I just had an LG mini split air conditioner installed in my listening room.
I am now getting noise @ 4khz thru my speakers.
The AC is all inverters, compressor, and fans.
I do not have the option of using another circuit.
Is there a filter I can use to help this.
I have tried and isolation transformer, Trip Lite power conditioner and inductor based filter.
It only seems to affect my Purifi amp....
Any ideas?
Thanks for your time.
I am now getting noise @ 4khz thru my speakers.
The AC is all inverters, compressor, and fans.
I do not have the option of using another circuit.
Is there a filter I can use to help this.
I have tried and isolation transformer, Trip Lite power conditioner and inductor based filter.
It only seems to affect my Purifi amp....
Any ideas?
Thanks for your time.
You need to figure out if the noise is conducted ( ac line cord) or radiated ( Local RF detection) by the front end of your amplifier. If AC line filters don’t cure it then it could be radiated noise. Try using metal baking trays or aluminum foil near the amp and see if you can / reduce eliminate the noise by moving them around. A ferrite bead or ceramic cap on the front end input can be the cure if it’s radiated.
Thank you both for your tips.
I have discovered that it is radiated EMI due to using an extension cord plugged into another circuit-just testing.... I carefully ran it elevated far away from any other wires.
When you say using ferrite and/or capacitors on input, the Purifi amp that is problematic is balanced input though I am using single ended converters that have what I believe is capacitors in them as filters.
Should I put ferrite on both + & - ?
I apologize for being thick in this department as I have used tube amps in the past and never had this problem until I started trying class d.
Thanks again,
Johnny
I have discovered that it is radiated EMI due to using an extension cord plugged into another circuit-just testing.... I carefully ran it elevated far away from any other wires.
When you say using ferrite and/or capacitors on input, the Purifi amp that is problematic is balanced input though I am using single ended converters that have what I believe is capacitors in them as filters.
Should I put ferrite on both + & - ?
I apologize for being thick in this department as I have used tube amps in the past and never had this problem until I started trying class d.
Thanks again,
Johnny
You mean you plugged the amp with an extension cord into another room, and the noise was still there?
This doesn't necessarily mean it's radiated: after all, all the wires are connected at the electrical panel.
You could put the extension cord on the AC unit, and move it to another room. if the noise diminishes with distance, then it's probably radiated. If it doesn't, then it's conducted.
I would avoid using the scope here, as it is not suitable for floating measurements.
Damage to the DUT and/or scope will happen.
Check the earthing on the A/C with a big incandescent bulb or similar load.
Inverters are brush less DC drives, switching transistors are involved. Those are the noise sources, the shields or heat sink must be connected to earth with a thick wire.
I am assuming this noise started after the unit was installed...
And also that your amp itself has a SMPS rather than linear supply?
If you can, calculate the capacitor values and build a frequency filter as the last resort.
And check that phase and neutral are not reversed in the supply to the A/C.
Inverters are brush less DC drives, switching transistors are involved. Those are the noise sources, the shields or heat sink must be connected to earth with a thick wire.
I am assuming this noise started after the unit was installed...
And also that your amp itself has a SMPS rather than linear supply?
If you can, calculate the capacitor values and build a frequency filter as the last resort.
And check that phase and neutral are not reversed in the supply to the A/C.
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I am not well up on "D" designed amplifiers but the specification for your amplifier is pretty good and I did read the full info and spec on the makers website .
The input impedance is pretty low only 4.4K ohms so either the noise from your air conditioner is exceptionally bad ( cheap design SMPS component--as in LED lighting ) or the radiated transmission is serious , easily tested with a cheap AM/FM radio near the unit .
Having seen all the LED SMPS lighting complaints in the UK and tried to help them over a long period most ended up returning the LED lamps to the supplier and demanding replacements .
I and others opened up those lamps and the quality of the SMPS parts were ---Dire --and that is putting it mildly and even worse some were well known companies --who on checking were getting supplied by --shall we say "overseas " exporters /manufacturers ---all down to profit margins .
The input impedance is pretty low only 4.4K ohms so either the noise from your air conditioner is exceptionally bad ( cheap design SMPS component--as in LED lighting ) or the radiated transmission is serious , easily tested with a cheap AM/FM radio near the unit .
Having seen all the LED SMPS lighting complaints in the UK and tried to help them over a long period most ended up returning the LED lamps to the supplier and demanding replacements .
I and others opened up those lamps and the quality of the SMPS parts were ---Dire --and that is putting it mildly and even worse some were well known companies --who on checking were getting supplied by --shall we say "overseas " exporters /manufacturers ---all down to profit margins .
This amp has a huge switching power supply. If it had bad PSRR, it wouldn't work at all with a switching supply.
If noise gets into it, it'll most likely be through the inputs, probably common impedance coupling via the ground wire of the input cable.
Can you say more about how the amp is connected to the source?
If noise gets into it, it'll most likely be through the inputs, probably common impedance coupling via the ground wire of the input cable.
Can you say more about how the amp is connected to the source?
Thank you all for your knowledge on this issue!
Amp is connected via Nuetrik single ended to balanced converters.
My system is multi use, Home theater & 2 channel.
I only really listen to records as I was once the owner of a record store it’s all I have really listened to most of my life. I haven’t listened since installing because the sound is just unbearable.
The source is an ARCAM avr390 single ended input and output only.
