TT Hum

[cpd]

Hoping you all can help me solve a humming issue. I just had some built in cabinets with dimmable LED lights installed for my records/TT.
In the new cabinets, I have a Project Debut Carbon TT hooked up to the phono input of a ‘70’s Marantz receiver with a pair of BJC RCA cables with a ground connector. I use the Marantz as a pre-amp running a set of monoprice RCA’s from the Tape Out to my Denon home theater receiver. The monoprice RCA’s exit the back of the cabinet to a 3/4” inaccessible space between the wall and the back of the cabinet. From there they go down into a drywall covered box the cabinet sits on top of. The wiring for the lights comes up the same hole. The monoprice RCA is 50’ long (probably only need about 15’).

When the phono input on the marantz is selected, I get a hum from my home theater speakers whenever I turn the cabinet light on. The hum goes away when I turn the Marantz to any other input (none of them are connected), or when I turn the lights off.

I’m not sure if I should try to run a better and shorter interconnect? Or do the ground loop hum eliminators your see online work?

Any thoughts would be appreciated.

 

[Swerd]

It sure seems the hum comes from the power line for the dimable LED lights. I doubt if the hum comes from a ground loop. If the lights are off, the hum is gone.

You mentioned the RCA cable going from the Marantz stereo receiver to the Denon AVR is 50 feet long. That's very long, but the real problem is that it runs parallel to the power line for the LED lights. The RCA cable carries AC music signals at line level voltage – about 100 to 200 mV – and the power line for the lights carries AC power – 60 Hz 120V and about 15 amperes if you're in the USA. No matter how well shielded the RCA cable is, that strong AC power will interfere with the much weaker turntable music signal, generating that hum.

Find a way to run those two lines so they aren't near each other. As little as six inches apart may be enough to make a difference. Never let them run adjacent and parallel. If they must cross, cross them at a 90° angle.

Just curious, how long is the RCA cable going from the turntable to the phono inputs of the Marantz receiver? It carries a much weaker signal, about 5 mV, and is even more prone to interference. Is it also near an AC power line? Usually these phono lines are hardwired to the turntable, and I hope its no longer than about 3 feet, or 1 meter. (Some modern turntables that include an internal phono preamp come with RCA jacks instead of hardwired cables.)

 

[cpd]

It sure seems the hum comes from the power line for the dimable LED lights. I doubt if the hum comes from a ground loop. If the lights are off, the hum is gone.

You mentioned the RCA cable going from the Marantz stereo receiver to the Denon AVR is 50 feet long. That's very long, but the real problem is that it runs parallel to the power line for the LED lights. The RCA cable carries AC music signals at line level voltage – about 100 to 200 mV – and the power line for the lights carries AC power – 60 Hz 120V and about 15 amperes if you're in the USA. No matter how well shielded the RCA cable is, that strong AC power will interfere with the much weaker turntable music signal, generating that hum.

Find a way to run those two lines so they aren't near each other. As little as six inches apart may be enough to make a difference. Never let them run adjacent and parallel. If they must cross, cross them at a 90° angle.

Just curious, how long is the RCA cable going from the turntable to the phono inputs of the Marantz receiver? It carries a much weaker signal, about 5 mV, and is even more prone to interference. Is it also near an AC power line? Usually these phono lines are hardwired to the turntable, and I hope its no longer than about 3 feet, or 1 meter. (Some modern turntables that include an internal phono preamp come with RCA jacks instead of hardwired cables.)

The turntable to Marantz RCA is 3 feet. It will be difficult, if not impossible to run the RCA to the Denon apart from the electrical wire. The cabinets are installed and there is not much space for running the cables.

It makes sense that it’s interference from the lighting wires, since it only hums when the lights are on. But then why wouldn’t you hear the hum on any other input on the Marantz? For example, using the tuner on the Marantz, there is no hum.

 

[TLS Guy]

The turntable to Marantz RCA is 3 feet. It will be difficult, if not impossible to run the RCA to the Denon apart from the electrical wire. The cabinets are installed and there is not much space for running the cables.

It makes sense that it’s interference from the lighting wires, since it only hums when the lights are on. But then why wouldn’t you hear the hum on any other input on the Marantz? For example, using the tuner on the Marantz, there is no hum.

LED lights are notorious for this. LEDs especially on dimmers produce a huge amount of radio interference. I would get rid of the dimmer this will greatly reduce the RF interference. If you absolutely can not get rid of the dimmer, then replace the dimmer with a Lutron Maestro dimmer. I had a hand in improving this series. To my surprise Lutron worked closely with me. The light will not dim as much. Unfortunately as you reduce RF radiation the dimming ability of the dimmer is somewhat impeded.

