1MHZ and 60Hz will cross-modulate several ways. In a big city, many ways for hum to modulate RF. Even out on my neck of land: anywhere near a road, the AM is awful hummy. At my last place, one mile of River Road was terribly buzzy, then the next mile was fine. After 5 years something failed or was replaced and hum/buzz was then low the whole way.
Long ago the authorities might investigate such interference. In the US today there is almost no investigatory force and they have bigger fish to fry. In the heart of a downtown with hundreds of low-bid buildings cheek to cheek, it may be impossible to identify the sources.
And yes a better radio DOES help, at least here. My 1948 GE will pull-up Boston cleaner than anything else. It's the RF stage! The buzz-crap in the air is so strong it overloads a standard front-end; the GE has a tank, a low-gain RF stage, and then another tank. But such rigs have been very rare for decades. (Early transistor car radios had RF stages but were poor in so many other ways. A late 1960s Cadillac may be the best of a sad bunch.)
As this thread is talking about a mains line conditioning,
A fancy mains generator won't do anything about the airborne RF pollution we live in.
A unit power supply that can't handle what the mains supply is junk. Buy a better box.
Line noise in cars is irreverent. It has gotten better because of all the computers fortunately.
In some cases, a DC filter on the mains may be helpful. Simple to do, cheap. With a generic industrial pi-filter, one can rely on even an MOV to be fast enough for protection. $100 at worst. Just physics.
A fancy mains generator won't do anything about the airborne RF pollution we live in.
A unit power supply that can't handle what the mains supply is junk. Buy a better box.
Line noise in cars is irreverent. It has gotten better because of all the computers fortunately.
In some cases, a DC filter on the mains may be helpful. Simple to do, cheap. With a generic industrial pi-filter, one can rely on even an MOV to be fast enough for protection. $100 at worst. Just physics.
There was a bit in AudioExpress way back about a mains cleaner.
Worth noting is that a pure sine wave only delivers power to the amplifier at the peak of the cycle. In the amplifier there are filter capacitors that store the energy and discharge a bit between cycle peaks. They only recharge when the applied voltage is greater than the stored voltage.
In some design rules the ripple voltage that results should be less than 5% of the peak stored voltage. Most audio designs have much less ripple. So the peak voltage demand current is much greater.
The flat topping distortion present on many AC mains power line is from serving these types of DC power supplies. In some places there are “Power Factor” regulations limiting this flat topping.
When you have an Audio AC power supply source some flat topping actually allows longer capacitor charging time!
The next trick is to increase the power supply AC line frequency. This recharges the capacitor bank more often so less droop! However as the power transformer losses go up with frequency, there is a limit to this. The usual compromise is to set the frequency to 90 hertz.
A decent design guide for an audio amplifier power source would be 90 hertz with 5% distortion and a line voltage a slight bit higher than standard.
In the U.S. the line voltage many places was 110 VAC RMS. This was increased to 117 V and then to 120 V. Today it is not unusual to see 125 V.
The is a deliberate move to slowly increase the line voltage to lower current demands. A wise designer will design to tolerate a line voltage of 132 VAC RMS.
Normally for most folks buying a U.S. power transformer it will be rated for 110 volts input. (Although you will see some rated for 115 VAC and others say 110/120 but are really 110 units.) The core will saturate and produce the correct output voltage. The excess input voltage results in a bit of heat, they can withstand. They then produce a flatter top AC waveform, which allows better filter capacitor charging. There are units really designed for 120 V but they can handle more input voltage and often have less “regulation” as the current draw increases.
Worth noting is that a pure sine wave only delivers power to the amplifier at the peak of the cycle. In the amplifier there are filter capacitors that store the energy and discharge a bit between cycle peaks. They only recharge when the applied voltage is greater than the stored voltage.
In some design rules the ripple voltage that results should be less than 5% of the peak stored voltage. Most audio designs have much less ripple. So the peak voltage demand current is much greater.
