DESPERATE FOR HELP- having amp trouble and leaving for tour in 15 hours

[joeoqt]

I have a Mesa Boogie Single Rectoverb. It started buzzing at our show tonight, and would only buzz on the distorted channel. I tried plugging into a different place, switching cables, guitars, speaker cables, tubes, checked the connections in the amp, ran direct instead of through pedals, and I can't think of anything else. I can't bring it to a shop because I'm leaving tomorrow for tour, and I need this fixed.

[verity38]

joe joe joe joe joe, two things, a dead cable even though you said you checked it already and possibly a weak connection with your guitar, the imput might be loose, which will cause a feedback.-- so try switching guitars.

hope this helps good luck on tour.

[OveriseFan]

The last show this happened to the other guitarist, and he told me it turned out the problem was with the cable, so I'd really just try getting a new cable and plugging that in.

[thefollowthroug]

Hey,

I have the amp your talking about.

Definitely look into your guitar cable. Also look at your guitar jack (is it loose). Straight up simple way to see if it's definitely your amp and not guitar: take your guitar and cable and plug into another amp and see if it is still happening. If it is, that would lead you to look at your guitar and not the amp. You could also try plugging a different guitar/cable into your amp. If it is still happening it is definitely your amp.

Unless..you have pedals or other devices in front. Make sure you are plugging straight in, guitar to amp.

Assuming it's not any of that stuff, and you're sure it's your amp I would start troubleshooting this way:

-Double check all your settings---Tube switch on the back (should be on 6L6 for stock tubes). Make sure you're speaker cab ohms match the output you are using for your speaker cable.
-Make sure you are plugging into a properly grounded electrical outlet. You can get hum from poorly grounded outlets. There are testers for about $5 at any hardware store that can show you this.
-Switch reverb on and off. Is it the reverb?
-Switch channels. Does it do it on both channels? Or just one?
-Try tapping the preamp tubes with the end of a pencil. You'll have to unscrew and remove the grill on the back to do this. If you get a squeling noise when you tap one of the tubes, that's the culprit.

Beyond these easy things, you absolutely need to have a tech look at it.

[patrickhowell]

-Make sure you are plugging into a properly grounded electrical outlet. You can get hum from poorly grounded outlets. There are testers for about $5 at any hardware store that can show you this.

This is a big possibility. The hum would be very subtle on a clean channel, but huge and obnoxious on an overdriven channel.

Also, are you sure that it's not present in the clean channel? Buzzes, hums, etc are a lot less apparent in clean settings, even if it is still there...

You said you checked everything, but I'd try plugging in a different guitar, cable, speaker cable, and speaker cabinet all at the same time and make sure it still produces that same problem.

Did you switch out preamp tubes, or just power tubes? A microphonic 12ax7 might be the culprit...

Have you been matching the impedance from your output transformer to your amp? Mis-matched ohms can burn out your power transformer over time, and yours might be on its way out.

[miketrondson]

So, I've got no ideas to remedy his problem, but have a question of my own.

My amp (Marshall JCM2000) doesn't buzz, but hisses loudly while on the clean channel. It doesn't hiss so much while on overdrive. What could be the cause?

I've been upgrading all my cables to eliminate it, but it hasn't stopped yet.

[patrickhowell]

So, I've got no ideas to remedy his problem, but have a question of my own.

My amp (Marshall JCM2000) doesn't buzz, but hisses loudly while on the clean channel. It doesn't hiss so much while on overdrive. What could be the cause?

I've been upgrading all my cables to eliminate it, but it hasn't stopped yet.

Have you tried switching out your tubes? It could be a microphonic preamp tube. You should be able to retube your whole amp for less than $100, and even if that's not the issue, it would still be a solid investment. EuroTubes.com sells retube kits for Marshall amps (LINK) (https://ssl.eurotubes.com/cart/index.php?page=view_submenu&category_id=9). They only sell JJ/Tesla tubes, which are definitely the best tubes in production today, plus they measure every tube and specifically match them together for your amp.

[thefollowthroug]

Yeah what Patrick said. Besides if it isn't the tubes then you'll just have an extra set, which is handy. If you are poor, you could try just getting one tube (probably less than $20) and replace one tube at a time, seeing if the hissing goes away (put your amp in standby or turn it completely off during tube swaps).

It's weird though that it does it on clean but not dirty. I don't really know how those JCM2000s are designed, but usually if there is a faulty preamp tube the hiss will be amplified more not less on dirty.