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Any issues not using ground lead on potentiometer?

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  • HiTechHillBilly
    replied
    "If you are unable to figure out where the hum/noise originates, then it's time to bust out your oscilloscope and start looking for the source of the problem"

    The problem is the local oscillator in the chip(s) getting back into the sub input. The added pot/wiring is acting as an antenna with no filtering on the board to stop it.

    The RC filter I added is a low pass filter and will only allow ~800 Hz and below to get into the amp. The oscillator on the chip(s) can be anywhere between 376 to 1278 KHz. The mod really cleans the amp up and is totally silent. I've modded several with great results..

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  • HiTechHillBilly
    replied

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

    I used the 10k audio taper pot from PE and wired it in. The noise is still quiet enough to be a non-issue.

    Funny thing is, grounding the pot or not really had no difference. I wired it in off of the alum. plate, ran it, then grounded the pot body to the 12v (-) and there was no difference in sound.

    Also, I've been playing some bass-heavy tunes for over a half hour at close to full volume with the sub at 90% and the heatsink doesn't get more than 6-7 degrees warmer than the rest of the objects on the workbench. The PS I've mostly been using is a 16v 4.5 amp Switching unit by the way. This PS sounds cleaner than the 12v 5 amp one, has more oomph.

    So, at any rate, it looks like I have a working solution to the whine issue.

    Thank you guys very, very much for the help.

    TomZ
    Last edited by tomzarbo; 05-22-2015, 07:17 PM. Reason: added heat sink info

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

    Quick update...

    This morning I soldered the resistors to the subwoofer pot on the alum. board mounted project. I turned it on expecting to need to ground the sub pot to the 12v (-) terminal, but the noise was again, basically gone. I did run a wire by hand to try and ground the sub pot to the 12v (-) terminal on the amp board, but when I did, the tiny and acceptable amount of remaining noise was not reduced.

    Here's what I think is happening...

    The subwoofer potentiometer is making contact with the alum. plate it is mounted in which is also making contact with the 12v (-) side of the power input jack which is also mounted to the alum. plate, thus essentially grounding the sub pot to the 12v (-) side of the amp board.

    I made no attempts to get a good ground on the alum. plate as I mounted any of the components. I just drilled the holes, cleaned the little shards of aluminum that were sticking out of the plate, and went from there.

    Here's what I think I should do from this point to be sure this will be a noise free project:

    When I get the new 10k pots hopefully tonight after work, solder the wires from the existing alum plate project to that pot free standing, not mounted to the alum. plate.
    Then if I still get the whine, I will ground that pot to the alum plate and/or the 12v (-) on the amp board to see if that fixes it.

    I just checked for continuity between the 12v input power jack casing and the outer negative (-) terminal and there is continuity, so mounting that jack does connect the 12v (-) to the alum. body if there is good contact.

    It sounds like I may just need to make sure there is a good metal to metal contact between the sub pot and the alum. plate, as well as the 12v input jack and the alum. plate. if my assessment is correct.

    If I get the parts in tonight, I'll test this out and report back...

    Again, thanks everyone for your continued input. I appreciate the much needed help!

    TomZ

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

    You have three wires from circuit board to pot, I'd twist them all together.
    AE, would that help with the noise issues? I'm new to this stuff, would you mind explaining a little on why that might help so I could understand things a bit better. I've seen this done before, but didn't know why.

    Thanks,
    TomZ

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

    Originally posted by tomzarbo View Post
    I just tried the other amp mounted on a sheet of 1/8" thick ABS and the amp made the same noise on the sub channel, loud when the sub pot was turned down, and it got slightly quieter when turned up, then quiet when all the way up. Could it just be a fault in this amp design? Two out of two amps present with the same symptoms.

    On that amp I went direct in with the power and inputs (used on-jack plug-in connectors)

    TomZ
    On one of the original S5 tube amps, there were several hum and noise issues. One of the fixes was to run a ground wire from the actual potentiometer body to the circuit ground.

    You have three wires from circuit board to pot, I'd twist them all together.

