Ground Loop Issue/Question

[ftv]

Hi,

I tried to hook up my new AVR as follows:

When I watch a movie from Apple TV and select Input 6 on my Amp, I get hum/noise through the front speakers (IIRC even if I pause the movie). Disconnecting the HDMI output to the TV stops the noise, I'm suspecting because I may have a ground loop as both the TV and the Rega DAC are 3-prong power cords plugged into different outlets, with RCA (and HDMI) between the units.

The AVR only has unbalanced pre-outs, but the AMP has balanced inputs - would an RCA to XLR cable between the two resolve the issue? If not, I have read good reviews about the Jensen Iso-Max CI-2RRRCA Stereo Line Input Isolator Hum Eliminator but that is kind of pricey at $240 (plus another interconnect and potential for impact on sound). Are there recommended alternatives that have been tested that are less expensive? Something similar for HDMI connections?

If all else fails, I can change the wiring in the basement - would the two outlets have to be on the same circuit, or just on the same 120V leg in the electrical panel?

Appreciate any advice!

Frank

 

[Blumlein 88]

Just as a test get one of these adapters to use on either the Rega or TV and see if the hum level drops or goes away. Might also want to try it on the SoulNote amp. Should be a buck or two at big box hardware stores or Walmart.

It is not fully safe to use this permanently, but as a test to see if the broken ground loop fixes your problem for diagnostic purposes it would work.

 

[radix]

Have you tried disconnecting Input 4 to the amp to break the loop and make sure the HDMI -> RCA -> Input 6 is OK?

If you use transformer or active RCA/XLR adapters then float the ground at the amp input, that would likely work.

You could also get an extension cord and put the Rega on the same outlet as everything else and see if that fixes it, then at least you know for sure that's the problem.

 

[ftv]

Just as a test get one of these adapters to use on either the Rega or TV and see if the hum level drops or goes away. Might also want to try it on the SoulNote amp. Should be a buck or two at big box hardware stores or Walmart.

It is not fully safe to use this permanently, but as a test to see if the broken ground loop fixes your problem for diagnostic purposes it would work.

View attachment 261158

Thanks! I have one of those in the basement, finding it will be the challenge.

 

[Speedskater]

Has a test get an AC extension cord and power everything from the same wall outlet.

 

[ftv]

Have you tried disconnecting Input 4 to the amp to break the loop and make sure the HDMI -> RCA -> Input 6 is OK?

If you use transformer or active RCA/XLR adapters then float the ground at the amp input, that would likely work.

You could also get an extension cord and put the Rega on the same outlet as everything else and see if that fixes it, then at least you know for sure that's the problem.

Have not tried disconnecting Input 4 as I believe the loop is formed via the RCA connection (AVR to Amp and Amp to DAC), but now the "problem" is that I cannot re-create the hum. I tried it twice yesterday, re-establishing all the connections and hum was there loud and clear. That even gave me the idea that the DAC has to be listening on its optical input where it receives the 2-channel audio from the AVR for the hum to be present, but just confirmed this is not the case.

Connecting the Rega to the power strip that the AVR is plugged in to (which is in the same outlet as the TV) is a good idea, thanks! That could even be a good interim solution until I can change the wiring (assuming re-wiring would actually fix it).

I should get my longer cables which will allow me to place the AVR into the cabinet today or tomorrow, we'll see if the gremlins re-appear and take it from there.

 

[stubaggs]

Have not tried disconnecting Input 4 as I believe the loop is formed via the RCA connection (AVR to Amp and Amp to DAC), but now the "problem" is that I cannot re-create the hum. I tried it twice yesterday, re-establishing all the connections and hum was there loud and clear. That even gave me the idea that the DAC has to be listening on its optical input where it receives the 2-channel audio from the AVR for the hum to be present, but just confirmed this is not the case.

Connecting the Rega to the power strip that the AVR is plugged in to (which is in the same outlet as the TV) is a good idea, thanks! That could even be a good interim solution until I can change the wiring (assuming re-wiring would actually fix it).