If you get the buzz with no dimmer then it is no light for you are you bite the bullet and separate the cables. One other option is to use Halogen lights, but you will need a different dimmer, again a Lutron maestro as SCR dimmers of all types radiate some RF. There are no other solutions, so don't waste time looking for them. One last point make sure the dimmer is the Lutron for LEDs. Dimmers for LED light and incandescent need to be of a different design.

I have a couple of LED lights in my turntable case but would not dream of putting them on dimmers, that is asking for trouble.

 

[highfigh]

If you turn the LED lights off, do you hear the hum? Can you shut off the power to the lights and not to the audio system? If not, use an extension cord to power the audio system and try it with AND without the lights being powered. If it hums with no power to the lights, you may need to reassign the audio system's power in the breaker panel, at least at one end. If the lights and audio system are on the same circuit, it's probably not going to be an easy fix.

 

[TLS Guy]

If you turn the LED lights off, do you hear the hum? Can you shut off the power to the lights and not to the audio system? If not, use an extension cord to power the audio system and try it with AND without the lights being powered. If it hums with no power to the lights, you may need to reassign the audio system's power in the breaker panel, at least at one end. If the lights and audio system are on the same circuit, it's probably not going to be an easy fix.

He already stated the hum goes away when he turns the light off.

He has also made the unforgivable mistake of having vital wiring inaccessible. He needs to redo it and place tech tubes for his wiring.

Tech tubes and or other forms of conduit keep wiring accessible.

NEVER place any audio cable in a way that it can not be easily replaced.

 

[highfigh]

It seems that the cause is the fact that the RCA cable and power wiring pass through the same hole, which is a cardinal mistake.

Does this place have a crawl space or basement?

 

[cpd]

LED lights are notorious for this. LEDs especially on dimmers produce a huge amount of radio interference. I would get rid of the dimmer this will greatly reduce the RF interference. If you absolutely can not get rid of the dimmer, then replace the dimmer with a Lutron Maestro dimmer. I had a hand in improving this series. To my surprise Lutron worked closely with me. The light will not dim as much. Unfortunately as you reduce RF radiation the dimming ability of the dimmer is somewhat impeded.

If you get the buzz with no dimmer then it is no light for you are you bite the bullet and separate the cables. One other option is to use Halogen lights, but you will need a different dimmer, again a Lutron maestro as SCR dimmers of all types radiate some RF. There are no other solutions, so don't waste time looking for them. One last point make sure the dimmer is the Lutron for LEDs. Dimmers for LED light and incandescent need to be of a different design.

I have a couple of LED lights in my turntable case but would not dream of putting them on dimmers, that is asking for trouble.

That is great info. A follow-up question. Would it be better to replace the bulbs/fixtures with non-LED or replace the dimmer switch with a non-dimmer? Or both? I suppose I would prefer to have dimmable lights but can live with it either way.

 

[cpd]

If you turn the LED lights off, do you hear the hum? Can you shut off the power to the lights and not to the audio system? If not, use an extension cord to power the audio system and try it with AND without the lights being powered. If it hums with no power to the lights, you may need to reassign the audio system's power in the breaker panel, at least at one end. If the lights and audio system are on the same circuit, it's probably not going to be an easy fix.

No. When I switch the lights off there is no hum.

 

[highfigh]

No. When I switch the lights off there is no hum.

Are these on a dimmer?

 

[cpd]

He already stated the hum goes away when he turns the light off.

He has also made the unforgivable mistake of having vital wiring inaccessible. He needs to redo it and place tech tubes for his wiring.

Tech tubes and or other forms of conduit keep wiring accessible.

NEVER place any audio cable in a way that it can not be easily replaced.

Whoa. I didn't realize it was unforgivable! LOL.

It is not that I cannot replace the audio cables, it is that I cannot separate them easily. I have access at both ends, and can certainly fish new wire up there or tie a new wire to the old to pull the new one through. But, there is only so much space behind the cabinet with lighting wires going to different locations so separation between the audio cables and the lighting wiring is not really possible.

At the end of the day, I can always dismount the cabinet and run everything again. Before I do that, however, I would try the switch and fixture ideas you mention before as that is much easier and more accessible.

You mentioned Tech Tubes. Do you have a link? It's possible that I could figure out a way to get conduit around the RCA if the conduit is less than 3/4" OD. That said, did you mention those simply for ease re-installation, or would those provide some shielding from the interference I am getting?

