Is it normal to hear slight hum at full volume (no input)

escorial

Active Member
New to tubes, my amp with out any input is dead quiet untill zi turn it up past 3/4 volume, then I hear a slight hum.

Is this nornal? My last tube amp was back in 74 and honestly I forgot
 
Is this an integrated amp, or a system of separate pre-amp and power-amp? Does it happen with the inputs shorted (i.e. the positive and negative connected together, on each input)?

If it's affected by the volume control, then the hum is coming from some stage that is before the volume control (i.e. not the driver / power stage). If it happens when the input is shorted, then it could be noise leaking into the circuit from the outside (due to lack of shielding around sensitive wiring) or it could be heater noise from one of the tubes between the input and volume control. If it does not happen when the input is shorted, then your test is picking up ambient noise from the input.
 
With a *shorted* input, my Fisher gear was always almost dead nuts silent - a touch of hiss barely audible unless you got close to the speaker. No different from SS gear. My Dynaco MkIIIs have a tad bit of hum. Sometimes a bit more when a 6AN8 starts acting like a 6AN8. If/when I get a Citation II or MC275 or such, I'd expect them to be dead nuts silent, though.

There's other factors that can affect things, though, besides the amp, which is why checking with the input shorted is important. I found my DAC had a 'fun' ground loop issue with it, my pre, and the MKIIIs that required hitting the ground-lift switch on the back of it. Oddly, the SA100 I have never cared, it just kept munching away on 7189s silently (no, it's not defective, that thing just eats tubes...)
 
Is this an integrated amp, or a system of separate pre-amp and power-amp? Does it happen with the inputs shorted (i.e. the positive and negative connected together, on each input)?

If it's affected by the volume control, then the hum is coming from some stage that is before the volume control (i.e. not the driver / power stage). If it happens when the input is shorted, then it could be noise leaking into the circuit from the outside (due to lack of shielding around sensitive wiring) or it could be heater noise from one of the tubes between the input and volume control. If it does not happen when the input is shorted, then your test is picking up ambient noise from the input.


Ok how do I short? I do have a 3.5mm MP3 player cable installed, can I just short that male part of the plug w/ a screw driver or foil?

FWIW its a integrated amp and again the noise is very minimal when turned up over 3/4 or a bit more. Most of the tubes have the origina covers on them, I have small table top speakers close by but that are small. Also when I tired turning up I had the amp set to aux and the MP3 cable was not connected to anything if that helps.

Thanks all
 
If your RCA end is connected to AUX but 3.5mm jack is not plugged into audio source, it becomes antenna and can pick up interference from AC power cord or power transformer nearby. Foil may work to short both channels to ground.
 
Ok put foil around the male end of the MP3 cable and turned up the volume %100 and zero noise of any type!

So looks to be good \

Thanks
 
None of my amps hum at full volume- they are dead quiet....with the exception of my 2A3 SET amp which has a slight hum. How efficient are your speakers and what kind of an amp is it? If it's an SET it might be normal.
 
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