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EMC amp help. Old electronics FTW...

Discussion in 'Amps and Cabs [BG]' started by Mutant Corn, Mar 3, 2008.

  1. So, I have this massive looking amp, an EMC B800. Based on the model name I'm assuming it's 800 watts total, or more likely 2x400w, as you can see from its layout. (2 power amps) It's designed to run 2 or 4 speakers at 4 ohms. Some people told me it wasn't likely that much wattage..but with a transformer as big as this, I'm pretty sure by now that if it's not 800(total) watts, I'm sure it's close. (my finger is touching that, btw) Am I wrong here?

    Anyway...I'm a little lost on a few things. First, the speaker output jacks. There's two identical PA circuits in this thing, you can see them both in that pic above. (front /back ) The plate that they are attached to is in direct contact with the metal casing. This is the only way I can see that these could be connected to the jacks. There's just one wire running from each of these to the speaker outputs, 2 outputs per circuit. (paint drawing ) Only one contact on each jack is connected... :confused: Is this a correct assumption? From what I can tell nothing has been removed and care was taken to insure that the circuits were in contact with the frame, as well as the jacks.

    Second, there appears to be a disconnected component on one of the PA circuits. It's hooked up, in the sense that the contacts are all still attached, but the one on the other circuit is bolted to the plate that is connected to the frame. Is this a ground, or was this to disable that circuit? I'm wondering because I know that such a thing could potentially cause problems...and the thing had a blown fuse when I got it.

    Third, what is this? There's one on each of the PA circuits. It's like a pot with the cover taken off... :confused: I'm sure it's to fine-tune something, but I'm a newb at this...hence me being here >_<

    Fourth, how would I go about hooking this up to a single cab with a single input?

    Fifth(and last, thank heavens), why on earth do I need bass/mid/treb and a 5 band eq? (labeled "spectrum control: 40, 80, 160, 320, and 640hz) It doesn't cover the full freq. range..so is it just for fine tuning? (also...single channel amp- master volume on right, another volume by the eq.. :confused: )


    edit: sorry for the length and crappy pictures...all I have is a low-end cameraphone
  2. I hate bumping...but I need help. :(
  3. Taylor Livingston

    Taylor Livingston Supporting Member Commercial User

    Dec 25, 2002
    Oregon, US
    Owner, Iron Ether Electronics
    I can't answer most of your questions, but since nobody else has given this a go...

    It's a trimpot, meant to be adjusted in the factory most likely. You should probably leave it alone until you get the amp working, unless you've already fiddled with it, in which case it doesn't matter.

    I'm probably not qualified to answer this, since I know nothing about this amp, but I'm guessing that that warning is just to tell you that you won't get the full rated wattage with one 4ohm speaker. It looks like the amp is designed to be run at 2ohms. So plug one speaker in, it's fine, you just won't get the full rated power.

    This is pretty common in amps. I always thought it was pretty pointless if you can't switch one EQ section off, but who knows. I'm pretty sure SVTs have this setup, and Carvin amps. The first volume is probably input gain, and the second one is output volume.
  4. thank you!

    I've moved it, just to see if it would, but I put it back where it was. Could this be similar to the bias pots in tube amps? I remember those being called trimpots as well...

    :confused: I vaguely understand this...I think I'm overthinking it. You're saying that 2 4ohm cabs per PA = 2ohm, right?

    So it's like most lead channels on guitar amps...makes sense. I guess both of them being labeled "volume" threw me off.
    I can use this to get a dirty tone, then?
  5. Taylor Livingston

    Taylor Livingston Supporting Member Commercial User

    Dec 25, 2002
    Oregon, US
    Owner, Iron Ether Electronics
    A trimpot is just a pot with a slot instead of a shaft. They are used inside of a device to adjust something that doesn't need to be tweaked often. I don't know what it would control in your amp, but nothing needs to be biased AFAIK except tubes.

    2 4ohm cabs in parallel = 2ohm, yes. You can plug one 4 ohm cab into one of the outputs and it will work.

    Actually, it's like pretty much every modern amp in existence. Modern amps always have input gain (controls the gain into the preamp stage) and output volume (the gain of the power amp stage), and many old ones do as well. This doesn't necessarily mean that you can get overdrive, as this is a solid state amp. Typically SS amps (at least old ones) have been designed not to distort because solid state distortion generally sounds bad. I'm sure you can clip it, but there's a good chance you won't like the sound.
  6. To try and answer your questions in a very much simplified way: the trim pots will be for setting the bias of each of the power amplifiers. The bias is also controlled by the transistor you call the disconnected component. It should be bolted to the heat-sink just as the other one is. Its job is to adjust the bias down as the heat-sinks get hotter to prevent thermal runaway.

    Is this thing actually working?? I would think that the two volume controls are for each input jack with a common bass, treble, a master level and EQ.

    The transformer is not that big for the age of the amp. I would guess at about 100W per amplifier. Your main fuse is 5A so the maximum draw from the mains should be in the range of 500 - 600 W. Assuming a 50% efficiency for the power supply that leaves about half that to be turned into audio power. Thus my 100W per amp.

    Hope this sheds some light on your amplifier. Now let's see if this post opens a can of worms! :)

  7. anderbass


    Dec 20, 2005
    Phoenix. Az.

    ... ;)
  8. Aww man...just when I thought I was on to something. I'm utterly confused now.

    I did some searching on TB, and Rickbass had an EMC B450, which was 450 watts according to him...and all of the other's I've seen do far match the wattage to the name, but on the other hand I've never seen another B800, and what you say does indeed make sense. :(

    Either way I'm pretty boned as far as finding a cab. I have to have a better amp than my 40W combo by June, so I'm thinking of just getting a couple of big 410's or 412's and rewiring them for 2 ohm...that way I won't blow it up if it really is a 2X400, and if it's not I still have some massive speaker area and room for a better cab later.

    edit: another person has told me that for an amp of this type, especially with the trans and those caps, 800 is about right...*more confusion shall ensue*


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