TLDR; amp is picking up interference from cellular equipment
Last week I picked up a Yaqin MC-10T for a great price and couldn't wait to get my first tube amp into my system. At first listen I was really happy with the way it sounded and settled in to spend some quality time. After about 10 minutes, the right speaker emitted a fairly loud BZT-BZT BZZZZZZZZZT sound, familiar though I haven't heard it in probably 15 years: that noise that GSM phones used to make if they were close to your car radio and about to receive a message. The noise appears like clockwork, every ten minutes. It's not dependent on volume level, or which input is selected. It's in both speakers but one quite a bit louder than the other. I've never heard this before in this room, even with other electronics. I listened to the amp in the previous owner's home for a good 30 minutes with no noise.
I have the schematic; there is nothing in this amp that could possibly be making that noise, nor anything else in the room that I could think of: I unplugged all the electronics in the room, including the DAC and streamer. I unscrewed all the LED smart bulbs. Still the noise continues.
Yesterday the entire country lost power for a day and while waiting for the lights to come back on I decided to move a big ecoflow power station into the room and see, now that NOTHING could possibly be generating RFI, if the amp continued with the noise. It did. What the hell? And then it finally occurred to me: my home has an alarm, and the control panel has a several-day battery backup, and I know there is a SIM card inside because I watched them put it in when they installed the alarm. Clearly it's using the old GSM/GPRS network to communicate with the alarm company, and is phoning home every 10 minutes. This alarm panel is not in my listening room; it's on the other side of a wall about 3M away.
I've tried moving cables around, switched interconnects, put a fancy "hifi" power cable on the amp, oriented the amp a different direction; nothing seems to make a difference. Can anyone offer advice for taming the interference problem? It isn't going to be practical to move the alarm. None of the other gear I've had in the room has had the slightest interference, so I'm guessing I need to look to the amp to solve the problem - is it normal for these amps to be so sensitive to RFI? Or is it possible it's got a fault of some kind?
System: Wiim Pro, Music Hall DAC2.5, Yaquin MC-10T, Dahlquist DQ-28s. AQ Ruby interconnects (tried Evergreens) and Indigo speaker cables.
Last week I picked up a Yaqin MC-10T for a great price and couldn't wait to get my first tube amp into my system. At first listen I was really happy with the way it sounded and settled in to spend some quality time. After about 10 minutes, the right speaker emitted a fairly loud BZT-BZT BZZZZZZZZZT sound, familiar though I haven't heard it in probably 15 years: that noise that GSM phones used to make if they were close to your car radio and about to receive a message. The noise appears like clockwork, every ten minutes. It's not dependent on volume level, or which input is selected. It's in both speakers but one quite a bit louder than the other. I've never heard this before in this room, even with other electronics. I listened to the amp in the previous owner's home for a good 30 minutes with no noise.
I have the schematic; there is nothing in this amp that could possibly be making that noise, nor anything else in the room that I could think of: I unplugged all the electronics in the room, including the DAC and streamer. I unscrewed all the LED smart bulbs. Still the noise continues.
Yesterday the entire country lost power for a day and while waiting for the lights to come back on I decided to move a big ecoflow power station into the room and see, now that NOTHING could possibly be generating RFI, if the amp continued with the noise. It did. What the hell? And then it finally occurred to me: my home has an alarm, and the control panel has a several-day battery backup, and I know there is a SIM card inside because I watched them put it in when they installed the alarm. Clearly it's using the old GSM/GPRS network to communicate with the alarm company, and is phoning home every 10 minutes. This alarm panel is not in my listening room; it's on the other side of a wall about 3M away.
I've tried moving cables around, switched interconnects, put a fancy "hifi" power cable on the amp, oriented the amp a different direction; nothing seems to make a difference. Can anyone offer advice for taming the interference problem? It isn't going to be practical to move the alarm. None of the other gear I've had in the room has had the slightest interference, so I'm guessing I need to look to the amp to solve the problem - is it normal for these amps to be so sensitive to RFI? Or is it possible it's got a fault of some kind?
System: Wiim Pro, Music Hall DAC2.5, Yaquin MC-10T, Dahlquist DQ-28s. AQ Ruby interconnects (tried Evergreens) and Indigo speaker cables.
Try to isolate output sections from VAS and splitter board: pull out/remove XS101, XS102 connectors.
Is noise exists?
Is noise exists?
You could try clip-on ferrites on all power and signal cables, as close to the amplifier as possible.
If that doesn't help, or not sufficiently, the next step is to look at the enclosure and grounding scheme. If it uses star grounding, all inputs and outputs that are insulated from the enclosure act as coupling loops to couple in RF interference.
If that doesn't help, or not sufficiently, the next step is to look at the enclosure and grounding scheme. If it uses star grounding, all inputs and outputs that are insulated from the enclosure act as coupling loops to couple in RF interference.
Since the sound shows up in a single channel, and you have identified the source as RFI, that means there is something different between the channels. Since RFI is often attributable to high impedance in ground circuits, I would begin the search by carefully checking all the grounding points on the right hand channel and any power filtering components which may be specific to that channel. The magnitude of the sound (you indicated "loud") would lead me to pay special attention to the circuits prior to any gain stages. Could be something as innocuous as a grounded connector which has come slightly loose or a cold solder joint which shifted slightly.
Good luck with your trouble shooting.
You can try clip on ferrite beads, add the usually lacking RC input filtering (or check it if it has one) and use a mains filter as first steps. The device and the mains filter need PE so check if it is plugged in in a PE wall socket and if PE actually is connected.
PS you are not crazy. RF is all around you and your audio is not a fan of it.
PS you are not crazy. RF is all around you and your audio is not a fan of it.
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Thanks for the suggestions everyone. I'll update when I get some progress made, or at least some more information.