bassman and dummy load

Discussion in 'Amps and Cabs' started by reflexmm, Feb 26, 2012.

  1. reflexmm

    reflexmm Member

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    Quick question:

    I have an 8 ohm cab. In my bassman, there's a speaker intput and an extension speaker input. The 2 inputs are wired in parallel and the bassman preffers 4 ohm of total resistance. Can I stick my cab into the speaker input, and wire a simple 8 ohm resistor into the extension speaker input? This would give me an overall resistance of 4 ohms, but would it do anything to the volume. I'd assume the amp would give 100% of the signal to both inputs, but maybe it would only send 50% to each? It would be great if someone could share some info. Thanks!

    By the way: I know everyone thinks its ok to run a bassman with an 8 ohm cab.
     
  2. '58Bassman

    '58Bassman Member

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    Using a resistor wastes energy and if it's not a non-inductive resistor, it could cause problems by making the amp unstable. If you want to use both the internal speaker and the one in the other cabinet, the parallel load will be 3.2 Ohms (4 Ohms parallel with 8 Ohms nominal resistance) and your amp should be OK with this. If you only want to use the external cabinet, get a second speaker and wire it so the amp is happy. BTW- amplifiers don't have speaker inputs, they have output jacks.
     
  3. 908SSP

    908SSP Supporting Member

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    Yes you should have no problem doing this. Resistive loads are used all the time for testing amps at full power and are more stable not less. But it will drop the volume by 3db which is not very much hardly noticeable and only when the amp is full up. It will also change the tone as it alters the amps interaction with the speaker by altering the fluctuating impedance of a speaker. Since it is only one step 3db it may not even be noticeable.
     
  4. reflexmm

    reflexmm Member

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    output jacks.... I thought speaker inputs didn't sound right. Thanks for the info.

    908... What's the reason for the 3db decrease. I've heard that running an 8 ohm cab from the bassman would also cause a volume decrease. Perhaps it would occuring from a similar mechanism?
     
  5. Tonesmiths

    Tonesmiths Member

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    Ohm resistance effects output. Overall wattage is formulated by squaring the output voltage, then dividing it by the ohms. And your only going to hear half of the output since the other half is going to a resistor rather than a speaker.
     

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