Any issues not using ground lead on potentiometer?

[tomzarbo]

I've been working with this 2.1 amp board:

http://www.parts-express.com/21-hi-f...8-vdc--320-608

And I'm having a problem with a high pitched whining noise coming from the .1 subwoofer channel.

I originally had the pot hooked up backwards I think, I reversed the in and out leads coming from the sub section. It used to make the whining noise all the time except when the pot was turned almost all the way up. Now after fixing the wiring, it makes a whining noise all the time except when the pot is at almost full volume or almost completely turned down; but anywhere in the middle where you would likely need it to be, it whines... kind of like where you can hear alternator noise coming through a car stereo.

So the next thing I was thinking of trying is to cut the ground line on the pot. I'm thinking that possibly there are ground issues floating around (see what I did there? ;) and if I cut the ground line it may mitigate the issue. I think this board is susceptible to ground/noise issues from the reviews I've read.

The 2 channel part of the deal is working fine, very well in fact. I like the amp board a lot and think that the fidelity is pretty good as well. When turned up all the way, the .1 section sounds nice and is working the voxel sub nicely.

By the way, the board is mounted on an alum. plate; but when I remove the subwoofer pot from the board it still does the same thing.

When I get home I'm going to clip the ground line, but if that doesn't work... Any other ideas?

Thanks,
TomZ

[1100xxben]

Re: Any issues not using ground lead on potentiometer?

Can you post a wiring diagram of how exactly you have the pot connected? The "ground" is kinda necessary for the unit to work correctly. Assuming the pot is just an inline voltage divider in the signal path: If you remove the connection from the pot to signal ground, then all you're doing is adding a variable series resistance to the signal and will probably only be able to adjust the subwoofer volume from full to something like -10dB. The pot needs the ground connection to make a proper, fully-adjustable voltage divider to give a range from full power to mute.

[tomzarbo]

Re: Any issues not using ground lead on potentiometer?

Sure, thanks. I can post a sketch and a pic when I get home.

[craigk]

Re: Any issues not using ground lead on potentiometer?

Sure, thanks. I can post a sketch and a pic when I get home.

are you sure what you are calling the ground on the pot is the ground ?

[tomzarbo]

Re: Any issues not using ground lead on potentiometer?

Here is a drawing I just made that explains how I wired it and some pics:









Keep in mind that I switched the blue and black wires on the Pot, They're not what it shows in the pic...I think I had them reversed. Also, there was a plastic connector covering the three pins just like the two-conductor connector to the left of it. I pulled it off and soldered directly to the pins. No connector cable was included with the amp. I did use heat-shrink on all the solder joints afterward.

Truth is, since there is no documentation with this amp board, I'm kind of winging it. Reading from Rory's answer to a question asked about it:

The two-pin connector at the front corner of the board activates a low-power "standby" mode when the two pins are shorted. The three-pin connector adjacent to that (with one jumper installed between pins 2 and 3) is there to allow an external bass level control potentiometer to be installed. (50k audio taper should work fine; remove the jumper first.) The potentiometer on the board is an overall volume control (affects both the subwoofer and main outputs).

So, I assume the left amp connection would be ground, the middle would be variable, and the right the power side. With the two left pins shorted there is no noise.

I'm wiring the pot going from this pic:



I tried removing the 'ground' line, the green one on my work, and it did nothing to remove the squeal.

The squeal does not increase with 'main' volume adjustment. It goes from bad to moderate to gone as you adjust the sub pot from minimum to maximum. The stereo part of the amp is fine-no noise at all, and pretty dang nice sounding.

I just switched from a 12v 3 amp to a 16 volt 4 amp PS and same issue. They're both SMPS's though, don't think I have one that isn't. That's pretty much what anyone would use anyway.

I'm stumped.

I have another amp partially assembled, I'm going to take that apart and wire it on a plastic board to see if the metal plate everything is mounted to could possibly be the issue. I need to get this figured out soon if possible. I also have yet another board on the way to make double sure everything is working fine once I get the issues ironed out.

Thanks for any help.

TomZ

[tomzarbo]

Re: Any issues not using ground lead on potentiometer?

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

[1100xxben]

Re: Any issues not using ground lead on potentiometer?

Without any paperwork on what you've got, or being able to probe it out myself, it's tough to say. It appears you have everything wired correctly, although your wire routing could be improved. You have your power input wire running directly across the pot wires, which is not the best idea. You could also try using a lower resistance pot, which might help eliminate any noise it is picking up. Have you tried the amp with the jumper on the right two pins (sub out at full volume). Maybe you just have a bad board?

[tomzarbo]

Re: Any issues not using ground lead on potentiometer?

Without any paperwork on what you've got, or being able to probe it out myself, it's tough to say. It appears you have everything wired correctly, although your wire routing could be improved. You have your power input wire running directly across the pot wires, which is not the best idea. You could also try using a lower resistance pot, which might help eliminate any noise it is picking up. Have you tried the amp with the jumper on the right two pins (sub out at full volume). Maybe you just have a bad board?

The one on the alum plate with the jumper attached (or the equivalent of it, wires shorted) was quiet. The other board now loose on the workbench is still noisy even with the two wires shorted. That setup is touchy when you touch the pot or any of the solder terminals... or even the wires that run to it, it will hum in varying degrees depending on how hard you grip the three wires with your fingers.

I can re-do some of the power lines if that helps, but on the other amp board I just used the rear mounted plugs without any wiring at all and it is still doing the same thing.

Lower resistance pot? I'm using PE's 50k log pot: http://www.parts-express.com/parts-e...meter--023-550

I was going to use the audio taper one but it was out of stock. This one actually seems to work well and the gain rate is progressive enough to make me happy. Could the pot be picking up noise? and how does it's resistance factor into it? Could you describe how that works a little please if you could. I'm not questioning the validity of what you're saying, I am just a little new to these types of problems and don't know where the possible solutions might be. Thanks for taking the time to help me, I appreciate it a lot.

I was attempting to use all PE parts for this project, but if there is a better pot option that will cut the noise, I'll look at it. I also thought that perhaps shielding the wires running from the pot to the board with alum. tape for some shielding may help, but in moving those wires all around the board there was no shift in the whining noise, so I'm guessing that won't help a lot.

I have another board coming in a few days; I can see how that one performs. If I have problems with that one as well, I think I may start leaning towards there being a problem with the board itself or it's design. I'll wait to see first, though.



It's a shame if that's the case. It's almost comical how loud this setup was getting with a pair of Nano Neo's and a Voxel sub. Real sonic performance for a dozen dollars and a quarter. Hope I can make this project work.

Thanks again,
TomZ

[1100xxben]

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.

[Wolf]

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

[tomzarbo]

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.

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

[craigk]

Re: Any issues not using ground lead on potentiometer?

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.

[1100xxben]

Re: Any issues not using ground lead on potentiometer?

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.

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 .

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.

[1100xxben]

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.

[PWR RYD]

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.