Negative Feedback Question

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Axekisser, Jan 21, 2008.


  1. Axekisser

    Axekisser Member

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    Hey folks,

    What is the effect/result if I put a capacitor in-line with the negative feedback pot/resistor in my Champ? I'm thinking that it will limit the bass being fed back and change the resulting "feel" if I use a .047 in-line with a 10K pot. I'd change the original resistor on the tag board to a 1K in addition to adding the pot.

    Any thoughts?

    Thanks!
     
  2. donnyjaguar

    donnyjaguar Member

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    I was just going to write try it and see. :) If the capacitor is in parallel with the resistor it will feedback more highfrequency component and reduce the output at the higher frequencies. Will it improve the bass? Technically no. It will reduce the highs. Generally reactive components added to the feedback loop in this manner can cause problems if other design criteria aren't considered.
     
  3. Axekisser

    Axekisser Member

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    I tried this and it seems to make the bass deeper and the highs glassy. The amp is a Champ and I put a .047 inline with a 10 k pot. Its a subtle effect but makes the amp sound a little bigger to me.

    I'll try it at gig volumes and see how it works.
     
  4. donnyjaguar

    donnyjaguar Member

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    Excellent. I should mention that by adding this component you've increased the likelihood of the amplifier breaking into ultrasonic oscillation. But don't let that stop you. :)
     
  5. Axekisser

    Axekisser Member

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    This is true! Especially since I removed the snubber cap! I checked the lead dress and it's decent.

    I noticed that some old gibson amps had this in the circuit (they called it tone expander) so I thought I'd give it a whirl. How do I tell if it's oscillating? Will the amp red plate or just lose power?

    Thanks!
     

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