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Audio Confusion - Page 2

post #16 of 53
Thread Starter 
Quote:
Originally Posted by chewy4 View Post

I'm not sure. From what I can find cheater plugs aren't really a thing in the UK so I don't know if I'd recommend that actually.

Thinking about it, I don't know where it could go. The Magni's power supply uses two pins so I couldn't even have one between that and the transformer. The search continues!

post #17 of 53
Quote:
Originally Posted by SamHedges View Post

Thinking about it, I don't know where it could go. The Magni's power supply uses two pins so I couldn't even have one between that and the transformer. The search continues!

 

Have you ruled out that it's the amp that's picking it up and not the source you have plugged into the amp?

 

se

post #18 of 53
Thread Starter 
Quote:
Originally Posted by Steve Eddy View Post

 

Have you ruled out that it's the amp that's picking it up and not the source you have plugged into the amp?

 

se

I think the hissing/squealing might be originating from my laptop (though grounding the Magni by touching a cable to a screw on the Magni and a radiator, for example lessens the noise) but the radio interference I've been having is present even with nothing plugged into the phono inputs at all. It could be coincidence but I could only hear the interference with the DT770 Pros and not with my Sennheiser HD439s, could it be something to do with cable length?

post #19 of 53

Could be. Traditional audio amps could pick up local radio broadcasts and this was usually by way of the speaker cables.

 

Heard anything back from Jason yet?

 

se

post #20 of 53
Thread Starter 
Quote:
Originally Posted by Steve Eddy View Post

Could be. Traditional audio amps could pick up local radio broadcasts and this was usually by way of the speaker cables.

 

Heard anything back from Jason yet?

 

se

 

Another thing I've noticed is that moving the cable around changes the pitch and volume of the interference. Does that have any significance?

 

Jason seems to think the issue is with the DAC (which it could be) and suggested trying a USB cable with ferrite suppressors or alternatively a mains powered USB hub. I've tried the ferrite cables but I've been having problems with a powered hub. Oliver from Epiphany Acoustics said they're trying powered USB cables for the DACs and that he would send me one out if they had any success with them.

 

Unfortunately Jason didn't comment on the radio interference.

post #21 of 53
Quote:
Originally Posted by SamHedges View Post

 

Another thing I've noticed is that moving the cable around changes the pitch and volume of the interference. Does that have any significance?

 

Jason seems to think the issue is with the DAC (which it could be) and suggested trying a USB cable with ferrite suppressors or alternatively a mains powered USB hub. I've tried the ferrite cables but I've been having problems with a powered hub. Oliver from Epiphany Acoustics said they're trying powered USB cables for the DACs and that he would send me one out if they had any success with them.

 

Unfortunately Jason didn't comment on the radio interference.

 

It certainly does. It indicates that the cable is your unintentional "antenna."

 

se

post #22 of 53
Thread Starter 
Quote:
Originally Posted by Steve Eddy View Post

 

It certainly does. It indicates that the cable is your unintentional "antenna."

 

se

But I don't hear it without the Magni, is the cable the antenna and the amp the radio? Is it just a bad pairing?

post #23 of 53

If you are up to some serious reading about interference:

 

A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing
Revision 5a 5 Jun 2010
by Jim Brown K9YC
Audio Systems Group, Inc.
http://audiosystemsgroup.com

http://www.audiosystemsgroup.com/RFI-Ham.pdf

 

Don't let the title fool you!  Jim Brown is the AES committee chair on EMI/RFI interference.  But he is also a Ham radio operator, so when he updated the interference paper, he added sections on ferrites & baluns and titled it 'A Ham's Guide'

post #24 of 53
Quote:
Originally Posted by SamHedges View Post

But I don't hear it without the Magni, is the cable the antenna and the amp the radio? Is it just a bad pairing?

 

It would seem that it's just a bad pairing as the Magni works fine with other headphones/cables.

 

se

post #25 of 53

I had a Modi / Magni on loan recently. When using my IE8's with an extension cable I could hear what sounded like an eastern european radio station.

To 'tune' I had to move my head around occordingly. Looked like Stevie Wonder.


Edited by MrQ - 5/15/13 at 5:45am
post #26 of 53

Is it possible that the amp may oscillate when driving some capacitive loads (long cables), and that is when it turns into a radio ?

post #27 of 53
Quote:
Originally Posted by stv014 View Post

Is it possible that the amp may oscillate when driving some capacitive loads (long cables), and that is when it turns into a radio ?

It's possible it may oscillate driving a capacitive load, but that's not usually what causes RF detection.  Typically a radio signal comes into a device that has some form of non-linear behavior causing the signal to be demodulated through partial rectification or a variance in frequency response at that RF frequency.  In circuit design, there basic idea to get something RF immune is to prevent the signal from coming in the first place.  This is done by filtering all external entrances and exits, inputs, outputs, power, and control lines.  You can also design for fewer high-gain circuits with non-linear devices.  Sometimes the use of a JFET device wins over a bipolar device because the bipolar device basically has, as its first element, a diode, which is all you need to demodulate an RF signal.  A JFET doesn't have that diode. There's a lot more to it, but you get the idea.

 

All of that costs money to design properly, and more money to make.  If you can get away with less RFI protection, you save manufacturing costs.  

 

It might help you to identify the RF source.  Is it an AM or FM broadcast station, or something else? Once you figure out what it is, you'll know the frequency involved, which helps to figure out  a good solution.  You can also find out where the source is, like a mile away, or down the block, which at some point may also be helpful.

post #28 of 53
Thread Starter 
Quote:
Originally Posted by MrQ View Post

I had a Modi / Magni on loan recently. When using my IE8's with an extension cable I could hear what sounded like an eastern european radio station.

To 'tune' I had to move my head around occordingly. Looked like Stevie Wonder.

I wonder if it's something to do with the UK transformer. I'm finding that when you put a bit of tension on the cable the interference gets louder.

post #29 of 53
Quote:
Originally Posted by SamHedges View Post

I wonder if it's something to do with the UK transformer. I'm finding that when you put a bit of tension on the cable the interference gets louder.


Sam, I've had a chat with the UK distributor who is testing out a few solutions. I'll get back when I hear more.

post #30 of 53
Thread Starter 
Quote:
Originally Posted by MrQ View Post


Sam, I've had a chat with the UK distributor who is testing out a few solutions. I'll get back when I hear more.

I've been in touch with Mark from Electromod, he said it could be to do with the DIY interconnects I made as I attached the ground at both ends of the cable which apparently you're not supposed to do? He's sending me a pair of the Schiit interconnects to try and I'm going to get a 230 to 16V transformer so I don't need the other one. Let me know what you find out though!

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