[Occam]

Some of you ASKAphiles are asking about buzzing toroids on AA's Tweakers Asylum.....

Oftentimes its a result of DC on your AC lines. A rather comprehensive discussion of DIY DC blockers may be found here -
http://diyaudio.com/forums/showthread.php?s=&threadid=2080&highlight=
Mlloyd1 has posted some useable schematics on pages 2 & 6 of this thread.

Kevin at Diycables.com offers a built version from LcAudio, but as you've built an AKSA, a DC  blocker is rather trivial.....

[Lost81]

In addition to lamp dimmers and hair-dryers causing toroidal transformers on the same circuit to hum, I will add halogen lamps to the list.

Also, if there are fans on the same circuit and they are turned off or on, it will result in pops from the speakers.


-Lost81

[Tonto Yoder]

PS Audio has a good article on hum as well; of course, they'd like you to buy a Humbuster or Power Plant, but they don't ram that option down your throat.

[zachslc]

I started that thread on AA.  I probably should have brought it here in the first place.

My aksa transformers hummed when I first built them some time ago, and it went away for a while, and now it is back.  It seems to be worse in the evening when usage of the grid is at its highest.

That seems like a simplified ersion of the circuit on diyaudio.com.  (it's from: http://diyparadise.com/dablok.html)

Since I am a total novice, could someone give me a bit of guidance about what caps and diodes I would need for 120?

Thanks.

[Lost81]

for safety's sake, the caps should be X2 rated.


-Lost81

[Occam]

Hey Zach,

That was me who resonded with the "DC on your mains..." post, under my less evil, alter-ego persona on AA.
The easiest way to implement the DC blocker is to use this circuit-
http://diyaudio.com/forums/attachment.php?s=ffd71bd5b855094b8f32a411fb1c67e7&postid=328821
from Mlloyds post on page 6 of the DiyAudio thread.

Just the diode bridge and the 2 electrolytics (bottom left corner of the schematic) which will allow dealing with dc offset of 2 diode drops. I'd use a packaged bridge with quitckconnects, >= 10Amps, mount the electrolytics directly on the bridge terminals, and attach the whole shebang with a single bolt and nut to the chassis via the bridge mounting hole. Use a Nichicon UHE high ripple electrolytic, the 35v 3,300uf or 25v 4,700uf caps(page 458 of the current Mouser.com catolog, everything needed is available from Mouser).

If you've questions about my comments and/or the DiyAudio thread, DON'T ATTEMPT TO BUILD IT!, as you are dealing with lethal voltages. The components and shipping is going to run you $15, so the availabillty to buy iit from Kevin at diycable.com @$45 simplifies everything and doesn't jeporadize your life. No kidding. As someone who has been blown accross a room multiple times with ill advised mucking about with AC, it simply isn't worth it.
http://www.diycable.com/main/product_info.php?cPath=32_88&products_id=206

[Occam]

for safety's sake, the caps should be X2 rated.
-Lost81

Lost,

.... I'm at a loss.... This is not an 'accross the line' situation, nor to my knowledge, are there any caps appropriate for the task that are rated such.  Please read the DiyAudio thread. But in reality you are correct, my cat, my wife, etc... should all be rated X2.

[zachslc]

Thanks.  I didn't read the DIYaudio thread too thoroughly and I couldn't get the schematic because the site would not let me log in.  I'll have a closer look.  I feel pretty comfortable building it is I know the parts I would use are going to tolerate the voltage.  I don't have a background in EE but I can follow diections which have gotten me through four aksa amps and a tube preamp.  But for only $45 I might just save some time.

Thanks again.

[Lost81]

for safety's sake, the caps should be X2 rated.
-Lost81

Lost,

.... I'm at a loss.... This is not an 'accross the line' situation, nor to my knowledge, are there any caps appropriate for the task that are rated such.  Please read the DiyAudio thread. But in reality you are correct, my cat, my wife, etc... should all be rated X2.

Took a look at the diagram again.
Yes, you are right, it is not an "across the line" situation, so it shouldn't matter if the caps fail open or close.

I may be wrong again here, however (I'm not EE trained).



