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OK I have a bad hum on two components torroidal transformers, and have long known that its probably DC on the main supply. Apart from the physical hum I'm told that humming transformers probably affect the audio quality as well, so it should be a very worthwhile tweak.I know about the commercial products available that block DC on the mains AC including the CIAudio XDC (I have CIAudio amps so this might make a good combo).
Anyway I started planning to DIY a new power strip then thought that I should build this in as it probably wont be much extra work and at least I can control the quality of the components inside (and save money).
Since I'm an electrics noob I thought I would post my plans here for peer review, for any guidance to make sure Im not doing anything that might detriment the sound and to get feedback on how to make it better. Im also thinking that others might want to know all of this as well.
We have probably all seen this DIY DC blocker:
http://diyparadise.com/dablok.htmlWhich was superceded by the discussion here:
http://www.diyaudio.com/forums/showthread/t-104626.htmlAnd revisited here:
http://sound.westhost.com/articles/xfmr-dc.htmTo end up with the circuit diagram from Ellliot Sound Products (shown above) also linked at:
http://sound.westhost.com/articles/xfmr-dc-f8.gif
(ignore the transformer to the right)My pick of components for 240V use:
2 x 15000uf/25V Polar caps (647-UFW1E153MRD)
4 x 10A600V Diodes (512-FFPF10UP60STU)Maybe Im going overkill on the diodes, and maybe I should have gone with the 33,000uf/6.3V as Bryston use with the DC blocker in their amps, especially since the DIY discussion tapers off with a preference for lower voltage and higher capacitance.
Any comments, opinions or guidance?
Edits: 03/07/09 03/07/09 03/07/09 03/07/09Follow Ups:
They have been using this circuit for a long time.
http://www.bryston.com/BrystonSite05/pdfs/SSTAmplifiers/4b+7bSST-SSB-SCH-6_20041013.pdf
Can this DC current be from a ground loop voltage or something separate? I've been breaking the loop by physically disconnecting the CAT when using the rest of the system but I did notice a slight vibration in my Outlaws when the ground loop was broken. How do I diagnose if there is DC contamination? What DC filters are available commercially? Not sure I want to DIY something on the AC lines. BillF
In my case, my power amp toroids hum loudly for a few minutes every school-day morning when my school teacher neighbor dries her hair. Some hair dryers use rectifiers to obtain the low power setting. This causes unbalanced I*R drop on the shared neutral and one way of analyzing this is as a small DC voltage in addition to the normal AC. The big toroids have very low DC resistance, so the DC current can be large enough to drive them into saturation.
A ground loop will not cause or cure DC on the AC.
If you want to try blocking any possible DC on your AC, PS Audio makes a Humbuster III with a money-back guarantee. An isolation transformer would also block DC, but you would need one big enough to support your system and it could cost a lot more.
Is this a potential DIY project? I'm pretty sure I could build a filter with some good safe plans. BillF
In the information era, people’s life is filled with hustles and bustles. Sometimes we just want a quiet environment to enjoy ourselves. Then you may need this WiFi Jammer which can be got from http://www.jammerfromchina.com/categories/WiFi%7B47%7DBluetooth_Jammers/ masking for acoustic interference against listening devices.
AC power is dangerous and DIY projects involving AC require complete awareness of the pitfalls. If you have not done this kind of thing before, you would do well to seek out a mentor to look things over before you plug it in.
Yeah, better to buy something like this from a good company. I'm happy enough with the sound I have. I've done quite a bit of house wiring. I know it has to be 'no doubt' right when you mess with lethal power. Since this music system comes under the 'toys' heading I should probably either live with the dirty AC or buy the fix. It doesn't have to be SOTA for my system just filter out most of the worst spikes and DC. Cable filters are one thing, AC circuits are quite another. BillF
At first glance I would say it looks like the diodes are just going to let the DC go right on passed the caps.
No matter what the polarity of the DC you have two forward biased diodes for it to pass through.
Better check your design again, because I don't see this doing anything.
I think the concept relies on DC being smaller than the forward threshold voltage of 2 diodes in series, about 1.4VDC depending on the diodes. I believe it would be fairly uncommon to find DC much higher than that in typical environements. Any DC voltage less than the series combination of threshold voltages of the diode would be blocked.
The thing that worries me about this circuit is the low voltage non line rated caps they seem to be using. Sure while the diodes work properly the caps are fine. If those diodes start failing (lightning etc.) there is a real fire hazard there.
Hopefully some of the pro electricians can pop in and comment on this. I suspect that by the time you make it safe with line rated caps the cost goes so high you can no longer afford to build it.
I would say it's OK.
Since the filter is all in series if parts were to fail short, say the capacitors due to a diode failure, no risk would ensue as the load is rated for the full line voltage and provides impedance limiting. The worst case would be a small fire hazard from the cap blowing which could be ameliorated by putting the assembly in a metal box.
Regards, Rick
Ah sure I see. A shunted failure would be much worse than this series stackup. Makes sense.
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