TT Hum

[TLS Guy]

I’m glad to see that cpd, the original poster, was able to eliminate the hum problem without requiring major rewiriing or drywall work. As it turns out, the solution took more than one single modification. Not surprising.

I’m also put off by TLS Guys tone in his last response. It was offensive. The rest of my comments are directed at him and not the OP.

First, let’s reiterate the known details of the OP’s problem. (Pay close attention to the sectons I've bolded.)

• The OP had audible hum through the loudspeakers during phonograph playback. He explained that his phonograph cartridge was connected to an older Marantz stereo receiver’s phono input, using it as a phono pre-amp, and then out from Tape Out jacks to a Denon AVR via RCA interconnects.
  
  
• Those RCA cables, containing line level audio signals, exit the back of the cabinet where they ran behind drywall adjacent to an electric power line for the LED lights. This inaccessible space was between the wall and the back of the cabinet.
  
  
• A photo showed the turntable, three LED lights, and Marantz receiver (containing the phono pre-amp and FM tuner) were close to each other. It did not show where the dimmer light switch was located. Nor did it show the Denon AVR, speaker cables, or speakers.
  
  
• The hum occurred only during phono playback, and only when the LED lights were on. The OP did not mention what other sound source devices he used, but he did say an FM tuner built into the nearby Marantz receiver did not suffer from any hum with or without the LED lights. Furthermore, this tuner operated without any antenna. I assume the antenna connection jack was left unoccupied. This suggests the OP lives in an area with strong FM signals, strong enough to dominate over many sources of interference. But it also suggests the unoccupied antenna jack could allow RFI to interfere with FM radio playback from a shielded radio receiver.

How to fix the problem? First try #1, and if it doesn’t eliminate the hum, try #2 and #3.

1. Relocate the RCA interconnects running between the Marantz stereo receiver and the Denon AVR, such that they don’t run nearby the power line for the LED lights.
2. Replace the dimmer switch for the LED lights.
3. Replace the LED lights themselves.

The OP first, relocated the wires described in item 1. This may have partially reduced the hum, but did not eliminate it. The OP next replaced the dimmer switch with a standard on/off wall switch, and that did completely eliminate the hum. His results suggest that RFI generated by the LED dimmer, entered the system by the phono level cable between the turntable and the Marantz pre-amp, by the line level cable between the Marantz pre-amp and the Denon AVR, or both.

TLS Guy's lengthy explanation indicates how RF interference, such as that generated by LED dimmers, could generate an audible hum in the presence of unshielded solid state amplifiers driving loudspeakers. If so, the OP would hear that hum regardless of the sound source. Yet, while using the FM tuner in the Marantz receiver, no hum could be heard while the LED lights were on. TLS Guy's lengthy explanation fails to address that.

But your efforts at schooling the readers of this thread does succeed at insulting their intelligence. I speak for myself. But I wouldn’t be surprised if others felt as I do.

Well I'm sorry if I offended you or anyone else. That was far from my intent. I did mention that turntables and cartridges are a special case.

I did not address the tuner issue and probably should have.

However the thing about RF interference is that it is hit and miss and at first glance appears to not make any sense and be totally confounding. That is because if you look at the crystal radio circuit the penetration of RF depends on a degree of random tuning of the affected circuits. In other words whether the an RF signal generated in the home will penetrate a given device or input depends on whether the circumstances are right for a circuit to tune or resonate with the said RF interference. The randomness of all this makes it so hard to predict. This also makes it next to impossible for designers of equipment to make it totally immune from any possible RF hash.

So the take home for designers of AV equipment and unfortunately home designers is to try and take steps not only to minimize generation of RF hash but more importantly reduce its opportunities for spread, distribution and reception. I see this as a bigger and bigger issue going forward with far better recognition and understanding of the issues involved.

As you can see from the OPs response unless you have at least some elementary understanding of electromagnetic propagation and reception by inadvertently tuned circuits these issues when they occur, and they will, will be hard to cure. This does require at least some understanding of electronic circuits and especially function of components like inductors, capacitors and solid state junctions. Earth loops are bad enough, but this issue is on a totally different level.

Once again I'm sorry for any offense, but this is an issue that needs much wider discussion and further understanding as sources of RF hash increase and proliferate.

I think this forum has a stellar record among these sort of forums and being more often correct and able to resolve issues that people bring to us than many others. That is entirely due to the selfless devotion of many members here to which you Swerd, have contributed to immeasurably.

At the end of the day do not loose sight of the fact we solved the OP's issue.

 

[Alex2507]

I learned a lot (mostly that I have a lot to learn).

I feel like that a lot around here but I think you said it better than I could have. And it's hilarious.

But I'm a lawyer, so you can't blame me for being dumb.

You did an admirable job seeing this through to a satisfactory conclusion without ripping your built-in shelving apart. Looks good on ya.

 

[highfigh]

So the cartridge coils can substitute for the inductor L1 and the cartridge loading capacitance for capacitor VC1 and the first base emitter junction of the phono preamp the diode D1. Now we have our crystal radio, but now with amplification!

