Studio Pre picking up AM radio, distorting

[partyofone]

Having a couple of odd things with a newly aquired studio pre:

1) Picking up AM radio station. Is there a quick fix for this one?

2) Rhythm channel distorts with Volume above 2, even with masters low.
The manual says 4 to 5 should be a clean sound. I play a Parker with active pickups and the distortion goes away when I turn Fly down a bit. Could it really be my pickups?

Any help greatly appreciated. Thanks!

 

[partyofone]

seems that a lot of people have trouble with cables picking up radio...I switched out several cables, as well as plugging headphones in but it doesn't seem to be cables. I was thinking my DC-5 didn't do this, but now that I think about it I believe it did as well. hmmm....

 

[MarkMcQ]

My clean channel does the same thing. I find it very hard to get a pure clean sound, there's always a tiny amount of grit in there somewhere.

Another thing I noticed on mine was when I change from the lead to rythm, there's a very brief overlap where the distortion seems to 'fade out' very quick, and it's not a straight change. Do you find this happens with yours at all?

 

[disassembled]

About your pickups:

Hell yeah it could be them if you are slamming the input stage with too much juice. Maybe try lowering your pickups so it doesn't distort so early. Are you running 9 or 18 volts?

About the radio interference:

Does it only do it when the guitar is plugged in? Does it happen on every channel? Is that the only amp you have that does that? Are you using a *good* cable? Is your amp grounded? Is there anything else connected to the pre?

I have never had an issue with radio interference but I always use good cable that I custom made and I always make sure everything is properly grounded.

Good luck

 

[partyofone]

On the fading in...
I haven't noticed mine doing this, but I'll need to go back and check because I haven't been really switching back and forth quickly.

I would say that for me I'm getting even more than grit to just straight distortion at 4 and 5.

About your pickups:

Hell yeah it could be them if you are slamming the input stage with too much juice. Maybe try lowering your pickups so it doesn't distort so early. Are you running 9 or 18 volts? <<<<< 9 volts



About the radio interference:

Does it only do it when the guitar is plugged in? <<<<<< No.

Does it happen on every channel? <<<<<<<<<< Yes.

Is that the only amp you have that does that? <<<<<<<<<< I haven't noticed my little solid state Fender practice amp doing it, but my DC-5 might have.

Are you using a *good* cable? <<<<< Yeah, Whirlwind. Tried a few others too.

Is your amp grounded? <<<<<<<<<Yeah.

Is there anything else connected to the pre? <<<<<<<<<Nope, just guitar straight in. Even tried input jack on back. But it does it w/o guitar being plugged in at all.

I have never had an issue with radio interference but I always use good cable that I custom made and I always make sure everything is properly grounded.

Good luck

 

[disassembled]

I think it's time to take the cover off and bust out the multimeter to test for a good ground. Make sure you have a clear connection from the third prong on your plug to the inside of the chassis. You possibly might have loose chassis screws that are lessening the integrity of the ground on certain places.

More than likely you have a ground loop that is acting like an antenna. To avoid ground loops unplug everything in the immediate area first to eliminate as many variables as possible. This includes: fluorescent lighting, CRT TVs and monitors, any type of motor equipped device, and really anything else that could possibly be plugged in nearby to your amp. Try as many different outlets as possible; especially ones outside of your house. Just to test, put a third prong eliminator on the preamp to lift the ground at your wall socket. I do NOT recommend leaving the ground lift adapter on the unit if the problem goes away as it can be an electrical hazard.

Just for testing purposes: with the amp plugged in and broadcasting your favorite ballgame, try hitting various areas on the outside of the chassis using your fist (with the cover sealed, we don't want you risking getting hurt). If you notice a modulation or a cutout in the radio you may have a loose component/loose ground inside. Also, grab a chopstick and start poking around inside and tap on the PCBs, tubes, etc to see if you can find a possible problem.

There is something really simple most likely causing this and you just have to systematically go through the process of finding it.

 

[partyofone]

killer advice man! sounds like an excellent place to start. I'll do those things and let you know what happens. thanks!

 

[partyofone]

man do I feel stupid! I pulled the pre out to and started unplugging things, knocking on it, etc. trying to narrow it down some. then I notice this switch on the back that I didn't really notice before. it was a ground lift that was set to 'lifted' position. I flicked it and voila...it stopped! I would actually think that the it would work the opposite though. oh well, it seems to be working.

also, I tried a tele in the pre instead of the parker and no distortion. I guess the parker really does have hot output. thanks for all the help!

 

[disassembled]

Awesome man. Glad it worked out. See, I told you it would be something simple! Enjoy your pre!