Strange ground loop...?

I just hooked up a new amp and I'm having a strange noise issue. Only in my right channel, I get this high-pitched whine... maybe around 2khz. My left channel is dead silent.

The problem seems to be an interaction between my DAC and my amp. If the DAC is off, the amp is silent.

At some point in your trial and error testing did switch, cross, the ics at the amp? (Switch the right with the left at the Amp, one end only of the ics.) See if the buzz then goes to the other channel of the amp. This will kill two birds with one stone, so to speak, the Dac as well as the ics.

The amp is an 84' yamaha, so the cord has no ground. There is a ground screw, though, and I have connected that to my power conditioner, hoping this would solve it... nope.

The amp, I assume, has a built-in phono preamp. The ground screw is for the ground wire of a TT, not to connect the amp to earth ground.

Is the plug on the cord of the amp polarized? One blade wider than the other? Can you plug the plug into the wall receptacle in either direction?

I suspect I just need to find a proper place to run that ground wire...

I would not recommend connecting the chassis of the amp to earth ground.... It can cause more harm than good.

Hmm, no phono in... just a pair of RCA's. It's a Yamaha M-40 power amp.

The plug isn't polarized.

In the manual, it says to connect the ground to the pre-amp ground if there is a buzz. Unfortunately my pre-amp has no ground.

You were right about switching the ICs. Last night I started to think... 'wait, this doesn't make sense that it would only be coming though one channel.' I swapped the ICs with another pair, and the issue was solved.

I have no idea how this could happen - maybe something is wrong with the shielding on one of my ICs? They are brand new, so I didn't suspect that at all.

Incidentally, I had to turn my amp on and off many times while switching power configurations around. Also, some music was distorted in that right channel (crackly, fuzzy) at times... could any of this have damaged my amp / speakers?

IC shield is grounded at one end only (if it's RCA). Try to reverse one that gives you trouble.

Hmm... interesting. Well, the cord is already going back... but that's good to know for the future.

Any chance the static distortion did speaker / amp damage? Everything sounds fine, but I would like to know if such distortion is the same as amplifier clipping...?

"If the cable is coax, the shield connected at both ends of the cable."

Bob - I was talking about interconnects.

Ok... I have to revive this thread. I just received my new replacement cable as well as a new passive pre-amp. I hooked everything up and **suprise!** the whining interference noise is back in full force!

So, I started to switch around the orientation of my interconnects. I have one from my DAC to my pre and the other from my pre to my amp. Pretty standard.

Now, I have found a configuration that works pretty well, but not perfect... there is still a very faint 'whining' noise when my volume on my pre-amp is set between 8 and 11 o'clock. Beyond that, it's dead silent.

Now, tell me how this makes any sense... at all:

Let's say interconnect 1 has terminals A and B. Interconnect 2 has terminals C and D.

Here here my results, running sequentially from DAC to pre-in to pre-out to amp:

A-B-C-D : loud whine
A-B-D-C : loud whine
B-A-C-D : loud whine
B-A-D-C : loud whine
C-D-A-B : loud whine
C-D-B-A : loud whine
D-C-A-B : loud whine
D-C-B-A : dead silent except for faint whine at low volume

I don't get it... at all. What gives? If it's a shielding problem, then shouldn't configuration A-B-C-D also work just as well?

What should I do?

Ok... definitely frustrated now.

Even with configuration "D-C-B-A" when at volumes other than 'full' on my pre-amp, I get this really fuzzy, static interference when lower frequencies are strong (deep base).

This is the second passive pre-amp that has done this and it is a different make than the first... sooooo, I think it's safe to rule that out at the culprit...

It's these cables I bet... They are BlueJeans cables, though... I thought these were supposed to be pretty good???

"I don't get it... at all. What gives? If it's a shielding problem, then shouldn't configuration A-B-C-D also work just as well?"

Shield should be grounded on the receiving end (in my opinion) so your configuration D-C-B-A suggests that terminals C and A have shield grounded.

Another update -

I just swapped out one of the BlueJeans ICs with an old Monster IC I had and the problem is completely gone... no whining or distortion at all.

Unfortunately, I don't want to use my old Monster cables... so I guess I will have to send all my BlueJeans cables back and get something else. Bummer.

Bob - what do you mean by "coax interconnects"? Are you talking about digital cable?

U guys think I should just try some different cable?

I seem to be out of options with my current BlueJeans LC1s.

You think so? IDK, it seems weird that just swapping out one of the interconnects fixed everything...

Plus it isn't the typical 60Hz humm.. it's like 2-3 kHz... more of a whine. Also, there is that strange distortion in my lower bass region.

All I can think is there is some sort of interference between 2 BlueJeans cables that are near eachother and have a different magnitude of the same signal going through them (the one after the pre-amp will be attenuated unless it's at full volume).

Sucks...

Bob - I asked since I've never had coax interconnect. Grounding shield on both ends is really bad, using shield as return is even worse. In addition coax cables, used in video applications, have not the greatest copper since at high frequencies signal travels only on the surface (often silver plated). Blue Jeans cables can still sound great (I don't question that). Capacitance, they are so proud of (12pF/ft) is nothing special (typical for polyethylene) since best cables have 3.5pF/ft and my cable has 5.1pF/ft. In order to get this capacitance foamed teflon in oversized tubes is required but it's expensive.

I am not talking about ground loops. If transmitting end (let say preamp) has ground/case at different potential than power amp's ground/case then it places this potential on the shield. Shield couples this difference (AC) to signal wire (referenced to different GND). When shield is grounded on the amp side then it has exactly the same level as the reference level of the signal wire and doesn't couple anything.

