[DervishD]

Hi all

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First, my setup. I have my FUBAR III connected to my Marantz amplifier. Both components are brand new and are working OK (I've tested them separately with different equipments. The connection is made using the cables shipped with the FUBAR III. I've tested with other cables and the problem is the same, so they are not the culprits

Second, a note. I have a ground loop and I'm still trying to solve the problem safely. This shouldn't be an issue, anyway, because the problem I'm relating now happens even with the ground loop open.

Third, the problem. Let's say I turn my FUBAR III and enjoy listening to music using the headphone output. But then I want to hear the music in my speakers, so I turn on my Marantz. Most of the times I do this, the FUBAR III stops when the relays are switching, after the green led turns red for half a second or so. It's like the relays were producing some pulse and that pulse fubars the FUBAR.

If I turn the amp first, the FUBAR III second, all goes OK... until I turn off the amp. Then the same thing happens, the FUBAR III red led flashes a moment and the sound stops. I've checked my computer logs and the FUBAR III doesn't disconnect at all, it's just that it stops producing sound.

I've performed some tests using different cables, different connections, etc. to discard I have a malfunctioning amp or a malfunctioning FUBAR III. Both of them are OK. In one of these tests I tried another power supply for the FUBAR III, 24V, DC, same polarity... but 300mA, which has blown the fuse, so I cannot perform more tests right now (I won't have the replacement fuse until tomorrow, probably). I can only say that the problem dissappears if I disconnect the audio RCA-RCA cables between the amp and the FUBAR, so it's not EMI.

Since I haven't tested thorougly to isolate the problem, I am consciouss that neither you nor me can spot the problem exactly, but I want to ask you about two suspects I have, just to see if I'm heading in the right direction.

First possibility: this is somewhat improbable, but... I am wrong and the problem is just EMI. The fact that it only happens with the RCA-RCA cables connected between the amp and the DAC may mean that the EMI is only properly "focused" thru the DAC if the cables are connected. This is almost impossible, I'm just writing it down just in case.

Second possibility: this one I cannot test now because my multimeter has run out of battery

It may happen that, I don't know why, there is some voltage difference between the audio ground in the amp and the audio ground in the DAC. So, when I turn the amp on or off, current flows between both ground paths, this makes some kind of voltage drop or whatever at the DAC and the chip in the DAC stops working. To fix this I was thinking about connecting the chassis of the DAC to the chassis of the amp permanently... Is this safe?

Third possibility: this is the one I would blame. When I turn on or off the amp, a voltage drop happens, and since both the amp and the DAC are plugged more or less at the same power strip, this makes the voltage at the DAC drop a bit, enough to make the DAC chip go mad. In one of the tests I made, I plugged the amp in a very far socket (using a prolongation cable), the problem stopped. This may indicate that this is the real problem, being the two plugs very near one to the other.

Well, that's all. Sorry for this enormous brick of a message, but I wanted to know if anyone was having a similar problem and how to fix it. Plugging the amp in a far socket is not a solution right now because the prolongation cable should run thru the middle of the room and I would like to avoid it. Anyway, if this is the solution, I'll post it here.

Thanks a lot in advance

Problem solved Finally the problem was solved as soon as I don't plug the amp in the same power strip... than the PC... Probably a transient pulse was travelling thru the ground signal, entering through the USB connector into the DAC and continuing through the RCA cables. I cannot make sure of this, since I don't have any measurement equipment at hand, it's just a blind shot.

If I plug the amp in the same circuit but not in the same power strip as the PC, the DAC doesn't "eat" the pulse or whatever. At first I tried a different circuit, and the problem disappeared, too, but then I thought about plugging the DAC in a different circuit... and it didn't work. So I thought that the problem was not that the amp plug and the DAC plug were very near or in the same circuit, no, the problem was a third equipment, connected to the amp or the DAC. The PC. As soon as the amp is not in the same power strip as the PC, the problem vanishes. Currently I have both the amp and the DAC in another power strip in the same circuit.

Raúl Núñez de Arenas Coronado

 

[infinitesymphony]

I'm not a power expert, but your problem seems to be due to power sag. Amplifiers really draw a lot of power during power-on, and I've seen the lights dim even in a house with good power. You might solve the problem by giving your audio equipment its own dedicated circuit, or you could try plugging one component into another circuit, which may be what you did by plugging in at a far outlet. However, plugging connected equipment into different circuits can cause a ground loop to occur due to the different ground potentials. The best solution is to correct the power sag from that outlet. Maybe a call to an electrician is in order.

 

[DervishD]

Hi, infinitesymphony

First, thanks for your answer. Second, the power sag may be the cause of the problem, and it may be confirmed after I get the replacement fuses and I can test plugging the elements in different circuits.

I was going to measure the voltage drop between the grounds of the amp and the DAC once the two were plugged in different circuits, so if a ground loop happens I may try to solve that later.

As for calling an electrician... I'm afraid that the problem is caused because the plug were the amp and the DAC are right now plugged is feeding my computer too (both the box and the monitor) and a couple of minor things more (a cell phone charger, for example). I calculated the power drain of everything plugged in that socket so they didn't exceed the max rating of the socket (10 A). With all the appliances plugged, the max drain should be around 2A or so, leaving plenty of room, but even with that extra cushion the amp may be draining enough current to drop the voltage enough to disturb the FUBAR. An electrician won't solve that, because I cannot use any other socket for the PC easily due to the place where it must be. Also, I have to check that the problem doesn't happen if I use the same circuit for the amp and the FUBAR *only*. Even with only two items plugged, the electrical system may choke with the extra current the amp wants when turning on.

I'm seriously planning to fix the wiring in my house, assigning a circuit for the PC and a different one for the audio equipments but with the sockets in the same wall, so I don't have to move everything around. That is the only real fix, because currently all sockets that are near to the PC are in the same circuit.

I'll carry some tests and I'll post here the results. Again, thanks for your answer. If everything fails I'll have to call an electrician and change the wiring

Raúl Núñez de Arenas Coronado.