A Hum in Audio in all modes of operating. The hum was a 60 cycles in nature. Since the power supply is a switching supply and it does not operate at line frequency I felt that the hum must be introduced from the line voltage input. However I was going to check the power supply input. Before removed the power supply I noticed that the FOUR mounting screws that held the power supply to the main chassis were not tight. Tightening the mounting screws solved the HUM problem .If the power supply is not grounded fully a ground loop hum will appear. I felt this may become a problem as the sets age. From a retired electronic tech RAY AI4DU
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one of the most common sources of hum is a failing power supply.
I don't know your radio specifics..... however, some things to consider/try : if it can be battery powered, try it with batteries.
If hum disappears, then source is power supply. Power supply
hums are usually 60 or 120 Hertz (cycles per second). The most
common failure component in power supply, causing a hum, are
the filter capacitors. If you do try to replace these, be very careful
and discharge the old caps before you remove them - to avoid a
(potentially dangerous) shock... caps can retain a charge for many
days, sometimes. Another source of hum is if the radio is close to
a flourescent light, or other appliance which may radiate power. If so,
try moving radio. If the hum is high pitched, then more info is needed.
Hope this helps!
You are using a shielded cable to connect the receiver to your amplifier, right? If so then I would suspect the cheaply regulated AC to DC power supply (wall wart). Unfortunately the filtering cap value is usually to small and it causes a slight 60 cycles hum to show up in the audio output. I build supplies for critical equipment myself and install larger value filtering caps for cleaner audio.
I assume you are using condenser mics as you would NOT be using phantom power with any other type connected or other devices plugged in while you have phantom power. It is important to have ALL interconnected equipment, including the computer, powered from the SAME receptacle or power source. Make sure the power supply you are using is SPECIFICALLY for the unit from Focusrite as some supplies have filtering within the wall transformer module and others do not. The power supply MAY be generating magnetic fields... try moving it around and see if hum is affected. The capcitive coupling in a power supply can let in higher frequency components from lamp dimmers. Make sure you have no lamp dimmers anywhere near the equipment.
Most hum is caused by a faulty electrolytic capacitors. If the hum is accross both channels, then it's most likely one in the power supply part. Maybe the big one that filters the 50/60hz mains hum. The reason you will hear it in playback, is that a switch will be opened up when the mechanism goes into play. This switch connects the tapes pre-amp to the audio out circuit.
When the speaker is connected only at the power line does it makes this noise?
If it does it's an internal amplifier's ploblem and you have to check out some fittings (electrolytic capacitorsat the power supply, power supply transformer, voltage stabilizers e.t.c.)
If the speaker is quiet you have to check your external wiring because there is a loop ground. That means that one "ground level" line is connected at the ground by two or more cables (e.g. the audio ground and the grond from the mains power source) In this case disconnect the second (and the 3rd e.t.c.) grounding point.
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due to the nature of the f.m. signal you may notice a hum when locked into a signal especially during times of no modulation(talk/music),otherwise if its severe enough,look for ground loops and bad solder joints that let signals radiate through out the receiver and create humming,also check the power supply filter capacitors if its a 60 cycle line noise hum
If the volume control does not effect the hum volume, then the hum is being introduced directly to the final amp section. Check for defective caps in the power supply for the amp section. This will be the nigher voltage supply usually 40V or more.
This sounds like it may be a loose connection (ground) generation common mode noise or it may be a capacitor in the power supply going bad and not providing enough filtering of the AC voltage (allowing for 60 cycle hum). You should get a schematic for the speaker or just take some rule of thumb measurements of the power supply output, with an oscilloscope (you will be looking for ripple voltage, what you could do is use one of your good speakers as a comparison of good to bad.
If you do not want to work on this yourself, you could take the speaker to any TV repair shop or audio repair shop.
What type of noise is it making? If it sounds like a load hum, you may have a 60 cycle hum issue. This is caused by a capacitor not filtering out the 60 cycle ripple on the DC voltage supplied by the power supply. If you have this problem I would suggest measuring the power supply with a DC voltmeter first and writing this measurement down. Then I would suggest you plugging the amp into an isolation transformer and taking an oscilloscope (plugged into the wall)and measuring the DC voltage while the oscilloscope is set to AC if you see an AC ripple voltage higher then .1mv you have a bad filter capacitor or a bad voltage regulator.