[JML]

I had the Sony D-25S running off a Radio Shack international adapter, the 9V - 1500 mA one. Well, whenever I plug the D-25S into my desktop Monsoons (amp and speakers), I get a 60 Hz hum. OK, I know it's a powerline hum or ground loop, and one that I was used dealing with because when I plug the Monsoons into my laptop's port replicator, I get the same hum, but only if my printer is connected. I figured the printer is the problem, and it's going across the 2-connector powerline or the shield on the printer cable -- the computer stuff uses only two-prong cords (the laptop runs off a two-prong cord and transformer, going into a port replicator). All the powercords are connected to an Isotel that is grounded, but no piece of equipment on the computer setup is really grounded.

But I get the same hum with the AC adapter connected for the Sony D-25S and the Monsoon, even if the printer is disconnected. If I disconnect the D-25S adapter, there's no hum if I'm running on batteries. Same thing if I use my Sony WM-D6C to the Monsoons; on batteries no hum, but hum appears if I use that unfiltered adapter.

If I don't connect either unit to the Monsoons, but use the unfiltered adapter and headphones, I do NOT get any hum via headphones running from the source unit.

Both of the universal adapters are regulated but not filtered.

So I just tried the RS 9 v regulated & FILTERED 800 mA adapter. I get NO HUM with the Monsoons. Problem solved.

If I connect the D-25S to my stereo, and use the unfiltered adapter, there is NO HUM through the headphones. So is the problem the Monsoon amp?

Everything in both setups is running through Isotel surge protectors, properly grounded, but the stereo equipment is properly grounded to earth via the house wiring. Is that why I get no hum in that setup?

Is this sort of miniplug ground problem rare? Am I cursed? I'm going to pick up another filtered wall wart for the WM-D6C, and wonder if I should get one for the stereo setup too.

Anyway, inquiring minds want to know.

Thanks.

 

[Audio Redneck]

'Evening JML!

Well your in luck. One of my doctors has a Monsoon on his PC, so I went back and did some checking. I set up like you said and couldn't replicate the problem (even with the crappy walwart I used), BUT, the APC ups that I have on his PC uses filtered/isolated outlets for wal-warts.

Now his Monsoon's transformer is internal with an attached cord, so tell me if yours is different.

So now, the only time you get the hum is if the Monsoon is plugged into the D-25 and both are plugged into the Isotel.
OR
the Monsoon and Printer are plugged into the computer and both the Monsoon and Printer are plugged into the Isotel.

Correct?

Test 1
If I stated it correctly, the first thing to try is to plug the Monsoon directly into the wall and everything else to the Isotel and try both connections that cause hum (Monsoon/D25onAdaptor and Monsoon/PCwithPrinter).

Test 2
Plug the Monsoon directly into the Isotel and everything else (except laptop) to the wall and try both connections that cause hum.

If neither now give hum, the transformers are affecting each other (groundloop) when the grounds(DC Negative) are connected.

If Test 1 ONLY causes hum, the non-filtered walwart (and maybe the printers transformer) are the weak links and are effecting each other.

If Test 2 ONLY causes hum, the monsoon is the weakest link and is not filtered well.

If BOTH 1 and 2 cause hum then the transformers are affecting each other, and the Isotel is not filtering (which it really is not desined to anyway, but the capasitors should have some noise filtering effect.)

I would think both or neither will be the result.
Reguardless, I would think that the filtered transformers would clear up the problem as isolating one, should isolate both.

Tell me what you find

 

[JML]

AudioRedneck, thanks.

The plot thickens and takes a detour.

I was curious about the output voltage of the filtered transformer. I was stunned to find the output was 11.8 volts (I was going to say "shocked," but figured I wouldn't). So today I went to Radio Shack with my multimeter and tried about a half-dozen samples of three different filtered transformers rated at 6, 9 and 12 V output voltages. Every single one was extremely high. The 9 V ones were all putting out 11.7-11.9 volts. The 6 V were all putting out 8.8 to 9 volts. And the 12 V were putting out 15-18 volts!

But the regulated international series were all within .08 of the rating.

None of the filtered Radio Shack transformers are regulated unless they say both. And none of the selectable-voltage units they sell are filtered (those are regulated).

I picked up an EMI filter box from them and tried it in the mix.

Well, the EMI box does next to nothing. A slight reduction in hum, but not worth it, if I use it between the Monsoon or the Printer, no effect when used between the source adapter and the source.

The Monsoon 700 has an internal transformer. I've played around with the various socket variations, even running a cord to another room on a different line in the house. No changes at all.

The filtered transformer at the source (the PCDP or casette deck) seems to be the only solution. The transformer in the Monsoon must not be filtered well -- and the printer's internal transformer must also not be filtered well. I can't find anything that will isolate the printer, because the hum appears if the printer cable is connected (there is a ground with either USB or IEEE cable). Opening the Monsoon amp is not something I'm comfortable with.

But now I'm worried about the high output voltage from the filtered but not regulated Radio Shack wall warts.

I wonder if anyone makes filtered and regulated high-power wall warts...

 

[Budgie]

Your exactly right. Most unregulated power supplies are rated for the voltage that will be produced at the maximum rated power output. If you are drawing less current the voltage will be higher.
This usually holds true for unregulated DC supplies and for AC transformers in general.

 

[JML]

Budgie, do you mean I'm right to be worried? The units draw less power than the adapters are rated for.

 

[Audio Redneck]

I'd like to hear Budgie's opinion too, but yes, the unregulated transformer could be a problem. If you remember, the first transformer I use should have worked, but didn't (over powered.) I am using an unregulated 500amp transformer (when I run from the wall) BUT I am on VERY clean power at the hospital.

An unregulated source will ALWAYS be high when measured without a load (the way you did with your meter). A regulated source will(should) never let voltage go more than x% above or below the stated voltage.

Stick with a regulated transformer, or go down a little (7.xV). Just be careful not to go too low if you are using the internal battery with the D25 as the internal charger will increase the required amp load.

Another option (but expensive) is a line conditioner. Some UPSs work as line conditioners, too. You might ask someone in the schools IT department if they have a UPS you could borrow to try.

Also, Morphsci has an Adcom Line-conditioner up in the Gear for Sale section $125.

Quote:

I wonder if anyone makes filtered and regulated high-power wall warts...

How "hi-powered" you talking?

 

[JML]

It's good to know that the little I understand about this stuff is accurate.

The adapter that most people bought for the D-25S was the filtered but unregulated 9V, 800 mA. The 6V one I need for the other unit would be at least 750 mA (Radio Shack has an 800 mA filtered and unregulated version). I have a regulated 1000 mA version. I tried searching the web for regulated and filtered adapters, but no luck so far.

I just don't want to spend more for power conditioning on my computer setup than I have to spend on my stereo setup! The Monsoon I have at the office does not have this hum problem with audio input that is on an AC adapter, and that's using an external transformer. I love the Monsoon's sound, but this hum issue is driving me nuts. The other thing I tried by the way was the auto noise filter. It did cut the level, but it was a pretty awkward set of cabling on the desktop; it caused worse problems if I put it at the amplifier end of things!

NEXT DAY: Bingo! Filtered and regulated, found under my nose at Radio Shack. Go to the new thread at http://www.head-fi.org/forums/showth...&threadid=8391

Thanks, guys.