 

[cpd]

Are these on a dimmer?

Yes.

 

[cpd]

LED lights are notorious for this. LEDs especially on dimmers produce a huge amount of radio interference. I would get rid of the dimmer this will greatly reduce the RF interference. If you absolutely can not get rid of the dimmer, then replace the dimmer with a Lutron Maestro dimmer. I had a hand in improving this series. To my surprise Lutron worked closely with me. The light will not dim as much. Unfortunately as you reduce RF radiation the dimming ability of the dimmer is somewhat impeded.

If you get the buzz with no dimmer then it is no light for you are you bite the bullet and separate the cables. One other option is to use Halogen lights, but you will need a different dimmer, again a Lutron maestro as SCR dimmers of all types radiate some RF. There are no other solutions, so don't waste time looking for them. One last point make sure the dimmer is the Lutron for LEDs. Dimmers for LED light and incandescent need to be of a different design.

I have a couple of LED lights in my turntable case but would not dream of putting them on dimmers, that is asking for trouble.

Just doing some quick research and I have one more question. Am I looking for a C.L. Maestro switch or do I want one dedicated only for LED? This is what I see at my Home Depot.

 

[TLS Guy]

Just doing some quick research and I have one more question. Am I looking for a C.L. Maestro switch or do I want one dedicated only for LED? This is what I see at my Home Depot.

That one will do the trick. However with LED and dimmers there is no way to have no RF generated by the system. It can only be reduced and not eliminated.

All SCR dimmers generate RF, as the +ve and -ve deflections are moved apart in time at the zero crossing. The more apart they move the better the dimmer, but the more RF. The maestro dimmers now also incorporate and RF filter, but these are never perfect

Home depot offer a selection of electrical tubing generically known as tech tubes.

I have thought of one more option that would help and that would be to use a good phono amp as close to the base of your pickup arm as possible. This would convert the low level signal to line level as close to the PU arm as possible and that would reduce the "antenna" length of the low level signal that has to have a lot of gain added.

All these measures I have suggested will be additive. So you can add these measures until you are happy with your signal to noise ratio. Small Halogen puck lights get pretty hot and I always concerned about them being a fire hazard. So try and stay with LED cabinet lights if you can, despite the hassle.

 

[Swerd]

The turntable to Marantz RCA is 3 feet. It will be difficult, if not impossible to run the RCA to the Denon apart from the electrical wire. The cabinets are installed and there is not much space for running the cables.

Just to review what has been said above:

You said the power line to the LED lights ran immediately adjacent to the interconnect RCA cable (from the Marantz to the Denon AVR). If so, this is the likely cause of the hum. This would be the case for ANY electrical device. If you remove the dimmer and replace the LED lights with other non-LED lights, you will likely still have the hum as long as electric power runs in that line. Got a photo that shows these two lines as they run along side each other?

TLS Guy is not wrong about interference from LED lighting and/or dimmers used for them, but I think your problem can be eliminated only by moving the RCA cable and lighting power line away from each other. His suggestion of using a tech tube to keep the RCA cable away from the light power line might get the job done. A simple alternative is don't use that light while playing records. There are also small LED lights that rely on battery power instead of AC line power.

It makes sense that it’s interference from the lighting wires, since it only hums when the lights are on. But then why wouldn’t you hear the hum on any other input on the Marantz? For example, using the tuner on the Marantz, there is no hum.

Tuners, including those that are built into receivers, are shielded to prevent such interference. If you have a another separate input device, such as a CD player, and if its connected by an RCA cable carrying analog signals, it would also be subject to hum from the light if it were near enough to the power cable. That is one reason why CD, DVD, and BluRay players connect via a line that carries digital signals. They are not subject to AC line hum or other forms of interference.

 

[highfigh]

Just doing some quick research and I have one more question. Am I looking for a C.L. Maestro switch or do I want one dedicated only for LED? This is what I see at my Home Depot.

You can use Lutron Caseta, too- these work well if you want to automate your lighting with the AV system.

Yes, you can use that Maestro switch because it's made for most kinds of lights but it won't guarantee eliminating the hum- that's probably a proximity issue between the Romex and RCA cable.

If you can't get rid of the hum in a reasonable way ($$$), you could consider using an analog to digital converter and then connecting the output to one of the digital coax inputs on the AVR, via the same coax cable (only one of them).