The flat topping distortion present on many AC mains power line is from serving these types of DC power supplies. In some places there are “Power Factor” regulations limiting this flat topping.
When you have an Audio AC power supply source some flat topping actually allows longer capacitor charging time!
The next trick is to increase the power supply AC line frequency. This recharges the capacitor bank more often so less droop! However as the power transformer losses go up with frequency, there is a limit to this. The usual compromise is to set the frequency to 90 hertz.
A decent design guide for an audio amplifier power source would be 90 hertz with 5% distortion and a line voltage a slight bit higher than standard.
In the U.S. the line voltage many places was 110 VAC RMS. This was increased to 117 V and then to 120 V. Today it is not unusual to see 125 V.
The is a deliberate move to slowly increase the line voltage to lower current demands. A wise designer will design to tolerate a line voltage of 132 VAC RMS.
Normally for most folks buying a U.S. power transformer it will be rated for 110 volts input. (Although you will see some rated for 115 VAC and others say 110/120 but are really 110 units.) The core will saturate and produce the correct output voltage. The excess input voltage results in a bit of heat, they can withstand. They then produce a flatter top AC waveform, which allows better filter capacitor charging. There are units really designed for 120 V but they can handle more input voltage and often have less “regulation” as the current draw increases.
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"Worth noting is that a pure sine wave only delivers power to the amplifier at the peak of the cycle. In the amplifier there are filter capacitors that store the energy and discharge a bit between cycle peaks. They only recharge when the applied voltage is greater than the stored voltage.
In some design rules the ripple voltage that results should be less than 5% of the peak stored voltage. Most audio designs have much less ripple. So the peak voltage demand current is much greater."
Yes this is key. It's a common mistake for people to think purely about the voltage domain. The current domain is just as important!
In some design rules the ripple voltage that results should be less than 5% of the peak stored voltage. Most audio designs have much less ripple. So the peak voltage demand current is much greater."
Yes this is key. It's a common mistake for people to think purely about the voltage domain. The current domain is just as important!
And if you can't build a power supply for an amp with 50 or 60Hz lines, find another advocation. It is not hard. Nothing fancy is needed. Nothing. DC blocking is handy for some transformers. You prevent droop by having enough current and enough filter bank. You reduce ripple by having enough filter bank and low enough ESR. I think folks are spending too much COVID time online looking for problems that don't exist and not enough listening to music or building equipment. No amount of magic line filtering is going to improve a well designed amplifier. Might I suggest researching SMPS and how they behave with dynamic loads? I have not found much but the likes of Benchmark seem to have figured it out in AB and most class D amps are SMPS.
I do wonder if people actually can hear the difference between 0.02 and 0.005% THD, particularly off a low bit rate recording in a not so ideal listening situation.
That said, no radio will work properly without an antenna.
My personal experience is that we used to lose the signal on our little transistor radio on SW after 830 AM, and after sunset it would be clear, this was Radio Ceylon, 11800 or 11792 kHz in the 25 Meter band.
Just for the heck of it, I tuned the military comm. set we had, a BEL LHP 319, to that frequency, it was clear at noon...it had a 20 meter dipole antenna, and synthesized tuning.
Obsolete now. It was a battlefield radio, HF.
For AM, you need a proper antenna, and a proper shielded wire from it till the radio, which also must have a proper superheterodyne / IF circuit.
https://www.google.com/url?sa=t&rct...yne_receiver&usg=AOvVaw1jF6G7xbeGXcrtOBlzVkqX
That said, no radio will work properly without an antenna.
My personal experience is that we used to lose the signal on our little transistor radio on SW after 830 AM, and after sunset it would be clear, this was Radio Ceylon, 11800 or 11792 kHz in the 25 Meter band.
Just for the heck of it, I tuned the military comm. set we had, a BEL LHP 319, to that frequency, it was clear at noon...it had a 20 meter dipole antenna, and synthesized tuning.
Obsolete now. It was a battlefield radio, HF.
