Ground Loop Isolation

[haklesup]

Mike, Have you ruled out the RCA cables themselves? A short or open ground wire could cause the humm. Could also be a marginally damaged connector that works well with some cables but not with others.<p>An impedance mismatch usually results in too high or too low volume (compensating for this usually results in hiss not hum)

[Edd]

RR:
Me thinks that possibly Mike has left the building….along with Elvis..<p>I was just referencing the Creative/Soundblaster/Audigy series and expecting a commonality in design specs.
I was in immediate agreement with the line INPUT Z of 47-50K Ω or even in agreement of a 4.7-5KΩ on some other units
I was unsure of the situation of the line output as to whether his unit was incorporating the Hi Z output or the low Z 600Ω,
more in the order of professional audio or radio stations. Or on units with a mini phone plug, an output Z in the order of 100Ω for driving headphones.
Now if his unit is utilizing the 600W Z he is in luck since Radius Shackamus happens to offer a 1:1 transformer for a mere Fo’ American Dollah @
http://www.radioshack.com/product.asp?c ... d=273-1374 <p><<<
Is it possible to connect a speaker set to the internal connections of a Audigy card?<p>Well, yes and no!…..
No. Because there is no internal pin-out for the SB-Live or Audigy cards that is the stereo analog output.
(NOTE: There are some OEM cards that do have the internal connections, but these are not available through retail outlets.)
But…
Yes. Because there is a work-around.
Use a stereo mini-jack to plug into the back of the card, then route the cable back into the machine. Add the required connector type, I suggest a shielded cable. Use a grommet for the cable to go through the case to keep it from wearing a hole in the cable over time.
The outputs on the back of the card are designed for line-level devices. The alternative is to use the Audigy Drive which has a converter from digital to analog built into it.
(NOTE. This does not use the case headphone jack, it has its own jacks.)<p>What are the line-in/out/mic specifications?<p>Line-In:
Line level inputs.
Sensitivity: 0v to 2v Most new PCI cards are RMS, (most or all the old ISA cards are peak to peak).
Impedance 47K-50K Ohms.
Normal input should be about 1V.<p>Line-Out:
Line level outputs.
0 to 2V RMS or peak to peak.
Normal output level about 1V.
Impedance assumed 10K Ohms, some cards 600 Ohms.
Described as: Given a full Sine wave at 1Khz tone and a 10K Ohm Load should produce about 1V RMS output. <p>Line-In and Line-Out connection suggestion: Use a ground-loop-isolator between the sound card
>>>
All above excerpts were as per:
http://developer.creative.com/faq/faq.a ... c=80#faq58<p>
73's de Edd
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<p>[ August 01, 2005: Message edited by: Edd Whatley ]</p>

[Mike]

Nope. Me thinks me is still here.<p>As I said before, I haven't had a chance to test any of your suggestions yet, since the home theater room it's going into has been under construction.<p>Just today the carpet was installed and we finished working on the room. So, I'll be trying your suggestions.<p>About the cables, I know it isn't the cables as I've tried three different ones.<p>About the resistors, I'm kind-of confused. I know that on my speakers I built I used 500-ohm resistors on the input to ground, and those do lower the volume quite a bit. I could change them, I just haven't had time to and the amps have enough gain to make up for the volume loss. Does this mean I've got a 600-ohm output on the card? I almost think it means my card is a 10k impedence.<p>I looked up the impedence specs for my receiver - a Denon AVR-2801, and found this page: http://www.usa.denon.com/catalog/pdfs/avr2801LIT.pdf<p>In that page it says the following: CD, DVD, VDP, TV/DBS, VCR-1 VCR-2/V-AUX, CDR/TAPE,
FRONT L/R, CENTER, SURROUND L/R,
SUBWOOFER....................... 200 mV/47 kohms<p>10K to 47K. There is a problem in itself. But as haklesup said, that would cause hissing - not humming, and I don't have any hissing.<p>So maybe the problem is a ground loop? I guess I could always but that isolator and if it doesn't work, bring it back, or for even less money I could get the coax to optical converter, which may be a good move if I want to watch dvds or play surround games on my system.<p>Or maybe I will try the 6-channel inputs and use the 6 channels from my sound card to drive those inputs. But if that humms theres 60 bucks worth of isolators.<p>Edd, with that transformer, would I need one per channel or one for left/right signals?<p>Thanks!

