I have a threshold s150 that has sat for 3 months in my absents. Upon my return I powered up the unit to a new sound. The Transformer makes a "arnn" sound instead of the usual slight hum sound. This new sound is loud and distinct enough to be heard from my listening chair so it is a new sound. The unit plays great as always with no hum on the output. I initially though it might be dc offset on the ac system as it measured 1.9v with my BK 2709B DVM. This is the only piece of equipment I have with a toroidal transformer and they are more susceptible to the dc offset issue. None of my other components has this noise. Not sure if the meter reads this offset correctly, and I have check other houses in the neighborhood that also have this measured offset. Meter reading correct? Has anyone had one of these encapsulated toroidal transformers fail?
I'd suspect DC on the mains.
Mains DC and Transformers (This article is a fantastic read!)
Build the circuit in fig.8 and see if that stops it.
Mains DC and Transformers (This article is a fantastic read!)
Build the circuit in fig.8 and see if that stops it.
Go elsewhere with it and plug it in to see if it hums there.
If you disconnect it from source and speakers, is the noise still there?
Also, is the noise continuous or intermittent?
If you disconnect it from source and speakers, is the noise still there?
Also, is the noise continuous or intermittent?
You can add a small circuit in series with the mains to kill DC.
Worth a try.
Mains DC and Transformers
The only other thing that would make the transformer grumble is an overload.
Worth a try.
Mains DC and Transformers
The only other thing that would make the transformer grumble is an overload.
He says he's tried other houses.
Thinking some more (he has another thread)-- same DC on multiple pole-pigs is unlikely. So is a fault in your amp transformer. Could there be a fault in the amplifier *rectifier*?? If one of a 4-diode bridge quits, it will still play, but draw an unbalanced load on the two sides of the AC wave.
FWIW: I had a microwave oven and a near-hit with lightning. After that the display was a bit dim and flickered. My theory was that the full-wave rectifier had become a half-wave rectifier after a diode popped from surge. But that was a half-Watt supply, wasn't stressing the house line, "worked" good enough for my cooking, didn't bother to crack the case.
Thinking some more (he has another thread)-- same DC on multiple pole-pigs is unlikely. So is a fault in your amp transformer. Could there be a fault in the amplifier *rectifier*?? If one of a 4-diode bridge quits, it will still play, but draw an unbalanced load on the two sides of the AC wave.
FWIW: I had a microwave oven and a near-hit with lightning. After that the display was a bit dim and flickered. My theory was that the full-wave rectifier had become a half-wave rectifier after a diode popped from surge. But that was a half-Watt supply, wasn't stressing the house line, "worked" good enough for my cooking, didn't bother to crack the case.
In my city neighborhood there are 11 other houses on the same pole pig as my house is on, so it is possible if he lives in an area where sharing transformers is common that any nearby houses he tried it in are on the same transformer.
I have had more than one bridge rectifier fail in service and have replaced a few for others as well. Usually they seem to fail short across one of the diodes, but I suppose an open is also possible.
I have had more than one bridge rectifier fail in service and have replaced a few for others as well. Usually they seem to fail short across one of the diodes, but I suppose an open is also possible.
Here is some new info. I reconsidered the measurement of the dc offset because I flipped the probs of the DVM and didn't get a + reading then a - reading. Wouldn't this happen if there was a true dc offset? Additionally, this "arnn" sound DISAPPEARED today. As of now the amp is stone quiet, go figure. Still puzzled here........
Here is some new info. I did measure the same offset 1.9v on another house that was not served by the utility transformer that feeds my house yesterday. I reconsidered the measurement of the dc offset because I flipped the probs of the DVM and didn't get a + reading then a - reading. Wouldn't this happen if there was a true dc offset? Additionally, this "arnn" sound DISAPPEARED today and the same 1.9v reading is still present. As of now the amp is stone quiet, go figure. Still puzzled here........