For AM, you need a proper antenna, and a proper shielded wire from it till the radio, which also must have a proper superheterodyne / IF circuit.
https://www.google.com/url?sa=t&rct...yne_receiver&usg=AOvVaw1jF6G7xbeGXcrtOBlzVkqX
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Antenna: I am in a hole. For FM I put up a 6 element YAGI. For TV, had to put the 8 element bow-tie up and still needed an amplifier. Towers are two obstructing hills and 47 miles away.
Still, don't need a perfect sine wave generator to power a stereo. We did not need it in the labs, they don't need it in hospitals either. Snake oil pure and simple.
Still, don't need a perfect sine wave generator to power a stereo. We did not need it in the labs, they don't need it in hospitals either. Snake oil pure and simple.
"I do wonder if people actually can hear the difference between 0.02 and 0.005% THD, particularly off a low bit rate recording in a not so ideal listening situation"
It depends on the frequency and level. That is one of the problems with traditional one-number measures. Another is we hear differently, and we interpret differently. They are a great baseline, but there is more to it than that. Ponder this: Why can we hear those differences through speakers producing .5%? We can. I don't know why, but we can. Or some of us can. More mysterious, why could I clearly hear the difference on some recordings on two DACs. One .00004, one .003. Others sounded the same. I have no explanation but it is real.
It depends on the frequency and level. That is one of the problems with traditional one-number measures. Another is we hear differently, and we interpret differently. They are a great baseline, but there is more to it than that. Ponder this: Why can we hear those differences through speakers producing .5%? We can. I don't know why, but we can. Or some of us can. More mysterious, why could I clearly hear the difference on some recordings on two DACs. One .00004, one .003. Others sounded the same. I have no explanation but it is real.
Oh, that's easy to explain (because I've explained it several times before). Yours isn't the first mention in this thread that THD is badly correlated with audible distortion - check out gedlee metric for a better attempt at putting distortion into a single figure representing audibility.
Audibility of distortion depends strongly on what harmonics are generated. Tube and FET circuits (and loudspeakers) have a smoothly curved transfer function that generates mostly low harmonics (2nd, 3rd, 4th), which are not easily audible due to the masking effect - it's hard to hear a low harmonic when the fundamental is 10dB to 20dB+ higher in level. Bipolar transistor circuits have discontinuities (sharp angles in an otherwise straight transfer function), such as from hard clipping of the peaks or crossover distortion, and this generates harmonics throughout the spectrum. Even a low amount of such distortion is clearly audible, because a low or mid frequency input will generate harmonics that go as high-pitched as you can hear, beyond where the masking of the fundamental could cover it up.
And depends on the frequencies and on the individuals training.
There is no good reason for hard clipping or even measurable crossover distortion. Maybe 40 years ago, but we can do better now. Clipping is from buying the wrong amplifier, user at fault. Measurable crossover is from sloppy design.
There is no good reason for hard clipping or even measurable crossover distortion. Maybe 40 years ago, but we can do better now. Clipping is from buying the wrong amplifier, user at fault. Measurable crossover is from sloppy design.
I chose a 24V battery and inverter because it offers more practical wiring and better efficiency. I'm using a well-known inverter brand designed for the RV market, as they tend to be robust and less likely to emit RF interference, which is important since most RVs have some AV equipment. I recommend starting with a single battery, like a 100Ah 24V setup. Connecting large batteries in parallel or series is not a simple task, as I quickly discovered.
By the way, be aware that a large AGM or Li-ion battery can be hazardous. Seek guidance and review safety rules before embarking on your project. A high-energy plasma release due to a short circuit can be just as dangerous as a high-voltage accident. I strongly suggest placing the heavy components on a cart with wheels for ease of handling.
If your inverter doesn't have tunable undervoltage protection, you'll need to add an undervoltage relay between the battery and the inverter. The charger should be specifically designed for on-vehicle installation, as standalone chargers may require manual disconnection and reconnection to initiate a charging cycle.
The systems I've built are used in a commercial application. I once experimented with my audio system, but I didn't notice any significant difference in sound quality. However, I believe such setups can be beneficial if the power grid is unreliable or unstable, especially for audio devices without regulated power supplies, such as many tube amplifiers.
