Good Example Balanced Input Circuit? (Ground Loop Isolation) - Page 3 - diyAudio
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Old 16th August 2008, 04:21 AM   #21
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Those circuits are for common mode noise reduction. That applies to pro audio, if I'm not mistaken.

I've never seen a head unit with a source resistor to ground but some of the Kenwood head units had balanced outputs and both outputs would have had the same source/output resistance/impedance.
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Old 16th August 2008, 06:32 AM   #22
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Brand names that did this sort of Balancing act to there car amps:

ADCOM< All amps ever made, no longer in production both RCA and Balanced line driver setup possible Built Mid to late 90's 5 pin DIN plug connections

ZAPCO < Many models over the years, some balanced line drive only requiring ZAPCO Balanced Line Driver module. < Local company to my area, just over the hill. Built currently on many models. Custom PS-2 computer like plug connection

Phoenix Gold ZPA 0.3 and 0.5 Amp series Audiophile grade car amplifiers again both RCA and balanced line drive capable using CAT-5 or 6 cabling. Used only on ZPA series but PG also built outboard line drivers to augment any stand alone system. You can find these on e-bay from time to time. Built mid to late 90's but not currently. Early models used PS-2 plug like connections but these had a issues of self disconnection (i.e. the plugs fell out of there sockets ) So the second version used CAT-5 and 6 plugs and cabling.


There were a few others over the years but I own two of the three listed above. I do have the modules on my bench for testing all of these amps since I work on them from time to time. I just have never installed them at this point. So I never have used the BLD setup before myself even though I own the stuff to do it with...Crazy eh?

I have heard horror stories about bad setups using BLD's and having all sorts of unexplained noise issues due mostly to inexperience and poor installation HISS related noise floor issues but this can be caused by mis-adjusted gains in most cases
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Old 16th August 2008, 07:36 AM   #23
Studio1 is offline Studio1  New Zealand
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Quote:
Originally posted by lumanauw
What do you guys think about this page http://www.dself.dsl.pipex.com/ampin...balanced.htm#1
At that page it is different between balanced line and balanced impedance (fig1).
To get balanced impedance, the RCA out ground of the head unit should be given Rs too, but I never saw a car head unit that do this.
I must be talking to myself I think. Did you not read what I posted a few posts up?

Balanced line connection does NOT solve ground loop issues, UNLESS:

At least one end of the balanced line has a transformer - and few pieces of equipment use transformers these days due to cost and the fact that saturation levels are more easily reached with a transformer than an active balanced circuit.

You are barking up the wrong tree if you think that balancing your signal from the head unit to the amplifier is going to cure your ground loops or hum issues.

Balancing is used to reduce or eliminate noise that might be picked up in the cables that run from the source unit to the amplifier.
Unbalanced cables such as RCA types with two wires are prone to picking up such noise.
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Old 16th August 2008, 09:22 AM   #24
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Surely a proper electronic balanced input/output scheme would prevent a hum loop though? If the hum is due to noise on the shield or different earth potentials (either of these cases superimposing unwanted voltage on the earth and only the earth) then the balanced input would reject it. e.g. say there is 2V of signal and 1V of rubbish on the sheild, at one point in time one side of the balanced input would see 1V and the other 3V therefore the output would be 4V which is correct.
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Old 16th August 2008, 05:02 PM   #25
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Default System Info/Diagrams

Sorry for the delayed response had to scan my document + scanner use problems.

Attached is the schematic of the amplifier modules. In my second post, a system diagram including the whole amplifier and source units, etc.

I will try again all suggestions above, and recheck how I applied Perry's suggestion.

Thank you again!
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Old 16th August 2008, 05:09 PM   #26
MartyM is offline MartyM  United States
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As a side note, originally I thought had resolved the noise. The source, the PXA-H701, measured continuity to chassis ground on its RCA shields.

I made a DC-DC isolation module, and isolated all power & ground to the Alpine PXA and 90% of the noise was gone. Increasing the input level on the amps revealed the ground loop noise, which is why I am here again!!

If I connect only one RCA or only one pair of RCA connectors from the source, each one/pair on a separate SMPS/amp, I don't hear noise. However any additional RCA connector in used per each SMPS/amp set reveals the noise.

My amplifier is really like 3 amps in one: all 3 SMPS outputs are isolated from chassis ground and each other, with a star ground configuration to the power connections.

All RCAs internal to the amp are direct to the PA100s & isolated from the amp chassis ground with the exception of the braided RCA shield, connected on only one end to amp chassis (chassis gnd). The reduced EMI picked up if I use cooling fans.

When the system is on I can verify no continuity to chassis gnd on the RCAs. I also disconnected the control cables going to the head unit (to break any ground connections there) and somehow still the noise was still present.

Right now I am having to run one one pair of audio per each SMPS + the sub channel to avoid noise.

I'm willing to try anything and really appreciate you guys helping me.
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Old 16th August 2008, 05:45 PM   #27
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Quote:
Originally posted by MartyM

I made a DC-DC isolation module, and isolated all power & ground to the Alpine PXA and 90% of the noise was gone. Increasing the input level on the amps revealed the ground loop noise, which is why I am here again!!

I'm willing to try anything and really appreciate you guys helping me.

I have done a similar DC to DC setup a long time ago back in 1993. and it worked well. The main difference is I DC to DC powered the entire low level system and isolated the antennas with blocking caps.
It was for a show car install, and the owner was a engineer, so he was looking to go as esoteric as possible. It worked. Plastic plates and mounting hardware. All grounds tied to a central point off the DC to DC converter regulator setup.
It was not cheap, but the client was happy with the results. He got a room full of trophies for the all the effort 2 years in a row. And no noise or hiss issues at all, ever.
But it was a very extreme situation, where SQ was the goal and the sky was the limit...
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Old 16th August 2008, 05:46 PM   #28
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With 3 isolated power supplies, you shouldn't be having ground loop issues.

Are all of the supplies driven by the same IC? If not, are the ICs sync'd together?

If you disconnect all RCA cables from the alpine processor, do you read 0 ohms between all of the shields on the processor?
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Old 16th August 2008, 08:55 PM   #29
MartyM is offline MartyM  United States
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Hi everyone-I tried all of the recent suggestions (above) and none worked.

Perry-yes, I have continuity (0 Ohms) between all RCA shields on the output of the Alpine PXA, and also to its ground wire, which now is normally isolated from chassis ground since I'm using my DC-DC isolator.

If I could get the amplifiers to stop popping fuses when I use ground loop isolators, I would settle for using those on the offending input pairs and that will allow me to use the unrestricted/unbuffered inputs on primary channels without noise.

I tried this earlier (using my Stinger gr. loop isolator) and had no noise, but popped 3 fuses either on amp start-up or at the end of music tracks. Also heard high-frequency ringing in the channels where they were used. (I'm assuming it's because the PA100 amplifier design has an input capacitor of 1uF and is causing oscillation?).

Thanks...the search continues....
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Old 16th August 2008, 09:44 PM   #30
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If the amplifier oscillates with the sec. CT and RCA input shield connected to chassis ground (when using the GLIs), the amplifier circuit may be unstable (it oscillates easily). Adding a small capacitor in parallel to the feedback resistor may improve stability.
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