Help me solve a mystery..

[dizzyorange]

My Eddie Current EC-01 amp seems to picks up computer noise from my laptop, even with an EMU 0404 USB in the signal chain. I am sure that the noise is from my laptop because of the following experiments:

--
NOISE: Laptop > EMU (usb) > EC01
SILENT: CD player > EMU (toslink) > EC01
SILENT: CD player > EC01
SILENT: Laptop > EMU > any other amplifier
NOISE: Laptop onboard audio > EC01
--

The noise changes and correlates directly with mouse movement (although it is still present when the mouse is still), and also seems to be affected by the hard drive spinning. It disappears if I turn off my computer. I know it is traveling through the USB wire, and not through the air, because moving the components farther from the laptop does not alter the noise at all. If I disconnect the USB, the noise disappears immediately, even if the EMU is still playing music from the TOSLINK output of a CD player.


My goal is to get the EC01 working with the laptop setup. I plan to buy a cheaper USB -> TosLINK solution, and send the optical SPDIF signal to the EMU (because I still want to use the EMU's DAC). Do you guys think this crazy idea will work? The assumption is that the laptop noise, whatever it is, cannot travel through an optical cable. Is this a valid assumption??

 

[dizzyorange]

One last experiment:

Laptop > EMU > EC01 (connected to headphone jack): NOISE
Laptop > EMU > headphones (connected to headphone jack): SILENT

So, whatever the noise is, it does not register on a pair of headphones. I would greatly appreciate any responses which may shed some light on this strange mystery, because the EC01 sounds fantastic with my CD player, but I'd rather use it on the laptop setup.

 

[Awk.Pine]

Quote:

Originally Posted by dizzyorange /img/forum/go_quote.gif SILENT: CD player > EMU (toslink) > EC01 ... If I disconnect the USB, the noise disappears immediately, even if the EMU is still playing music from the TOSLINK output of a CD player.

I'm confused. Is there noise with CD -> EMU -> EC-01?

Is the EMU bus powered? Is your mouse optical? Do you have specs for the EC-01, namely the input impedance?

My initial hit is that the EC-01 simply is drawing more current than your USB bus can provide. If the EC-01 has a low input impedance (which isn't unusual among tube amps), it might draw more current than the EMU or internal card was designed to swing. If that's the case, your problem isn't getting noiseless sound to the EMU but getting the EMU to power the EC-01. This explains why the internal sound card to the EC-01 has the same problems, but why the EMU and internal card can power headphones just fine; this also predicts that you'll hear the noise any time you use the laptop or EMU with the EC-01, regardless of source. My ideas: Free fix: if the USB devices are strung together, attach the EMU to its own port. Cheap fix: wall wart for the EMU. Less-cheap fix: a powered USB hub. Less-cheap semi-fix: rolling, not optical, mouse (LogicTech TrackMan highly recommended). Not-cheap fix: a preamp with gain (EMU -> preamp -> EC-01). (None guaranteed to work. I just slept at a Holiday Inn last night.)

Or it could be that the USB bus is simply too noisy. My firewire DAC, with very sensitive headphones, reveals my firewire hard drives spinning up. The question then is whether it is the USB bus generally, or the USB audio signal. I'd place my bets on the USB bus generally, because the USB data should have robust error correction and not change any bits on the way. In this case, you'll need a DAC that isn't on the USB bus at all--whether the EMU can operate that way, I don't know. My firewire DAC cannot operate independent of the computer, so I'm guessing yours won't either. So, optical won't help because the noise isn't in the signal but the EMU output stage. If this is the case, a powered USB hub might sufficiently isolate the EMU, but my guess is that you'll want a laptop -> S/PDIF -> non-usb DAC, or a different USB DAC with a better power supply. But this doesn't explain why you get noise with either the laptop -> EC-01 but not the EMU -> headphone or EMU -> other amp approaches, so I'm skeptical.

Hope this helps. Let us know if anything new turns up.

 

[dizzyorange]

Thanks, that was a very thoughtful answer. To answer your questions:

The EMU is powered by a wall wart. CD -> EMU -> EC-01 results in perfect playback with no noise.

I am almost 100% sure that the noise is due to some type of EM noise in the laptop, which is transferred over the USB cable to the EMU. The EC-01 + EMU combo works perfectly fine with TOSLINK input from a CD player.

The weird thing is, with any other amp, there is no noise with the EMU connected to the laptop with USB.

So whatever the noise is, it only shows up in two situations:

EC01 & EMU connected via USB to laptop
EC01 directly connected to laptop's onboard sound

The EC01 must be strangely sensitive to this EM noise, whereas any other amplifier is not sensitive. The problem cannot be in the EMU's output stage because the EMU works fine as long as it's not connected to the laptop.

I guess my question is: can electricity travel through an optical cable? If it can't, then my solution of using a separate USB transport, then shooting the signal optically to the EMU, should work.





