Will this hurt my amp?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Ferg Deluxe, Oct 26, 2004.


  1. Ferg Deluxe

    Ferg Deluxe Gold Supporting Member

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    I have discovered that I can run my MXR 10 band eq in the loop of my amp to control volume (as well as shape the overall sound). The pedal works very well as an attentuator....that is, allowing me to get the power tubes cooking at a more reasonable volume.

    If I use it in this fashion will I hurt the amp? Of course, I realize I'm pushing the power tubes harder, but is anything else at risk?

    Thanks!

    Fergie
     
  2. Swarty

    Swarty Member

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    It may allow you to turn up the preamp, much like any master volume control, but I don't see how it would any effect on the power tube signal?
     
  3. John Phillips

    John Phillips Member

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    You could certainly use it to drive the power tubes harder - by turning it up. But that way you'll get more volume too. The only way to get more power tube drive and less volume at the same time is to use a proper attenuator between the amp and speakers.

    If you use the graphic to turn the level down, you're hearing pure preamp distortion as Swarty says.

    It might sound great though. FWIW, the classic Mesa Graphic EQ is at this point in the circuit too.

    Pure power tube distortion isn't necessarily what you want anyway... despite nearly everyone believing that it is :).

    If you're turning the level down, no harm can happen. If you were cranking it up a LOT, it's an outside possibility - you could stress some part of the power stage that wasn't expected to be driven that hard.
     
  4. Ferg Deluxe

    Ferg Deluxe Gold Supporting Member

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    Thanks for the responses, guys!

    I am using the eq to pull the volume down. In order to compensate, you have to crank the master volume significantly higher, which I assume gets the power tubes cooking more.

    The tone certainly changes significantly depending on where the master volume is set, and I was assuming this is because of the power tubes having to work harder to amplify the weaker preamp signal (since the preamp signal was attenuated with the eq levels).

    For instance, if I run the amp with nothing in the loop and use the master volume strictly to adjust volume, the amp (predictably) doesn't sound so great at lower-than-gig volume. However, if I put the eq in the loop, pull the overall volume of the eq down (keeping the frequency sliders flat) I can get a much better tone at the same volume.

    The amp with the master volume on 7 sounds pretty good, but it very very loud. I can insert the eq, pull the volume down, and not kill the neighbors. It's still loud but not frightfully so. :D

    I guess what I'm saying is, there is a definite tone difference as I sweep the master volume from say 4 to 8 -- the amp thickens up and gets beefier. I can retain that beef but lower the volume with the pedal in the loop (which is a series loop, and I'm assuming it's in between the preamp and power amp sections).

    Are my assumptions here wrong? I admit that they certainly could be since I'm no expert.


    Fergie
     
  5. John Phillips

    John Phillips Member

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    The master volume comes before the power tubes. Whether it comes before or after the FX loop depends on the amp design.

    The power tubes are only 'working as hard' as the actual physical acoustic output volume of the amp requires. Low volume = power tubes not working hard. It doesn't matter how you get to the low volume (unless you're using a post-amp attenuator in the speaker circuit).

    Yes, the internal circuitry responds in different ways to different gain at different parts of the circuit, and some parts of it are pretty non-linear, especially when any distortion is occurring. So increasing the level at one place and reducing it equally somewhere else can drastically alter the actual tone.

    But don't think for a minute that just because it 'sounds better', that you're getting 'the power tubes cooking more'. You're not, unless the real output volume goes up significantly. If it actually goes down, they're running them less hard.

    What you're hearing is the effect of different-placed level controls on purely preamp distortion.

    And what's more, the transistors in your pedal may be improving the tone of your tube amp :). Really. Shocking, given the usual myths that solid-state always sounds bad - and that the only good distortion is not only tube, but power tube. Ain't necessarily so...
     
  6. Stringrazor

    Stringrazor Member

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    Wha!? Fasten that man to the dish rack and poke him with the soft cushions! "no one ever expects the Spanish Inquisition!" :D
     

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