiometer?

    Originally posted by tomzarbo View Post
    So one good connection point on the aluminum plate which I can tie a grounding terminal to from every component until the noise ceases?

    For instance, I'd drill a hole and tap a screw through the aluminum plate, then secure it on the back side with a nut, then proceed to 'ground' things... the sub pot, negative side of the power supply input, negative, on the amp board, etc. until the noise stops.... if I'm understanding the concept correctly. So I pretty much need to do this on a metal plate and not have stuff just sitting on my workbench for this to work.

    Thank you for the suggestion Craig. I'll give it a shot after I mow the grass tonight... if I can still see and breathe... allergies are killing me this year.

    TomZ
    you have the correct idea. I hope it works.

    Leave a comment:


  • tomzarbo
    replied
    Re: Any issues not using ground lead on potentiometer?

    Originally posted by craigk View Post
    since nothing is working try star grounding.
    So one good connection point on the aluminum plate which I can tie a grounding terminal to from every component until the noise ceases?

    For instance, I'd drill a hole and tap a screw through the aluminum plate, then secure it on the back side with a nut, then proceed to 'ground' things... the sub pot, negative side of the power supply input, negative, on the amp board, etc. until the noise stops.... if I'm understanding the concept correctly. So I pretty much need to do this on a metal plate and not have stuff just sitting on my workbench for this to work.

    Thank you for the suggestion Craig. I'll give it a shot after I mow the grass tonight... if I can still see and breathe... allergies are killing me this year.

    TomZ

    Leave a comment:


  • craigk
    replied
    Re: Any issues not using ground lead on potentiometer?

    since nothing is working try star grounding.

    Leave a comment:


  • 1100xxben
    replied
    Re: Any issues not using ground lead on potentiometer?

    Originally posted by tomzarbo View Post
    Okay, that makes sense, what should I ground it to, the negative terminal on the power supply incoming?
    Yes, without knowing any other details of the board, that would be the safest place to tie the plate to.

    Originally posted by tomzarbo View Post
    ...Wonder why they just didn't build it with the sub pot built in?
    Maybe because it's noisy?? ;)

    Leave a comment:


  • tomzarbo
    replied
    Re: Any issues not using ground lead on potentiometer?

    Originally posted by 1100xxben View Post
    When you wrap in foil, are you attaching the foil to a good ground? If you're just wrapping the foil around your wires and not attaching it to anything, then you may as well wrap it in a piece of paper. If the foil is picking up any noise, it needs a ground path to shunt the noise to.

    Hmm, can you remove the heatsink and see what the amp chip(s) is/are, or is it epoxied in place? You have me very curious now as to what this little amplifier really is. Especially with the power numbers they claim, and the difference between the L/R channels and the sub channel.
    Okay, so my little 'shielding' experiment didn't have a chance.

    The heatsink is glued on there, but Rory in his statement on the Q&A section said that the markings on the chips were 'obliterated' before gluing on the heatsink, so I guess we're outta luck there.

    Originally posted by 1100xxben View Post
    I just looked at the amp board again, and it appears this is an inductor-less class-D design. That design will generate a lot of stray noise, and it could just be inherent to the design. If designed properly, that noise should be out of the audible band, but you never know.
    I'm beginning to think that this little board may have problems.

    Originally posted by PWR RYD View Post
    FWIW I always ground the potentiometer's case. I had a noisy tube amp project and grounding the case cured it. Now I just make it standard practice.
    Okay, that makes sense, what should I ground it to, the negative terminal on the power supply incoming? I can drill/tap a screw on the alum. plate to ground things to if it helps, no problem there. I would ground the pot body and what else would you suggest grounding? The amp board is only touching the alum. plate where the main volume potentiometer is bolted to it, but the board itself is basically right next to the alum. plate. The red piece of electrical tape is there to prevent any direct contact between the board and the alum.

    If I wanted to 'ground' the amp to the board, how would I even do it? I don't see metal showing on any of the mounting holes on the amp board. The only place I can think of to ground it would be on the negative terminal of the power coming in.
    I'm assuming that the main volume pot mounted on the amp board although it is metal, would not actually be conducting anything to anything else.

