Infernal Ground Loop Hum!!! - AVS Forum
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post #1 of 59 Old 12-15-2013, 04:23 PM - Thread Starter
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I've been experiencing a ground loop hum problem in my system which I originally thought was due to the cable. Whenever I would hook up the cable box, I'd get a hum that was very clearly audible at my seat. Today, I had a tech from Optimum come over and he re-grounded the cable and did a whole bunch of stuff that dramatically lessened the hum. Now, you can only hear it if you put your ear up to the speaker. It's still there, but much quieter. When I turn my Integra DHC-80.3 off, the hum is gone completely. As soon as it powers on and boots up, the hum is back. Thinking it was still due to the cable, I disconnected it with the tech still here, powered everything on, AND THE HUM IS STILL THERE!!!! So it must of been partially due to the cable, and partially something else.

So my question is, where do I go from here? What could be causing this much more faint, 60hz hum? I'm banging my head against the wall here.
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post #2 of 59 Old 12-15-2013, 05:09 PM
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Quote:
Originally Posted by Blackdevil77 View Post

I've been experiencing a ground loop hum problem in my system which I originally thought was due to the cable. Whenever I would hook up the cable box, I'd get a hum that was very clearly audible at my seat. Today, I had a tech from Optimum come over and he re-grounded the cable and did a whole bunch of stuff that dramatically lessened the hum. Now, you can only hear it if you put your ear up to the speaker. It's still there, but much quieter. When I turn my Integra DHC-80.3 off, the hum is gone completely. As soon as it powers on and boots up, the hum is back. Thinking it was still due to the cable, I disconnected it with the tech still here, powered everything on, AND THE HUM IS STILL THERE!!!! So it must of been partially due to the cable, and partially something else.

So my question is, where do I go from here? What could be causing this much more faint, 60hz hum? I'm banging my head against the wall here.

Hopefully your electrical system is reasonably new. Plug all ac cables into the same circuit. What happens then? Also unplug everything, then plug one thing in at a time until you hear the hum. Separate all ac cables from line level and speaker lines...don't run them parallel with each other.

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post #3 of 59 Old 12-15-2013, 05:19 PM
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post #4 of 59 Old 12-15-2013, 05:19 PM - Thread Starter
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Quote:
Originally Posted by Espo77 View Post

Hopefully your electrical system is reasonably new. Plug all ac cables into the same circuit. What happens then? Also unplug everything, then plug one thing in at a time until you hear the hum. Separate all ac cables from line level and speaker lines...don't run them parallel with each other.

From what I can tell, there is only 1 ground for the electric in the house, and it's corroded on the cold water pipe. There was no other ground outside that I saw, but the neighbors have a ground outside the house where the electric come in. All the wires are in the wall for the speakers and aren't near electrical wires. They are also balanced XLR cables. I'll try your method of unplugging everything now.
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post #5 of 59 Old 12-15-2013, 05:32 PM - Thread Starter
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I have powered speakers. The problem is inconsistent. When I power on my pre-amp with nothing else attached, SOMETIMES it hums, sometimes it doesn't. When I power on my Oppo, the hum doesn't start. As soon as I start playing something and the pre-amp switches to it's proper mode, the hum starts.
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post #6 of 59 Old 12-15-2013, 07:40 PM
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Quote:
Originally Posted by Blackdevil77 View Post

I have powered speakers. The problem is inconsistent. When I power on my pre-amp with nothing else attached, SOMETIMES it hums, sometimes it doesn't. When I power on my Oppo, the hum doesn't start. As soon as I start playing something and the pre-amp switches to it's proper mode, the hum starts.

Hopefully your gear receptacles are not shared with other ones in the home. Sometimes appliances, tube lights, and light dimmers can cause things to act inconsistent.

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post #7 of 59 Old 12-16-2013, 03:36 AM - Thread Starter
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Quote:
Originally Posted by Espo77 View Post

Hopefully your gear receptacles are not shared with other ones in the home. Sometimes appliances, tube lights, and light dimmers can cause things to act inconsistent.

