Newbie questions and Marshall JCM 800 1960A compatibility?

[dhoward455]

Hello everyone, I'm brand new to this forum. I have a few questions about general guitar amplification and compatibility. I'm sure that many of you hate it when a new guy joins the forums asking questions that have already been asked. In my defense, I did do a little searching throughout the forums and on google, but simply wanted some guidance and direction from an actual person that knows what he or she is talking about.
First things first, I've done some researching and attempted self educating myself on how amplifiers work in general, ohms and amperage and whatnot, and every guide or walkthrough that I come across just seems to confuse me...I'm wondering if anyone here knows of any good guides or online links for this sort of thing to break it down into easy to understand language for simple minded people like me. Heck I might even need a coloring book to help me out with this, it really does confuse me quite a bit

Now this is where I really need the help, and what prompted it in the first place. I've always wanted to get into guitar. I have an Epiphone Les Paul 100 that I can play a little bit, few chords here and there, some scales and blues riffs, I know how to tune it and all that stuff. When I got the guitar, however, I also acquired a fairly rare(from what I've heard) Marshall JCM 800 model 1960 "A" lead 4x12 half stack from a buddy of mine for a pretty fair price(couple hundred fair). He had all 12 speakers reconed and basically refurbished from what I understand. It's 300 watts RMS at 16ohms...quite a bit of overkill for my garage. Now this is what prompted me trying to educate myself...he also included with the half stack a Crate GX1200H amplifier that says 120watt @ 4ohms minimum impedence. I know nothing of ohms, amperage, wattage, all that, but i have some basic math skills and can see that 4 ohms is not equal to 16 ohms. Neither is 120watts equal to 300 watts, let alone 300watts RMS(which from my EXTREMELY limited understanding of car audio subwoofers, RMS means half power, peak meaning full power). My question is a simple one, with an extremely complicated answer, I presume. Are these two units compatible with each other? My guitar makes a horrendously deafening howling noise,(feedback?), when I turn the amp volume above 2, max being 10. I'm quite confident that about volume level 6 would shatter my windows, and 10 would probably get the authorities called, as I'm sure it would go out with a deafening boom. With that being said, I do have a bit of common sense, and have only turned it up to 3. The howling stops as long as my fingers are muting the strings, but there is still a lot of "fuzzy" noise that emits from the speakers.

I would appreciate ANY input on the matter.
Thanks

[Steve Conner]

The GX1200H is a solid-state amp. It doesn't care too much about impedance, it will happily drive any speaker stack greater than or equal to 4 ohms. The higher the impedance of the speaker, the less power you get: you're probably getting about 40W. Seems to be plenty of power for your needs though.

A certain amount of feedback and fuzzing is to be expected from a high-gain amp. The match between speaker cab and amp is certainly not the cause of it. If you don't like it, reduce the gain (should be a knob for that somewhere) or try the amp's clean channel.

[52 Bill]

Your post has confused me, but with me that's real easy to do.

You have a Marshall half stack with a JCM800 head and a 1960A cabinet. Additionally you have a Crate GX1200H head. And you play an Epiphone guitar.

The four 12" speakers have been reconed and are rated at 300 watts and 16 ohms.
You want to know if the Crate head is compatible with the speaker cab?

As Steve points out, a solid state head will work with almost any impedance load, but the power that the amp puts out will change depending upon this load. Your speaker is rated at 16 ohms impedance and can take 300 watts RMS of input power. As long as the amp that you are driving the cabinet with can deliver no more that 300 watts of audio power, you should be safe.

When the amp feeds back, are you standing in front of the speaker cab? You may be causing the guitar pickups to feedback into the amp. Try standing to the side or behind the cabinet when you do this and see if the amp can be turned up without feeding back.

[dhoward455]

Thank you for the reply, Steve. What you say makes sense. I will try turning the gain down and see how it sounds. It sounds just fine on the clean setting, so it would make sense that this could be part of if not the whole problem.

Sorry for the confusion 52 Bill. The marshall half stack is the upper of the the two cabinets(from what I understand, this series came with the bottom stack of larger speakers and the top half with 12 speakers, I believe. The top cabinet has a rearward slant on the front grill, from about where it says "Marshall" to the top of the cabinet. This top cabinet is the one that i have)
I believe that this cabinet has 12 speakers in it, at least I think that's what my buddy said when I got it from him.
And no I do not have the JCM800 head(I wish I did, they're worth a fortune), Im pretty sure that "JCM800" is what the plate on the bottom left of the grill said, along with "model 1960A".
So, my setup is the top half of the stack along with a crate gx1200H amp.
Hope that clears up the confusion

And I have experimented with what you said, standing facing different directions. Also tried standing as far away as my cable would allow(15' I believe) and none of it makes any bit of difference in the feedback.

[dhoward455]

ok i took a look at the gain knob on the amp and it wasnt even half way up, it was set at 4. turning it down to 1 gets rid of most of the feedback and howling, but then it doesn't sound anything like that awesome "overdrive" sound i'm used to

[dhoward455]

any further thoughts from anyone? any input is appreciated

[52 Bill]

If you haven't done it already, go to the Crate site and download the owner's manual for this amp. It will help you to understand the controls and features that you have available to you.

The amp has a clean channel and a distortion channel that has two different gain options.

Use the Channel Select button to set the amp to the clean channel. The Level control is the volume and then there are three tone controls. Set the Level control full counterclockwise and the tone controls to the midpoint. Slowly turn up the Level control to a reasonable volume level. Can you get a nice clean sound without howling? Do each of the tone controls work? Turn up the Reverb Level control, does the reverb work?

If the clean channel works fine, then test the distortion channel the same way. Start with the Level control for the distortion channel all the way down. Set the Gains and the tone controls to the midpoint and switch to the distortion channel. Now turn up the Level control until you get a reasonable volume level. Can you get a distortion sound without howling?

There are two Gain controls that can be switched in or out. Switch between then and listen to the difference. The second one has the Contour control, which is a separate tone control just for that Gain setting. See if it works as well.

If you still can't get the amp to work without the howling, try it with a different guitar. Does it still do this?