Wall wart supply makes my amp humm loudly ???

[jibreel]

I run a Hughes and Kettner half rack tube preamp either into a TC RH450 or a Bose amp. Don't use the preamp on the RH450, just into the effects return so amp only.

When I plug in the low volt transformer for my ART Tube MP, the Bose amp humms noticeably but the RH 450 does not hum. And this happens regardless of whether the ART is being used or not. Just plugging in the transformer does it. Again, only with the Bose.

Plugging in my One spot does not make the hum.

Any suggestions ?

Thanks

[SurferJoe46]

I'd look elsewhere for the 60~ hum. I've got two ART MPs and they are stone silent.

Is there a possibility that you have an unshielded cable somewhere in the sound train? A speaker cable - which looks pretty close to the same, can do this and in spades!

If in doubt and you can unscrew the jack and look inside it, try to see if it's just two wires that are soldered to the prongs or there's really some sheath - braided - on the ground side of the jack spades.

It should be obvious - but you may have to look pretty close to tell.

If the jack isn't open-able, EG: hermetically sealed, then you may never know unless you substitute a real shielded cable in and see if the hum goes away.

[jibreel]

Dude !!!!!!! Speaker cable. I was using a cheap cable between the pre and the amp. Replaced it and no more hum. The reason I did not think of this was because there was no hum with the RH 450.

Thanks !!!!!

[staindbass]

maybe shielding the plastic cased wall wart will make it go away ? a quick test with tinfoil grounded to the 3rd lug (earth ground) of the wall socket might be worth a try. any flourescent lights or dimmers in the house ? or neon signs nearby in the neighboorhood will help it hum too..

[staindbass]

oops you found the problem, awesome !

[SurferJoe46]

I like to think horses when I hear hoof beats, not zebras.

*No dis to those living in Africa where you very well might think zebras first.

[SGD Lutherie]

Originally Posted by jibreel

Dude !!!!!!! Speaker cable. I was using a cheap cable between the pre and the amp. Replaced it and no more hum. The reason I did not think of this was because there was no hum with the RH 450.

Speaker cable is not shielded. You should only use that for speakers! Only use shielded coax cable for signals, and never use shielded cable for speakers!

[bongomania]

To be fair though, they can look exactly identical in some cases, unless you disassemble them. Sometimes the writing on the exterior is faded, tiny, worn off.

[jibreel]

Originally Posted by SGD Lutherie

Speaker cable is not shielded. You should only use that for speakers! Only use shielded coax cable for signals, and never use shielded cable for speakers!

Thanks. It is working correctly and it is actually the cable that came with the Bose so I mis-wrote when I said speaker cable.

I have certainly mixed the two up before