For the last couple of months I had not been able to use my music PC because the moment I connect the output of PC to preamp/buffer (via analog output of sound card) or DAC (via digital coax) there was a huge hum that overwhelms everything. I have been playing music from my PC for years now using the analog unbalanced output of a PCI sound card (not the onboard motherboard sound card) without any noise or hum issues. The hum was a recent development. I also use the sound card as a DAC sometimes by using a Blu-ray player as CD transport and feeding the Blu-ray player digital coax output to the sound card. Same hum observed even when using this path. I also borrowed a standalone DAC from a friend and connected the digital coax output of the sound card to the borrowed DAC. Same hum issue was observed.
In the meantime, the motherboard of the PC developed a fault. Luckily, it was reparable and after repairing it, the PC worked fine for everything except music playing via the internal sound card or PCI sound card.
Since I've never faced this kind of issue it took me lots and lots of reading internet forums to guide in troubleshooting. One of the forums I read was the user forum of the sound card I use, and in each instance the technical support of the card manufacturer blamed the PC itself for the hum and noise issue. To make troubleshooting very difficult, the sound card is an old PCI card. Nowadays most PCs have PCIeX slots and it's very hard to find old PCs with the legacy PCI slot.
But the clincher that it was not the PCI sound card but the motherboard or something in the PC itself that was giving rise to the problem, was the fact that even the headphone output of the motherboard had the same hum issue. Further, the noise shows up as full level signal in hardware input 1 and 2 (analog stereo input 1) only when the PC was physically connected by an interconnect cable to my Kuartlotron buffer. This gave the hint that the PC needed an electrical path to another device to complete the path of the spurious signal.
I had opened the PC numerous times, checking for ground path from motherboard to chassis (which was okay) and also from the ground pin of IEC power socket of the PC's SMPS to the chassis (this was okay too).
The next step was to closely relook the internals of the buffer. On the second time I inspected it occurred to me that I have not bothered to implement a ground loop breaker in the buffer. I had also not done it on the outboard power supply of the buffer.
So I fitted ground loop breakers on both the outboard power supply unit and the buffer, and the result was a completely hum-free operation.
I used Rod Elliott ground loop breaker circuit.
This type of ground loop is very common in studio environments where a computer's analog output drives monitor speakers. This problem is more common if the computer and powered monitor speakers are powered from different power outlets. My PC and the rest of the audio chain are powered from a single power distribution board, but I still faced this problem.
I thought I'll share my terrible experience so that in future it could possibly help someone resolve a similar problem.
I still don't know how this problem suddenly arose because I had been enjoying PC playback without any problem. It would be of great interest to me (and others) if someone knowledgeable could explain why a ground loop arose out of nowhere. To be sure, I have not made any changes in the PC or buffer or power distribution board.
In the meantime, the motherboard of the PC developed a fault. Luckily, it was reparable and after repairing it, the PC worked fine for everything except music playing via the internal sound card or PCI sound card.
Since I've never faced this kind of issue it took me lots and lots of reading internet forums to guide in troubleshooting. One of the forums I read was the user forum of the sound card I use, and in each instance the technical support of the card manufacturer blamed the PC itself for the hum and noise issue. To make troubleshooting very difficult, the sound card is an old PCI card. Nowadays most PCs have PCIeX slots and it's very hard to find old PCs with the legacy PCI slot.
But the clincher that it was not the PCI sound card but the motherboard or something in the PC itself that was giving rise to the problem, was the fact that even the headphone output of the motherboard had the same hum issue. Further, the noise shows up as full level signal in hardware input 1 and 2 (analog stereo input 1) only when the PC was physically connected by an interconnect cable to my Kuartlotron buffer. This gave the hint that the PC needed an electrical path to another device to complete the path of the spurious signal.
I had opened the PC numerous times, checking for ground path from motherboard to chassis (which was okay) and also from the ground pin of IEC power socket of the PC's SMPS to the chassis (this was okay too).
The next step was to closely relook the internals of the buffer. On the second time I inspected it occurred to me that I have not bothered to implement a ground loop breaker in the buffer. I had also not done it on the outboard power supply of the buffer.
So I fitted ground loop breakers on both the outboard power supply unit and the buffer, and the result was a completely hum-free operation.
I used Rod Elliott ground loop breaker circuit.
This type of ground loop is very common in studio environments where a computer's analog output drives monitor speakers. This problem is more common if the computer and powered monitor speakers are powered from different power outlets. My PC and the rest of the audio chain are powered from a single power distribution board, but I still faced this problem.
I thought I'll share my terrible experience so that in future it could possibly help someone resolve a similar problem.
I still don't know how this problem suddenly arose because I had been enjoying PC playback without any problem. It would be of great interest to me (and others) if someone knowledgeable could explain why a ground loop arose out of nowhere. To be sure, I have not made any changes in the PC or buffer or power distribution board.
