Ashdown MAG300 - Fried?

[Eight]

Luckily for me, last week I bought a nice Warwick Pro Fet 5.2 (a little too loud for the house but looks like my neighbours will just have to learn to live with it for a while).

Anyway...

I just stood on my cable while moving and yanked the jack out - not the first time I've done that. Except now my MAG 300 head seems to have suffered an injury from it. The input gauge is shooting straight into the red with even the smallest of signals, and what comes out is a natural british fuzz.

Tried two different basses and two different cables so I'm pretty sure it's the amp. The signal was going through my new Korg DTR tuner so I don't know if that's made it worse (the tuner seems fine thankfully).

Any ideas?

[escholl]

What did the cable get pulled out of, the Korg or the Ashdown? Sorry I'm just confused as you mention the signal was going though the Korg.

[Eight]

Ah right, yes, good point.

It was pulled out of the guitar. With the tuner in the chain between the guitar and amp. Turned off the head, plugged the cable back into the guitar, restarted the amp and got nothing but fuzz.

Put the same stuff (same signal routing etc.) into the Pro Fet and everything is fine, so nothing has gone awry with the guitar/cables/tuner... just the Ashdown.

Edited April 25, 2010 by Eight

[escholl]

Ah, ok. Well, the following is purely speculation, but this is my best guess:

Some amplifiers, including my own, have a FET input stage with no over-voltage protection. While this is usually not a problem, the input FET in my own amp once randomly began to exhibit symptoms very similar to what you describe, after being plugged in one day. My theory was that static electricity had damaged the unprotected input FET, as that was the only thing I could think of -- static electricity discharging into the input after the tip of the cable came into contact with whatever was charged. Replacing the FET fixed the problem that time and I've been meaning to install input protection, but that's another story.

Anyways, if your Korg does have input over voltage protection it wouldn't have been damaged, and if it has a direct, unbuffered signal pass-through from input to output, then the tip of the cable could have passed a static charge from you, or the carpet/floor, through the tuner's I/O (as unbuffered it would basically just be a bit of wire) and into the input of your amp, possibly damaging it.

The likelihood of all these factors occurring is incredibly small, and my theory is based upon several guesses as to the internal workings of equipment to which I am unfamiliar. Furthermore, my amp did not exhibit -identical- symptoms, and I only guessed at the cause of it's own failure, so again I am hypothesising here. Someone may certainly have a more likely theory!

Anyways, that's the only way I can think of that the plug falling out could cause such a distorted sound upon re-powering. Did it make a massive noise when it happened? I suppose if it was up loud enough, the massive *thump* noise you usually hear when the cable is unplugged could have damaged an output transistor, or I could be wrong everywhere and it could be something totally different! Do you get a clean signal from the effects loop output? Or if you go direct into the effects return, is the amp clean then?

[Eight]

Cheers for the thoughts Escholl. It's appreciated.

It did make a fairly loud noise, but not really any worse than usual - I do this quite a lot to be honest. Need to find some locking jack system for my guitars.

[quote name='escholl' post='818769' date='Apr 26 2010, 01:22 AM']Do you get a clean signal from the effects loop output? Or if you go direct into the effects return, is the amp clean then?[/quote]
I'll try the effects loop - good thinking there. Should help narrow down where the problem might be.

[escholl]

[quote name='Eight' post='818891' date='Apr 26 2010, 09:08 AM']Need to find some locking jack system for my guitars. [/quote]

Have you tried looping it over the bottom strap button? I used to pull mine out all the time too until I started doing that

[flyfisher]

Unprotected inputs on any item of electronic equipment is pretty bad design really.

[Eight]

[quote name='escholl' post='819435' date='Apr 26 2010, 02:37 PM']Have you tried looping it over the bottom strap button? I used to pull mine out all the time too until I started doing that[/quote]
I do when I remember... which obviously isn't as often as it should be.

Perhaps it was the fates trying to tell me that I don't need two amp heads.

Edited April 26, 2010 by Eight

[escholl]

[quote name='Eight' post='819939' date='Apr 26 2010, 09:01 PM']I do when I remember... which obviously isn't as often as it should be.

Perhaps it was the fates trying to tell me that I don't need two amp heads.[/quote]


pfff...two is the minimum, i thought everyone knew that?

[Eight]

[quote name='escholl' post='818769' date='Apr 26 2010, 01:22 AM']Do you get a clean signal from the effects loop output? Or if you go direct into the effects return, is the amp clean then?[/quote]
Finally had a chance to take another look at this amp.

With the bass going into either the low/high input jack, if I take an XLR cable from the Post-EQ out into my mixer and studio monitors then I get the horrible fuzzing sound and the VU gauge redlines.

If I plug the bass (or other sources) into the Effect Return then it comes out clean.

So have I blown the input/pre-amp stage?

[Eight]

[quote name='escholl' post='820189' date='Apr 27 2010, 02:01 AM']pfff...two is the minimum, i thought everyone knew that? [/quote]
Hmm... that means I'm now under-equipped.

On the plus side, I get to go shopping.

[escholl]

[quote name='Eight' post='824839' date='May 1 2010, 02:06 PM']So have I blown the input/pre-amp stage?[/quote]

Yes, that is exactly what has happened. The good news is, at my best guess, it should be an easy (read: inexpensive) repair from any decent and competent tech -- you could even try getting in touch with Ashdown.

I've only got one head as well -- in fact I really have none at the moment, as mine is in storage in the UK while I'm stuck back in the US for now -- so I am under-equipped too!

[Eight]

[quote name='escholl' post='825288' date='May 2 2010, 04:13 AM']The good news is, at my best guess, it should be an easy (read: inexpensive) repair from any decent and competent tech[/quote]
Fingers crossed - it doesn't seem worth spending a lot of money on but I would quite like to get it working again.

Cheers for all the help mate.

[quote]I've only got one head as well -- in fact I really have none at the moment, as mine is in storage in the UK while I'm stuck back in the US for now -- so I am under-equipped too! [/quote]
Hahaha. Get yourself to a sam ash or something and rectify that.

[lowfer]

this has been a really useful post for me. I have an Ashdown mag 400 combo, that sounds asthough it has developed a similar problem, altyhough i can't trace the problem to a particular incident. Mine doesn't fuzz all the time but does so periodically. When the input lead in the amp is moved or the gain knob is turned it gives a huge amount of white noise like a loud scratch asthought static is being trnsfered throught the input stage to the output stage. I must admit i went out and bought a LM11 but still have it sat in my shed gathering dust. I think i will dif it out and try going in through the effects send and see what happens

N