I should get my longer cables which will allow me to place the AVR into the cabinet today or tomorrow, we'll see if the gremlins re-appear and take it from there.

If the cheater plug suggested above by Blumlein 88 works, a 'Hum Eliminator' is a reasonable option. It has power limitation (so not good for a large power amp), but for a smaller components works well.

 

[radix]

but now the "problem" is that I cannot re-create the hum. I tried it twice yesterday, re-establishing all the connections and hum was there loud and clear. That even gave me the idea that the DAC has to be listening on its optical input where it receives the 2-channel audio from the AVR for the hum to be present, but just confirmed this is not the case.

Do you know if all our electrical outlets go to a common ground inside the same junction box, or are some outlets wired to their own spike in the ground or cold water pipe? Or are you sure that the outlet boxes really have a ground, sometimes in older houses people install 3-wire outlets without a ground.

 

[JSmith]

Disconnecting the HDMI output to the TV stops the noise, I'm suspecting because I may have a ground loop

You could try a HDMI over Ethernet adaptor in between, which may break the ground loop.


JSmith

 

[ftv]

Do you know if all our electrical outlets go to a common ground inside the same junction box, or are some outlets wired to their own spike in the ground or cold water pipe? Or are you sure that the outlet boxes really have a ground, sometimes in older houses people install 3-wire outlets without a ground.

Common ground, and all outlets should be grounded (house was built 25 years ago), but you never know for sure I suppose. I bought a long power cord to plug the DAC into the same circuit as the AVR/TV, hopefully that will do the trick when I put the AVR inside the cabinet.

 

[Speedskater]

A Neutral/Safety Ground wire swap to just one of the outlets can cause that type of problem.
And a little 3 LED tester won't find that type of problem.

 

[boxerfan88]

Try this diagnostic: with everything switch on and humming, disconnect the TV antenna. Does the hum stop?

 

[levimax]

If you have cable or satellite TV try disconnecting the cable. I have never had a system with satellite or cable involved that didn't hum. To fix Jensen makes an isolater... I tried the cheap ones and they either didn't stop the hum or killed the TV reception. If you want to try a free fix I connected the ground on the cable to the ground on the outlet with a heavy gauge wire and the hum stopped (only try this if you are comforatable with mains wireing and can test the outlet is wired and grounded properly).

 

[Mr. Widget]

When I watch a movie from Apple TV and select Input 6 on my Amp, I get hum/noise through the front speakers (IIRC even if I pause the movie). Disconnecting the HDMI output to the TV stops the noise, I'm suspecting because I may have a ground loop as both the TV and the Rega DAC are 3-prong power cords plugged into different outlets, with RCA (and HDMI) between the units.

The AVR only has unbalanced pre-outs, but the AMP has balanced inputs - would an RCA to XLR cable between the two resolve the issue? If not, I have read good reviews about the Jensen Iso-Max CI-2RRRCA Stereo Line Input Isolator Hum Eliminator but that is kind of pricey at $240 (plus another interconnect and potential for impact on sound). Are there recommended alternatives that have been tested that are less expensive? Something similar for HDMI connections?

If all else fails, I can change the wiring in the basement - would the two outlets have to be on the same circuit, or just on the same 120V leg in the electrical panel?

Appreciate any advice!

Frank

Our technicians carry these in their vans and use them all the time. They will remove a ground loops and will not affect the sound, they are extremely high quality transformers and I promise you they are invisible.

That said, you need to verify the connection(s) that need to be severed before tossing around money on possible solutions.

Start at the speakers and one by one connect your gear until the hum shows up. This is where you need to isolate the signal.

 

[Krusty09]

The easiest way to test is just run an extension cord to the TV and plug all the gear there to the same outlet as the stereo and if the hum goes away you have your answer.

This would mean the 2 outlet s are on different phases and could be fixed for free by putting the breakers on the same phase in your breaker pannel.

