Ground loop isolator fixed hum but now there is distortion - AVS Forum
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post #1 of 23 Old 03-21-2013, 09:32 PM - Thread Starter
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i used a ground loop isolator to get rid of hum i had on my subs, but now there is distortion. it sounds like the drivers are blown or something. Anyone have experience with this?

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post #2 of 23 Old 03-22-2013, 06:21 AM
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Originally Posted by brian6751 View Post

i used a ground loop isolator to get rid of hum i had on my subs, but now there is distortion. it sounds like the drivers are blown or something. Anyone have experience with this?

My experience with audio ground loop isolators is that they can handle consumer and the much higher pro audio signal levels without audible distortion. Measurable distortion is typically 80 dB down or better, if memory serves.

If there is distortion in these little transformers you should be able to turn up the gain at the subwoofer end and turn down the signal level at the source and make it go away.

You may have turned levels up too high at the source to reduce the audibility of the now-vanished hum.

Transformer saturation is usually soft clipping and less obnoxious than clipping in active components. It is very possible that you have gain staging problems and the distortion is in the active componentry.

It is possible that the hum was masking your perception of other technical problems.
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post #3 of 23 Old 03-22-2013, 08:05 AM - Thread Starter
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i left the isolator in the chain and turned off Audyssey. the distortion and the hum is gone so that was the issue. i will rerun it later to see if it returns and go from there. thanks for your help!

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post #4 of 23 Old 03-26-2013, 11:17 AM - Thread Starter
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That actually did not fix it. It's definitely the isolator. I think it's doing something with the signal. Either way, I decided to try and fix it without the isolator. It's actually coming from my projector and my Direct tv coax. I strapped the direct tv shield to my amps. That cut down a lot of it. I also have a cheater plug on my projector until my Hum-X gets here. That makes the hum almost inaudible unless you put your ear right up to the cone. There is also no distortion to the sound. Does all this sound ok to do?

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post #5 of 23 Old 03-28-2013, 06:18 AM
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I thought I would post my experience with hum here, hope you don't mind. I bought the ground loop isolator from radio shack to connect between my receivers pre out and my amp. It works, but it is very sensitive to the position of the isolator. I had to move it around to find the best place. Some positions it actually made the hum worse! Anyway, I used some electrical tape to keep it in the best position to the back of my stand.
Hope this can help anyone else with a similar problem.

NHT speakers, Denon 4520, 65VT50
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post #6 of 23 Old 03-28-2013, 07:24 AM - Thread Starter
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Don't mind at at. Thank you. I tried moving it around to no avail. It did get rid of the hum but it distorted the signal at the same time. Almost like the signal became to weak and the sound was distorted at low levels.

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post #7 of 23 Old 03-28-2013, 09:05 AM
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Quote:
Originally Posted by mnc View Post

I thought I would post my experience with hum here, hope you don't mind. I bought the ground loop isolator from radio shack to connect between my receivers pre out and my amp. It works, but it is very sensitive to the position of the isolator. I had to move it around to find the best place. Some positions it actually made the hum worse! Anyway, I used some electrical tape to keep it in the best position to the back of my stand.
Hope this can help anyone else with a similar problem.

My ground loop isolator had the same problem, which I resolved by putting it into an empty tomato paste can. I even found a jar cap that was a tight fit in the can, punched a hole in it, and slipped the wires through it for a more finished appearance.
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post #8 of 23 Old 03-28-2013, 09:11 AM - Thread Starter
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Quote:
Originally Posted by arnyk View Post

My ground loop isolator had the same problem, which I resolved by putting it into an empty tomato paste can. I even found a jar cap that was a tight fit in the can, punched a hole in it, and slipped the wires through it for a more finished appearance.

Was that to get rid of the hum or were you getting distortion as well?

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post #9 of 23 Old 03-28-2013, 09:21 AM
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Quote:
Originally Posted by brian6751 View Post

Quote:
Originally Posted by arnyk View Post

My ground loop isolator had the same problem, which I resolved by putting it into an empty tomato paste can. I even found a jar cap that was a tight fit in the can, punched a hole in it, and slipped the wires through it for a more finished appearance.

Was that to get rid of the hum or were you getting distortion as well?

The can was to get rid of the hum.

I've done some bench tests on the RS ground isolator and its hard to imagine how it would cause audible distortion with consumer gear. No consumer gear should be putting out more than a volt or two, and at those levels the thing has very low distortion.

The only way I can figure out to make it distort would involve an active subwoofer with a very insensitive input, or its input level control turned way down.

I don't know about competitive items.

Here's my test results from an earlier post on a different forum:

"
I just did some bench tests of Radio Shack's "Ground Isolator" 270-054 using
test signals that maxed out around 2.5 v RMS. ZSource = 150 ohms, ZLoad =
5Kohms.

The measured performance was truely amazing for a pair of transformers case
and cables selling for only $16.65.