They aren't, they are all brand new and the pair of receptacles in the equipment closet is on it's own dedicated circuit. This one really has be scratching my head. Last night my family watched a movie on "Vudu" and after the movie, I paused it during the end credits, and put my ear to the speaker. No hum at all. Then the next time I power up and go to watch or listen to something, the hum may be there.
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post #8 of 59 Old 12-16-2013, 03:51 AM
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Originally Posted by mtbdudex View Post

Have you read and followed the advice in this FAQ sticky here?
http://www.avsforum.com/t/322698/hum-faq

I looked at that FAQ and can't see any mention of the use of isolating transformers.They are also called ground loop isolators which is a good description of what they are.

There are two kinds, one for antenna lines and one for audio lines:

Antenna or cable system ground isolator (try first if an antenna or cable sytem is attached to the system):

http://www.amazon.com/Viewsonics-VSIS-EU-Cable-Ground-Isolator/dp/B0017I3K9M



Audio ground loop isolatore (use if no antenna or cable system is involved or as a second step if one is):

http://www.radioshack.com/product/index.jsp?productId=2062214

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post #9 of 59 Old 12-16-2013, 09:34 AM
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good point arny, I used one of these before I fixed my ground loop issue, paid $20 in late 2008 in my memory, I still have it in my box of goodies.
We should post into that FAQ these boxes....
Behringer MicroHD HD400 2-Channel Hum Destroyer
http://www.zzounds.com/item--BEHHD400



OP, best is fixing it via correct ground plane established.
If you can't do that easily, then getting one of the product listed is next best way.

Please don't use a cheater plug.....
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post #10 of 59 Old 12-16-2013, 09:41 AM
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Originally Posted by mtbdudex View Post

good point arny, I used one of these before I fixed my ground loop issue, paid $20 in late 2008 in my memory, I still have it in my box of goodies.
We should post into that FAQ these boxes....
Behringer MicroHD HD400 2-Channel Hum Destroyer
http://www.zzounds.com/item--BEHHD400

If that comes in a steel box, the slight extra cost (street price ca. $30) would be offset by the improved shielding.
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post #11 of 59 Old 12-16-2013, 10:26 AM
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But you'll need four of these for that Behringer box:
http://www.amazon.com/Hosa-Cable-GPR101-Inch-Adaptor/dp/B000068O3S
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post #12 of 59 Old 12-16-2013, 12:30 PM - Thread Starter
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Thanks for the suggestions guys. If possible, I'd like to do it the legit way and find out what is causing the hum and why and get it fixed the right way. Finding out what's causing it seems to be the hard part since it's so inconsistent. If there's a breeze or a mouse farts, it seems to change the severity of the hum or whether it happens at all.
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post #13 of 59 Old 12-16-2013, 03:39 PM
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Quote:
Originally Posted by Blackdevil77 View Post

Thanks for the suggestions guys. If possible, I'd like to do it the legit way and find out what is causing the hum and why and get it fixed the right way. Finding out what's causing it seems to be the hard part since it's so inconsistent. If there's a breeze or a mouse farts, it seems to change the severity of the hum or whether it happens at all.

Adding a ground isolator to your cable line could work,and if it does work that would be a legiit fix and it would be a stable fix.
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post #14 of 59 Old 12-16-2013, 03:46 PM - Thread Starter
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Originally Posted by arnyk View Post

Adding a ground isolator to your cable line could work,and if it does work that would be a legiit fix and it would be a stable fix.

Yes, I was going to do that and asked the cable guy. He told me it wouldn't help because the cable isn't the problem anymore. He re-grounded it and tested the grounds "amperage" and it was good. The hum was dramatically lessened after he did this, and when I completely disconnect the cable box, the hum is still there so I don't think it's the cable anymore. I could be wrong, I don't know but wouldn't disconnecting it stop the hum if it was the cable?
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post #15 of 59 Old 12-16-2013, 04:04 PM
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Quote:
Originally Posted by Blackdevil77 View Post

Quote:
Originally Posted by arnyk View Post

Adding a ground isolator to your cable line could work,and if it does work that would be a legiit fix and it would be a stable fix.

Yes, I was going to do that and asked the cable guy. He told me it wouldn't help because the cable isn't the problem anymore. He re-grounded it and tested the grounds "amperage" and it was good. The hum was dramatically lessened after he did this, and when I completely disconnect the cable box, the hum is still there so I don't think it's the cable anymore. I could be wrong, I don't know but wouldn't disconnecting it stop the hum if it was the cable?