To assess the effectiveness of this solution for your system, consider using a power quality monitor for measurements. The one we use at work (Fluke) is expensive (8k euros), but some companies rent them for a few days. You'll need to connect it and interpret the results, of course. For a basic idea, you can also use a digital oscilloscope and a small output transformer to isolate and step down mains voltage in the 20Hz-20KHz range.
By the way, be aware that a large AGM or Li-ion battery can be hazardous. Seek guidance and review safety rules before embarking on your project. A high-energy plasma release due to a short circuit can be just as dangerous as a high-voltage accident. I strongly suggest placing the heavy components on a cart with wheels for ease of handling.
If your inverter doesn't have tunable undervoltage protection, you'll need to add an undervoltage relay between the battery and the inverter. The charger should be specifically designed for on-vehicle installation, as standalone chargers may require manual disconnection and reconnection to initiate a charging cycle.
The systems I've built are used in a commercial application. I once experimented with my audio system, but I didn't notice any significant difference in sound quality. However, I believe such setups can be beneficial if the power grid is unreliable or unstable, especially for audio devices without regulated power supplies, such as many tube amplifiers.
To assess the effectiveness of this solution for your system, consider using a power quality monitor for measurements. The one we use at work (Fluke) is expensive (8k euros), but some companies rent them for a few days. You'll need to connect it and interpret the results, of course. For a basic idea, you can also use a digital oscilloscope and a small output transformer to isolate and step down mains voltage in the 20Hz-20KHz range.
You can feed DC after the PSU in the radio, no need to multiply to AC from DC using inverter, then bring it down to low volts in the radio PSU, and then rectify it back to DC.
Less chance of noise that way.
YMMV...
Less chance of noise that way.
YMMV...
I was looking into possibly using a UPS or an inverter to solve a problem my friend has. When he turns on/off fridge or washer, the preamplifier either turns off, or shoots the volume to the max. Most scaringly, one day he left he house with music playing softly, when he return, he found the system playing at max voliume. Fortunately nothing bad happened, but clearly this is a problem.
We tried to use a UPS running off batteries, and of course the problem disappears. I haven't sees this problem anywhere else I tried his pream in, so the problem must reside on his electrical system.
He told me the earth connection on each apparent, goes to the roof of the building and then runs to the ground; to me this doesn't seem to be an ideal configuration, however it is something that cannot be changed nor am I sure this is indeed the root cause of his problem.
I don't necessarily like the idea to introduce a switching inverter, so my question is: would there be a better solution to treat this problem by perhaps adding isolation transformer and CLC filtering? Wouldn't an isolation transformer inherently filter everything slightly above it's frequency of operation?
Someone also recommended this
https://www.tortech.com.au/three-phase-custom-transformer-designs/balanced-transformers/
Unfortunately, this is only available in Australia, but my friend lives in Italy. What is this the principle of operation of this device?
Thanks!
We tried to use a UPS running off batteries, and of course the problem disappears. I haven't sees this problem anywhere else I tried his pream in, so the problem must reside on his electrical system.
He told me the earth connection on each apparent, goes to the roof of the building and then runs to the ground; to me this doesn't seem to be an ideal configuration, however it is something that cannot be changed nor am I sure this is indeed the root cause of his problem.
I don't necessarily like the idea to introduce a switching inverter, so my question is: would there be a better solution to treat this problem by perhaps adding isolation transformer and CLC filtering? Wouldn't an isolation transformer inherently filter everything slightly above it's frequency of operation?
Someone also recommended this
https://www.tortech.com.au/three-phase-custom-transformer-designs/balanced-transformers/
Unfortunately, this is only available in Australia, but my friend lives in Italy. What is this the principle of operation of this device?
Thanks!
Ferro resonant transformers are sold, as are medical isolation transformers, and line filters.
Poor man's solution: 275V/20mm MOV across line and neutral, permanently connected.
