svt hummmmm is killing me (not so) softly

[todzilla]

i'm a newbie to posting, but i've appreciated your input from the back row in the past. i've finally worked up the intestinal fortitude to ask for some direct input.

i've got an (awesome!) 1978 svt that i run through a 2x15. i wish i could just leave it at that, but no...there's more. i've recently been trying to record without mic'ing (but wanting to take advantage of all those preamp tubes) and i've run into a hum problem with the following qualities:
1. the hum is not present when my rig is NOT connected to the recorder;
2. hum appears when i connect to the recorder (1/4" to 1/4") from the preamp out on my svt;
3. hum is even worse when i connect to the recorder (1/4" to 1/4") from my strobostomp DI out instead of the preamp out.

my first vague, newbie thought is "ground loop," but maybe could be something else....? strobostomp and eQ are daisy-chained; i have a tonebone hot british on a separate wall wart, but running to the same power strip with the daisy-chain. the svt and the digital recorder are plugged into separate outlets (so we're talking about 3 different grounded outlets total).

where should the troubleshooting begin?

thanks, tribe.

 

[thewanderer24]

I'm no expert, but a few simple things to try.

1. Play with the ground lift switches on each of said devices (i.e., try various configurations of some grounded vs lifted

2. Check the cables you are using for the connections. Are they good/flakey?? Are they the right kind of cables (shielded vs. not?)

3. Get a new powerstrip - spend $20 on something quality, not just something to add plugs.

#3 actually fixed a hum problem I was having on my home recording setup once upon a time.

 

[anderbass]

Good advice already, but also try powering all these devices through the same
wall outlet (and try all 3 different outlets), and also try without any added devices
connected to your amp to see if anything helps or not.

 

[thewanderer24]

good thoughts. You definitely can get noise from other things plugged into the same circuit (i.e., a space heater, tv, computer peripheral, etc.)

 

[todzilla]

I'm no expert, but a few simple things to try.

1. Play with the ground lift switches on each of said devices (i.e., try various configurations of some grounded vs lifted

2. Check the cables you are using for the connections. Are they good/flakey?? Are they the right kind of cables (shielded vs. not?)

3. Get a new powerstrip - spend $20 on something quality, not just something to add plugs.

#3 actually fixed a hum problem I was having on my home recording setup once upon a time.

i've been off-line for a couple of days, so i'm just getting these responses now.

thanks for the suggestions. i tried playing with the ground lift, but got no significant hum relief.

i hadn't thought about extraneous appliances adding to the problem. i also hadn't thought about the quality of the powerstrip i'm using. so, lemme try suggestions 2 & 3. and anderbass' suggestion.......

 

[todzilla]

curious/looking for recommendation: what kind of powerstrip did you use to kill the hum in your home studio?

 

[Baleen]

If you have the original 2-prong plug, have you tried the SVT's polarity switch in both positions? On my '68 fliptop and my B-25B, I eventually found this technique a safe way to check the polarity, i.e. without shocking myself.

Plug a patch cable in and turn up the volume (there's nothing on the other end of the patch cable). Switch the polarity. The bad polarity setting makes more hum than the good.

The safest thing, though, is to have a grounded plug installed on the head... Finally did this on the fliptop. Works great.

Other than that, perhaps an (unpowered) passive DI with a ground lift to eliminate one of the possible ground loops?