RB 1080 balanced input has static noise

[Alex Tang]

I just got a used RB 1080, and connect it to my Denon receiver using a RCA - XLR cable, but there are static noise. I tried connect with RCA - RCA unbalanced, and it is fine.

It seems it is just plain simple that there is a problem with my Rotel. Before drawing the conclusion, would like to check in the forum .... could there be any setting I need to configure?

[mjb]

Nope, there's nothing to set. Unfortunately it sounds like a problem with the XLR input, or cable. Have you tried another RCA-XLR cable?

[Alex Tang]

Well, I bought 2, and has static noise on both channel. So, it is unlikely that both cables are having problem.

[vifferboy]

There is a switch on the back of the amp I think you have to change if you use the balanced outputs, did you change that ?

[Alex Tang]

There is a switch on the back of the amp I think you have to change if you use the balanced outputs, did you change that ?

Yes I did. I found out if I didn't change to balanced, there is no sound. So, I am confirmed that I have changed that.

[SkyDover]

Have you tried XLR to XLR and make sure it works that way. Maybe it's picky about using an RCA to XLR?

I had a similar problem with a different brand amp when I tried this with a RCA to XLR and got some static and sometimes hum. When I tried XLR to XLR the static went away but just the hum. When I plugged the amp into a dedicated outlet shared by nothing else, the static and hum went away completely on either cables, so I guess it was ground lope causing it somewhere in the house. Any outlet in the house would cause the problem for me unless I used the dedicated outlet and the problem was solved. Just a thought. Good luck.

[Alex Tang]

Have you tried XLR to XLR and make sure it works that way. Maybe it's picky about using an RCA to XLR?

I had a similar problem with a different brand amp when I tried this with a RCA to XLR and got some static and sometimes hum. When I tried XLR to XLR the static went away but just the hum. When I plugged the amp into a dedicated outlet shared by nothing else, the static and hum went away completely on either cables, so I guess it was ground lope causing it somewhere in the house. Any outlet in the house would cause the problem for me unless I used the dedicated outlet and the problem was solved. Just a thought. Good luck.

Thanks for the reply. Unfortunately, I don't have a preamp with XLR, so, I cannot test. I currently plug it to a Monster power bar .. not sure if it makes a difference, I can try plug it to a wall and try. I bought the amp used, so, I don't think I will send it in for fix since the RCA cable is working fine.

[Alex Tang]

I tried the 2 leg adapter between my Rotel amp and Monster surge protector, and it works! No more hissing sound.

But I have a dumb question. I can see that is a Ground light on my surge protector .. I am not quite sure what that means .. is the Ground used to project the equipment like if it got strike my lighting? If I switch to the 2 leg without the round ground, does that mean my amp is not surge protected.

Also .. I have an Adcom preamp that I can plug my Rotel to it such that it will turn on when the Adcom is turned on. It is definitely more convenient, but is there any disadvantage doing that?

Thanks.

[Glen B]

Why are you using an RCA to XLR cable when there is no need to ? Your receiver has RCA outputs only, and the Rotel amp has RCA and XLR inputs. You should use the RCA inputs. I'm surprised that no one has yet pointed out to you that there is no benefit to using the balanced inputs of the amp with an unbalanced source. You have no noise using the amp's RCA inputs, therefore no need to lift the AC ground.

I am not familiar with Monster products but the ground light is likely showing that a ground connection is present. It is highly likely that the surge protection devices in the Monster unit shunt power surges from hot to ground, and neutral to ground.

The amplifier ground is a safety feature, meant to shunt any ground fault in amp (i.e., internal failure that energizes the chassis) back to the household neutral, which is grounded at the electrical panel. If the amp AC ground is lifted, you will still have surge protection because the Monster unit is grounded.

If you are thinking of plugging your amp into a switched AC outlet of your Adcom preamp, don't do it. Such outlets are rated for only a few hundred watts, The amplifier draw will be more than the preamp's power switch and outlet can handle.

[Alex Tang]

Thanks for your reply. The first thing I do is to unplug it from my Adcom preamp.

Although using RCA-XLR has no benefit, but interestingly, the sound is "different" comparing to using plain RCA cable. In fact, I think the plain RCA cable sounds better. It sounds more musical, dynamic, and lively. The RCA-XLR cable sounds dull.

I don't know if it is because of the cable, or some thing inside the amp that makes the difference. Actually, both cables are cheap, ordinary cables, so, I don't think it is the cable itself. I think the difference is caused by the amp. So, I switch back to RCA cable, and wasted $20 for the RCA-XLR cable.

[Glen B]

I don't know if it is because of the cable, or some thing inside the amp that makes the difference.

What you are hearing is probably the effect of the op-amp used to convert a balanced signal at the XLR inputs to single ended. The signal at the RCA input goes directly into the input differential stage of the amp. In balanced mode, the inverted and non-inverted signals pass through the op-amp then on to the input diff.

[Alex Tang]

Base on my Electrical engineering 200 level classes, obviously I don't understand the diagram, but thank you for the info.

to confirm I am not biased, I ask my wife to do a blind test. She can also tell there is a difference. The RCA is brighter, and she thinks sometimes it is too loud and annoying. The RCA-XLR cable is more soft .. so, even though it is not as musical, she thinks it is more pleasant to listent to. But I like the RCA cable more. I feel the sound stage is also bigger for RCA cable.

So, now ... it leads me to think, maybe this is one of the reason of the mixed reviews. Some people said the Adcom pre-amp or the RB 1080 is dull and boring ... maybe they are using the XLR cable. But why would Rotel design in such a way that different connection yield different result? Is it a design flaw?

[Kevin D]

Rotel amps with balanced inputs are not truly balanced inputs. They get immediately converted to an unbalanced signal inside the amp. That is what Glen is showing you.

You're either hearing this conversion, hearing the cable conversion to balanced, or a combination of both.

Bottom line, if you only have RCA outputs use the RCA inputs, if you have RCA and balanced outputs, try both (but RCA would probably win), if you only have balanced outputs, then use the balanced inputs.

Kevin D.

[Glen B]

Based on my electrical engineering 200 level classes, obviously I don't understand the diagram, but thank you for the info.

I've edited the diagram. The yellow line is the path taken by the signal(s) at the XLR inputs. The purple line is the path taken by the single-ended signal. The latter is the simpler path, without any sonic influence of the op-amp and its associated parts.

But why would Rotel design in such a way that different connection yield different result? Is it a design flaw?

Its not a design flaw but a design choice. Rotel could have used one half of the op-amp as the single-ended input, but then there would have been an unnecessary stage always inserted in the signal path when the single ended inputs were used. Of course, when using long cables and a balanced source, the benefits of the op-amp would most likely outweigh any disadvantages.

The way Rotel designs their amps that have balanced and unbalanced inputs, when the RCA input is used, the signal is fed directly into the input differential (usually the first stage in an amp) and the more direct path. When the XLR input is used, the signal(s) pass through the op-amp, which converts the inverted and non-inverted source signals to single ended, which is then sent to the input differential stage.

Different op-amps each have their own sonic signature, pros and cons. IMHO, I believe the op-amp is a contributor to the differences you are hearing. If you visit a site like diyAudio.com and search for discussions on op-amps, you will find concensus that they all sound different. It all boils down to what you like.

In my system I have the option of either single ended or balanced connections. I have tried both, and while neither one was superior to the other, they were both just a little different. I preferred the sound of the balanced connections, and that is what I have been using for the past several years.

You prefer the single ended input, and your wife prefers the XLR input. I say go with what you prefer.

[Alex Tang]

Thank you for all the replies, I am clearer now. :T