What are you going to believe? The cable guy or your own experiences?

if the cable guy is a god in your eyes and I'm trash then I should stop wasting my time with you because you are trapped in a fantasy world.

I've seen this one coming all along. I've played the cable guy's game and IME it is a losing game.

It is possible to decrease the hum that a ground loop adds by beefing up the wiring that forms the loop. But the loop remains and various changes to the operational environment can make the hum problem come back. Sound familiar? This is the battle that your cable guy is fighting and losing.

Trying to beef up the loop is a losing battle because all he is doing is desensitizing the loop, he isn't making it completely go away.

A ground loop isolator actually makes the ground loop completely go away.

You must be impossibly impoverished since at most about $30 is on the table. ;-)
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post #16 of 59 Old 12-16-2013, 04:18 PM - Thread Starter
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Originally Posted by arnyk View Post

What are you going to believe? The cable guy or your own experiences?

if the cable guy is a god in your eyes and I'm trash then I should stop wasting my time with you because you are trapped in a fantasy world.

I've seen this one coming all along. I've played the cable guy's game and IME it is a losing game.

It is possible to decrease the hum that a ground loop adds by beefing up the wiring that forms the loop. But the loop remains and various changes to the operational environment can make the hum problem come back. Sound familiar? This is the battle that your cable guy is fighting and losing.

Trying to beef up the loop is a losing battle because all he is doing is desensitizing the loop, he isn't making it completely go away.

A ground loop isolator actually makes the ground loop completely go away.

You must be impossibly impoverished since at most about $30 is on the table. ;-)

No need to get so defensive and no, I'm not in a "fantasy world." I'm simply questioning this because when I DISCONNECT the cable, the problem persists. Before this guy did his stuff, disconnecting the cable would immediately have the effect of killing the hum. Now, since he did whatever the hell he did, disconnecting the cable has no effect on the hum, what so ever. This is the only reason I'm questioning if the cable is at fault, don't think for a second it's simply because that's what some cable guy told me.

And it was really tough, but I dug up enough pennies from inside the couch to buy a ground loop isolator. I honestly hope your right and it fixes the problem.
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post #17 of 59 Old 12-16-2013, 04:48 PM
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Quote:
Originally Posted by arnyk View Post

What are you going to believe? The cable guy or your own experiences?

if the cable guy is a god in your eyes and I'm trash then I should stop wasting my time with you because you are trapped in a fantasy world.

I've seen this one coming all along. I've played the cable guy's game and IME it is a losing game.

It is possible to decrease the hum that a ground loop adds by beefing up the wiring that forms the loop. But the loop remains and various changes to the operational environment can make the hum problem come back. Sound familiar? This is the battle that your cable guy is fighting and losing.

Trying to beef up the loop is a losing battle because all he is doing is desensitizing the loop, he isn't making it completely go away.

A ground loop isolator actually makes the ground loop completely go away.

You must be impossibly impoverished since at most about $30 is on the table. ;-)
This is the type response people that get pissed off about. You're supposed to be helpful with a little tact. Nasty response....mad.gif
amirm likes this.
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post #18 of 59 Old 12-16-2013, 05:37 PM
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Originally Posted by ratman 
This is the type response people that get pissed off about. You're supposed to be helpful with a little tact. Nasty response....mad.gif

Trust me, I'm not surprised.

This ground loop problem or something like it has been flogged since no later than this post http://www.avsforum.com/t/1360965/integra-dhc-80-3/2460#post_22151709 dated 6/20/12 showing that things can be slow.
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post #19 of 59 Old 12-16-2013, 05:40 PM
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Quote:
Originally Posted by Blackdevil77 View Post

Quote:
Originally Posted by arnyk View Post

What are you going to believe? The cable guy or your own experiences?

if the cable guy is a god in your eyes and I'm trash then I should stop wasting my time with you because you are trapped in a fantasy world.

I've seen this one coming all along. I've played the cable guy's game and IME it is a losing game.

It is possible to decrease the hum that a ground loop adds by beefing up the wiring that forms the loop. But the loop remains and various changes to the operational environment can make the hum problem come back. Sound familiar? This is the battle that your cable guy is fighting and losing.

Trying to beef up the loop is a losing battle because all he is doing is desensitizing the loop, he isn't making it completely go away.

A ground loop isolator actually makes the ground loop completely go away.