 

[ftv]

Thanks for all the suggestions!

I thought for a couple of days that the issue resolved itself (and it is definitely not as pronounced as earlier), but alas, it's still there. Tried disconnecting the TV, put the amplifier (which turns out to have a 3-wire plug contrary to my drawing) on the same circuit as the receiver/TV (even with a cheater plug), but a hum is still there. It only happens on two of the inputs though, the one with the phono preamp and the one coming from the front preouts of the receiver.
The hum is there even with no turntable playing or with the apple tv on pause, and it gets worse the more I crank up the volume on the amp. If I switch to the Rega DAC, no hum at all whether apple tv is on pause or playing music.

As I was typing this, I tested out another configuration and I decided to unplug a power conditioner (Panamax M5400-PM), and guess what? Now the hum on input 6 (preout from AVR) is gone. None of the equipment was even plugged into the power conditioner, but I guess its proximity put noise on the RCA interconnects coming from the AVR (but strangely enough, not on the ones from the Rega DAC to the amp).

Only one left now that still produces hum is the phono preamp (no turntable connected to it), though I really have to crank up the volume on the amp to hear it. Used a cheater plug with it, same power strip as the amp, no power conditioner plugged in. I used the MC High (Medium Gain Output) and 47000ohm settings on the phone preamp (cartridge is Ortofon 2M Blue which is MM but I had to really turn up the volume if I set the preamp to MM), but again, the hum is there with no turntable connected to the phono preamp.

The input sensitivity/impedance on the RCA inputs of the amp is 700mV/16kohm, the phono preamp's input/output impedance is 100kohm/600ohm. The phono preamp is a hybrid design with 2 12AX7 tubes.

Anything I've got wrong in the settings, possible mismatch between phono preamp and amp, or something wrong with the phono preamp (have not biased the tubes since I bought it years ago but also not used it much)?

 

[AnalogSteph]

As I was typing this, I tested out another configuration and I decided to unplug a power conditioner (Panamax M5400-PM), and guess what? Now the hum on input 6 (preout from AVR) is gone. None of the equipment was even plugged into the power conditioner, but I guess its proximity put noise on the RCA interconnects coming from the AVR (but strangely enough, not on the ones from the Rega DAC to the amp).

The Panamax only has a small toroidal transformer, but perhaps that was enough to inductively couple into an existing ground loop. With the SoulNote amplifier being identified as a Class I device (it's probably the A-2?), it only takes one of the HDMI-connected devices on the AVR to complete it.

Only one left now that still produces hum is the phono preamp (no turntable connected to it), though I really have to crank up the volume on the amp to hear it. Used a cheater plug with it, same power strip as the amp, no power conditioner plugged in. I used the MC High (Medium Gain Output) and 47000ohm settings on the phone preamp (cartridge is Ortofon 2M Blue which is MM but I had to really turn up the volume if I set the preamp to MM), but again, the hum is there with no turntable connected to the phono preamp.

The input sensitivity/impedance on the RCA inputs of the amp is 700mV/16kohm, the phono preamp's input/output impedance is 100kohm/600ohm. The phono preamp is a hybrid design with 2 12AX7 tubes.

A relatively high-gain device like a phonopre should be tested with inputs shorted, not inputs open. Most people won't have RCA shorting plugs, but maybe you can improvise something similar.

Do you have any more specifics on the phonopre? Type of power supply / mains connection, make / model, circuit design, anything? (You said cheater plug (yuck), so it seems to be IEC Class I?) I wouldn't rule out a constructive issue like insufficient power supply filtering or poor grounding practices.

Most integrated amps with built-in phonopres tend to have an input sensitivity of 150-200 mV, around 12 dB below 700 mV, so I'm not surprised you had to crank up the gain on the hybrid pre. The input sensitivity on the A-2 was designed for loudness ware era CD player levels, which often gave traditional integrated amps trouble with volume pot channel balance as they had to be turned down so low.

You clearly have a knack for picking audio equipment that makes your life difficult while lightening your wallet, I'll give you that.