In parallel with that, 0.1uF/400V capacitor with 10K/2W resistor in series.
Both are decent line noise filters, particularly switching spikes.
I am not responsible if this breaks the laws in your area.
And connect the earth to the water lines, if metal, or have a spike put in the ground, I suspect a broken or corroded earthing path from the flat to the ground.
So an alternate method of earthing is needed.
The test here is to use a 200W filament bulb, line to earth, must be bright.
After some experience, can use 40W bulb also.
In fact, do this first, to know what is going on.
Poor man's solution: 275V/20mm MOV across line and neutral, permanently connected.
In parallel with that, 0.1uF/400V capacitor with 10K/2W resistor in series.
Both are decent line noise filters, particularly switching spikes.
I am not responsible if this breaks the laws in your area.
And connect the earth to the water lines, if metal, or have a spike put in the ground, I suspect a broken or corroded earthing path from the flat to the ground.
So an alternate method of earthing is needed.
The test here is to use a 200W filament bulb, line to earth, must be bright.
After some experience, can use 40W bulb also.
In fact, do this first, to know what is going on.
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thank you indeed for your answer. Let me summarize your suggestions:
1) you want me to get a 200W filament bulb connect it between line and neutral and then between line and earth and in both cases brightness should be the same? If brightness on the earth path is less, this would suggest a higher impedance on the earth path, correct? or you are suggesting using a filament to absorb noise from the line and shunt it to ground?
2) using MOV and low pass filter added to the mains, however I have to add, he has tried already two different UPS systems, and while with one of them the situation improved, it was not resolved until he switched to battery operation. Wouldn't UPS already have Spike and line filtering built in?
I was looking at this particular device, it is expensive, but would it worth a consideration? Would this eliminate noises enough to eliminate the issue?
https://tripplite.eaton.com/dual-vo...isolation-115-230v-1000w-8-outlets~IS1000HGDV
Thanks.
1) you want me to get a 200W filament bulb connect it between line and neutral and then between line and earth and in both cases brightness should be the same? If brightness on the earth path is less, this would suggest a higher impedance on the earth path, correct? or you are suggesting using a filament to absorb noise from the line and shunt it to ground?
2) using MOV and low pass filter added to the mains, however I have to add, he has tried already two different UPS systems, and while with one of them the situation improved, it was not resolved until he switched to battery operation. Wouldn't UPS already have Spike and line filtering built in?
I was looking at this particular device, it is expensive, but would it worth a consideration? Would this eliminate noises enough to eliminate the issue?
https://tripplite.eaton.com/dual-vo...isolation-115-230v-1000w-8-outlets~IS1000HGDV
Thanks.
The filament bulb is being used as a test device, to check whether the earthing system can take the current, the alternate is an earthing insulation tester, not very useful, waste of money for a single task.
It should glow almost equally bright L-N and L-E.
Test time is about 2 seconds...
That Eaton thing is overkill in my opinion, hospital grade isolation transformer!
And UPS are generally high frequency sine wave conversions from square wave, methods vary, again not needed.
The results vary, as reported by you...
The Neutral link to mains input had got loose and corroded, needed replacement. Our 3 phase wire systems are generally direct neutral link, switch / breaker on live wires only.
Italy may have a different system in place.
I have already suggested that a battery or transformer to give pure DC to the low voltage section may work.
Also, tell your person in Italy to check volts E-N, sometimes back EMF can cause issues, I had that when a computer was on the same phase with the apartment lift, starting spike caused issues, solved by above method.
And the apartment owner should check if there are any loose wire terminations in the entire apartment, from breaker to individual wall outlets, maybe a loose wire is radiating spark energy.
It should glow almost equally bright L-N and L-E.
Test time is about 2 seconds...
That Eaton thing is overkill in my opinion, hospital grade isolation transformer!
And UPS are generally high frequency sine wave conversions from square wave, methods vary, again not needed.
The results vary, as reported by you...
The Neutral link to mains input had got loose and corroded, needed replacement. Our 3 phase wire systems are generally direct neutral link, switch / breaker on live wires only.