So what alternatives to BlueJeans do you guys think I should try? I need to stay around that same cost, unfortunately ($40 per cable max).

Djembeplay - I did not read your posts about cables carefully. If it's Blue Jeans cable and is grounded on both ends, like Bob says, then switching cable direction wouldn't make any difference.

It is difficult to find something in this price range (and I don't have a lot of experience). You might be able to find used AQ King Cobra (previously Python). It is very nice and neutral cable.

Ya... I'll try the grounding thing and let you know how it goes.

Would this be the same as grounding my amp to my power conditioner? I tried that... and it altered the nature of the distortion, but did not remove it.

Grounding issues are always 60Hz hums though, right?

This one is like 2-4KHz... and varies as I alter the volume levels of my pre-amp.

Ya, in that early post I had thought that going straight into the wall had worked. It ended up that it repressed the noise quite a bit, but the distortion of lower frequencies was still there and the high-pitched whining had turned into a static 'fuzzy' background.

I'm going to go try some old cheap interconnects I have laying around real quick. I'll report back.

Bob - It makes sense, but why reversing interconnects makes difference? If it's BlueJeans then it's grounded on both ends and reversing it would not make any difference. He says that in one configuration of ICs noise is gone.

Why is it only in one channel - ground loop should affect both channels. Something is fishy here. Could it be defective cable? He mentioned that switching to Monster Cables eliminated noise completely.

Ok, test complete. Yes, this is essentially the same test as when I swapped one cable out for the Monster cable.

The result was the same. There is no distortion. The bass is clean and there is no hint of any "whiny" interference noise as I change the volume.

It's like whenever two LC-1 cables are used in tangent, this is the formula for opening the gates of hell...

WAIT! NO! I was mistaken. Upon closer listening, I do still have some distortion in my right channel... right channel only. And this is only with lower frequencies.

The 'whine' sound is certainly gone though.

Ok, so... now I'm going to bypass my pre-amp all together and run straight into my amp from my DAC via a 2ft LC-1 cable.

I just wanted to add... this distortion, again, completely goes away with my pre-amp turned all the way up.

Sooo... actually there is no need for me to run straight into the amp from my DAC... I know it will be perfect. It has been that way for a few days and it was fine. Also, the fact that it goes away with my pre-amp turned up all the way indicates that something is awry in that area of the chain.

Sorry for all the posts -

Ok, what I'm going to do is try a different amplifier and see if the same thing happens.

03-11-09: Djembeplay
I just wanted to add... this distortion, again, completely goes away with my pre-amp turned all the way up.

That rules out ground loop hum imo.....

Humor me and try another source other than the DAC.
I think the problem is the DAC

The thing is... it sounds perfect when I run my DAC directly into my AMP.

OK, so.. here's what I just did:

I didn't use my other amp (integrated) simply because I didn't have the right terminals on my speaker wire. I did, however, use it solely as a pre-amp feeding my amp (whereas the pre-amp I have been using was a little passive w/ volume control).

Using my older integrated as a pre-amp, the noise was MUCH MUCH worse. Again, it was primarily in the right channel.

I switched the RCA's connected at the back of my power-amp, and sure enough, the distortion completely switched channels as well. So, we know it isn't a malfunction on the part of the amp I suppose.

It must be line interference somehow... I really don't get it still.

I'm now going to try connecting my amp chassis to the ground on my temporary pre-amp.

Ok, Chassis on amp connected to chassis on DAC or pre-amp = zero difference at all (full distortion still present).

oh no I havent tried that... I will right now.

Jea48 - Your on the right track.

I just hooked up a long run of crappy RCA cable from the analogue outs of my PC. It was the same set-up just with a different source than the DAC... and there is no noise or distortion at all.

So... the problem isn't the cables, but rather something with the output of the DAC interacting with the pre-amp.

It's weird that the DAC sounds excellent when going straight into the AMP.

So, Tvad - I'm going to take your advice and try to ground the DAC to the pre-amp. What is the best way to do this? There is no 'ground' provision on my pre-amp or my DAC, unfortunately.

"I just hooked up a long run of crappy RCA cable from the analogue outs of my PC." - quality of the cable is probably not important but this crappy cable probably doesn't use shield as return. Try the same cable from the DAC.

You got it Kijanki.

That sounds perfect now. Man, that was crazy.

Ok, so... for some reason I can run LC-1 from my DAC directly into my amp without a problem... but I cannot run LC-1 from my DAC into my pre-amp.

I would have never guessed this... how weird. I had to try a thousand different things to figure this one out.

So, why would this be the case? I'm pretty clueless on this one.

It was caused by the LC-1 using shield as the return? What does this mean? Why was it bad only when connected to my pre-amp? What types of cable should I be looking at as a replacement?

Thanks everyone for the help - much appreciated.

Djembeplay - I'm still not sure that cable was the problem. In general using shield as return is a bad thing but in case of hum or interference we enter the area of "black magic". Bob is right about your problem originating in unit being plugged into different outlets but the certain cables can exaggerate this effect. Why can't you plug everything to the same outlet?

I do have everything plugged into the same outlet. It's all on a power conditioner, actually. I think the confusion there arose when I was switching my power plugs around everywhere to see if that would make a difference.

I tried grounding the DAC to the pre-amp chassis earlier but it didn't seem to make the slightest bit of difference. The screws on my DAC are really small, but I made pretty good contact with them.

So, even though LC-1 cables use shield as a return, I still shouldn't have this problem? What exactly does it mean to use shield as return?