Capacitor to eliminate speaker hum

[audioguru]

It is too bad that your AC-DC adapter is the high frequency polluting type that is not completely isolated like a low frequency transformer type.

 

[rjenkinsgb]

Also, if the adapter would have had a third grounding wire, could I have eliminated the buzz by joining power negative and power ground at the beginning of the chain, before sending those wires to the amplifiers? If not, could this have been handled differently just using one plug?

If it was a power adapter with a trailing lead and AC plug as opposed to a "wall wart" type that plugs in directly, you could have changed the plug to a screw terminal one and added the amp ground cable to the ground pin.

The plug ground could be linked to the power adapter output negative to avoid the floating problem, as you say.

 

[Hacdrag]

If it was a power adapter with a trailing lead and AC plug as opposed to a "wall wart" type that plugs in directly, you could have changed the plug to a screw terminal one and added the amp ground cable to the ground pin.

The plug ground could be linked to the power adapter output negative to avoid the floating problem, as you say.

This is what I purchased:

https://www.amazon.com/dp/B09CKTJ96N?ref=ppx_yo2ov_dt_b_product_details&th=1

I'm assuming this is a power adapter with a trailing AC lead. If so, I'm assuming I can save an outlet by slightly modifying the current setup. I can buy another one, (this time keep the RF choke in place )change the plug to the one I purchased, send positive and negative to the appropriate screws, then split the other end of negative, sending one wire to the amplifier inputs, and the other to the ground pin of the plug.

Wow, I'm having fun with this.

Please confirm that this alternate plan would work, as I believe it is what you are describing, however, there is no amp ground plug.

 

[rjenkinsgb]

OK, you could either change the plug on the AC cable and add the ground wire to that, or get a pair of C13/C14 connectors and make a very short link cable to go at the PSU block end, with the ground wire added in to that - slightly more expensive but neater, as no extra wire at the wall plug end.
eg.

1 Pair C13 IEC Rewirable Male & Female Inline Socket Plug 10A 250V 3 Pin Kettle 7625881808465 | eBay

Product Range: IEC Series. Complies with IEC 60320-1:2001(2nd Edition)+A1:2007. Gender: Socket. Repairing a cable or for install when the cable need to be threaded through a hole or trunking. Connector Mounting: Cable Mount.

www.ebay.co.uk

Having cut the ferrite sleeve off the DC power cable should not matter, just join the ground anywhere on the DC negative side.


I'm unsure of what you are describing, eg.

send positive and negative to the appropriate screws,

You existing power supply positive and negative go to the wago terminal blocks, then on to the amps.

The wires at the wall plug end, 120V or 240V mains AC, are Live (aka Line, in the USA), Neutral and Earth (ground).

Positive and negative are the 12V DC side of the power unit.

I don't know if you mean screws in the Leviton plug you were buying [bad], or the amplifier boards [good].
(Just for safety, I want to be 100% sure there is no possible confusion between the AC and DC sides of the power supply).

 

[Hacdrag]

I don't know if you mean screws in the Leviton plug you were buying [bad], or the amplifier boards [good].
(Just for safety, I want to be 100% sure there is no possible confusion between the AC and DC sides of the power supply).

My writing is a bit convoluted sometimes. This should explain my plan better:

Take my current setup:

Remove the existing wall wort PSU completely and remove the set of positive and negative wires that were going from the PSU into the master end of the terminal block. Take my Leviton out of the outlet, and remove the negative wire from the grounding screw. Cut off the plug end of this (https://www.amazon.com/dp/B09CKTJ96N?ref=ppx_yo2ov_dt_b_product_details&th=1) and replace it with the Leviton by wiring the positive and negative wires from the lead wires that came with the above linked PSU to the positive and negative screws in the Leviton. On the other end of the leads, connect the positive wire to the terminal blocks in the same fashion that I use now, which gets sent to the power positive inputs of both amp boards. Do the same with the negative lead, but use a second terminal block to make a second split, and from the output of that negative, connect another wire and connect it to the ground screw of the Leviton. Then, plug the Leviton into an outlet. I already have a second terminal block which I use for the current negative split. Please see the attached which shows the setup without one set of wires connected. Currently, I use a second wire to go from positive to positive between terminal blocks, before getting the other two positive wires to the power positive inputs of the amp boards.