    So again, it works fine with a jumper in place, no real noise. The only noise is when I try to wire in a potentiometer... and again to reiterate, the same thing is happening with both the bare naked board and the one mounted to the alum. plate.

    I'm a bit bummed, this little board is quite nice otherwise. But without a way to adjust the sub volume, it's not going to fly in my book. Wonder why they just didn't build it with the sub pot built in?

    TomZ

    Leave a comment:


  • PWR RYD
    replied
    Re: Any issues not using ground lead on potentiometer?

    FWIW I always ground the potentiometer's case. I had a noisy tube amp project and grounding the case cured it. Now I just make it standard practice.

    Leave a comment:


  • 1100xxben
    replied
    Re: Any issues not using ground lead on potentiometer?

    I just looked at the amp board again, and it appears this is an inductor-less class-D design. That design will generate a lot of stray noise, and it could just be inherent to the design. If designed properly, that noise should be out of the audible band, but you never know.

    Leave a comment:


  • 1100xxben
    replied
    Re: Any issues not using ground lead on potentiometer?

    Originally posted by tomzarbo View Post
    I also wrapped the wires coming from the board to the pot with aluminum foil to see if that may provide some signal shielding -- not the best I know -- but just to see if it helped at all... it didn't. When I get close to touching those wires with my hand the squeal gets louder and if I squish the wires together, louder still, even when wrapped up in alum. foil. On the bright side, I believe that unintended radio transmissions to extra-terrestrials was temporarily thwarted by my attempts with the foil.
    When you wrap in foil, are you attaching the foil to a good ground? If you're just wrapping the foil around your wires and not attaching it to anything, then you may as well wrap it in a piece of paper. If the foil is picking up any noise, it needs a ground path to shunt the noise to.

    Originally posted by tomzarbo View Post
    I'll try adding the 5k resistors tonight after work since I don't have a 10k pot available. Also... You meant between pins 1 and 2, and then between 2 and 3 right?
    Ha, yes, pins 1/2 and 2/3. That's what I get for staying up and posting at 2 AM. That might be the norm for Wolf, but it's way past my bedtime .

    Originally posted by tomzarbo View Post
    One more thing to add just fyi... when I kill the power, the whine goes quickly up in pitch like a sine sweep until it's not audible, takes like 2 seconds.
    Hmm, can you remove the heatsink and see what the amp chip(s) is/are, or is it epoxied in place? You have me very curious now as to what this little amplifier really is. Especially with the power numbers they claim, and the difference between the L/R channels and the sub channel.

    Leave a comment:


  • craigk
    replied
    Re: Any issues not using ground lead on potentiometer?

    Originally posted by tomzarbo View Post
    I have an amp board not wired as in the pic, laying bare on the bench using the built-in rear plugs for input signal and power. The only wires in use are the three for the sub volume pot. 3 inches long or so. When I short the two that would be shorted by the jumper, it's quiet and functions fine, but of course then the sub volume is too loud.

    I had a very high quality ALPS pot (50k) that I hooked up real quick just to see if it made a difference, the whining sound was still there very similar to the PE 50k pot.

    I also wrapped the wires coming from the board to the pot with aluminum foil to see if that may provide some signal shielding -- not the best I know -- but just to see if it helped at all... it didn't. When I get close to touching those wires with my hand the squeal gets louder and if I squish the wires together, louder still, even when wrapped up in alum. foil. On the bright side, I believe that unintended radio transmissions to extra-terrestrials was temporarily thwarted by my attempts with the foil.

    I'll try adding the 5k resistors tonight after work since I don't have a 10k pot available. Also... You meant between pins 1 and 2, and then between 2 and 3 right?

    One more thing to add just fyi... when I kill the power, the whine goes quickly up in pitch like a sine sweep until it's not audible, takes like 2 seconds.

    Thanks again guys for the help. I'll post up what happened as soon as I can try it out.