-Lost81

[Jens]

Guys,

I've been using exactly that schematic for two or three buzzing toroids in various gear in my system - works a treat. It's safe, as you are only working with the live wire. Any component failing will not cause a hazard. The worst that could happen is that the circuit stops working.  

Cheers,

Jens

[GBB]

The idea of the diodes is to protect the capacitors against too high forward and reverse voltage.  Thus you want at least 2 diodes across each capacitor, one pointing in each direction.
Something like this:


---Gary

[StevenACNJ]

I started that thread on AA.  I probably should have brought it here in the first place.

My aksa transformers hummed when I first built them some time ago, and it went away for a while, and now it is back.  It seems to be worse in the evening when usage of the grid is at its highest.

That seems like a simplified ersion of the circuit on diyaudio.com.  (it's from: http://diyparadise.com/dablok.html)

Since I am a total novice, could someone give me a bit of guidance about what caps and diodes I would need for 120?

Thanks.

Does anyone know if this circut will work to block DC on an amplifier's main power inlet?

Thanks

[AKSA]

Yes, no doubt it will.  Any DC will be unable to get through to the toroid, a good thing, as toroids are highly intolerant of DC currents.

The rating of the capacitors should be on the order of 16VW, and the diodes should have a rating around 200 PIV to be on the safe side.  Use quality caps rated at 105C, and it's a good idea to fully insulate caps and diodes in heatshrink as this is operating at mains potential and should NEVER be touched in operation.

Cheers,

Hugh

[StevenACNJ]

Thanks Hugh for your reply.

Do you see any downside to this circut as far as hurting sound quality?

Thanks in advance.

[Jens]

Hi Steven,

From experience over a couple of years there does not seem to be any downside.

Since there are no coils in the circuit, there shouldn't be any limiting factors. Coils are usually regarded as having a limiting influence, since their output impedance is higher than that of the "raw" AC outlet. This is also why it is usually not a good idea to use normal line filters in connection with power amps. They work fine with preamps, CD machines, etc., as these have a very small power consumption that usually does not vary very much.

But as Hugh says, make sure to wrap this DC blocker properly into some kind of insulation and never ever muck around with it with the power on!!  

You are dealing with a potentially deadly voltage!

Cheers,

Jens

[andyr]

Hi Steven,

You are dealing with a potentially deadly voltage!
...

C'mon, Jens,

"Ordinary Men" are quite happy brushing their fingers across AC terminals and delighting in the kick which their fingers get!!

"Real Men" delight in putting their tongue across AC terminals!!  

What are ya, a man or a mouse!!

Regards,

Andy (an ordinary man)

[Jens]

Hi Steven,

You are dealing with a potentially deadly voltage!
...

C'mon, Jens,

"Ordinary Men" are quite happy brushing their fingers across AC terminals and delighting in the kick which their fingers get!!

"Real Men" delight in putting their tongue across AC terminals!!  

What are ya, a man or a mouse!!

Regards,

Andy (an ordinary man)

Haha - I wasn't thinking about myself here!

However, I don't see any need to decimate the number of members on this delightful forum  

Cheers,

Jens

[Occam]

And another reason for adding a DC blocker -

The only type of simple power conditioning I'd reccomend for amps beyond an accross 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.  Of course, PSAudio will be more than happy to sell you their DC blocker for $299 to go with their UO.

And Jens is absolutely correct, the 2 diode, 2 cap DC blocker is perfectly adequate for the task, assuming the offset is less than one diode drop?  The only reason I suggested the packaged bridge and 2 cap solution is that, for me, being mechanically challenged,  its easier to mount within a component, via the bridge's own afixing hole....

[StevenACNJ]

I posted about this topic over at Audio Asylum - Tweak Forum - and got mixed opinions.

Link here:

http://www.audioasylum.com/audio/tweaks/messages/106948.html

There was also a post for a different schematic. I am not totally sure but it looks different in how the caps & diades are connected from the schematic above.

 http://home.swipnet.se/~w-50719/hifi/dct01/index.html

[Tonto Yoder]

The Swedish site offers the printed PCB for 150 Kronas ($20 US dollars) but one supplies the caps and diodes and connectors; probably wouldn't be cost-effective compared to the LC Audio filter ($43?) but it might make an interesting project (with the PCB lending some reassurance that one was doing things correctly?)