I thought this would work, as I'm just replacing a PSU end negative wire going into a separate plug's ground screw, with a different PSU's negative end going into its plug's ground screw; the only difference is that in this plug I'll already have positive and negative wired to the appropriate screws.

So, assuming I explained my plan clearly enough, is the workable and safe?

See the terminal block on the right. I'd connect power positive to the red slot on the right, and then on one of the left red slots, connect a short wire to one red slot on the other terminal block. This gets to the power positive inputs of both amps. On the terminal block on the right, I'd connect power negative to the blue slot, then on one of the left blue slots, connect another short wire to the blue slot of the other terminal block. This gets to the power negative inputs of both amps. On the second blue slot on the left side of the terminal block on the right, I'd connect another wire, and then connect the other end to the ground screw of the Leviton, which would already have the positive wire of its own lead connected to the positive screw, and the negative wire of its own lead to the negative screw.

I think I described my plan clearly enough now to get a definitive answer. Will this work and be safe? I have no problem keeping my existing setup; I just find it a little odd to have a second, dedicated plug just for ground, and if my proposed solution works, I'd prefer to use it.

 

[rjenkinsgb]

Cut off the plug end of this (https://www.amazon.com/dp/B09CKTJ96N?ref=ppx_yo2ov_dt_b_product_details&th=1) and replace it with the Leviton by wiring the positive and negative wires from the lead wires that came with the above linked PSU to the positive and negative screws in the Leviton.

Again:

The wires at the wall plug end, 120V or 240V mains AC, are Live (aka Line, in the USA), Neutral and Earth (ground).

Get the naming correct, please! to avoid possibly lethal confusion:

A 120V / 240V wall plug does not have positive or negative, it has live (aka line or hot) and neutral (or possibly two live pins, for a US 220/240V one).

Positive and negative are strictly at the low voltage DC end of the PSU.


US type power outlet socket pin identification:

 

[Hacdrag]

Again:


Get the naming correct, please! to avoid possibly lethal confusion:

A 120V / 240V wall plug does not have positive or negative, it has live (aka line or hot) and neutral (or possibly two live pins, for a US 220/240V one).

Positive and negative are strictly at the low voltage DC end of the PSU.


US type power outlet socket pin identification:

I'll rephrase:

Cut off the plug end of this (https://www.amazon.com/dp/B09CKTJ96N?ref=ppx_yo2ov_dt_b_product_details&th=1) and replace it with the Leviton by wiring the positive lead into the Brass screw (hot/live) of the Levitron, and then wiring the negative lead into the silver screw (neutral) of the Levitron, and then wiring the second negative lead info the green screw (ground) of the Levitron.

My Levitron, as shown, doesn't have different colored screws for hot/live and neutral, but with the ground pin facing downward, the screw on the right is associated with the pin that would plug into the narrow slot in the wall, so that one must be hot/live.

Is this correct?

 

[rjenkinsgb]

wiring the positive lead into the Brass screw (hot/live) of the Levitron, and then wiring the negative lead into the silver screw (neutral) of the Levitron, and then wiring the second negative lead info the green screw (ground) of the Levitron.

You do not connect positive or negative to an AC power plug.

The 120V or 240V cable to the power supply will have either black & white (or brown & blue, depending where its made) for LIVE and NEUTRAL respectively.
Plus green or green & yellow for ground/earth.

Sorry, but I cannot confirm anything as long as you use terminology that confuses the 12V DC side with the mains AC side, as I'm not sure what you are intending to do.

 

[Hacdrag]

You do not connect positive or negative to an AC power plug.