You must be impossibly impoverished since at most about $30 is on the table. ;-)

No need to get so defensive and no, I'm not in a "fantasy world." I'm simply questioning this because when I DISCONNECT the cable, the problem persists. Before this guy did his stuff, disconnecting the cable would immediately have the effect of killing the hum. Now, since he did whatever the hell he did, disconnecting the cable has no effect on the hum, what so ever. This is the only reason I'm questioning if the cable is at fault, don't think for a second it's simply because that's what some cable guy told me.

And it was really tough, but I dug up enough pennies from inside the couch to buy a ground loop isolator. I honestly hope your right and it fixes the problem.

Remember that I recommended two different ground isolators, one for cable coax and one for audio. From thousands of miles away its hard to resolve the situation much closer than that.
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post #20 of 59 Old 12-16-2013, 07:07 PM - Thread Starter
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Quote:
Originally Posted by arnyk View Post

Trust me, I'm not surprised.

I imagine that in your great wisdom and intelligence Mr. Rodent you think that your response isn't the least bit nasty? ;-)

This guy has been flogging this ground loop problem since no later than http://www.avsforum.com/t/1360965/integra-dhc-80-3/2460#post_22151709.

That was when the set-up was in another room. At the time I dismissed it hoping the problem would go away once I moved everything to the theater room
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post #21 of 59 Old 12-16-2013, 07:11 PM - Thread Starter
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I think I've pinpointed the source of the hum. My Oppo BDP-93 seems to be the culprit. When I powered down, the hum went away. When I powered it back on, it came back. Only sometimes when I power it on is the hum not there. The Oppo is connected to the pre/pro via HDMI only. Those audio cable isolators won't do anything for me then.
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post #22 of 59 Old 12-16-2013, 08:11 PM
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Quote:
Originally Posted by arnyk View Post

Audio ground loop isolatore (use if no antenna or cable system is involved or as a second step if one is):

http://www.radioshack.com/product/index.jsp?productId=2062214

Only use this device if you absolutely don't care about audio fidelity and want to flip a coin as to whether it fixes anything. These are its specs which are missing from the product page:

"ELECTRICAL DATA:

Impedance Ratio:
Z1:Z2................................................1000 Ohms:600 Ohms
Z1:Z2................................................1000 Ohms:600 Ohms
Frequency Response:.............................300 Hz to 4000 Hz +/- 3 dB
DC Resistance:...............................................@25 degrees C
Z1:....................................................200 Ohms +/- 20%
Z2:....................................................150 Ohms +/- 20%
Insulation:.........................500 VDC apply to primary and secondary
more then 100 Meg Ohms Min.

(ALL-01/26/95)"


Note the highly limited 300 to 4000 Hz frequency response which itself is not even flat! (+- 3 db). And of course that all important spec for noise rejection is completely absent!!

Amir
Founder, Madrona Digital
"Insist on Quality Engineering"

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post #23 of 59 Old 12-17-2013, 03:30 AM - Thread Starter
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Only use this device if you absolutely don't care about audio fidelity

That would completely defeat the purpose. I don't want to sacrifice audio quality for the hum. I want to eliminate the hum and that's it. I've already done enough experimenting to know it's not the cable and my Oppo is the culprit. What do I do in this case?
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post #24 of 59 Old 12-17-2013, 04:47 AM
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Contact Oppo directly?


Via my iPhone 5s using Tapatalk
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post #25 of 59 Old 12-17-2013, 04:57 AM
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Quote:
Originally Posted by Blackdevil77 View Post

Quote:
Originally Posted by amirm View Post

Only use this device if you absolutely don't care about audio fidelity

That would completely defeat the purpose. I don't want to sacrifice audio quality for the hum. I want to eliminate the hum and that's it. I've already done enough experimenting to know it's not the cable and my Oppo is the culprit. What do I do in this case?

I agree with you that if the device were as bad as has been claimed, it would be a problem. I don't know where those specs came from as they don't appear to be on RS's web site. Note that no link was provided, so they could be someone's invention or representative of some other device. They are questionable to me as they seem to be inconsistent among themselves.

Edit - I searched around and found a matching document at http://support.radioshack.com/support_auto/doc9/9542.htm . Besides the internal inconsistency, it appears to be dated 01/26/95 - almost 20 years ago. Apparently the product was updated or there was a big difference between how it was tested then and how I tested it. All I can say is that my tests were designed to be representative of likely actual use.

