So some more news from our thread on head-fi (argh I'm not allowed to post links yet, but it's in the Taboo MKIII appreciation thread).

It seems that the differentiating factor to whether you have the constant humming or not is whether there is that physical noise coming from the transformer.  Those with silent Taboos are reporting that they don't hear this sound.

I'm really hoping there's something we can do about this.

I just got my 5 posts! YAY!

I can post the link to the Head-Fi thread. Page 72 is where I begin to discuss the issues I have. Thanks!

http://www.head-fi.org/t/655788/the-decware-taboo-mk-111-appreciation-thread

One thing I can tell you is that some people also seem to be a lot more sensitive to the sound of hum than others.  I've got a slight hum in my Mini Torii.  I had a friend come over who said he thought he could hear it when his ear was against the speaker.  Wasn't even sure he was hearing it then.  I can actually hear it if there is zero ambient noise later at night with nothing playing in my listening chair 6 feet away.

He thought I was crazy and was imagining the noise.  We tried a test  with him turning the amp on and off without me being able to tell what state the amp was in while I was sitting in the chair.  I guessed when it was on every single time, he swore he couldn't hear a thing.  I wonder if some who say they hear nothing, really do have the same issue but just aren't sensitive to it.

Have you tried measuring the hum in your amp?
You need an AC voltmeter that has millivolt range. Just measure the voltage across the speaker or headphone terminals. You should get a reading of less than 1 mv.

I don't think I'm being overly sensitive to the hum coming from my Taboo, though I do have somewhat mixed feelings.  Reading that paper that Steve wrote, my hum is definitely of the type that you hear when music isn't playing.  It's not really noticeable or annoying when music is playing, apart from in occasional very quiet passages.  I could probably live with it, but it doesn't seem right when Steve says that the Taboo is supposed to have a low noise floor and that others experience exactly that.  I'd always be haunted by the niggling feeling that something is 'wrong' with my precious Taboo.  The high noise floor is a stark contrast to my beautiful Violectric stack and its infinitely black silent background - I'd like to think that the Decware amp can achieve something similar.

I don't have a multimeter type thing so I can't measure the hum myself.  I'm basically going to wait to see if thegrobe fixes his issue with that conditioning device and will then maybe consider doing something similar.  

Just to let you know I don't have a taboo but would love to get one in the future. I read through this thread and have some ideas to try. I am not an expert but these are ideas I would try. To me it seems that the transfomer it humming to the point you can hear it physicaly and not throught headphones or speakers. Is it possible that the hum is getting transfered through the chassis into the tubes? I know on my other amps, if I tap the the top I can hear it through the speakers. I would say for the fun of it get sme Dynamatt and put some on the metal chassis and see if that helps any. Dynamatt is suppose to help stop vibrations. Also you can try rubber washers under the transformer or those tube dampners. Try that and report back.

Okay, here's a weird one...

Of course you folks following this thread remember my comments about background hum I can faintly hear it with LCD-3, and very much with IEM's, pretty much makes the amp not useable for me with CIEM's. I sent the amp back to have it checked out, everything was normal, warranty was transferred so it wasn't a wasted trip at least.  

So I continue to fool around with this, Trying power conditioning, etc. as I REALLY want my Taboo background silent so I can use my CIEM's. The CSP3 background is dead quiet, the CIEM's work well with that side of the pair, but not on the Taboo side.

Well the Taboo is most certainly sensitive a sensitive instrument.

Check this out. I have the Taboo next to the CSP3, naturally. I plugged my CIEM into the Taboo, with the Taboo TURNED OFF. But the CSP3 was turned on. I could hear the background hum.... with the Taboo turned OFF. Weird. So I figure something is coming through the cables maybe? I disconnect the speaker wires, the RCA interconnect, event the power cable feeding the Taboo. Nothing hooked up to it.

I turn the CSP3 on, plug my CIEM into the Taboo and guess what? Background hum. The same noise I'm hearing when the Taboo is on by itself. This is crazy. I pick the Taboo up and move it about two feet away and the noise stops. Something inside the Taboo is acting as an antenna and picking up "hum" from the transformer. Either the transformer of the CSP sitting beside it, or naturally it would pick up the hum from it's own parts as well. So this explains why it hums.

Soooo...should I send it back again? Or does anyone have an idea of why this is happening and a possible fix? I feel that this info may be helpful in troubleshooting, that the hum is present when it's fully disconnected, turned off, but even SITS next to another amp! I LOVE this amp but this one thing bugs me and would like it not hum. Totally weird that it can be fully disconnected and have a background hum by just sitting next to another amp.

Also anyone else with a CSP pre and a Taboo that has a little background hum, see if you can recreate this?

TOTALLY WEIRD

...TABOO?

It has been quite some time that this thread has not been attended...

I recently bought a TABOO as well, which is a great amp.  I also hear the hum on my LCD-2 and after tracing the source of the hum I figured out that it is the transformer.  I have not had a chance yet to measure the noise (that will be the next), but do we have any solutions for the transformer hum apart from checking the screws, bolts and nuts, etc?

The hum is not in the way of the music, so it should be acceptable, but with such an amazing sound quality, one wants everything to be perfect (if there is such a thing!).

Best,

Alper

I actually tried four different rectifier tubes with the TABOO so far.  In terms of the hum, they did not make any change.  

I also measured the AC voltage at the speaker outputs yesterday and it reads 0.4-0.5 mV which is significantly below the threshold Steve has mentioned before in his white paper from 2003.  

Maybe, I should stop being obsessive compulsive about this next to negligible hum!  :)

Steve just got back to me mentioning that the transformers on the TABOO and SE34I.2+ are the same...

Over the weekend, I tried a BlackNoise Extreme filter on the mains, and it reduced the hum, just by a tad though.  Along with a friend who has an audiophile store and who is very experienced in the field (he designs and builds his own tube amps), we listened to the amp with different AC filters and our conclusion was not touching the amp at all, as it sounds so good already and any change would not be worth the attempt.  So I think I will live with the little hum!  :)

The causes of hum can be incredibly benign. I noticed a hum from one of the channels of the Zen CKC I have at my office, a loud 60hz hum from the right speaker. I changed the rectifier - no difference. Then I swapped the power tubes around and voila! Hum gone! It appears that the right power tube was simply not making proper contact in the socket.