Marshall AVT and distortion

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TexRoadkill

TexRoadkill

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Here is one for any AVT users out there. I've been using a AVT50 half stack for a few months and I finally started recording it and I noticed there is this really crappy buzzy sound with the distortion. At first I thought I had a blown speaker but with carefull adjustment of the gain I was able to blast the amp with a clean sound and not get the buzz.

I didn't really notice it until I was listening to recordings with headphones. It is a high pitched, almost digital sounding buzz that seems to occur on top of the regular saturation distortion and only on the peaks.

Has anybody else noticed that or is there possible something wrong with the tubes on the preamp? I'm not much of an amp tech so any help is appreciated.
 
What kind of speakers do you have? Somewill let more high end through than others, which can lead to much sharper distortion sounds. I'm not totally familiar with the AVT series, those are solid state power amps right? I heard some samples on the marshall site a few weeks back and they sounded pretty good, but you know how it is with compressed audio...
 
I'm using a Marshall 1960 Cab. I don't really know what is in it. I bought the rig used in like-new condition but now I'm thinking there may be something wrong with it.

The distortion is really weird because it cuts in at the highest peaks but it is different sounding then the regular distortion. It really sounds like a blown tweater but it won't distort on a clean tone with the main volume way up. Obviously it doesnt have tweeters but that is the best way to describe the sound. Usually a blown 12" is very floppy/woofy/distorted and this is a high/grainy/thin distortion that appears on top of the regular distortion on peaks. I'm hoping somebody can confirm if that is just the way the AVT's distort or if there is really something screwed up.

The problem with those sample MP3's is that they are full on metal distortion and I'm using a more dirty, bluesy sound so it's hard to compare.

Buck62 where are you?
 
I have an AVT50 and have used the DI output for recording. I have not hear any bizzare sonics coming out of that output. Sounds like something could be wrong. Check and make sure you have a good ground on your power source.
 
One question ... are you using any distortion pedals in front of the amp?
 
No pedals. I was thinking of getting some to see if I still hear it. I guess I should try another cab to make sure that is not the problem.
 
I'm having this SAME problem with an old Fender amp and recording. It's a little VibroChamp and when it comes through the cans I'm getting that overtoned, thin, digitally distortion you're describing, it's driving me crazy!

I'm swapping out every piece in the signal chain to see what is the problem and I might be narrowing it down. I replaced the mic cables, bypassed compressor and switched channels going into my mixer and I've noticed a change but havn't had time to really focus and see if that buzzing is gone. I know it's not in my soundcard, i can hear it at the mixer. I would suggest just methodically checking all the equipment. I suspect it's not just a problem with the AVT.
 
Thanks for the input Blip. At first I thought it was input distortion somewhere else in the recording chain because it is a lot more noticeable when listening to the recordings. But now that I've noticed it I can hear it live out of the amp/cab. My rig is so basic it's just guitar-cable-amp-cab so there isn't too many pieces to troubleshoot.

The fact that it only happens when using the amp distortion leads me to believe it is not the guitar, cables or speakers. Please keep the suggestions coming in case there is something obvious I'm overlooking.
 
I'm taking a semi-educated guess and say that it's possible that the power tube is starting to go.

My partner had an Ampeg V-4 (all-tube head and 4-12 cab) that started to buzz when overdriven. Not too long after that started happening, the amp would just lose volume after being played for more than a half hour or so. The volume would actually dip and then come back to the set level after a minute or two.

Replacement of one of the power tubes solved the problem.

I know that Ampeg and Marshall are two different animals, but the problem could be the same in theory.
 
True, but the point is that a tube may be on it's way to the garbage can, and in this case that one single tube in the preamp may be the culprit.
 
Right Buck. I was assuming you knew that, but I didn't want someone elso to get the wrong idea about it.
 
Tex,
I have an AVT 20 I use for practice and recording. Overall I like the tone of this amp (it has the Marshall beefy punch), but I know what you mean about the overdrive sound. (or think I do)

Is what you're hearing sound like a character of the overdrive itself? (as opposed to something rattling?) Kind of like the fuzzy/static sound of digital distortion? Or something like, an all tube overdrive is very "open/full" sounding, and this is a bit more "closed/muffled" sounding?
I think that's just the Marshall overdrive sound in the AVT line - it's not all tube overdrive, it's one tube to add some tone and overdrive. Many of their other all tube amps are using at least 2 tubes for overdrive. So I think they compromised and used the tube for part of the overdrive sound, and either diodes or something else for the rest of it - probably the part that sounds raspy.

Have you, or anyone else, tried changing the 12Ax7 (ECC83) tube that's in the AVT? Maybe to either another manufacturer type, or to a 12AY7 tube (which would have about 30% less gain output). That *may* make a different flavor of overdrive. Not sure, I haven't tried it yet.
 
thank god there are AVT users!

my initial plan is to buy the avt150 that has 4 digital effects and since it has some pretty good sounding distortion. i thought about getting the AVT50H but the distortion options didnt seem as good so i wasnt sure. do you guys enjoy that head? i kinda thought 50 watts through a 4x12 cab would be kinda weak. my style is more of the rock rap deal. does it have a good distortion for that?
 
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