That's why I obtained one, hooked it up and measured its performance. Suffice it to say, it measured a whole lot better than that.

One is currently de-humming my subwoofers and if it really rolled off everything below 400 Hz like Amir seems to be claiming, that would be a big, big problem.

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
"

There are over 400 reviews of this device online according to google - if you are so inclined read them for yourself!
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post #26 of 59 Old 12-17-2013, 05:06 AM
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Quote:
Originally Posted by arnyk View Post
 
I agree with you that if the device were as bad as has been claimed, it would be a problem. I don't know where those specs came from as they don't appear to be on RS's web site. Note that no link was provided, so they could be someone's invention or representative of some other device. They are questionable to me as they seem to be inconsistent among themselves.
 

 

Arny, I googled around and found this:

 

http://support.radioshack.com/support_auto/doc9/9542.htm

 

Appears to be the same device. It would appear that there is something not right about the specs - as you say, a 300Hz cutoff wouldn't work brilliantly on a subwoofer ;)  I think I'd prefer to follow someone who has actually tested the device than someone who has read the specs on the Internet.  

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post #27 of 59 Old 12-17-2013, 05:12 AM
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I agree with you that if the device were as bad as has been claimed, it would be a problem. I don't know where those specs came from as they don't appear to be on RS's web site. Note that no link was provided, so they could be someone's invention or representative of some other device. They are questionable to me as they seem to be inconsistent among themselves.

 

Arny, I googled around and found this:

http://support.radioshack.com/support_auto/doc9/9542.htm

Appears to be the same device. It would appear that there is something not right about the specs - as you say, a 300Hz cutoff wouldn't work brilliantly on a subwoofer wink.gif  I think I'd prefer to follow someone who has actually tested the device than someone who has read the specs on the Internet.  

As the saying goes, a little bit of knowledge can be a dangerous thing!

There are a lot of questions about that report - it is dated almost 20 years ago. As I mentioned in the other post there are some internal inconsistencies - believe it is a 1:1 transformer but the primary and secondary DC resistances are different. That's not impossible but it is a bit unexpected.

Usually products like these are produced in batches every once in a while under contract by someone who gets a set of specs that they are expected to meet or surpass. The operative word would appear to be surpass. ;-)
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post #28 of 59 Old 12-17-2013, 05:21 AM
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Originally Posted by arnyk View Post


I agree with you that if the device were as bad as has been claimed, it would be a problem. I don't know where those specs came from as they don't appear to be on RS's web site. Note that no link was provided, so they could be someone's invention or representative of some other device. They are questionable to me as they seem to be inconsistent among themselves.

 

Arny, I googled around and found this:

http://support.radioshack.com/support_auto/doc9/9542.htm

Appears to be the same device. It would appear that there is something not right about the specs - as you say, a 300Hz cutoff wouldn't work brilliantly on a subwoofer wink.gif  I think I'd prefer to follow someone who has actually tested the device than someone who has read the specs on the Internet.  

As the saying goes, a little bit of knowledge can be a dangerous thing!

There are a lot of questions about that report - it is dated almost 20 years ago. As I mentioned in the other post there are some internal inconsistencies - believe it is a 1:1 transformer but the primary and secondary DC resistances are different. That's not impossible but it is a bit unexpected.

Usually products like these are produced in batches every once in a while under contract by someone who gets a set of specs that they are expected to meet or surpass. The operative word would appear to be surpass. ;-)

 

Quite :)  I hadn't spotted that it dated from 1995!  Makes it pretty unconvincing as a source.

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post #29 of 59 Old 12-17-2013, 06:09 AM - Thread Starter
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But how will that device help me with my oppo if it's hooked up via HDMI?
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post #30 of 59 Old 12-17-2013, 07:21 AM
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But how will that device help me with my oppo if it's hooked up via HDMI?

It probably won't.

For obtaining ground isolation of HDMI lines you need something like this:

Rainbow Fish Fiber Optic HDMI Cable

http://www.ebay.com/itm/20-6m-Rainbow-Fish-Fiber-Optic-HDMI-Cable-Best-Picture-Sound-Quality-/281159562297

http://store.rainbowfishcorp.com/c/home-series - minimal length suffices for your purposes.

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