 

[ftv]

The Panamax only has a small toroidal transformer, but perhaps that was enough to inductively couple into an existing ground loop. With the SoulNote amplifier being identified as a Class I device (it's probably the A-2?), it only takes one of the HDMI-connected devices on the AVR to complete it.

A relatively high-gain device like a phonopre should be tested with inputs shorted, not inputs open. Most people won't have RCA shorting plugs, but maybe you can improvise something similar.

Do you have any more specifics on the phonopre? Type of power supply / mains connection, make / model, circuit design, anything? (You said cheater plug (yuck), so it seems to be IEC Class I?) I wouldn't rule out a constructive issue like insufficient power supply filtering or poor grounding practices.

Most integrated amps with built-in phonopres tend to have an input sensitivity of 150-200 mV, around 12 dB below 700 mV, so I'm not surprised you had to crank up the gain on the hybrid pre. The input sensitivity on the A-2 was designed for loudness ware era CD player levels, which often gave traditional integrated amps trouble with volume pot channel balance as they had to be turned down so low.

You clearly have a knack for picking audio equipment that makes your life difficult while lightening your wallet, I'll give you that.

Appreciate the assistance! The phono preamp is a Jolida JD9, here is a link to the manual: https://www.manualslib.com/manual/1015268/Jolida-Jd-9.html#manual
It does mention that it must be connected via a 3prong plug to a "wall" receptacle or similar heavy-duty source, and to avoid extension cords (guilty on all charges initially but did just try the receptacle as well).

Had not heard of RCA shortening plugs before but just ordered some to see if there is a noticeable difference in the noise at a given amp volume level between the turntable connected and the plugs shortened out. I do have to mention that my turntable is a VPI Player (hey, I had to save money somewhere) that has a built-in phone preamp section which I disabled (following VPI's youtube video). I read that someone had noise issues as doing so renders the ground screw useless (VPI's answer when he contacted them), so he somehow wired it where the ground screw could be used again. Maybe that's all I need to lower the noise from the phono preamp, I suppose those ground screws on turntables and next to the phono inputs on amps/preamps must be there for a reason .

And yes, my recent purchases have lightened my wallet a fair bit, and I won't argue over diminishing returns, but I formally retired a couple of years ago and then returned as a contractor so it's mostly fun money. I spent big time when I started this hobby back in the 70s (in .de actually, born and raised there) when I dropped multiple paychecks on a Revox turntable and tuner, and Bose 901 IV speakers (I know, I know), and then went pretty conservative all these years until recently when I bought the A-2 (always wanted one of those nice Japanese amps, and the A-2 is still cheaper than most of them), the Rega CD/DAC, and Perlisten speakers. Oh, and the Arcam AVR but that was relatively inexpensive. Now I just need some high dollar cables to extract every ounce of performance out of my system! Oops, wrong forum!

 

[Speedskater]

Anyone can make a RCA shorting plug.
Just sacrifice a old RCA cable. One with a braided shield not a foil shield.
Cut to about a 6 inch length. Strip about an inch of insulation. Tightly twist the braid and central conductor together.

 

[SSS]

At a recording studio a power conditioner was used. That one created hum in nearby amplifiers. Reason was the inductors in the power conditioner. If a wall jack has enough amperes to my opinion a power conditioner is not neccessary. You never know how it is internally connected and what it really does. Regarding the turntable (which I did not see in the installation drawing above) unplug the mains cable. If hum is still there move the tonearm whether the hum changes. If it does then there is a hum magnetic field in the vicinity. If the MM preamp hums by itself without the pickup outlet connected then also magnetic field can be the reason. Therefore move the preamp around whether the hum changes. If not then there is something wrong with the cabling or the MM preamp has mains earth connection. If yes then it gets hard. Perhaps using the same mains outlet bar with the amplifier may help. Further a ground connection cable between MM preamp and the amplifier could help, but not always unfortunately. It is hard to evaluate from distance.