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Loudness control on a guitar amp?

Discussion in 'Shock Brother's DIY Amps' started by jam66tn, Jun 10, 2018.

  1. jam66tn

    jam66tn TDPRI Member

    I was wondering if a loudness control would work well on a guitar amp? I love building small amps out of scavenged parts, and I'm always looking for odd tone controls and such to incorporate into the design.

    This idea got stuck in my head so I did some research and can't find any real info regarding guitar amps. I found this schematic but it looks like it would dump a lot of signal. Has anybody tried this?

    [​IMG]
     

  2. Papa Joe

    Papa Joe Friend of Leo's Silver Supporter

    Age:
    88
    Jun 30, 2007
    Swanton Ohio
    Welcome aboard
     
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  3. David Barnett

    David Barnett Poster Extraordinaire

    In hifi amps often a simpler circuit was used, but it required a volume control with a "loudness" tap. But there would be no signal loss.
     

  4. jam66tn

    jam66tn TDPRI Member

    I think the version in the schematic was designed to work as a compensated volume control.
     

  5. Mr. Lumbergh

    Mr. Lumbergh Poster Extraordinaire

    Jun 13, 2013
    Initech, Inc.
    Isn't a loudness control just a fixed bump in the bass and low mids? I'd think just a 3-band EQ on the amp would be enough, or an EQ pedal.
     

  6. FenderLover

    FenderLover Friend of Leo's

    Jun 11, 2009
    Minnesota
    Funny you should ask...

    First a little detour:
    One design that I'm working on is my take on a Dumble SSS amplifier, which is more my take on the the Two Rock version, the John Mayer Signature. Two Rock uses a "contour" control to replace the Hi and Low step filters on the SSS.

    The Contour control that Two Rock used was described as a tilt EQ in their John Mayer Signature Amplifier User Manual. A tilt EQ is also commonly known as the tone control found on the Electro Harmonix Big Muff. Bass decreases while treble increases, and visa versa; center position is flat. It was described in the User Manual that it was intended as a fine EQ adjust when output volume was adjusted. Very thoughtful, but I wondered why would I necessarily want more bass if I decide to cut treble?

    back on track:
    Remember the stereo receivers from yester-year that had Loudness buttons? They were used to increase bass and treble response when volume was low to make up for the Fletcher-Munson effect. Turn up the volume, and we'd turn the Loudness off so that it didn't get too boomy. I bought a Yamaha integrated amplifier in 1980 because the Loudness control wasn't a switch, but a continuously variable control on a pot. The circuit worked well on my stereo system, and suspect that it may also works well when tweaked a little for guitar amplifier use.

    This is where I left off, but have not tried it yet. Go ahead and be the first. This is for low impedance, used after a cathode follower, feeding the LTPI. (your version above is also intended for low impedance, BTW). The Volume control can be omitted, or operate as a Master.
    upload_2018-6-12_11-50-14.png
     
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  7. jam66tn

    jam66tn TDPRI Member

    Very interesting. I was intending to use it after a cathode driven Baxandall tone stack, based on the RCA Bass & Treble Tone-Control Amplifier circuit. The RTM mentions that a loudness control may be used in place of the volume control following the recovery stage. I'm not sure that it would be necessary with that much bass boost/cut available, but it's pretty easy to implement and remove if I don't like the result.
     

  8. jonrpick

    jonrpick Friend of Leo's

    Mar 17, 2014
    Marietta, GA
    I have a question about the tilt control... because it boosts treble while cutting bass, does the overall gain/volume *seem* to be uniform (or closer to it) throughout the entire range of the control?
     

  9. jam66tn

    jam66tn TDPRI Member

    Another note, I'm going to be using it with a single-ended 6L6 amp so no LTPI. This is a modified schematic I've been working on based on a Stromberg Carlson PA amp. I've built one version of this amp already and it sounded great using the passive Baxandall circuit from robrob's site.

    [​IMG]
     

  10. FenderLover

    FenderLover Friend of Leo's

    Jun 11, 2009
    Minnesota
    The circuit is passive, so all passive EQ's have a loss, and none of them are capable of boost, they just loose more or less signal. In the center (flat) position there is a little loss, CW passes treble (looses less treble) while cutting bass. In that respect in may seem fairly constant in amplitude as the control is rotated, but if the circuit were bypassed the total loss would be much more evident.
     
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  11. jonrpick

    jonrpick Friend of Leo's

    Mar 17, 2014
    Marietta, GA
    I know... I'm not talking about actual loss. Asking about perceived loss throughout the sweep of the knob.
     

  12. FenderLover

    FenderLover Friend of Leo's

    Jun 11, 2009
    Minnesota
    I see...Actual loss aside, frequencies on a Tilt are being added as others are cut, so extreme changes might make you readjust the volume across the full sweep. However, one probably doesn't make full sweep changes, but little tweaks from a base point. In that case, I'd say the overall volume is fairly constant because I don't usually feel the need to adjust volume after EQ changes.
     
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  13. middy

    middy Friend of Leo's

    Age:
    47
    Apr 28, 2010
    Dallas, TX
    The treble boost in a Fletcher Munson curve is over 5K, so no need in a guitar amp, only in a full range amp. Just turn up your bass control. A tilt control would be cool...
     

  14. jonrpick

    jonrpick Friend of Leo's

    Mar 17, 2014
    Marietta, GA
    Thanks @FenderLover

    I'm interested in a tilt control because my recent build has split EQ controls. The bass cut is between V1a & V1b. The treble cut is after that. Cutting bass that early in the circuit is great for controlling flub, but you lose a lot of gain. I'm thinking a tilt in it's place with some more gain on the initial stage would keep it more consistent.

    I would implement it using a resistor in series with a pot that that full-up would be flat and turning it down would remove bass while un-attenuating the highs.
     

  15. FenderLover

    FenderLover Friend of Leo's

    Jun 11, 2009
    Minnesota
    The Yamaha circuit that I started with was closer to 10KHz, but yeah, that's why I said "tweaked a little for guitar amplifier use". In the end, I may be going back to a Tilt also, but I had to get the Yamaha circuit out of my system. I haven't heard anyone complain about the Two Rock JM amplifier, so they must have done something right.;)
     

  16. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Fletcher Munson. Was he the Yankee slugger or the millionaire on Gilligan’s Island?
     
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  17. robrob

    robrob Poster Extraordinaire Ad Free Member

    Dec 29, 2012
    United States
    The simple bright cap is the guitar amp's version of a loudness control. The lower the volume the more high freq bypass we get. I can't imagine an amp like the 5E3 needing more bass at lower volume. Tweaking a mid control will also do what a loudness control does, just turn down the mids as you lower the volume.
     

  18. aerhed

    aerhed Tele-Afflicted

    Age:
    59
    Dec 24, 2016
    Boulder, WY
    Scooper knob.
     

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