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Quick question on amplifier hum

V

vinyl_paul

pfm Member
I have a Destiny Amp and have noticed a slight hum from both speakers under the following circumstances:

- Turntable disconnected from mains, but inputs attached to amp
- All other inputs disconnected
- Speakers connected
- Volume turned up (from about 12 o'clock onwards, 7 o'clock is off)
- Using standard mains kettle cable

Quick question: Is this an indication of something that needs service/repair? Or is it just an artifact of the amp and I should get over it? eg; yes they all do that.

Because there are no inputs, other than the unpowered turntable, I am assuming this is not the common ground loop hum? Turntable being powered on or not makes no difference.
Thanks
 
That sounds like life. You haven't said if it is less when the cable is not connected to the amp. The cartridge, or cable from cartridge to amp are picking up some EM field in the air. Better screened cable, an arm and cable earthed to the amp so that the metal arm acts as an extra screen [usually there is a screw on the back of the amp for this] can all help.
 
Thanks for your comments.
The turntable is an RP3 and they are infamous for not having any extra grounding points?
I don't have the TTPSU so can not try the grounding off a screw on the TTPSU case.

If I disconnect the turntable altogether then the Creek Destiny doesn't like it at all and locks out the speakers all together - some sort of overload circuit or similar?
I have just done some more testing and I think it might be a problem with the amp.
If I disconnect the turntable and keep the volume below 9 o'clock then it is all fine with no hum at all.
If I then increase the volume there is a loud sound and the overload kicks in. If I wait and reset the overload with the volume in the same position it immediately locks out again.
All of that suggests its to do with the amplifier?
 
If it doesn't witth cd its a deck issue. What cart are you using, I assume its an internal phone stage?
 
Sounds like the amp. I had a destiny and it didn’t and shouldn’t shut down with nothing connected
 
It’s because the amplifier is earthed through the turntable, if it isn’t earthed the 0V picks up interference, it needs to be tied to ground to drain away the interference.

Pete
 
/\ Very wrong I'm afraid.

The op could make up some shorting plugs to test if the amp is properly quiet with no input. It shouldn't go into protection if it's operated without an input though.
 
The OP's last post reads as though he tried disconnecting the turntable leads with the amp set to phono and the volume turned up past twelve.

Perhaps all was fine until that maneuver sent it into oscillation?
 
Craig B said:
The OP's last post reads as though he tried disconnecting the turntable leads with the amp set to phono and the volume turned up past twelve.

Perhaps all was fine until that maneuver sent it into oscillation?
Click to expand...

One of the more likely scenarios indeed.
 
Sorry for the delay guys.

I should have said, that I am using the Creek internal phono card.

Here is what Creek replied to my initial query:
"When the phono card is installed without a load connected to that input, it will produce a small amount of DC on the input, hence why the unit is shutting down when you increase the volume. A level of hum is very normal on phono input due to the level of amplification."
 
vinyl_paul said:
Sorry for the delay guys.

I should have said, that I am using the Creek internal phono card.

Here is what Creek replied to my initial query:
"When the phono card is installed without a load connected to that input, it will produce a small amount of DC on the input, hence why the unit is shutting down when you increase the volume. A level of hum is very normal on phono input due to the level of amplification."
Click to expand...

Pure bovine based fertiliser. Unless it's very incompetently designed.
 
Well, I have no knowledge to comment on that. However I would always listen to others who know what they are talking about. I will maybe go back for clarification!

Mr Creek is not know for bad amp designs is he? I had thought he was well thought of?
 
You haven't said what volume position is needed to listen to the turntable. Lots of equipment produce noise when the gain is much higher than needed for listening. It's a shame if it locks out when you turn the gain up, but if you have a turntable connected it doesn't do it - correct? Presumably if you switched to tuner/video/etc it would disconnect the phono section that causes the problem?
 
Good point @demotivated

I turned the input to tuner, then disconnected the phono. Now I can turn the volume right the way to full without any issues. There is the faintest hum but it is very slight and only at top volume. Not concerned about that at all.
( There is one odd thing - when I touch the volume knob (even gently) there is a slightly louder hum and but this is at full volume so probably expected?)
Nothing of concern in that test.

I then reconnected the phono, leaving input to tuner, and repeat. Full volume, nothing - as above.

Finally, switch input back over to phono, and repeat. The hum comes in noticeably at about 12 o'clock (eg; about 50%). Full volume is about 5 o'clock, zero volume is about 7 o'clock. I would estimate my normal listening is in the 10-12 o'clock. Needless to say if I am listening to Rock then this is not an issue, however it is for the quieter genres that I notice it. I guess it could still fit in the allowable limits of amplification of the phono input?
 
Does the Creek have a 3 wire mains lead? Is the earth actually connected on it? This is the only thing I can think of that would cause the extra hum when touching the (I assume metal) volume knob.
 
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