[Martyn]

This question builds on a thread Occam started several years ago on the Aspen board. I have a small amount of hum (not really significant) from my Arcam receiver (which uses a toriodal transformer) and rather more hum from the twin toroids in my AKSA (which is a slight irritant). I'd like to try whether a DC blocker will eliminate this. Occam's thread (http://www.audiocircle.com/index.php?topic=12706.0) refers to the use of a diode bridge and a couple of capacitors. He specifies the caps as Nichicon UHE high ripple electrolytic, 35v 3,300uf or 25v 4,700uf, but doesn't specfy the diode bridge. Can anyone help me out with an appropriate part, please? A Digikey part number would be the most useful for me. Thanks,

Martyn

[Occam]

Martyn,

Sorry for the late response; I missed your post. I'd suggest (as you're in a 240vac country) using a standard screw mounted >= 400v, >=20amp bridge





Any of there should work fine -
http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&keywords=GBPC2506
The ones with the 'W' designation have wires (2nd pic), and are a bit less expensive that the others with quick connect terminations (1st pic), same ratings.

[JoshK]

Those big ass bridges (BABs) are very useful tools in the DIY'ers arsenal.  I find them particularly useful in constructing yin/yang ground loop isolators (search elliot sound projects for an article on this).  I bought a bunch a while back from an online surplus site for cheap. 

[Martyn]

Actually, I used to live in 240-land (where I learned great respect for bare wires), but these days I live in Canada with 120V (or 113 to 117 more typically in my house). Does this affect your recommendation?

[Martyn]

It's been a while since I've cruised Rod Elliott's site, Josh, so I've spent the last couple of hours there. There's more info than you can shake a stick at. I didn't chance across much that pertained to my 240V versus 120V question except a couple of references that seem to suggest that it doesn't really matter - if it's OK for 240V, it'll be OK for 120V.

I guess the next question is whether it would be a smart or stupid idea to tack this DC blocker onto the supply side of a Felix in the same enclosure, but maybe I should ask that one on the Felix thread...

[Gordy]

Quote from Occam on the original thread...

The only type of simple power conditioning I'd recommend for amps beyond an across the line cap is a common mode choke, i.e. the PsAudio Ultra Outlet, the DeZorel?, or DIY. But the efficacy of this approach is severely compromised by and unequal DC offsets between Line and Neutral. So even if your transformer isn't sensitive to DC offset, if you use a CMC power conditioner, the DC blocker is essential. 

[JoshK]

Martyn,

Occam's suggestions will work fine for 120v too.  Those are what I use.  Adding this DC trap before a Felix is a convenient thing and worthwhile.

[CSI]

An alternative might be the CIA XDC-2. Check it out in the CIA Circle on this site.

[Martyn]

Thanks, fellas. The 120 - 240 compatibility would be convenient if I were ever to return to Europe in retirement (as if I could ever afford to). The CIA unit is a typically neat design, but I tend to like to DIY within reason, especially if I have confidence in the designers. A DIY project is all the more exciting and satisfying when it lies outside one's area of expertise but still produces an outstanding result. That's not to say that I don't have my share of failed projects languishing under my bench...

[CSI]

Hey, that's the fun of it! Just watch out for those high voltage rails.

[Martyn]

I'll wear my rubber gloves just in case!

Just to make sure I've got this right...as per lower left here: http://diyaudio.com/forums/attachment.php?s=ffd71bd5b855094b8f32a411fb1c67e7&postid=328821...

1. One AC line is broken and the bridge inserted (and connected via its AC terminals).

2. The bridge's + and - terminals are left unconnected.

3. The caps are connected across the AC terminals with opposing polarities, i.e. one + and one - leg connected to the input side of the bridge, and one + and one - leg connected to the output side.

Does it matter whether the live or neutral AC line is used?

[Occam]

2. The bridges (+) and (-) are jumpered with a wire (bridged). Otherwise the bridge is not actually in the circuit, with just the antiphase caps paralleled, in series with the AC. When the wire bridge is in circuit, the AC passes through 2 diode drops.

I've redrawn the circuit and labeled it as the 2 Diode drop DC Blocker.
I've also included 'Redundo' which uses that same bridge, but is configured for a single diode drop. If any  component fails 'open' it will still work, hence the name.
A single drop DC blocker can remove up to a single Vf (voltage forward drop), typically 1.1vDC. A dual drop blocker, 2.2vdc.



As to which side, hot or neutral, you should insert it into serially, dunno.
Typically, like Brystron, which the referenced schematic comes from, its in the neutral line.

[Martyn]

Paul, this is terrific. It seemed somehow counter-intuitive, even to an ME like me, that the + and - were not connected; now it makes sense.

One of the perennial problems for people like me on these boards is that you folk chatter away among yourselves posting your various concept sketches and modification ideas, while all the time there's so much implicit understanding of what's going on that you don't need to bother with the details. Thus unless someone eventually summarises the discussion, posts the final circuit, and lists the BOM, we ignorant lurkers are left with bald patches from all the head-scratching.

What I'm trying to say is that I very much appreciate the time you've spent tidying up all the loose ends for me. You have turned this project from a head-scratcher to a no-brainer for me - thank you.

Martyn

[JoshK]

We've all been there at one point. 

I found that a minimal amount of reading up on some basic electronics really helped my ability to follow along, but I still have a hard time in some forums.  For instance, go over to diyhifi.org and read some of the threads in the digital subforum.  I get about 5% of it.     We all start somewhere.