The "arnn" is back again this morning at 7:30 am. I have never before experienced this issue in 20 years at this location. I have owned this amp for a short time (9 months) and used it for six months before leaving it for the summer. Didn't have this issue before during the 6 months I used it. The main caps have been replace. If it is truly a dc offset problem, how can I measure it? I understand that I can build or buy a filter to prevent the hum, but would like to find the source first. How harmful is this to the transformer or the rest of the amp?
I don't think you are going to get to the bottom of this with a meter. A scope would be very illustrative if you know how to use it safely.
And yes if your meter is actually measuring DC offset on the AC mains it should read the same regardless of lead orientation, it is more likely that the meter is misreading the DC present on the mains. I have only one meter that can do this feat you talk about directly and it is a laboratory grade instrument. You may have more success if you make an LPF to remove most of the 60Hz component when attempting to measure DC present.
Really the easiest way to check this would be to build something to block suspected DC on the mains.
It could be that you or one of your neighbors have something new that produces a DC offset on the mains and that does not run all the time.
It may also be that your AC waveform is asymmetrical due to heavy clipping on the peaks, and heavily distorted.
It seems unlikely that something would go wrong with a power transformer during a short period of disuse provided it wasn't stored in a swamp.
And yes if your meter is actually measuring DC offset on the AC mains it should read the same regardless of lead orientation, it is more likely that the meter is misreading the DC present on the mains. I have only one meter that can do this feat you talk about directly and it is a laboratory grade instrument. You may have more success if you make an LPF to remove most of the 60Hz component when attempting to measure DC present.
Really the easiest way to check this would be to build something to block suspected DC on the mains.
It could be that you or one of your neighbors have something new that produces a DC offset on the mains and that does not run all the time.
It may also be that your AC waveform is asymmetrical due to heavy clipping on the peaks, and heavily distorted.
It seems unlikely that something would go wrong with a power transformer during a short period of disuse provided it wasn't stored in a swamp.
Some power utlities will come and test/ measure their "product" as delivered to your house.
Ask them?
Ask them?
I have a nice older HP voltmeter which I don't use for DC offset with signal
because it displays the presence of DC with a large AC signal.
I have a new and expensive voltmeter from Tektronix which does not.
The intermittent nature of the noise points to AC line. Somewhere somebody
is probably using a Triac or similar controlled appliance which is putting some
asymmetry on the line.
because it displays the presence of DC with a large AC signal.
I have a new and expensive voltmeter from Tektronix which does not.
The intermittent nature of the noise points to AC line. Somewhere somebody
is probably using a Triac or similar controlled appliance which is putting some
asymmetry on the line.
There is 19 houses on the 25kva transformer that serves my house. 2 are occupied all year long. Due to the holiday many more are occupied in the resort area. I will check again tomorrow and for the next few days to see if conditions change. Seems a dc blocker is in my future.
I monitored the amps behavior over a week and found that the loud hum was intermittent. Believing the dc offset was the issue I took the lazy way out and bought a Emotiva CMX-2 filter system. I then assured myself that this day was a loud hum day by turning on the amp, then I installed the device and the correct leds lit on the CMX. Plugged in the system and turned the amp on, same loud hum as before (?). No difference. Where to go now?
The Threshold s150 operates 2/3 of the time with total silence with a momentary slight inrush hum (1 sec long) and relay latches . The other times the hum varies in intensity from some to a noticeable hum from the listening chair. So most of the times it is working fine!
What would be learned from relocating the power up location? The only change from stock is the mains cap bank, and that was done back in time enough that it had operated fine for a year.
I have turned off all the breakers in the house and eliminated any device born interference here.
What would be learned from relocating the power up location? The only change from stock is the mains cap bank, and that was done back in time enough that it had operated fine for a year.
I have turned off all the breakers in the house and eliminated any device born interference here.
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Have you pushed, probed of otherwise manipulated the transformer while it is buzzing? Can you feel any vibration?
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