    TomZ
    can you make jumper and ground the faceplate to a good ground. just curious.

    Leave a comment:


  • tomzarbo
    replied
    Re: Any issues not using ground lead on potentiometer?

    Originally posted by 1100xxben View Post
    Again, I will say that without a schematic or the board in hand, this is all a "shot in the dark". IF the reason for the noise is related to having the pot in place, then there's noise coupling on to the signal path. When you use something like a 50k pot, you have a very high impedance to ground (especially when the wiper is in the middle). A very weak signal radiating onto the path can easily create the necessary voltage for you to hear it. If you decrease the impedance to ground, by using a 10k pot for example, then it requires a stronger radiated signal to create a voltage on that line and the noise may be reduced. If you don't have a 10k pot laying around, you could always put a 5k resistor between pins 1 & 2 and a 5k resistor between pins 3 & 4. This would simulate a 10k pot with the wiper right in the middle. This would at least help verify where the issue might be coming from.

    I hope we're not headed in the wrong direction, but it very well could be that the design is noisy. You may get lucky and have found a real gem (and I hope that is the case), but for a 3-channel amplifier board, I personally wouldn't expect a whole lot for $12.
    Originally posted by Wolf View Post
    Some amp builders ground the pot-cases to avoid noise too. Other than that- I agree that it could be a too high of resistance pot, and better wire routing could improve it. It's amazing what different routing of wires can do....
    Later,
    Wolf
    I have an amp board not wired as in the pic, laying bare on the bench using the built-in rear plugs for input signal and power. The only wires in use are the three for the sub volume pot. 3 inches long or so. When I short the two that would be shorted by the jumper, it's quiet and functions fine, but of course then the sub volume is too loud.

    I had a very high quality ALPS pot (50k) that I hooked up real quick just to see if it made a difference, the whining sound was still there very similar to the PE 50k pot.

    I also wrapped the wires coming from the board to the pot with aluminum foil to see if that may provide some signal shielding -- not the best I know -- but just to see if it helped at all... it didn't. When I get close to touching those wires with my hand the squeal gets louder and if I squish the wires together, louder still, even when wrapped up in alum. foil. On the bright side, I believe that unintended radio transmissions to extra-terrestrials was temporarily thwarted by my attempts with the foil.

    I'll try adding the 5k resistors tonight after work since I don't have a 10k pot available. Also... You meant between pins 1 and 2, and then between 2 and 3 right?

    One more thing to add just fyi... when I kill the power, the whine goes quickly up in pitch like a sine sweep until it's not audible, takes like 2 seconds.

    Thanks again guys for the help. I'll post up what happened as soon as I can try it out.

    TomZ

    Leave a comment:


  • Wolf
    replied
    Re: Any issues not using ground lead on potentiometer?

    Some amp builders ground the pot-cases to avoid noise too. Other than that- I agree that it could be a too high of resistance pot, and better wire routing could improve it. It's amazing what different routing of wires can do....
    Later,
    Wolf

    Leave a comment:


  • 1100xxben
    replied
    Re: Any issues not using ground lead on potentiometer?

    Again, I will say that without a schematic or the board in hand, this is all a "shot in the dark". IF the reason for the noise is related to having the pot in place, then there's noise coupling on to the signal path. When you use something like a 50k pot, you have a very high impedance to ground (especially when the wiper is in the middle). A very weak signal radiating onto the path can easily create the necessary voltage for you to hear it. If you decrease the impedance to ground, by using a 10k pot for example, then it requires a stronger radiated signal to create a voltage on that line and the noise may be reduced. If you don't have a 10k pot laying around, you could always put a 5k resistor between pins 1 & 2 and a 5k resistor between pins 3 & 4. This would simulate a 10k pot with the wiper right in the middle. This would at least help verify where the issue might be coming from.

    I hope we're not headed in the wrong direction, but it very well could be that the design is noisy. You may get lucky and have found a real gem (and I hope that is the case), but for a 3-channel amplifier board, I personally wouldn't expect a whole lot for $12.

    Leave a comment:

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