Blown channel on sub amp. Fixable??

Discussion in 'Home Theater Projects' started by Jeremy Stockwell, Jul 30, 2003.

  1. Jeremy Stockwell

    Jeremy Stockwell Supporting Actor

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    I've been using an old Pro-Logic amp (Kenwood KR-V7040) to power my Tempest, but the other day I noticed that only one channel is working. I tried swapping wires/inputs and I tried running full-range speakers. I believe that I've blown one channel of the amp.

    My questions are:

    1.) Could there be a simple fix such as a fuse or something? I opened up the unit, but didn't see anything obvious (like a sign, "BAD FUSE HERE!"). Any suggestions will be appreciated.

    AND . . . in the meantime; and perhaps more importantly;

    2.) Am I going to blow the other channel by running it with one already blown? (It seems to work fine this way) I had it connected with one channel going to each VC as recommended. So now I've got the one good channel powering one VC and I guess the other is shorted out for all intents and purposes.

    Or . . . have I finally gotten an excuse to get an actual plate amp for this sub? (As much as I'd like to have the 250W plate amp, I'd really rather find a way to make what I've got work for now.)

    Thanks, in advance, for any help!

    JKS
     
  2. JohnSer

    JohnSer Stunt Coordinator

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    I am not familiar with your receiver, but many new receivers have just one fuse on the power supply. If it blows, all channels will be out. Some older receivers use to have fuses per channel. I haven't seen that in a while. See if you can find a nearby repair shop that will do a free estimate (hard to find these days). Most likely the cost of repair will not be worth it over buying a new plate amp. I think you can get a new 250W one from Parts Express for around $120.

    Another thought is to try to use another channel on the receiver, if the center and/or surrounds put out the same power. Old prologic units sometimes had reduced watts on the surrounds. This depends on how you have it hooked up today and if you have 5.1 digital ready inputs.

    JohnS
     
  3. Jeremy Stockwell

    Jeremy Stockwell Supporting Actor

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    JohnS,

    Thanks for your reply.

    This receiver would be circa. 1993-94 if that makes any difference.

    Specs on this unit indicate 100 watts x 2 in stereo; in any surround mode is 65 watts L/C/R and 15 watts to each surround.

    I considered using a center channel, but in Pro-Logic, isn't it some kind of matrixed signal? I know that the sub-pre out is mono, but I'm splitting it into the CD L/R input. Wouldn't it still try to process the signal? If I could get a non-processed signal out of the center channel, would a 65W signal being sent to each VC on the Tempest be preferable to a 100-110W signal being sent to one VC?

    Any hints on how to tell if there's more than one fuse or if one is bad? I can't tell the difference between all of the wires and circuit boards in there.

    Thanks again for any additional help!

    JKS
     
  4. JohnSer

    JohnSer Stunt Coordinator

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    From your specs, I would assume that any two of the L/C/R would be able to do 100W. It drops to 65W with all channels driven. Probably because the PS can't keep up, but only guessing. Also, don't be surprised that the actual rating is less the manufacturer rating.

    All this is moot, if you don't have a 5.1 direct input. If your receiver said "digital ready", I would have expected the inputs. If they were there, you could tie into whatever two channels you wanted.

    I highly doubt you have per channel fuses on this unit. I have an old stereo receiver that had external fuses on the back, for the channels.

    Have you tried a different analog input? There is a remote chance it is just a bad CD input. Otherwise, I think it is time to decide repair shop qoute or just get that plate amp you always wanted [​IMG]

    JohnS
     
  5. Jeremy Stockwell

    Jeremy Stockwell Supporting Actor

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    Yeah, I've tried a couple different inputs with same results. [​IMG]

    I'm still wondering if I'm going to damage either the Tempest driver or the one remaining channel on my receiver/sub amp by running it with one channel. Any thoughts there?

    JKS
     
  6. JohnSer

    JohnSer Stunt Coordinator

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    If the root cause of the channel going out is because the the Tempest load is too low impedance for the receiver, you will eventually blow the other channel. Probably sooner because you will turn the volume up to compensate. I think the Tempest is a dual 8 ohm, so it shouldn't be an issue. It could be just the fact of trying to drive low frequencies from a marginal amp.

    Sub drivers are generally pretty tough. But if an output device blows such that the PS rail voltage is applied to the speaker, it can be more than it can take.

    If you are going to try running the driver on one voice coil on one channel, you might try to put both voice coils in series (16 ohm).

    JohnS
     
  7. Jeremy Stockwell

    Jeremy Stockwell Supporting Actor

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    JohnSer,

    Thanks again for taking an interest. I appreciate your advice.

    Unless something changes, I'll probably just keep things the way they are for now.

    But, I'll gladly accept any other thoughts that you or others may have.

    JKS
     
  8. Michael R Price

    Michael R Price Screenwriter

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    Why not try replacing the output transistors? It'll cost you $10 and 30 minutes with a soldering iron, and if it doesn't work, oh well. Just look at the markings on the big transistors, and buy the appropriate quantity.
     

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