Nashville 400 with buzzzzzzz

Bob Mainwaring · Post by **Bob Mainwaring** » 22 Sep 2005 9:49 pm

I seen to have aquired quite a hum these last few weeks until our singer says - "no more" - I cant stand it!!!
I tried the ground switch and it will go away for quite some time then come back again. I do the same thing and switch it in the other direction and it goes away again ...... then comes back. What might the problem be....any ideas??

Bob Mainwaring Z.Bs. and other weird things.

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Jack Stoner · Post by **Jack Stoner** » 23 Sep 2005 2:01 am

It sounds like something else and switching the ground switch justs temporarily masks the problem.

It could be in your pickups, cables, or anything in the chain before it gets to the amp. It could be something in the amp or it could be something in the AC power line.

You'll have to do more testing to help isolate what is really wrong.

Ken Fox · Post by **Ken Fox** » 23 Sep 2005 5:14 am

A loud 120hz buzz would be filter caps, typically. Does the amp do it with no instrument plugged in?<font size="1" color="#8e236b"><p align="center">[This message was edited by Ken Fox on 23 September 2005 at 06:14 AM.]</p></FONT>

John Daugherty · Post by **John Daugherty** » 23 Sep 2005 7:55 am

Bob, Everyone in that band needs to get their power grounds right. I have had that problem if another amp on the bandstand is not grounded properly. Last week, a sound man had to use an AC adapter to lift the ground on my NV 112 to get rid of the hum in their monitor system. We had a lot of amps onstage and I think the wall receptacle was faulty.
As was mentioned previously, you need to determine if the buzz is there when nothing is plugged into the input of the amp.
If the problem is power supply caps in the amp, it will hum with the gain controls set at minimum.

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Alan Pagliere · Post by **Alan Pagliere** » 23 Sep 2005 1:20 pm

I had a buzz develop in my N400. It would come and go. Over time, it got louder and just plain nastier. It was old. I called Mike Brown at Peavey and he suggested I send it in. I shipped the chassis and in short order I got the thing back in great shape, to factory specs. It turned out to be a bad power supply.

I've had it about a year now since then and it is clean, clean, clean. I don't remember it sounding so good since I bought the thing new....

Of course, your problem may have nothing to do with an old and bad power supply, but I just thought I'd throw in my 2 cents of experience.

Good luck.

Ken Fox · Post by **Ken Fox** » 23 Sep 2005 1:30 pm

As Jack said: "If the problem is power supply caps in the amp, it will hum with the gain controls set at minimum".

The reason being is the pulsing DC acts as a signal right into the power transistors!

I just did power supply filter caps on a LTD400 and a Session 400 this week. Mighty quiet after that was done!

Easy to see it on a scope, the DC has little "church steeples" on top of the sawtooth wave. There is alway a bit of ripple (sawtooh wave) in filtered DC, but these little steeples will show up on the old caps. They often amplify as a buzzing noise at the end of a note! When they really get bad the sawtooth pattern is quite large and there is a loud audible hum.

Bob Mainwaring · Post by **Bob Mainwaring** » 25 Sep 2005 6:02 pm

Many thank's guys for all the "come-backs"

I still haven't had time to sort it out as yet but will give all the replies a tryout.

Bob Mainwaring Z.Bs and other weird things.