Modify an Ampeg SVT400T

Discussion in 'Amps and Cabs [BG]' started by Gabu, Nov 26, 2002.

  1. Gabu


    Jan 2, 2001
    Woodland Hills, CA
    I was thinking about going to my local tech to ask him about attempting a mod on my SVT400T to allow it to bridge a 4 ohm load. The manual states to bridge only an 8 ohm load.

    Is this crazy? I figure the main issue would be keeping it cool, wouldn't it?

    All suggestions would be very welcome!!
  2. I doubt it'd be possible. The issue is the amount of current the output transistors can deliver. Hey, they can only do so much....
  3. Gabu


    Jan 2, 2001
    Woodland Hills, CA
    So it's not possible for the output transister to be replaced?

    This amp has one limitation that I don't like. It get's it's full power on either power amp at 4 ohms, but bridged it get's it's full power at 8 ohms. So if you want to utilize it fully you are usually stuck with one 8 ohm cab or two 4 ohm cabs.
  4. Generally speaking, there wouldn't be any simple way of unplugging one transistor and plugging a "more power" version in. The lower impedance requires more currrent (in inverse proportion to the impedance for a given voltage), so going from 8 ohms to 4 ohms requires a doubling of current. Many amps increase the numbers of output transistors to get the extra current required....And by the way, your amp's power supply will need to double the amount of current it can deliver. Chances are the power transformer doesn't have anywhere near that much extra oomph. Sorry...I've got the same situation, I've got a single rack-space Fender pwer amp that only runs bridged into 8 ohms. It would be nice to run that into 4 ohms but oh well.
  5. Gabu


    Jan 2, 2001
    Woodland Hills, CA
    Bump! Anyone else know about this? Not to diss nashvillebill, I am just hoping for good news. ;)
  6. Chasarms

    Chasarms Casual Observer

    May 24, 2001
    Bettendorf, IA USA
    you would definately have to upgrade the power supply, and I am not even sure it would be possible to change out the output transistors.

    You'd spend more than another slave amp will cost on something that may not even work.
  7. Gabu


    Jan 2, 2001
    Woodland Hills, CA
    Hmm... So perhaps a used DCM1000 may be in order. Thanks for the tips guys.
  8. Rock City

    Rock City

    Apr 8, 2001
    I don't know why companies design amps like this. That was the reason I didn't buy an Eden years ago!
  9. Gabu


    Jan 2, 2001
    Woodland Hills, CA
    I realized something though in comparing it to the Carvin. The two work the exact same, but Carvin draws it's full power per channel at 2 ohms, rather than 4. Then when you bridge it, just like the Ampeg, you have to have double the minimum ohmage rating per channel. (4 for Carvin and 8 for Ampeg). So it's not that either is better, just different. In fact, one could Argue that the Ampeg was a better design because you can draw full power from 4 ohms, instead of 2.

    But in any case, in order for me to Maximize the wattage I can use with this Ampeg, I should really be getting two 4 ohm cabs.

    But they are offered in 8 ohms... ce la vie!!
  10. ESP-LTD


    Sep 9, 2001
    I had an SVT-400T for several years; nice rig. I agree with the others that the amp can't reasonably be made to put out 2x the power. It does have a decent line out and I'd say your Carvin power amp is the way to go.

    I'm don't know enough about the subject to speak with any authority, but it might well be that the Ampeg can push a 2 ohm load, but since that makes for more wear and tear, they don't rate it that way (I wouldn't try it myself).

    Watch the cooling fan; I had to replace mine every 18 months of hard use; the only way to know it's working is to feel for air coming out the left side of the cooling tunnel. Mouser Electronics had them for $25 or so and it was a quick job to replace.