5f1 saga... ground issue?

[martinman]

Long story short, I had the wrong PT in the amp. Swapped it out for a 330-0-330. Had some input jack wierdness through the speaker. My chopstick test suggested that the input jacks were crap (and they were). Replaced these with switchcraft.

Now...

Everything works perfectly, and it sounds great. Except for one thing: Diming the amp with only a patch chord (no guitar) in input 1 produces this strange type of feedback. It's not a squeal though - very low frequency almost like the speaker is bottoming out. It starts happening when the volume is around 9 and progressively gets louder the more you turn it up. When I plug my guitar in everything is fine - I get full volume sweep w/o any strangeness. Input 2 is a different case all together - it works as it should. So, in summary:

Input1:
No guitar cable, things are fine.
Guitar cable w/o guitar - Noisy low frequency above 9.
Guitar cable w/ guitar - everything is fine

Input2:
No guitar cable = fine
Guitar cable w/o guitar = fine
Guitar cable w/ guitar = fine

The amp w/o any input at idle works perfect. Even turning up the volume there isn't any strangeness.

When I installed switchcraft jacks I read somewhere that they "self ground" to the chassis, so I don't have a ground wire attached. I could hook up some patch cables to both inputs and then to the pre-amp ground spot on the turret board. Thoughts? Is this a ground issue?

[g1]

Diming the amp with only a patch chord (no guitar) in input 1 produces this strange type of feedback.

As it should. This is a non-real world problem, no one would operate the amp in this manner.
If it's good with the guitar set up in this manner, then it's good.
The input jack can only ground the input when no cable is plugged in.
Amps can do strange things when we ask them to operate in a manner they were not designed for.

[eschertron]

+1

People have spent lifetimes using their bodies, toasters, power tools, etc. as musical instruments.

You are using a patch cord that way. It is an antenna when plugged into the amp with nothing else, because the cord has no path to ground on the 'instrument' end. Wave it around, bring it near some electrical devices, tape it to your body - you'll have more variety of sound than the low pitched 'feedback' that you've heard in the past.

[Justin Thomas]

Try touching some different types and sizes of metwl witg it for some (potentially) interesting effects. My buddy's delay was making some funny noises; in process of checking it, I hit a piece of bare ungrounded metal on my Bassman head - the slide out clip. Only that particular piece of metal did it... A high pitched tunable shriek, ocmbined with the delay effect, real sci-fi soundtrack stuff. Seriously, if you just spend enough time mucking bout doing things NOT as intended, who needs keyboard players? Have fun with your new strange noise!!!

Justin

[g1]

And you may be wondering, why doesn't input 2 do it then? I'm actually surprised it doesn't, you just got lucky. It probably has to do with the routing of the wires, or if #2 is a lower level input.

[martinman]

And you may be wondering, why doesn't input 2 do it then? I'm actually surprised it doesn't, you just got lucky. It probably has to do with the routing of the wires, or if #2 is a lower level input.

g-one: Good catch -- it is a lower level input. Thanks everyone for the feedback! My 5f1 is probably the best sounding amp I've ever had. Low volume combined with the breakup in such a small package. No wonder it's one of the most recorded amps.