    If you are unable to figure out where the hum/noise originates, then it's time to bust out your oscilloscope and start looking for the source of the problem.

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

    Originally posted by Gordy View Post
    I have read the thread and could not find or maybe I missed it but the pot needs to be grounded to the amp. Using the aluminum mounting plate is only adding to your issues. I have been though this exercise several times. Touch a wire to the metal case of the pot and the ground of amp input. See if that works. With issues like this that I have had this has pretty much solved it.

    Find a flat metal spot on the pot. Use sand paper to rough the surface up. Solder a wire to it. run that wire to the negative input on the amp. start their.

    Also dump the aluminum plate. You are mounting the pot's metal shaft to a metal plate with a metal power input and a possible metal collared 3.5mm input that is not isolated then you will get noise. Anytime I mount a power input with either a pot or 3.5mm line in I always use a plastic plate. I found these from Erse work well and are plastic.

    http://www.erseaudio.com/Products/TerminalCups/TC9

    http://www.erseaudio.com/Products/TerminalCups/TC-5
    Gordy, I appreciate your input.

    I had some concerns going with an alum. plate because of the issues you mentioned. I will try the resistor and grounding fixes on the alum. plate version and see if it works. If the power in is grounded, that's probably not a big deal since the negative on the 12v is getting grounded anyway... the input as you mentioned is another thing. I'll see if what I've mentioned works okay or not. Hopefully it will.

    TomZ

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

    Originally posted by tomzarbo View Post
    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. TomZ
    I have read the thread and could not find or maybe I missed it but the pot needs to be grounded to the amp. Using the aluminum mounting plate is only adding to your issues. I have been though this exercise several times. Touch a wire to the metal case of the pot and the ground of amp input. See if that works. With issues like this that I have had this has pretty much solved it.

    Find a flat metal spot on the pot. Use sand paper to rough the surface up. Solder a wire to it. run that wire to the negative input on the amp. start their.

    Also dump the aluminum plate. You are mounting the pot's metal shaft to a metal plate with a metal power input and a possible metal collared 3.5mm input that is not isolated then you will get noise. Anytime I mount a power input with either a pot or 3.5mm line in I always use a plastic plate. I found these from Erse work well and are plastic.

    http://www.erseaudio.com/Products/TerminalCups/TC9

    http://www.erseaudio.com/Products/TerminalCups/TC-5

    Leave a comment:


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

    Originally posted by [email protected] View Post
    Why not just get more resistors and forget the pot all together.
    Because if I don't actually physically use the 10k pot I won't be able to feel 100% sure that it will work as expected. Judging from this thread I suspect there may be others who would like to duplicate this.

    http://techtalk.parts-express.com/sh...ighlight=micro

    If I can be sure the noise is gone for sure this will make a really nice micro-sized setup for most of the small speakers/subwoofers that are available. Even though 8 ohm drivers are suggested I was using it with a set of Neo Nanos and a Voxel sub... both 4 ohms if I'm not mistaken... and the heat sink never even got warm, even at fairly loud volumes, playing for several minutes. This was with both a 12v and 16v power supply, I think 18v is the max recommended.

    At this point, I'm going to try just grounding the sub volume pot to the negative 12v on the amp board. If that does it, then I won't fiddle with any more grounding at that point.

    TomZ

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

    Originally posted by craigk View Post
    your diagram is not a correct representation of what a star ground is.
    This is exactly my point...

    You suggested to try a star grounding scheme:
    Originally posted by craigk View Post
    since nothing is working try star grounding.
    Tom suggested what I drew in my diagram above:
    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....
    You informed him that his idea of creating a start ground was correct:
    Originally posted by craigk View Post
    you have the correct idea. I hope it works.
    I was simply trying to show that this method is not truly creating a star grounding scheme and would most likely create a ground loop.

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  • arlis_1957@yahoo.com
    replied
    Re: Any issues not using ground lead on potentiometer?

    Why not just get more resistors and forget the pot all together.
    No star ground is possible as no ground wire goes to the amp. Its a wall wart with just plus and minus.