Quote:

Originally Posted by Awk.Pine /img/forum/go_quote.gif I'm confused. Is there noise with CD -> EMU -> EC-01? Is the EMU bus powered? Is your mouse optical? Do you have specs for the EC-01, namely the input impedance? My initial hit is that the EC-01 simply is drawing more current than your USB bus can provide. If the EC-01 has a low input impedance (which isn't unusual among tube amps), it might draw more current than the EMU or internal card was designed to swing. If that's the case, your problem isn't getting noiseless sound to the EMU but getting the EMU to power the EC-01. This explains why the internal sound card to the EC-01 has the same problems, but why the EMU and internal card can power headphones just fine; this also predicts that you'll hear the noise any time you use the laptop or EMU with the EC-01, regardless of source. My ideas: Free fix: if the USB devices are strung together, attach the EMU to its own port. Cheap fix: wall wart for the EMU. Less-cheap fix: a powered USB hub. Less-cheap semi-fix: rolling, not optical, mouse (LogicTech TrackMan highly recommended). Not-cheap fix: a preamp with gain (EMU -> preamp -> EC-01). (None guaranteed to work. I just slept at a Holiday Inn last night.) Or it could be that the USB bus is simply too noisy. My firewire DAC, with very sensitive headphones, reveals my firewire hard drives spinning up. The question then is whether it is the USB bus generally, or the USB audio signal. I'd place my bets on the USB bus generally, because the USB data should have robust error correction and not change any bits on the way. In this case, you'll need a DAC that isn't on the USB bus at all--whether the EMU can operate that way, I don't know. My firewire DAC cannot operate independent of the computer, so I'm guessing yours won't either. So, optical won't help because the noise isn't in the signal but the EMU output stage. If this is the case, a powered USB hub might sufficiently isolate the EMU, but my guess is that you'll want a laptop -> S/PDIF -> non-usb DAC, or a different USB DAC with a better power supply. But this doesn't explain why you get noise with either the laptop -> EC-01 but not the EMU -> headphone or EMU -> other amp approaches, so I'm skeptical. Hope this helps. Let us know if anything new turns up.

 

[Gatticus]

I get this issue if I use my X-Fi but using my EMU0404 USB it is dead silent. Maybe try using digital out of your soundcard to the EMU instead of the USB.

 

[Awk.Pine]

If you have any wire around, try connecting only the signal wire from the EMU to the EC-01. (For instance, you might plug an RCA cable in the EC-01, but touch one end of a wire to the center pin of the RCA and the other end of the wire inside the EMU's RCA jack.) The noise might only be in the grounding wire.

(Your post motivated me to fix my DAC's noise. Moving it to the end of the chain got rid of it. But, in the playful mood, I tried using my iPod as a source in my home rig, and apparently the firewire chain doesn't want anything to do with the stereo's grounding when the iPod is involved. I think the audio ground is connected to the power ground somewhere. Giving up on that, for the time being...)

Yes, the optical connection won't carry any electrical noise. Many folks use optical to connect a PC to a stereo for that very reason. I just keep thinking that you shouldn't have to use a USB optical-out to cleanly feed a USB DAC.

Oh, and... Go Mets.

 

[dizzyorange]

Sorry to dig up an old thread, but I am (reluctantly) selling this amplifier currently and would like to provide an update to this issue. Adding an optical stage did indeed solve the noise issue with the old laptop.

However, I have since acquired a new laptop (with a USB 2.0 port), which is silent when used as the source for the EC-01, even without an optical stage in between.

This leads me to believe that the USB noise issue only affects certain types of USB ports, perhaps only USB 1.0 ports. I tried it on a friend's laptop (also a new system), and there was no noise there either.

Anyway, buyer beware if you plan on using this in a computer based setup which involves a USB port from 3 or 4 years ago.

To clarify, as mentioned above, the amplifier does NOT pick up noise from being located near computers.



BTW thank you Awk.Pine for your thoughtful responses.

 

[cerbie]

It is not, and won't be, some certain kind of port. It was your previous notebook maker's fault. I'll wager there was either noise on the ground that that amp was not able to properly reject, but that others did, or that the amp's input design helped make an antenna for you. If you had the ability to test every other amp out there, I'm sure you'd find many more that had problems.

Most computers are not made to be electrically silent. Just enough to pass under the government regulations radars is good enough (that does not mean they pass the regs!). When buying or building, using all quality parts increases the chances of getting it acceptably quiet, but there's always risk of audible noise, and it's a PITA when it happens. Typically, USB is one of our ways of sidestepping the problem, but I guess notebooks can always be problematic.

It's an issue with computer audio that I personally have had experience with since the early 90s (well before I was in high school, and well before I cared about audio quality). It hasn't gone away yet, and probably won't go away for a very long time, and has always (to my knowledge) been somewhat rare. Caveat emptor!