 

[Swerd]

You said that the tuner in your Marantz stereo receiver does not suffer from the hum problem. That further suggests the hum problem you hear during phono playback is caused by AC power line hum and not radio frequency (RF) interference from the LED lights and/or the dimmer.

Where is the antenna and antenna line for FM radio reception located? Is it near the Marantz receiver, or is some distance away? The antenna line probably does not run near the LED light power line, or it might also pick up that hum.

 

[highfigh]

You mentioned Tech Tubes. Do you have a link? It's possible that I could figure out a way to get conduit around the RCA if the conduit is less than 3/4" OD. That said, did you mention those simply for ease re-installation, or would those provide some shielding from the interference I am getting?

This is also called 'Smurf tube" because the blue kind is about the same color as a Smurf but the type commonly used for low voltage (what we're discussing) is usually orange. Home Depot doesn't carry the large sizes, usually up to 1-1/4" but it's available up to 2-1/2" inside diameter from electrical supply houses like Greybar, etc. You can use the blue tubing, but mark it as Low Voltage because electricians can be lazy and opportunistic.

You won't be able to fit the RCA ends and cable through 3/4" tubing without a fight- consider removing the RCA plugs from the end going through the tubing but you do need to put some distance between the RCA cables and the electrical lines. If their paths absolutely must cross, do it at a right angle.

 

[cpd]

That one will do the trick. However with LED and dimmers there is no way to have no RF generated by the system. It can only be reduced and not eliminated.

All SCR dimmers generate RF, as the +ve and -ve deflections are moved apart in time at the zero crossing. The more apart they move the better the dimmer, but the more RF. The maestro dimmers now also incorporate and RF filter, but these are never perfect

Home depot offer a selection of electrical tubing generically known as tech tubes.

I have thought of one more option that would help and that would be to use a good phono amp as close to the base of your pickup arm as possible. This would convert the low level signal to line level as close to the PU arm as possible and that would reduce the "antenna" length of the low level signal that has to have a lot of gain added.

All these measures I have suggested will be additive. So you can add these measures until you are happy with your signal to noise ratio. Small Halogen puck lights get pretty hot and I always concerned about them being a fire hazard. So try and stay with LED cabinet lights if you can, despite the hassle.

A picture of the setup is at the bottom. The RCA cable runs under the baseboard molding to the left in the picture. The Denon is about where the photo was taken. The RCA then enters the drywall box the cabinet sits atop about where the white HVAC vent is. In the back of the dry wall box is a hole in the top. I don't have a picture of it. The electrician cut it, but I would estimate that from left to right in the photo that hole is directly below the tuning dial on the Marantz. That hole is about 2" wide and both the RCA cable and the wire for the light go up that hole.

There is 3/4 inch gap behind the cabinet, under the cabinet, and along the roof line on the left. The electrician ran the lighting wire from that hole at the bottom to the top light first, then down the left side for the two other lights in the triangle cubbies, and then back along the back to the TT compartment. So the RCA cable runs in the same direction and next to the wiring until it hits the hole behind the Marantz.

In the bottom left corner of the drywall box there used to be a can light. The hole is still there. So I could fish the RCA cable through that hole. That would separate the RCA cable from the electrical wiring running to the top by about 18 inches. Maybe that could solve everything depending on how the wire runs from the lower left light to the TT compartment. If that wire runs at an angle from the lower left light to the TT light, then they might converge on each other again. If that wire is tacked and runs along the back parallel to the ground at the height of the light in the TT compartment then they may never get near each other.

Do you think it's even worth trying the switches first? If not, I can try to rerun that line tonight and if worse comes to worse pull the cabinet off the wall and rewire the lights so they are nowhere near the RCA cable.

 

[cpd]

Like I sai

This is also called 'Smurf tube" because the blue kind is about the same color as a Smurf but the type commonly used for low voltage (what we're discussing) is usually orange. Home Depot doesn't carry the large sizes, usually up to 1-1/4" but it's available up to 2-1/2" inside diameter from electrical supply houses like Greybar, etc. You can use the blue tubing, but mark it as Low Voltage because electricians can be lazy and opportunistic.

You won't be able to fit the RCA ends and cable through 3/4" tubing without a fight- consider removing the RCA plugs from the end going through the tubing but you do need to put some distance between the RCA cables and the electrical lines. If their paths absolutely must cross, do it at a right angle.

Accessing and fishing an RCA cable is not going to be a huge issue. Unless these tubes provide shielding from the interference, I don't think there is much need for them in my application. I assume the answer to that question is that they do not shield from interference.