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

    Originally posted by 1100xxben View Post
    If you're going to start randomly grabbing "ground" points of a circuit and connect them to another common point (star ground), then you first need to check continuity between them and verify they are not already connected. If they are already connected and you pull off your own "ground" wires to another common point, you will quite possibly end up with ground loops.

    Ground loops do not always occur between two different "devices". Ground loops can easily occur within a single piece of electronics, and even within a single circuit board if the grounding scheme is not designed properly. Ground loops through the ground wire in your house will generally cause a 50/60 Hz issue, but they can easily occur at any frequency when you're dealing with inter-device ground loops.

    Here is a rough picture of how I'm guessing the circuit (the relevant portion of the circuit) is laid out, and why tying the input power ground to the aluminum plate AND the "potentiometer ground" to the aluminum plate is a bad idea. Adding both of the red wires will create a ground loop. Now, tying the case of the pot to a ground potential at some point should be just fine, as long as it's completely isolated from any other ground point.
    [ATTACH=CONFIG]57496[/ATTACH]
    your diagram is not a correct representation of what a star ground is.

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

    Originally posted by 1100xxben View Post
    Just to clarify something here... When you say "negative, on the amp board", are you referring to the negative speaker output? If so, you should never tie the speaker output negative to anything unless you know for sure exactly what type of amplifier output stage you have. I would bet money that these boards are a bridged output, which means the negative speaker output is being driven and is anything but ground.
    What I meant by "negative on the amp board" was where the (-) side of the 12v in from the power supply comes in. I did not do any grounding to the speaker outputs.
    There doesn't seem to be any place on the amp board to 'ground' anything. I've seen plenty of amp boards where the mounting holes on an amp board will have an uncoated portion around the hole that has exposed metal that is meant to be a 'grounding' point, but this amp board doesn't have that... so I picked the 12v (-) point to ground the amp board to.

    Attempting to ground the main volume on-board pot to ground did nothing to reduce the noise.

    The tweaks I tried last night were on the raw board... I have not yet done this to the version that is mounted on the alum. plate. It was getting late and I already goofed up on the resistor values... I didn't want to mess something else up potentially worse.



    I'm having two of each of the above listed 10k pots overnighted and as soon as I get them, I'll take the 50k pot out of the alum. plate project and replace with the 10k, as well as ground that pot to the 12v negative terminal on the amp board. Hopefully there will be a similar noise reduction.

    I have another amp board coming and will construct another plate amp on another alum. plate I have with the new 10k pot. If both re-do's are good, then I'll believe we have the problem licked. Fingers crossed...

    Thanks you guys for the guidance and help.
    I'll be sure to post up what happens when I get the parts in.

    Gracias,

    TomZ

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

    Originally posted by tomzarbo View Post
    ... the sub pot, negative side of the power supply input, negative, on the amp board, etc...
    Just to clarify something here... When you say "negative, on the amp board", are you referring to the negative speaker output? If so, you should never tie the speaker output negative to anything unless you know for sure exactly what type of amplifier output stage you have. I would bet money that these boards are a bridged output, which means the negative speaker output is being driven and is anything but ground.

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

    Originally posted by craigk View Post
    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.
    If you're going to start randomly grabbing "ground" points of a circuit and connect them to another common point (star ground), then you first need to check continuity between them and verify they are not already connected. If they are already connected and you pull off your own "ground" wires to another common point, you will quite possibly end up with ground loops.

    Ground loops do not always occur between two different "devices". Ground loops can easily occur within a single piece of electronics, and even within a single circuit board if the grounding scheme is not designed properly. Ground loops through the ground wire in your house will generally cause a 50/60 Hz issue, but they can easily occur at any frequency when you're dealing with inter-device ground loops.

    Here is a rough picture of how I'm guessing the circuit (the relevant portion of the circuit) is laid out, and why tying the input power ground to the aluminum plate AND the "potentiometer ground" to the aluminum plate is a bad idea. Adding both of the red wires will create a ground loop. Now, tying the case of the pot to a ground potential at some point should be just fine, as long as it's completely isolated from any other ground point.
    Click image for larger version

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