No wonder the OP has a buzz from his LED light and dimmer.

The easy test for this is to move the turntable closer to the receiver and if the problem stops, it means the interference is closer to the original position and making the changes at the receiver end will be fruitless. If it persists, your theory about the cartridge being the pickup of this interference can be tested by removing it from the tonearm.

RF is at the upper limits of the audio frequency range and that's why I referenced RF and AF. Lighting devices output interference that can be found easily with a cheap pocket AM radio- EMI is easy to find using a cheap cassette Walkman device with the play button engaged. If the noise is present with either, it's a matter of moving the one that picks it up closer to the suspected source. If someone wants to make a noise sniffer for either, a shielded cable with bare tip can be attached to a portable radio that has an extendable wand-type antenna and moving the tip of the cable around the room- the source can be found when the noise becomes louder. To make a sniffer for EMI, a shielded cable can be connected between the Walkman device and its tape head, moving it in a similar way in order to find the source.

I suspect the houses' wiring is at fault. Old buildings with owner-installed wiring are much more likely to have resistance on the neutral, which influences its ability to conduct to the grounding conductor(s). Some have knob and tube wiring and with that, all bets are off.

 

[Swerd]

RF is at the upper limits of the audio frequency range and that's why I referenced RF and AF. Lighting devices output interference that can be found easily with a cheap pocket AM radio- EMI is easy to find using a cheap cassette Walkman device with the play button engaged. If the noise is present with either, it's a matter of moving the one that picks it up closer to the suspected source. If someone wants to make a noise sniffer for either, a shielded cable with bare tip can be attached to a portable radio that has an extendable wand-type antenna and moving the tip of the cable around the room- the source can be found when the noise becomes louder. To make a sniffer for EMI, a shielded cable can be connected between the Walkman device and its tape head, moving it in a similar way in order to find the source.

Those noise sniffer tips are useful. I'll remember them even though it's been decades since I had a cheap AM pocket radio or a Walkman type cassette player. Thanks.

 

[cpd]

I’m glad to see that cpd, the original poster, was able to eliminate the hum problem without requiring major rewiriing or drywall work. As it turns out, the solution took more than one single modification. Not surprising.

I’m also put off by TLS Guys tone in his last response. It was offensive. The rest of my comments are directed at him and not the OP.

First, let’s reiterate the known details of the OP’s problem. (Pay close attention to the sectons I've bolded.)

• The OP had audible hum through the loudspeakers during phonograph playback. He explained that his phonograph cartridge was connected to an older Marantz stereo receiver’s phono input, using it as a phono pre-amp, and then out from Tape Out jacks to a Denon AVR via RCA interconnects.
  
  
• Those RCA cables, containing line level audio signals, exit the back of the cabinet where they ran behind drywall adjacent to an electric power line for the LED lights. This inaccessible space was between the wall and the back of the cabinet. For clarity, the wires and cables were not behind drywall. The cabinets were built with 3/4' gap between the walls and the cabinet back and diagonal (top) side panels. In their initial configuration the RCA cable to the Denon definitely paralleled the lighting wire for at least 18 - 20 linear inches.
  
  
• A photo showed the turntable, three LED lights, and Marantz receiver (containing the phono pre-amp and FM tuner) were close to each other. It did not show where the dimmer light switch was located. Nor did it show the Denon AVR, speaker cables, or speakers. For supplemental purposes, the dimmer is on a wall to the right and behind where the picture was taken. It is about 15 feet from the cabinet in the picture and 10 feet from the cabinet on the other side of the room (also with LED lights).
  
  
• The hum occurred only during phono playback, and only when the LED lights were on. The OP did not mention what other sound source devices he used, but he did say an FM tuner built into the nearby Marantz receiver did not suffer from any hum with or without the LED lights. Furthermore, this tuner operated without any antenna. I assume the antenna connection jack was left unoccupied. This suggests the OP lives in an area with strong FM signals, strong enough to dominate over many sources of interference. But it also suggests the unoccupied antenna jack could allow RFI to interfere with FM radio playback from a shielded radio receiver. If I said it happened only during playback then I misspoke. The hum happened whenever the (1) Marantz was powered on, (2) the phono input was selected on the Marantz, and (2) the lights were on. Whether the TT was on or off, or playing a record or not did not impact the hum. The antenna jack was unoccupied.

How to fix the problem? First try #1, and if it doesn’t eliminate the hum, try #2 and #3.

1. Relocate the RCA interconnects running between the Marantz stereo receiver and the Denon AVR, such that they don’t run nearby the power line for the LED lights. I re-positioned the RCA cable through another hole in the drywall box under the cabinet. I did so based on a phone conversation with the electrician about the sequence and general wiring path of the lights. I did not see that wiring path before the cabinet was mounted and I cannot see how it looks now to determine separation between the RCA cable and the closest wires. Depending on exactly how they were run they could still be close. Let's call what I did an educated guess. Where the RCA cable exits the drywall box now to get to the Denon, it runs underneath another hot line (although I made sure that was at a 90 degree angle), and then is tucked under the baseboard running parallel to that same hotline separated by drywall and anywhere from 2 - 4".
2. Replace the dimmer switch for the LED lights.
3. Replace the LED lights themselves.

