webmiztris

I just bought a Marshall 1960A JCM 900 412 cab and a MG100HDFX head.

Overdrive 1 is 'OK' sounding. Overdrive 2 sounds SWEET and is exactly what I was looking for tone and sound-wise.

The problem is this....if I turn my head's master volume up any higher than 1 or 1 1/2 while I"m in OD2, I get feedback and squealing like crazy. It doesn't just sound 'hot'. It sounds bad. I am using a guitar with Seymour Duncan hot rodded humbuckers in it. What is going on? What can I do to my amp to make it so I can turn it up higher than two without squealing like crazy??? Is this even normal?

And another question....when I bought the cab, the salesman at Pianos and Stuff said I should always plug into the 4 ohm input on the back of the cab....then a friend of mine who is a guitarist who's been playing FOREVER tells me I should be plugging into the 16 ohm output. ??? Who is right?

I love this rig but I need some serious help!!!

ZoomZilla

Your cab has a 4 ohm input? Can you show a picture of the back of the cab? That would help. If your cab is doing what I think it is, you probably have an input for series/parallel, which would be 16 ohms, and a parallel, which would be 4. I don't know what the output of your head is.

I will research this and get back to you.

On the other subject, what you are getting is gain feedback. It's normal and undesireable. What I recommend you do is to add a noise gate to your signal path. You can get a good one, like an ISP decimator or a cheaper one like a BOSS NS2. That will allow you to kill the feedback.

webmiztris

I'm at work, so I can't take a picture right now, but yes, there are two inputs on the cab: one labeled 4 ohm, one labeled 16 ohm. and then there is a mono to stereo switch also...that's all that's back there.

ZoomZilla

Ok, now I get it. Here is what I would do. The cab that is supposed to go with the MG is 8 ohms. So what I would do is to use both outputs on the back of your MG and switch your Cab to stereo and use the stereo inputs. Then you would be using the correct ohms for both. The feedback issue will be solved with a noise gate like mentioned before. If I stand in front of my Mesa with the gain cranked and have the master at a low level it will howl like a beast. Step on the noise gate, zero sound other than white noise from the amp.

webmiztris

thank you for your help. I will buy a new cable that will allow me to hook the head into both OHM inputs and also purchase a Boss NS2 or similar and see if that does the trick.....

ZoomZilla

Happy to help. You don't HAVE to use the stereo input if you do not want to. You can safely run the head with the one cable, but I would stay with the 16 ohms. I don't think solid state heads suffer from the same issues as tube heads, so an 8 ohm output to a 16 ohm input is fine. I recommend the ISP decimator over the Boss. The ISP does not color your tone at all. I have not heard the same thing about the Boss. But then again, since you are running SS, either will probably be fine. Good luck and let us know how it turns out.

Adwex

Your amp prefers a 4 ohm load, so keep the cab switch on mono, and plug into the jack labeled 4 ohms (the one on the left when facing the back of the cab). The amp can handle loads higher than 4 ohms without damage because it's a solid state amp not tube, but 4 ohms is the only way to get the full 100 watt potential from the amp. The guy in the music store was right, and your guitarist friend probably plays tube amps, and most tube amps are either 8 or 16 ohms. Your amp is solid state, not tubes...different animal, with a different sound, and different needs. Use the 4 ohm cab input.

Here's a link to the manual for your amp:
http://www.marshallamps.com/download...0hbk%20Eng.pdf
Read page 4.

I'm not sure what's causing the squeal at higher volumes, can you try a different guitar?
Maybe your pickups are not wax potted and are causing the squealing.
Try turning the gain down a little, does that help?
Try standing further away.
Try facing away from the amp.
Does it squeal while you're playing, or just when you stop?

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ZoomZilla

Nice catch Adwex. I never thought to look at the manual. Duh! I know the MG412 cabs are 8 ohms, so I assumed the output was 8. Oh well. Yeah, listen to Adwex, use the 4 ohm input on your cab. Then you can use one cable and spend the money you would have spent on a cable towards a noise gate. I am guessing that she stands too close to the setup or she has the gain cranked. I know if I have my Mesa on Modern mode and have the gain up high, it screams like a mother without the noise gate.

webmiztris

my friend does use a tube head, so maybe that's why he suggested I use the 16 OHM input...I will go back to using the 4 OHM instead. I will mess with using less gain and also try out my other guitar (which just has factory pickups in it) to see if it causes the same noise issues....

I will keep you posted and thanks again for the help!

Adwex

I wonder if the squeal you're hearing is just normal solid state high gain squeal. It's entirely possible that there's nothing wrong with the amp or the guitar. I've heard solid state amps squeal before when they're set for high gain. Definitely try a different guitar, it might be the pickups too. Which Duncan pickup do you have in there? What kind of guitar is it?

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stryker59

it good be normal high gain squeal. how close are you standing to the amp? thecloser you are the more they will squeal!
as far a noise suppressor goes check into the mxr smartgate as well.
and adwex is on the money as usual!!

webmiztris

I think I got it sounding pretty good now....apparently I did just have the gain cranked too high for it to handle....if it starts acting up at my gig on Friday, I'll be back to pout about it on this forum, but it seems to have fixed my problem so far.... thanks for your help, everyone!

stryker59

lolol cmon back and pout if you need to!!!

Adwex

Cool. Post some pics of your gig if you can.

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ZoomZilla

As payment for our help, we are going to need gig pics and soundclips!

ZoomZilla

Uh, hello. You had a gig on Friday, where are the pics and soundclips?

stryker59

yeah! cmon w/ the pics!!

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Adwex

We charge interest around here, y'know. For every day without pics, the picture requirement goes up by 1.

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AndyHighTides

You guys are starting to sound like pervs.

stryker59

nooooooooooo! not us!

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ZoomZilla

Starting?

stretchfurgo

if only one cabinet use mono switch..Very important otherwise you will cause speaker damage.. The ohms setting is mostly for when you are running more than one cabinet and the rule of thumb is to split the ohms setting in half so if you have a 16 ohm cab run it at 8 ohms and so on and so forth..... the distortion thing try different settings with your knobs.. turn the gain down and the master way up.. and vise versa experiment... it likes to be played with...lol

jcm 2000

the squealing i have the same problem with my first act when i use it it is single coil and when i have it just on the treble pickup it squeals like hell and i have to turn down or blend the middle and treble and my pickup is pretty high output like yours so it is probably the guitar or if you raised the pickup close to the strings for higher output just skrew it down