Thanks for the informitive post, I'll check it out. I have been using powervar units for over a year now with excellent results. But one of them does have a low level hum 24/7. Don't know if this is the cause (can the voltage & frequency to 1 outlet be different than it is to 3 other outlets,where I have no hum at all,.. when all the outlets are feed from the same breaker box?) Thanks again!
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to remove that pesky DC from your mains supply. Remember, only a few mV of DC can make toroids hum like there's no tomorrow. I used this same basic design when I built my DIY Armegeddon-clone power supply for my Linn, and it cut the mechanical noise in the 1:1 isolation toroid by about three quarters (yes, it's that effective). Check DIY Audio for the abundant debate on HOW this circuit actually works. Pretty spiffy if you ask me. Regards,
Mdhoover, found these on diyaudio Forums
I use an EI isolation transformer ahead of my Arcam Alpha 9 CDP to eliminate dcv offset on its toroidal transformer. Have not tried the above filters.
Maybe you guys can help me or point me in some direction.
My apartment seems to be the King of Hum.
About a year-and-a-half ago, I "upgraded" from a CJ amp to Art Audio monoblocs. To my dismay, they hum like a bumble bee. I've tried an Exact Power unit, a BP 3.5 and a humbuster. Not only did they not work, but each transformer within these devices hummed. About six months ago, I bought a turntable - and the speed controller hums. The vendor says he has hever heard of one of his speed controllers humming and suggested I have my wall socket tested. More on that in a moment.
The only device I found that kills 90% of the hum at the monoblocs is a PS Audio 1000; which I just sent to PS Audio because it is blowing my equipment fuses. (I should know shortly whether there is a defect with the PS Audio unit - and to PS Audio's credit they are examining it at no charge even though I bought it here on Agon). The PS Audio only kills the hum when I set it to mode #3, which according to PS Audio, "adds a little 3rd order harmonic distortion, which makes the transformers operate a little more efficiently". The PS Audio hums, but it is much quieter than the monoblocs. The PS Audio has no affect on the speed controller hum.
I have tried all sorts of versions of lifting the grounds. I have tested the grounds at the so wall socket, which are ok. I have unplugged what devices I can from my apartment one by one.
Any suggestions? If I hire an electrician to test the wall sockets, can anybody tell me exactly what I should ask him or her to test for? What do I do with the results once I know? I am adrift in hummmmmmmmmmmmmmmmmmmmmmm.
BTW, kudos to Conrad-Johnson for manufacturing the only amp that does not hum at Jeff's pad.
I've been playing with transformers for the past year or so in several configurations, including TVC's, autoformers, power, isolation and balancing. I've made every mistake imaginable and managed to make them work. What I've learned is that they're as much of an art as a science. They can forgive blunders and be intolerant of the slightest problem. I'm losing my hair, by scratching and pulling, wondering how one configuration works and another doesn't.
The other thing I learned is that you need a very good ground. Pound that galvanized deep into the earth. It's ironic that one of their greatest benefits is their greatest weakness, DC.
I built the second link Jea48 mentions in his post, which is essentially the same as the link I posted. I kept it simple and used a piece of perfboard mounted on nylon standoffs. Everything can be configured point to point, and takes up no more than 3" square. There are no exotic/expensive parts here, and whole shebang ought not to cost more than $10 to build (including the mounting hardware). The thing to remember is that you MUST know what you are doing - this is the AC line we're talking about here, and obviously, the DC blocker is NOT UL approved. I will take some pictures of my DIY Armegeddon, which was based around a Powervar medical isolation device. All I wanted was the isolation TX and the chassis which were nicely adaptable for this use. I removed all the Pi filters and other crap between the AC in and out, and then built the Armegeddon circuit inside the Powervar case (and later installed the DC blocker after the Powervar proved too noisy).
DC offset seems to be a big problem for tranformers especially when driven to saturation. If possible, the best is to unplug the offending device that is feeding DC offset back to the mains (AC or DC motor or another power supply like a chopper power supply for a PC).
If manufactuers used more costly transformer designs that were less easily driven to saturation then DC offsets and acoustic noise would be much less of a problem.
Jea48: Thanks for the links. Now if I just knew how to read the diagrams.....
"The thing to remember is that you MUST know what you are doing - this is the AC line we're talking about here, and obviously, the DC blocker is NOT UL approved."Palasr: That would disqualify me from this endeavor, at least for now. DANG!
Good post! I Hope this isn't straying too far off topic. EI frame transformer magnetic fields brought up a thought i've been thinking about ie. separating the Amp from the preamp. I've heard 3 feet to be a minimum to avoid magnetic field effects fom the power amp. That would require a awfully large space around your amp, perhaps even removing it off the component rack. This, at least for me, would result in at least 1.5 meter interconnects which doesn't fit in the shorter is better camp. Recently i came across quarter inch stainless steel plate. Would this when added to shelving be enough to shield the preamp from the EI frame transformer? If not are there any other solutions beside distance.