I'd prefer the robust over kill nature of the device to be top notch, feeding my Krell amplifiers (had I paid the $ to own them) that may have some peaks. I'd also use compression mounting. (I have some silver over copper box tube things with set screws)
The affect on sound will be relatively close to a diode bridge in the equipment because it's on a 60hz cycle. It's not "infinitely" open.
Also diodes are not entirely linear. I'd prefer to stay in the window of closer to linear function with current shifts. You get less reverse voltage that way for example.
The affect on sound will be relatively close to a diode bridge in the equipment because it's on a 60hz cycle. It's not "infinitely" open.
Also diodes are not entirely linear. I'd prefer to stay in the window of closer to linear function with current shifts. You get less reverse voltage that way for example.
Last edited:
The reason for diagrams 2 and 3 is the idea that it might be safer to use polarity-opposed (back-to-back) electrolytics in series, otherwise obviously you just need figure 1.
If you impose a small ( ~ 1 or 2 volts) AC across back-to-back series electrolytics, how evenly do
they share the voltage?
Its very real. I used a 600va toroid some years ago and it could go from silent to growling at a moments notice as the quality of the mains varies. The load on the transformer at these times was minimal and constant (class ab amp at idle). The only thing changing was the mains.
Yes, hence why I started with a specific question, one which (FWLIW) hasn't actually been answered . . .
I don't have a 'scope but I did own a solid state amp whose large toroidal used to buzz like an angry hornet whenever things like electric blankets, fires, hairdryers etc were used. I built a clone of the Bryston circuit which entirely solved the problem. So yes, it's a real problem. Rod Elliot gives a pretty thorough breakdown here.
Its when the mains deviates from a pure sine that the problems start. If there is asymmetry between top and bottom halves of the cycle, the net result is that the average value is no longer zero... so by interpretation there is a DC shift in one or other direction (I'm not entirely happy with the term DC although it seems the common way of expressing the issue).
You could say that the long term integral of the mains voltage waveform, rises steadily. In exactly the same way that the long term integral of a DC voltage, rises steadily. But that's a mouthful.
you could say that (I had an uneasy relationship with calculus. This is about my level.WWU Planetarium - Math Jokes
Attachments
Got a ATI 2003 amplifier, without a DC blocker sometimes was silent, sometimes humming loudly, and worst when I plugged it into a APC Smart UPS.
Had a ATI 1807 before that (and pretty sure that has larger power supplies than 2003) as it has more channels and that never hummed.
With Kemp DC-X the hum has mostly gone, however when I switch on a coffee machine (it has a hotplate) the ATI 2003 hums again. Also last night the coffee machine wasn't on, but it hummed for a minute or so.
Would you think
a) Something wrong with the ATI amp
b) Kemp DC-X not working and still passing DC - kemp said something about low harmonics
c) Something up with the house mains.
Had a ATI 1807 before that (and pretty sure that has larger power supplies than 2003) as it has more channels and that never hummed.
With Kemp DC-X the hum has mostly gone, however when I switch on a coffee machine (it has a hotplate) the ATI 2003 hums again. Also last night the coffee machine wasn't on, but it hummed for a minute or so.
Would you think
a) Something wrong with the ATI amp
b) Kemp DC-X not working and still passing DC - kemp said something about low harmonics
c) Something up with the house mains.
Last edited:
Yes this type of "mains DC blocker" contains a built-in assumption, that any DC offset which might be present, is smaller than two times V-Forward. If the assumption is wrong then the circuit does not block all of the incoming DC offset.
If the DC offset is 50 volts, for example, then this type of circuit will not block all of it. Very true.
If the DC offset is 50 volts, for example, then this type of circuit will not block all of it. Very true.
I have a JL Audio F112 sub which, despite being powered by an SMPS, has a large toroidal transformer in it. It buzzes and annoys the proverbial out of me when the room is quiet. I raised the prospect of "DC on the mains" as a potential cause of the problem with JL Audio tech support, questioning why an SMPS powered sub would have a large toroidal transformer. They said that there was no such issue, that the Elliot Sound Products article I referenced was incorrect and that if I fitted a DC blocker into the power cord supplying the sub they'd void my warranty!
Maybe the large toroidal transformer does not connect to the mains. If it doesn't then no amount of jiggery pokery on the mains, is likely to affect the cause of its buzzing.
A galvanically isolated, battery powered, handheld digital multimeter, plus a couple of crocodile clip leads, can tell you whether or not the transformer terminal voltages are what you'd expect from the mains. If not then mains DC blocking becomes an activity with small chance of success. On the other hand if the toroid appears to be dealing with mains like voltages, mains DC blocking might do a lot of good. I agree with Rod Elliott; if executed competently, it won't do any harm at all.
There used to be a standalone product containing a mains DC blocker and nothing else. It was the PS Audio Humbuster. Here is it's user guide (pdf) and here are some pictures on Google Images. You could pretend your DIY mains DC blocker was this commercial device instead.
A galvanically isolated, battery powered, handheld digital multimeter, plus a couple of crocodile clip leads, can tell you whether or not the transformer terminal voltages are what you'd expect from the mains. If not then mains DC blocking becomes an activity with small chance of success. On the other hand if the toroid appears to be dealing with mains like voltages, mains DC blocking might do a lot of good. I agree with Rod Elliott; if executed competently, it won't do any harm at all.
There used to be a standalone product containing a mains DC blocker and nothing else. It was the PS Audio Humbuster. Here is it's user guide (pdf) and here are some pictures on Google Images. You could pretend your DIY mains DC blocker was this commercial device instead.