The tone at 4 kHz is 10dB louder than either 3kHz or 5kHz.
It is perfectly 1 octave below my occasional Tinitus tone so it really sings when my ears are not having a bad day like today...
Amp is connected via Nuetrik single ended to balanced converters.
My system is multi use, Home theater & 2 channel.
I only really listen to records as I was once the owner of a record store it’s all I have really listened to most of my life. I haven’t listened since installing because the sound is just unbearable.
The source is an ARCAM avr390 single ended input and output only.
The tone at 4 kHz is 10dB louder than either 3kHz or 5kHz.
It is perfectly 1 octave below my occasional Tinitus tone so it really sings when my ears are not having a bad day like today...
I have also discovered that the RFI is entering other amps( can hear it faintly in all other speaker) but the Purifi amp is absolutely horrible.
If I unplug the RCA cables from Purifi amp it is absolutely quiet.
But no matter what interconnects I use (shielded or not) as soon as I plus in the hum starts.
If I run only the fan (compressor off) I get zero noise.
If I unplug the RCA cables from Purifi amp it is absolutely quiet.
But no matter what interconnects I use (shielded or not) as soon as I plus in the hum starts.
If I run only the fan (compressor off) I get zero noise.
Try a ferrite filter clamped on each RCA cable, like these.
https://www.amazon.com/stardrift-10...keywords=ferrite+chokes&qid=1620230398&sr=8-4
https://www.amazon.com/stardrift-10...keywords=ferrite+chokes&qid=1620230398&sr=8-4
Can you able to you try it with different amplifier?
The source could affected by the noise not amplifier.
Can you post a link?
> If I unplug the RCA cables from Purifi amp it is absolutely quiet.
OK. Things to try:
Amp without any cable: quiet.
Plug in just the single ended to balanced converter, with no cable connected to it. Noise?
Plug a cable on the converter, leave other end of cable unconnected. Noise?
Short signal and ground at end of cable (you can use a RCA plug or cut off a junk RCA cable and solder the wires together).
Make contact between the shorted RCA connector made at previous step and the ground of RCA on your source (just ground, no signal).
Connect ONE rca cable, not two (one ground loop at a time!)
etc...
Basically, divide and conquer, try to find one difference that makes the noise appear or not.
As you have stated its when its under its heaviest load that this noise gets worse does point to a money saving smaller PFC inductor which to a large extent controls the harmonics given out by the supply .
Its "built -in noisy " due to design limitation caused by profit margin increases, increasing the size of this inductor would help .
The drive pulses ( mosfet switching ) usually have a fixed frequency --sadly it can be across the full audio range and upwards with a variable duty cycle giving a voltage pulse train of --in your case --excessive amplitude .
As its probably not worth opening up the SMPS and making design changes as has been said above a filter will have to be made or bought that can reduce that particular frequency .
That can be tuned in different ways depending on whether its CM or DM .
At the end of the day the unit you bought wouldn't be at the top end of SMPS design engineering standards but that's down to costs.
Its "built -in noisy " due to design limitation caused by profit margin increases, increasing the size of this inductor would help .
The drive pulses ( mosfet switching ) usually have a fixed frequency --sadly it can be across the full audio range and upwards with a variable duty cycle giving a voltage pulse train of --in your case --excessive amplitude .
As its probably not worth opening up the SMPS and making design changes as has been said above a filter will have to be made or bought that can reduce that particular frequency .
That can be tuned in different ways depending on whether its CM or DM .
At the end of the day the unit you bought wouldn't be at the top end of SMPS design engineering standards but that's down to costs.
In Inverter compressors the electronically commuted DC motor speed is changed by variable voltage, frequency or both.
But you see a fixed frequency, and the supply is from drive card to compressor.
You can open up the unit, and void the warranty, or simply put a thick earthing wire from the outdoor unit housing to the nearest earthing suitable, a metal water pipe works with galvanized iron wire. Some of the pipe has to be buried, of course.
You can use insulated copper wire, and check for corrosion regularly.
But you see a fixed frequency, and the supply is from drive card to compressor.
You can open up the unit, and void the warranty, or simply put a thick earthing wire from the outdoor unit housing to the nearest earthing suitable, a metal water pipe works with galvanized iron wire. Some of the pipe has to be buried, of course.
You can use insulated copper wire, and check for corrosion regularly.
Well, I haven’t had much time to troubleshoot but had time to just test by floating the ground on the air conditioner and it removes all of the noise.
So , it seems the receptical is not properly grounded.
The house was built in the 40’s , it was cut up and moved and the room with noise issues was an added in the late 90’s.
The house is on pier and beams except my audio room which is on a slab in the rear of house. This was all done by the previous owners. The only pipe I could possibly rig a ground to is natural gas pipe, I guess someone needed a heater in here at one time..
I can not afford to have an electrician come out and install a dedicated line.
I am not sure what my options are....
I really appreciate all of the help.
So , it seems the receptical is not properly grounded.
The house was built in the 40’s , it was cut up and moved and the room with noise issues was an added in the late 90’s.
The house is on pier and beams except my audio room which is on a slab in the rear of house. This was all done by the previous owners. The only pipe I could possibly rig a ground to is natural gas pipe, I guess someone needed a heater in here at one time..
I can not afford to have an electrician come out and install a dedicated line.
I am not sure what my options are....
I really appreciate all of the help.