[Robert Reed]

OK guys, now I am thoroughly confused. I thouht Hi-Z lines went the way of the Phono cartridge, vaccuum tube and dinosaur. In this day of 'OP Amps do everthing" why would we use Hi-Z output terminals. EXEPT for special transducer situations.
I do not get into nor am I familiar with computer add on devices such as media gadgets, so anything I read is taken as gospel (just a babe in the woods on this subject). It seems to me that good engineering practice is to have any output at a usable level ( 1Vrms) and be able to hold up against low impedances (>500 ohm). This not only is an easy task but is almost automatic with todays chips or yesterdays transistors.
Input impedance can be relativly hi (as in the ideal amplifier) because we are not dealing with POWER here, a luxury that tranferring high levels of power does not have.
The line impedance is still held low by virtue of output Z.
Have the computer geeks changed all good engineering practice as they have terminology? Or am I missing something here? Please help me out on this one as I have an open mind when it comes to learning something new.
Now as to the subject of ground loops-i.e. such as a heavy enough signal current(or a long enough line) of one type interferring with a smaller signal of a desired type, by causing actual voltage gradients on a common ground line ,is the usual cause of this annoyance. My experience with ground loop problems (or should we call it common ground) has only occurred when involved with extremely lo signal levels or very hi amplification, or both. This is usually an intercircuit problem and is adressed before final proccesing and outputing signal to another device (again at proper voltage and impedance levels). From the description of Mikes problem, with this level of interference, it sounds more like an incorrect ground or NO ground.
I hope I am not steering this post off the subject too much But as I had mentioned I am thoroghly confused (not hard to do where I'm concered ).

[EPA III]

You can't have a "ground loop" problem withour a ground loop. So you have to ask yourself, where's the ground loop? Your computer card and amp were connected via the shield so there is one side of a potential loop. So, is anything else connected between them? If not, then, the most likely path for the other side of the loop is the power grounds in the two power cables. You could try a ground lifting adapter on the amp's power cord. This may stop the hum and thereby prove that it was a ground loop. If it doesn't and there are no other connections, then it is likely not a ground loop. <p>Other things can cause hum. Does the amp have hum when no input is connected? It may have a bad filter/regulator in the power supply. Does the hum appear if the ground connection is made without the center conductor being connected. That points back to a ground loop. Does it happen if the shield is lifted at one end of the cable? This may indicate poor shielding (the hum is being picked up by the cable). <p>As for high impedance vs low, you can do a simple test. If you put a 600 Ohm resistor across the line either at the output of the computer card or at the input of the amp, and the level drops just 3db (about half level) them it is low impedance, likely 600 Ohms. If the level drops far more and is or almost is inaudible, then it is high impedance and more suceptable to picking up hum and noise. If it is 600 Ohms, then a 600 Ohm resistor at the input of the amp will provide the proper termination and a further measure of noise immunity. (I say 600 Ohms but that is not a standard value so 580 or 610 are close enough and will do.)<p>Problems like this are many and are the principal reason why professional audio is run with 600 Ohm balanced lines instead of single ended, high impedance with only one conductor and ground.<p>[ August 18, 2005: Message edited by: Paul A. ]</p>

[Robert Reed]

Paul A
If you bridge the line with a 600 ohm resistor and the voltage drops 3db--then its already terminated. This is called double terminating . If the line was unterminated, then the bridging resistor would drop the voltage by 6db.This would tell you whether to add term. or not to add.
I still beleive his problem is other than ground loops. Ground loops are annoying. But the hum level he is experiencing would drive one out of the house.<p>[ August 18, 2005: Message edited by: ROBERT REED ]</p>