The 120V or 240V cable to the power supply will have either black & white (or brown & blue, depending where its made) for LIVE and NEUTRAL respectively.
Plus green or green & yellow for ground/earth.

Sorry, but I cannot confirm anything as long as you use terminology that confuses the 12V DC side with the mains AC side, as I'm not sure what you are intending to do.

I'm more awake now then when I composed my last reply, so I'll try and get all the terminology correct. The cable to my power supply only had two wires. I don't remember the color convention, but it was easy to verify with my multimeter which was live, and which was neutral. When I plugged the power supply in, and I touched the red multimeter lead to the live wire and the back multimeter to the neutral wire it measured 12.25V. Reversing the connections resulted in a measurement of -12.25V. So, this is what I'd like to do:

Connect the live wire to the hot/live screw of my Levitron. Connect the neutral wire to a conductor terminal block. Connect two wires to the opposite same-colored side of the terminal block. Connect the other side of one of those wires to the neutral screw of my Levitron. Connect the other side of the other wire to the ground screw of my Levitron.

Is this workable and safe?

 

[rjenkinsgb]

When I plugged the power supply in, and I touched the red multimeter lead to the live wire and the back multimeter to the neutral wire it measured 12.25V. Reversing the connections resulted in a measurement of -12.25V. So, this is what I'd like to do:

That does not make any sense, sorry.

The 120V volt side has live and neutral.

The 12V side has positive and negative.

 

[audioguru]

You still have the connections wrong.
Live and neutral are 120VAC.
+12.25V and 0V are the DC output.

The amplifier creates hum when the switching power supply is used because the 0V of the amplifier must be connected to an earth ground.

Do not connect the amplifier 0V to the electricity neutral because the receptacle might be wired backwards causing your amplifier and things connected to it to be 120VAC live.

 

[Hacdrag]

I wired it up with the last known working no hum configuration, which has power negative split between power negative inputs of both amp boards and the ground screw of the Levitron plug, with nothing else connected to any of the other screws in the Levitron plug. I'll have to live with the oddness of having two plugs for the setup.

I do remain confused regarding my proposed alternative setup but have given up trying to fully understand it for now.

I very much appreciate all of the diligence and concern for safety, as well as all of the informative replies.

 

[SWISL]

My stereo Bluetooth project is almost perfect, but when I switched from 9-volt batteries to an AC wall adaptor, this introduced a little bit of hum into the speakers. It's not that bad, but I'm wondering if I could eliminate it altogether by placing a small value capacitor between the power supply and the amplifiers.

What's the recommended way to handle this?

Ty

Likely the output of the wall wart is DC. 1) if the blades of the AC outlet side are the same width turn it around in the outlet. I have personally seen this help. 2) Try a different wall wart with same dc voltage and current rating. 3) try adding a separate ground wire from the chassis of the device to a known ground in the area. I’m not a big fan of reinventing the wheel (I.e. redesigning the power supply). I’m surprised it isn’t rechargeable but hey, you walk with the shoes you got, or something like that…

 

[audioguru]

The AC adapter must have a DC output to power an amplifier.
Placing a capacitor between the adapter and the amplifier will block the DC then the amplifier will not work.

Instead, place a high value capacitor (1000uF or more) parallel to the DC adapter's output as a filter.

 

[Hacdrag]

I solved this back in June. See my post two replies back. Here is a paste of the relevant info:

I wired it up with the last known working no hum configuration, which has power negative split between power negative inputs of both amp boards and the ground screw of the Levitron plug, with nothing else connected to any of the other screws in the Levitron plug.

The Levitron plug goes into a wall socket.

No more hum, even if I bypass the Bluetooth receiver, and directly connect an audio source via a 3.5 mm audio jack.

Happy to see more replies, but I eliminated the speaker hum without using a capacitor. Looks like my power negative hack eliminated the ground loop, which is why there is no more hum.

I'm always learning from posts, but don't need any more help here.