All IM, THD, and noise artifacts were at least 80 dB down with most in
the -100 dB range or better. Frequency response showed a 2 dB peak at 20 Hz
and then 10 dB down at 10 Hz. There was a 3 dB peak at about 51 KHz falling
to about 10 dB down around 100 KHz. +0.5 dB at 20 KHz.

I repeated the tests with the secondary loaded with 1.5K, and the peak at 51
Khz became well-damped with only about 0.6 dB rise.
"

I found another guy's tests online:

"
I bought a RadioShack "Ground Loop Isolator" today and decided to test the IMD of the transformers (there are two in the device).

I used Digipan in its IMD measurement mode and looped the output of my soundcard directly back into the input with a
straight-through cable. Playing with the output and input levels, the typical IMD measurement in Digipan was about -61 to -58. I
then inserted one of the transformers of the RadioShack device and the IMD did not change. I played with the levels and was able to
put the transformer into saturation and could see the signal in the display, but with every level tested, and regardless of
frequency (used 1kHz, 2kHz & 3kHz) when the level was below saturation there was no difference whether or not the transformer was in
line.

I was expecting a higher IMD reading with the transformer inserted between the input and output of the soundcard as compared to the
straight-through cable. What am I missing?

73, Don AA5AU
http://www.aa5au.com
http://www.rttycontesting.com
"
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post #10 of 23 Old 03-28-2013, 09:26 AM - Thread Starter
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i am using a Behringer EP4000 pro amp. also a balanced MiniDSP. i was putting the isolator between the AVR and the MiniDSP. the connections are XLR from the DSP to the amps.

i was using only one channel of the isolator. would using y connectors to enable use of both channels help you think?

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post #11 of 23 Old 03-28-2013, 09:37 AM
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Quote:
Originally Posted by brian6751 View Post

i am using a Behringer EP4000 pro amp. also a balanced MiniDSP. i was putting the isolator between the AVR and the MiniDSP. the connections are XLR from the DSP to the amps.

i was using only one channel of the isolator. would using y connectors to enable use of both channels help you think?

If the source is mono, I don't know why you would need more than half of the (stereo) ground isolator. I'm only using half of mine, and my subwoofer has stereo inputs.

If you are matching a balanced output to a balanced input, then most times the isolator would not be needed.

The isolator could be needed if there are serious grounding problems that active balanced I/O such as you have can't handle exist. One example would be the amp and MiniDSP being on different AC circuits.

Is the input gain on the EP4000 set high or low?
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post #12 of 23 Old 03-28-2013, 10:17 AM - Thread Starter
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the gain is at about half way on both amps. the amps and the dsp ARE on different circuits

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post #13 of 23 Old 03-28-2013, 11:41 AM
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Quote:
Originally Posted by brian6751 View Post

the gain is at about half way on both amps. the amps and the dsp ARE on different circuits

For the purpose of debugging, you might want to run an extension cord from the outlet that the MiniDSP is plugged into for the power amp. You should be then able to run it without the transformer and without the hum.

With the settings you have, you shouldn't have enough voltage to make the transformer distort that badly. Transformer clipping is usually soft clipping.

I guess the MiniDSP doesn't have an output level control so that you could run the power amp at max gain?
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post #14 of 23 Old 03-28-2013, 12:02 PM
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I have several pro grade isolation transformers in Mu-metal cans. These are rated flat from 20-20k at +18 DB. These can handle any audio level found in commercial or pro signal chains. These are available from OP-Amp labs in Hollywood, CA. They are built with a solid octal pin connection but you can easily solder wires right to the gold flashed pins. These are immune to positional issues and the transformer cores are attached to the can shield. These have solved a multitude of ground loo issues in the filed for me over the years. I built several stereo versions using the 600/600 x-formers and the 10k/10k x-formers into cast aluminum enclosures with Neutrik XLR connections. neat and totally quiet. I installed ground lifts on the input sides of the transformers just in case. They work like a champ.
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post #15 of 23 Old 03-28-2013, 12:11 PM - Thread Starter
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Quote:
Originally Posted by arnyk View Post

For the purpose of debugging, you might want to run an extension cord from the outlet that the MiniDSP is plugged into for the power amp. You should be then able to run it without the transformer and without the hum.

With the settings you have, you shouldn't have enough voltage to make the transformer distort that badly. Transformer clipping is usually soft clipping.

I guess the MiniDSP doesn't have an output level control so that you could run the power amp at max gain?

i still have the hum without the dsp. maybe i should try putting the AVR on the same circuit as the amps? problem is, that outlet is tripped by the avr's 12 volt trigger so ill have to install a separate outlet. not a big deal since this is all in my utility room.

