Attenuator weirdness

Discussion in 'Amp Tech Center' started by ce24, Nov 28, 2019.

  1. ce24

    ce24 Poster Extraordinaire

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    So I built a nice l pad attenuator. But it won't produce the clean on my 5e3 that I get without it.... Bright or normal channel on 3 or even less. It gives a nice OD that I like but even rolling off the volume on my guitar it doesn't come as clean as it is without it. What am I missing here?
     
  2. corliss1

    corliss1 Friend of Leo's

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    Tried with another amp?
     
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  3. ce24

    ce24 Poster Extraordinaire

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    Here is what I built without the 4-8 ohm switch.....oh crap I just think I solved the problem.....I didn't put in the 4/8 ohm switch and im going intoa 4 ohm load as im using an ext. Speaker. I believe it is wanting 8 ohms. Nope still there... Will try with a cleaner amp. 1574964031124.jpg
     
    Last edited: Nov 28, 2019
  4. radiocaster

    radiocaster Poster Extraordinaire

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    You might have fried it. Because it says 100 W doesn't mean it will really take that much.

    Also I'm not sure what's going on with that treble switch. It looks like most of the signal is passing through there and bypassing the L-pad.
     
  5. ce24

    ce24 Poster Extraordinaire

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    It's a 15 watt amp.
     
  6. radiocaster

    radiocaster Poster Extraordinaire

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    That's borderline, but maybe o.k.

    I don't think it's working if you have that treble switch like that. Most of the sound is going straight to the output. Very little sound is going through a cap if switched to it, and I don't see why signal would go to the L-pad if it's obviously shorted.
    nonatt.jpg
     
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  7. Alamo

    Alamo Doctor of Teleocity

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    That's not the purpose othe L-pad. it's behind the power amp and before the speaker. you can crank the input more and still get lower over all volume, with nice tube destortion.

    you need it the other way around to get a clean sound. that means hitting the input of the amp not so hard. your volume knob does just that.
     
  8. Bitsleftover

    Bitsleftover Tele-Meister

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    I built one like that and I can’t hear any difference in tone whatsoever when I switch the bright cap in and out.
    I don’t know how it sounds for cleans. I only ever use it to bring on low volume breakup. My 5F2A sounds good through it dirty.
    My Marshall gets a bit dull at lower settings like you say.


    Sent from my iPhone using Tapatalk
     
  9. ce24

    ce24 Poster Extraordinaire

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    Yep amp speaker out to lpad attenuator...out from attenuator to speaker....I know how to hook it up.
     
  10. Asmith

    Asmith Friend of Leo's

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    That diagram definitely wrong, its just putting load in parallel with the speaker and that teble switch wont do anything either the caps will just be shorted.
     
  11. Asmith

    Asmith Friend of Leo's

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    I assume with is the original image

    Screen-Shot-2016-07-14-at-10.27.32.png

    And this is the correct modification to make it work with a spst switch

    20191128_192547.png
     
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  12. Asmith

    Asmith Friend of Leo's

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    Also make sure the switch is definitely an on/off/on. I also think the treble caps are a high in value, not sure what would be normal but I would expect to see something in the region of nF not uF.
     
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  13. LightningPhil

    LightningPhil TDPRI Member

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    Which notes are distorted - lows or mids?

    Assuming the speaker is nominally 8 ohms, it’ll only be so from about double it’s resonance to 1 kHz or so. Around resonance, they scream up to 100 or more ohms and slowly increase in the upper frequencies too - as it’s an inductor.

    Thus, a speaker/amp setup will behave differently with and without an L-pad. From the amps prospective, with it fitted, the load impedance will change from lumpy to flat. And from the speakers prospective the amps output impedance will appear to increase. Which is all made a little more complex as the effect changes a bit as the L-pad is twiddled.

    I like them though, for the purpose of dispensing with clean headroom. Presently have an AC30 feeding a sealed bass cabinet through one and dialled for mild dirt.
     
  14. ce24

    ce24 Poster Extraordinaire

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    Yes you have the correct original...i will check my wiring but it works great with my vibro champ....no distortion at all....the bypass works. Maybe just the nature of the deluxe and its natural hair.....thanks for all the help gentleman.....!!!!?
     
  15. ce24

    ce24 Poster Extraordinaire

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    Well i checked out my wiring and it is all good...i do have an on,off,on Dpdt switch in there....the treble switch works but very subtle.....it actually sounds slight overdriven compression. But like i said it doesn't do it on my vibro champ. Weird! UGGHH im watching NTC127 on the morning show.....trying to hold breakfast down.
     
  16. Asmith

    Asmith Friend of Leo's

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    I would definitely check as the schematic provided isnt wired to work as an attenuator should. And even if 'it works fine' I would strongly recommend you look at doing it properly as your attenuator wont be matching the impedance correctly and could be putting strain on your output transformer and output tubes.

    Lpad attenuators work by putting your speaker in parallel with a resistor and that network in series with another resistor. The resistances change to keep the impedance constant for the output transformer.
     
  17. Asmith

    Asmith Friend of Leo's

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    Can you post a pic of what youve wired im surprised the bypass switch works at all.
     
  18. ce24

    ce24 Poster Extraordinaire

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    View post #11. The original image not the edited one.
    I should note that the 4/8 ohm switch is not implemented. I did not put it in. Of there is a mistake in the original schematic please define. It is wired exactly like the original except for the 4/8 ohm switch.
    Thanks
     
    Last edited: Nov 29, 2019
  19. ce24

    ce24 Poster Extraordinaire

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    This is exactly how it's wired without the 4/8 ohm switch.
     

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  20. johnDH

    johnDH Tele-Meister

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    The original version, and asmilth's spdt version are both fine, ie they should work, and are also quite common ways to use an Lpad, in DIY and some commercial designs. The cap values should be OK, they are larger than on line-level, or guitar=level volume pots to get an impedance from them that competes with the low impedance of the output and Lpad circuit.

    It is a terrible design though (IMHO!) It will inherently muffle the tone as you turn down, hence the need for the work-around cap circuit, which then entirely messes up the impedance seen by the amp!
     
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