The OP first, relocated the wires described in item 1. This may have partially reduced the hum, but did not eliminate it. The OP next replaced the dimmer switch with a standard on/off wall switch, and that did completely eliminate the hum. His results suggest that RFI generated by the LED dimmer, entered the system by the phono level cable between the turntable and the Marantz pre-amp, by the line level cable between the Marantz pre-amp and the Denon AVR, or both.

TLS Guy's lengthy explanation indicates how RF interference, such as that generated by LED dimmers, could generate an audible hum in the presence of unshielded solid state amplifiers driving loudspeakers. If so, the OP would hear that hum regardless of the sound source. Yet, while using the FM tuner in the Marantz receiver, no hum could be heard while the LED lights were on. TLS Guy's lengthy explanation fails to address that.

But your efforts at schooling the readers of this thread does succeed at insulting their intelligence. I speak for myself. But I wouldn’t be surprised if others felt as I do.

My post seems to have sparked a lot of thought and debate on a topic of interest to people. That's great. If any of you are still noodling this one for academic interest, then I thought it a good idea to clarify a few statements in your post that it appears I failed to adequately explain. Whether they are of any moment to your analysis is unclear to me, I just didn't want anyone's analysis flawed as a result of issues with the clarity in my posts. My comments are in the quote in blue.

 

[Swerd]

My post seems to have sparked a lot of thought and debate on a topic of interest to people. That's great. If any of you are still noodling this one for academic interest, then I thought it a good idea to clarify a few statements in your post that it appears I failed to adequately explain. Whether they are of any moment to your analysis is unclear to me, I just didn't want anyone's analysis flawed as a result of issues with the clarity in my posts. My comments are in the quote in blue.

Thanks for added details – they help.

Finding sources of interference or other electronic-related noise can be difficult. What one person experiences in his home with his audio gear can be quite different from what others encounter. So a little experience can be both a benefit and a distraction. As they say, the devil is in the details – but not all the details, only some. Which details to fix first can be a problem – or an interesting puzzle.

Just curious (and off-topic), why do you use the FM tuner on your old Marantz receiver instead of the Denon AVR's tuner? Did the Denon tuner pick up the interference from the dimmer, and not the Marantz? In my hands, the FM tuners built into two modern AVRs that I've owned, work just as well as that in my older 1972 Marantz 2230 stereo receiver. I live in the Maryland suburbs where there are many powerful FM radio and TV broadcast stations. Most are about 15 miles away in Washington DC. I can also easily receive FM radio from Baltimore, about 50 miles away. I do use a turnstyle type antenna in my attic, but it doesn't have any more gain than the simple folded dipole antennae made from flat antenna wire that are usually included with receivers. My problem is not RF noise, but too many powerful broadcasters. Others, who live far away from FM or TV broadcast sources, have to use more sensitive (high gain) antennae that require rotors to aim them, and often require more effort at eliminating sources of RFI.

 

[highfigh]

Those noise sniffer tips are useful. I'll remember them even though it's been decades since I had a cheap AM pocket radio or a Walkman type cassette player. Thanks.

Goodwill and other thrift stores often have them.

 

[cpd]

Thanks for added details – they help.

Finding sources of interference or other electronic-related noise can be difficult. What one person experiences in his home with his audio gear can be quite different from what others encounter. So a little experience can be both a benefit and a distraction. As they say, the devil is in the details – but not all the details, only some. Which details to fix first can be a problem – or an interesting puzzle.

Just curious (and off-topic), why do you use the FM tuner on your old Marantz receiver instead of the Denon AVR's tuner? Did the Denon tuner pick up the interference from the dimmer, and not the Marantz? In my hands, the FM tuners built into two modern AVRs that I've owned, work just as well as that in my older 1972 Marantz 2230 stereo receiver. I live in the Maryland suburbs where there are many powerful FM radio and TV broadcast stations. Most are about 15 miles away in Washington DC. I can also easily receive FM radio from Baltimore, about 50 miles away. I do use a turnstyle type antenna in my attic, but it doesn't have any more gain than the simple folded dipole antennae made from flat antenna wire that are usually included with receivers. My problem is not RF noise, but too many powerful broadcasters. Others, who live far away from FM or TV broadcast sources, have to use more sensitive (high gain) antennae that require rotors to aim them, and often require more effort at eliminating sources of RFI.

Sorry I missed this.

I actually don't use the tuner in either very often. I did not test whether there was interference when using the Denon tuner, but I did not get interference using any other input on the Denon when the lights were on with the dimmer switch installed. When I do use a tuner I have used the Marantz because (1) my use of the tuner is so fleeting that I haven't bothered to connect an antenna to either yet and the Marantz picks up a strong enough signal without it while the Denon does not pick up any signal, and (2) it gives me an excuse to turn on the Marantz -- I like the blue lights!

 

[davidscott]

I don't know if this has been addressed or is even a factor but some phono carts like the Grados are unshielded and can produce a low level hum usually when getting close to a TT motor.