Ha, just reading the title before I clicked on the thread, I'm thinking to myself this sounds like DC riding on the AC and wondering where it might be coming from...then I open the thread and I'm like Ha! One point for the Raven.

It's good that the device eliminated that DC, but I'd like to find the source. IMHO, I usually find it's coming from a cable connection. Disconnected the main coax line to the house and suddenly your problem goes away. The hard part is getting them to fix it!

Don't know about all digital multi-meters, but mine will read any DC that is on the AC line.  Just set it to DC volts and plug the leads into the AC socket, being careful not to electrocute yourself of coarse  :)

The higher voltage ranges, 40 and 400, work fine.  The lower range, 4, reads "over" all the time.  The way to test is with a hot air gun, or a hair dryer.  My hot air gun puts .34 vdc on the line in low and 1.7 vdc in high.  My cheap $5 Harbor Freight meter also works, but does not read 0 when there is no DC, but rather flickers between 0, .1, and .2 (200v scale which seems to have the least flicker) so you might interpret this as a false positive.

Audio by VanAlstine (www.avahifi.com) also makes a DC blocker, the HumDinger, that sells for $140.  They have sold quite a few and have had very few, if any, returned under their 30 day money back satisfaction guarantee.
https://avahifi.com/collections/used-demo-and-quick-ship/products/humdinger-dc-l...


Dan

Correction:  The hot air gun puts much more DC on the AC line when its in LOW.  Typically a diode is used to to block half the AC to the heater in low and this causes a large imbalance and hence the large DC component on the AC line.

Geno:  Try plugging a hair dryer in the same circuit as your Zstage and turn it on/off.  You can use a long extension cord to get the hair dryer in another room if its too loud.  If your hum changes noticeably as the hair dryer is turned on/off it will tell you that your Zstage is sensitive to DC.  If there is no change in hum your Zstage is relatively immune to DC and the blocker probably won't do much good.

Dan

So, I’m the guy that had the DC offset issue for years, and that’s my note that Steve posted a few days ago.  Over the years, I tried several possible solutions, really thinking that the problem was anything other than DC on my AC, although, the DC offset issue was always in the back of my mind.  Installation of dedicated AC lines, heavily shielded AC power cables, shielded IC cables, careful positioning of all equipment and cables, weights on transformers, using isolation transformers that themselves hummed, even attaching clamps directly to transformers and tightening them down, were some of the things I tried.  Some had some affect, but none solved the problem.

The results of using the Emotiva CMX-2 DC offset eliminator go far beyond silencing extremely noisy vibrating transformers.  Steve told me that it would be like listening to my Torii Jr for the first time, and of course, he was right!  To my great surprise and delight, every aspect of music reproduction has improved!  A huge perceived increase in power was immediately noted.  The deeper bass and incredible control over my eight 15” OB woofers is simply hard to believe.  I thought I had a very clean sounding system prior to buying the CMX-2, but only now do I realize that there was significant distortion.  Treble sounds have completely opened up, as if I added tweeters to my system.  Sound staging/imaging have improved too, but in unexpected ways—the apparent spaces and silence between instruments and singers is now spooky good.  It’s all truly better than what I’m writing.....I just don’t know how to describe it.  And here’s the biggest surprise of all; not only are all of these things true when driving my PAP Quintets with my Torii Jr, the improvements are even bigger when using my LFD solid state amp that has a huge toroidal transformer.  This transformer was dead silent before using the CMX-2, so I was expecting little to no enhancement of sound.  Man, was I wrong!

I will be purchasing another $129 Emotiva DC offset eliminator and plugging my CD player into it.  Will I see more refinement in sound?  Based on what has happened so far, my guess is yes, but if not, it’s only $129 and it certainly won’t hurt anything.  I’ve read on various forums that DC offset filters cause overall compression of music reproduction, but my experience has been the exact opposite.  There has been a substantial increase in dynamics, especially on the low end.  My OB woofers now have as much tight slam as my corner bass horns (Klipsch copies) loaded with Altec 515B’s.  I am one happy guy today!

