REL T5i Subwoofer Hum issue

Al, thanks very much for your feedback. Sounds like you really know your stuff. 

The Decware amp is somewhat unusual in that its outputs are described as "floating," i.e., not referenced to ground. That is done to make it possible to bridge it into a higher powered mono amp (although there are other ways in which that is accomplished in other designs).

A consequence of that is that by connecting the negative wire from the sub to the negative left channel output terminal of the amp there is not a good return path to the amp for the signal provided to the sub by the amp’s right channel positive output. So it’s somewhat surprising that the results are as good as they are. And that may have been a factor in the hum issue as well.

I’m not sure what the results would be if you were to connect the negative wire to the amp’s chassis, as REL recommends for situations involving amps whose outputs are balanced or bridged. It would depend on the amp’s internal grounding configuration, and if the outputs are truly floating the result might be a big hum.

An inquiry to Decware might be in order, to ask what they would recommend regarding connection of that wire.

In any event, adding a second sub would eliminate that issue, as well as presumably providing sonic benefits. Regarding whether to connect the subs in that situation to the amp outputs or to the speaker terminals, while it may not make much if any difference it would probably be worthwhile trying it both ways. My perception is that in the majority of such cases people connect to the amp outputs.

One final note: I can’t tell from your post if the interference from the ST-70 occurred only when it was powered up, or if it occurred even when it was turned off (in which case interference from its power cable may have been responsible). But keep in mind that a tube amp having output transformers should not be operated without a speaker or equivalent load resistors being connected to it, at least when it is processing a signal.

Good luck. Regards,
-- Al

Guys, thank you all for the feedback. The mono vs stereo issue was very interesting since I've always wondered about that. I may want to get a second sub for stereo bass then, assuming that means it may sound even better? Thanks for sharing that info.

I was able to solve the problem. There were two tube amps. One was a 2 watt Decware SE84UFO and the other, a Bob Latino Dynaco VTA ST-70 which I switch to for various reasons. The Decware was getting the hum while the Dynaco was not, so I just moved the Decware to a different location and the hum went away so I'm guessing some interference? I'm using an Erhard Audio Aretha tube preamp and a pair of Heresy II's. 

This REL is absolutely stunning in tight bass as well as low end extension. The REL's red wire is connected to the positive right speaker channel of the amp while the REL's yellow wire is connected to the positive left speaker channel. The black wire is connected to the left negative speaker channel per the instructions for my stereo setup. The issue was originally caused from the right positive channel.

I heard that if I get a second sub, one for each channel, the ideal setting is to connect each sub directly to the input of the speakers? Not sure of that's true but so far I'm overwhelmed with amazement on how incredibly good this whole things sounds now with the REL. It may be worth getting a second REL sub? 
Thank you again

Not quite sure how all the bickering is helping to resolve the ops ground ( assumed ) hum issue?

Would be nice to know the amp the op is using to drive the Rel.

A Rel Arro should fix the ground loop issue that you are having.  My buddy had the same issue with the T9i.  Pm me if you want to buy an arro...

millercarbon

You might also want to read up on the reality that all low bass is mono. Theoretically there might be some recording somewhere that is not. In practice no one has ever produced such a thing.

Nonsense - even though it’s a claim commonly repeated - and I have recordings to demonstrate it. They’re consistent with the science of stereo LF - so you might want to check the references I previously provided to you. But again, if your system is wired for monophonic bass, then of course it will never produce stereo bass.

On the subject of stereo LF, you might want to review this thread that quotes Richard Vandersteen:

Modern sources such as streaming, CDs, DVDs, digital high-resolution music files, and Blu-ray Discs maintain full stereo separation to below 20Hz. Summing the channels into a single subwoofer reduces or cancels all the low-frequency information containing phase differences between the channels. Stereo subwoofers reproduce all of the bass information complete with the phase differences that help provide the imaging and location cues we use to place people and things at distinct points in the sound field.

Yes, a lot of stereo LF involves phase differences, as I’ve already explained to you.

I still don’t know why you’d suggest reversing system inputs (or outputs) to determine if a recording is stereo. There are easier ways, such as using your preamp’s mono switch. Of course, not everyone uses a preamp and not all preamps have mono switches, so while you may not have many alternatives, many do.

This is such an elementary first step standard trouble-shooting thing to do I just assumed everyone here would know about that. So okay, thanks for reminding me, lower the bar.

I understand that insulting others makes you feel "better," but you should know that an ad hominem attack is a basic form of logical fallacy. Your illogic simply reveals your fuzzy, disordered thinking. It joins your claim that "no one has ever produced such a thing" which is also a logical fallacy, because it’s logically impossible to prove a negative. Not that it matters much in this instance, because your premise is demonstrably wrong.

Be certain the amp and subwoofer are powered from the same outlet. 

One assumes you are using the speaker level inputs because your amp does not have a RCA sub out?

I suffered a ground hum using same method from my old Ayre ax7e integrated , never solved it.

Not sure if I paid any attention to whether it was specifically the pos or neg wiring that was the cause.

Some amps and subs will need a different connection for the negative.
Some will be fine off the negative speaker terminal, some will need the sub negative connecting to chassis ground instead.

Depending on your amp you may need contact manufacturer to see what they recommend.

I cheated and used a wireless Martin Logan sub.

@rankaudio

More details would probably be helpful. What is the make and model of the amplifier and the main speakers? And what is the negative wire from the sub connected to?

Regards,
-- Al

No cleeds, its not my system. My system if you would read my posts has five subs- two each on two amps, plus one self-powered. I’ve tried every combination you can think of for running those. You might also want to read up on the reality that all low bass is mono. Theoretically there might be some recording somewhere that is not. In practice no one has ever produced such a thing.

The "move" is to unplug the R from the R and plug it into the L. This is such an elementary first step standard trouble-shooting thing to do I just assumed everyone here would know about that. So okay, thanks for reminding me, lower the bar.

millercarbon

All the bass at low frequency is mono anyway ... Don’t believe me? Play some music you think has stereo bass. Okay now move the R to L and play it again. See how it sounds exactly the same?

I’m not sure why you’re moving things around. Recordings with stereo bass will have it coming more from one side than the other at times, depending on the instruments and how the recording was made. (I provided a few references to the science of stereo bass in another thread. The research on this goes back to the ’30s, at least. It’s really all about phase.)

Of course, if you set up your system with mono bass, then monophonic bass is all you are ever going to hear from it. That can be a very satisfying presentation and in some problematic rooms, it can be preferable.

It’s true that many LPs are cut with mono LF. But that doesn’t mean there’s no such thing as stereo bass. For example, I never sum the bass on recordings that I make myself. Yes, you can hear the difference.

In the earlier days of hi-fi, it was quite common for audiophiles to make their own recordings. I think it’s unfortunate that has fallen out of fashion, because the practice can give you a meaningful reference, and help you understand some of hi-fi’s common myths.

All the bass at low frequency is mono anyway. So don't connect it. Problem solved.

Don't believe me? Play some music you think has stereo bass. Okay now move the R to L and play it again. See how it sounds exactly the same? Because its mono.