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post #16 of 23 Old 03-28-2013, 12:12 PM - Thread Starter
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Quote:
Originally Posted by Gizmologist View Post

I have several pro grade isolation transformers in Mu-metal cans. These are rated flat from 20-20k at +18 DB. These can handle any audio level found in commercial or pro signal chains. These are available from OP-Amp labs in Hollywood, CA. They are built with a solid octal pin connection but you can easily solder wires right to the gold flashed pins. These are immune to positional issues and the transformer cores are attached to the can shield. These have solved a multitude of ground loo issues in the filed for me over the years. I built several stereo versions using the 600/600 x-formers and the 10k/10k x-formers into cast aluminum enclosures with Neutrik XLR connections. neat and totally quiet. I installed ground lifts on the input sides of the transformers just in case. They work like a champ.

they seem to have a lot of products. do you have a link to the one you use?

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post #17 of 23 Old 03-28-2013, 01:06 PM
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Quote:
Originally Posted by brian6751 View Post

Quote:
Originally Posted by Gizmologist View Post

I have several pro grade isolation transformers in Mu-metal cans. These are rated flat from 20-20k at +18 DB. These can handle any audio level found in commercial or pro signal chains. These are available from OP-Amp labs in Hollywood, CA. They are built with a solid octal pin connection but you can easily solder wires right to the gold flashed pins. These are immune to positional issues and the transformer cores are attached to the can shield. These have solved a multitude of ground loo issues in the filed for me over the years. I built several stereo versions using the 600/600 x-formers and the 10k/10k x-formers into cast aluminum enclosures with Neutrik XLR connections. neat and totally quiet. I installed ground lifts on the input sides of the transformers just in case. They work like a champ.

they seem to have a lot of products. do you have a link to the one you use?

I'll bet money - this one:

http://opamplabs.com/products/logic-module-plug-in/transformer-audio/t-10k.html
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post #18 of 23 Old 03-28-2013, 01:41 PM - Thread Starter
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I'll bet money - this one:

http://opamplabs.com/products/logic-module-plug-in/transformer-audio/t-10k.html

wow. ok. not sure how i would wire that though.

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post #19 of 23 Old 03-28-2013, 02:55 PM
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Yep, that is the transformer I use. Wiring is easy. The leads marked with a dot on the can are the "phase" leads, that is the hot or center conductor of a RCA cable. The shields go to the other side of the winding. The winding are identical so it makes no difference which winding is the input side or output side. The pin 6 from the core of the transformer goes to the enclosure for the two transformers and there you go!

I use these for high impedance (single ended interconnects) and the 600 ohm version wired as a balanced interface (XLR) if necessary

You MAY need to tie the enclosure to the low or non--phase terminal of the output winding going to the input of your AVR.
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post #20 of 23 Old 03-30-2013, 11:19 PM
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This one is only $5 more and is rated for down to 20 hz instead of 30. It might sound a little better if you are using it on your sub.

For extreme linearity at subwoofer frequencies look at Jensen Transformer sub isolators. They do cost a bit more but may be worth it to you.
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post #21 of 23 Old 03-31-2013, 06:24 AM - Thread Starter
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I would order that Jenson one but after strapping the direct TV shield to the amp chassis and putting the Hum-X on the projector, you have to put your ear right up to the cones to hear any hum.

After trying two other isolator's an having the sound issues, I'm also a little sceptical of that Jenson one not having the same result.

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post #22 of 23 Old 03-31-2013, 09:40 AM
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It's hard to say for sure without knowing all of your details. The Jensens are simply fairly high quality but still somewhat affordable version of isolation transformer solutions similar to what many many companies produce, not a magic bullets. The only reason I even mentioned them was since transformer saturation was brought up and Jensen has models designed to sound good in the subwoofer band unlike most companies who focus on the 20-20kHz range. If subwoofer isolation turns out to be a valid approach to solve whatever causing your system noise, you'd be hard pressed to find a lower distortion solution for less money. That's all.

Edit: BTW did you ever try going toslink between the satellite receiver and the avr? questionable cable/sattelite guy installations are suspect gnd loop generators.

Edit 2: projector? Let me guess you have it plugged into a different panel circuit than the avr? if so theres a potential gnd loop.

Good luck!
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post #23 of 23 Old 03-31-2013, 10:33 AM - Thread Starter
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Quote:
Originally Posted by Ugly1 View Post

It's hard to say for sure without knowing all of your details. The Jensens are simply fairly high quality but still somewhat affordable version of isolation transformer solutions similar to what many many companies produce, not a magic bullets. The only reason I even mentioned them was since transformer saturation was brought up and Jensen has models designed to sound good in the subwoofer band unlike most companies who focus on the 20-20kHz range. If subwoofer isolation turns out to be a valid approach to solve whatever causing your system noise, you'd be hard pressed to find a lower distortion solution for less money. That's all.

Edit: BTW did you ever try going toslink between the satellite receiver and the avr? questionable cable/sattelite guy installations are suspect gnd loop generators. The Direct TV box has functions only available through HDMI

Edit 2: projector? Let me guess you have it plugged into a different panel circuit than the avr? if so theres a potential gnd loop. Yes. its on a different circuit. im starting to think i should have used one 40 or 60 amp circuit for everything. im fine with the results i have now though so ill just keep it how it is. i do appreciate the info on the Jenson though and ill remember it should i visit the issue again.

Good luck!

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