Archie, I think that’s a question for someone with far more technical expertise than I possess, but my question is this.  Are any of your larger transformers audibly vibrating/humming beyond your expectations?  The smaller transformer on my CSP3-25 was nearly dead silent prior to purchasing the CMX-2, and I have been unable to sense any improvement in sound quality with it plugged into to the CMX-2.  So, it seems to be the pieces with very large transformers that are negatively impacted by DC offset.  Maybe Steve or the guys at Emotiva can give you some advice.

Same thinking here......maybe it’s the missing link to creating the perfect chain!

+1 on the Emotiva DC eliminator.  I have kept one around for years - they work if/when you encounter the problem.  I don't have a DC offset problem in my current setup/listening room.  But I carry the CMX-2 around with me to my audio buds house in case we encounter that dastardly beast when swapping gear around.  If you have DC offset, you can also see it displace the cones on your speakers drivers(mids and woofs) from their neutral resting positions when you hook your amp to the speakers.

I just wanted to thank Carlsbad for sharing his story. In my case, with a SE34I.5, I suspected a DC Offset issue, based on posts here on the forum, and I tried the iFi DC Blocker without any improvements and then I decided to check the fuses and one was blown (the one on the right). Once replaced the hum was gone. Too bad that there is no access to them via the bottom and you need to open it up. I hope this information will help others.

Ditto with Nick. I tracked down my hum in a Torii MKIV to a blown a fuse. Once replaced,  no perceivable hum from the listening position.

I am waiting for a Sarah, hence my presence on this site, but currently using a Soundgate Ongaku copy (copper instead of silver however), and it hums.

230 Volts 50 cycle AC, shielded discrete power source with upgraded sockets and power cords. There are hum adjustment screws that have been adjusted to get the lowest hum, but still present. Tried the vertexaq JoRez ameto DC buster and filter, but no joy.

The hum from bass speaker (Altec A7 voice of the theatre) is about 50 cycles and volume increase increases heard hum. The transformers are Tango. The power transformer hums audibly at the same frequency that I hear over the speakers. I tried sorbothane pads under the feet and they might of helped a little, so I ordered some BrightStar IsoNode feet for the amplifier, the phono stage and each SUT. One YouTube video has some old electrician saying that if I place a sheet of wool felt between that transformer and the chassis it will go, but with voltages exceeding 1000 volts inside, I daren't fool with it.

My speakers are sensitive and the amplifier (at twenty watts) is probably too powerful for them. I am hoping the Sarah will be a better (quieter) fit. In the interim, I just barely crack the volume and the music covers the hum fairly well.

Have you swapped all the tubes on the right channel with the ones on the left channel to see if the hum changes sides?  (You will probably have to set the hum pots again when you swap the 300B tubes left for right.)

Hey Charles, as a future Sarah owner, this is very unsettling to hear. If I remember correctly, you sent your amp back to Steve, and it was returned with adjustments made to eliminate this problem—do I have that right? I'm sure that Steve will have a solution, but I'm sorry to hear that you are struggling with this issue.

Tony

Hi Charles,

If the hum is getting louder as the volume increases, then the issue is related to the 12AU7 input stage and we know that the output tubes and corresponding driver tubes are OK.

Also, this is not transformer hum, as the thread is titled.  This is hum coming from the speakers, and it is 103dB speakers.  We test the amps on 100dB speakers so you are hearing 3dB more hum than we would no matter what.

I agree the hum whatever it is should be the same on both channels provided the input tube has matched sections and the noise spec is the same on both sections.  

You are welcome to send the amp back in, or the input tubes that you have to be tested for noise, left for right sections of the tube.

All of this is assuming that you are making this test without any interconnects hooked to the inputs of the amplifier to rule out cables or upstream components.

-Steve : )

Contact Sarah for an RA and lets get to the bottom of it.   Both channels measured identical when it was here so lets see what happened and fix it.

-Steve : )