Italy may have a different system in place.
I have already suggested that a battery or transformer to give pure DC to the low voltage section may work.
Also, tell your person in Italy to check volts E-N, sometimes back EMF can cause issues, I had that when a computer was on the same phase with the apartment lift, starting spike caused issues, solved by above method.
And the apartment owner should check if there are any loose wire terminations in the entire apartment, from breaker to individual wall outlets, maybe a loose wire is radiating spark energy.
Again, thank you Naresh. I will have my friend tun the bulb test today. Battery operation is only achievable by modifying internally the preamplifier so it's not an option for him. This is why I was considering for him battery operation with pure sine wave inverter (not modified or square wave). This would achieve full isolation and resolve the issue by getting around the problem.
How can he check E-N voltage without using a scope? He has no access, nor would he know how to use an oscilloscope to capture fast transients.
It's a great idea to have the electrician go and check all the connections from the breaker to make sure there is no loose connection as this could be a potential cause.
So you want me to:
1) try the bulb test to see if the earth connection is valid
2) have the electrician check for loose connections
3) check if there is any back EMF on E-N (this might require skills my friend doesn't have)
4) try MOV and low pass filer across mains to attempt to filter out spikes.
Wouldn't the isolation transformer also lower overall noise by killing CM noise and break ground loops due to its balance operation?
The eaton might be an overkill as you say, however if it would solve the problem, my friend would be ok with it. Regular lower quality transformers will generate higher distortion, Unfortunately, there is no reinsurance the problem disappears once having bought this or similar devices.
How can he check E-N voltage without using a scope? He has no access, nor would he know how to use an oscilloscope to capture fast transients.
It's a great idea to have the electrician go and check all the connections from the breaker to make sure there is no loose connection as this could be a potential cause.
So you want me to:
1) try the bulb test to see if the earth connection is valid
2) have the electrician check for loose connections
3) check if there is any back EMF on E-N (this might require skills my friend doesn't have)
4) try MOV and low pass filer across mains to attempt to filter out spikes.
Wouldn't the isolation transformer also lower overall noise by killing CM noise and break ground loops due to its balance operation?
The eaton might be an overkill as you say, however if it would solve the problem, my friend would be ok with it. Regular lower quality transformers will generate higher distortion, Unfortunately, there is no reinsurance the problem disappears once having bought this or similar devices.
Electrician can test back EMF, earthing and loose connections.
We use a volt meter to check E-N, more than 5V is too much.
All you need to do is put probes in the socket, and switch on, bypass safety shutter in socket by a suitable item if needed. And read the volts on the meter, no need for scope.
MOV plus filter is less than 1 Euro + labor.
Even a ready line filter is about $5 here, just plug it in.
Isolation transformer at part or low load has its own issues, hysteresis loss is also there at light loads, so it is a last resort option, it is also expensive.
A switching auto or double winding transformer type voltage regulator / line conditioner will be adequate in place of isolation transformer, that should absorb line noise in the circuit (isolation transformers basically do not induce spikes in secondary, and are much better quality than line conditioners). And should be quite cheap, you need about 250W rating for most audio systems at home, unless TV and a big amp are also in place at same place.
We use a volt meter to check E-N, more than 5V is too much.
All you need to do is put probes in the socket, and switch on, bypass safety shutter in socket by a suitable item if needed. And read the volts on the meter, no need for scope.
MOV plus filter is less than 1 Euro + labor.
Even a ready line filter is about $5 here, just plug it in.
Isolation transformer at part or low load has its own issues, hysteresis loss is also there at light loads, so it is a last resort option, it is also expensive.
A switching auto or double winding transformer type voltage regulator / line conditioner will be adequate in place of isolation transformer, that should absorb line noise in the circuit (isolation transformers basically do not induce spikes in secondary, and are much better quality than line conditioners). And should be quite cheap, you need about 250W rating for most audio systems at home, unless TV and a big amp are also in place at same place.