2 ?? on a DIY Attenuator

Discussion in 'Amp Central Station' started by CLewisW, May 21, 2019.

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  1. CLewisW

    CLewisW TDPRI Member

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    I'm rocking a Bugera V55 Infinium head. The specs state that it puts out 55 watts. I want to put together a DIY attenuator and I'm wondering if a 100 watt L Pad will be enough to handle any peak spikes. I can't find any L Pads with higher wattage handling that are priced reasonably. Also, here's a hypothetical: If I set the amp at 8 ohms and send it into an L Pad with say 10-15 ohms will there be trouble or will the amp use only the 8 ohms it needs? I'm slightly new to amp tech stuff so I appreciate any help. I haven't been shocked yet and I don't plan on today being that day.
     
  2. W.L.Weller

    W.L.Weller Tele-Meister

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    The impedance- matching you allude to is one of the challenges with attenuation. I think you may need a T-pad to prevent issues with reflected impedances between the speaker and output transformer.

    Do you plan to have the amp wide open (everything on 10) and use the pad to clamp it down to a whisper? That's the scenario where power handling and heat dissipation matter most.
     
  3. Finck

    Finck Tele-Afflicted

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    The best choice would be a 8ohms LPad. But if you get a 10ohms LPad, depending on the position of the cursor, the impedance seem by the amplifier will be out of an acceptable value.

    Let's say the L-Pad is in its middle position (5 + 5 ohms). You'll have 5 ohms in parallel with the 8 ohms speaker, plus a 5 ohms in series with that combination, so, 8.08 ohms. Now, with the LPad at 10% position (9 ohms + 1 ohm), you will have 1 ohm in parallel with the 8 ohms speaker, plus 9 ohms in series, what give you 9,9 ohms. Finally, with the LPad at 90% position (1 ohm + 9 ohms) final value will be 5.2 ohms. That said, I guess the safe range of attenuation will be between 35% and 65%.


    Also, remember that when you attenuate the power too much, the tone of the amp changes a lot. If the tone is good or no, only you will be able to decide.

    Regarding to the dissipation, 100W LPad is acceptable for a 55W amp.

    Personally, I prefer fixed Bridget T attenuators, specially when agressive attenuations are the target.
     
  4. CLewisW

    CLewisW TDPRI Member

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    I was planning on having the master volume around 5-7. Just enough to get the power tubes working without frying them too quickly. I don't wanna fry the transformer either. I don't need it to be a whisper. Loudish but comfy. My main concern is the 55 watts peaking at double that. I wasn't sure how 110 watts going into a 100 watt L Pad would turn out. Also I only mentioned the 10 ohm L Pad because I saw one on ebay. I wondered if it was close enough. For this project I plan on getting an L Pad at the appropriate 8 ohms
     
  5. W.L.Weller

    W.L.Weller Tele-Meister

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    Last edited: May 24, 2019
  6. Alamo

    Alamo Doctor of Teleocity Silver Supporter

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    Your Bugera sports an 8 Ohm speaker, right? so you need a 8 Ohm L-pad and it will shave off excessive spikes just nice.

    regardless of the position of the control knob, the total resistance of the L-Pad device remains constant.
    at least this one:

    DSCN2188.JPG
     
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