Go from clean to nasty sound with the Monprice 15 watt Stage Right mod.

Discussion in 'Amp Tech Center' started by V52S, Oct 20, 2019.

  1. V52S

    V52S TDPRI Member

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    Hello to all,

    As a harmonica player I like the gritty nasty sound I can get from this Monoprice 15 watt amp.
    There are those times that I like to play easy and clean though.
    So, by reducing the negative feedback resistor value of the amp you can increase your volume and have a cleaner signal.
    By increasing the resistor value in the NFB circuit you can get back to that nasty harp or guitar sound for those heavy blues numbers.

    So how do you do it?
    Look at the schematic and notice R22, 47K ohm resister, that comes off the positive speaker lead.
    By removing it and replacing it with a 5K resistor in series with a 100K pot you can have a variable NFB circuit.
    Turn the pot to it's minimum position and you have 5K in the circuit which allows for more NFB thereby cleaning up the sound and allow for more headroom. Go to the maximum control setting and you can get a real nasty sound or dial it to where you'd like the sound to be and leave there.

    As with all mods you must take extreme care when working within an amplifier.
    Be cautious of the high voltage and be sure to discharge the filter capacitors before working on it.

    Do this mod at your own risk.
    Not responsible for incorrect procedures that lead to damaged amps or bodily harm.
    If you are not sure how to do this mod then I suggest you go to a tech in your area for assistance.

    Keep on Harpin'
    -v-


    Monoprice Schematic LARGE 10.jpg



    Laney - Monoprice Schematic.jpg
     
    Last edited: Oct 21, 2019
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  2. corliss1

    corliss1 Friend of Leo's

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    Yup - NFB tweaks are one of the most common changes you can make to help control the point the amp breaks up. Some people even do a switch so you can choose multiple values.
     
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  3. rangercaster

    rangercaster Poster Extraordinaire

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    I would attempt to not mod the amp ... A preamp/ eq solution seems easier ...
     
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  4. archetype

    archetype Fiend of Leo's

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    What the OP describes is a very common mod and is easily rerversable. Modding an amp isn't for everyone, but many folks do this specific mod.

    A preamp or eq solution of any kind doesn't do the same thing as changing the NFB. The amount of NFB can change EQ a bit (increase NFB = less midrange, decrease NFB = more midrange), but it has a different result vs. doing it at the preamp or inline with an effects loop.

    Less NFB, as the OP is describing, also can increase harmonic content. It can also produce more noise, hiss, and "trash" in the sound, depending on the circuit.
     
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  5. MrClint

    MrClint Tele-Meister

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    You had me at "Gritty Nasty" sound right out of the box! I play harmonica mostly straight into my DAW, but haven't experimented playing through my MP15W amp. If it doesn't take the thread too far off the tracks, I would be interested in the rest of your rig for harpin' as well (mic, fav EQ settings, etc).
     
  6. V52S

    V52S TDPRI Member

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    Sure MrClint here we go.

    MonoPrice 15 watt settings:
    Gain at 2, Volume at 6 (or more), Tone at 5, Bass at 2, Middle at 6, Treble at 1, and Reverb at 2 or more depending on environment we're jamming in.

    Retubed- V1 Mullard Long Plate 12AT7, V2 JJ 5751, V3 Mullard Long Plate 12AX7, Output tubes are matched Mullard EL84.

    Reverb - is now a MOD 8EB2C1B. Cleaner than stock with a touch more drip to it.

    Speaker - Eminence Legend GB128, a little more bass and the highs are not as shrill.

    Bulletini mic with volume control. This mic has lots of output and bass too.
    That's why my bass control is set to 2, the mic and the speaker do the rest for me.

    Shure Wireless GLXD4 with rechargeable transmitter. Transmitter battery can go for 16 hours straight before it needs to be recharged and the clip fits right through my belt loop nice and tight, (I don't wear a belt).

    Suzuki Promaster Harps. (exclusively)
    Suzuki Chromatix 16 hole. Still learning that one, it's a completely different animal. :eek::D

    Keep on Harpin'
    -v-
     
    Last edited: Oct 20, 2019
  7. V52S

    V52S TDPRI Member

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    Yes, and I've done that but it did not give me the results that I wanted. See my post, #6, for the tube swap that I did. As a harmonica player I like easy tones on ballads and nasty on hot blues tunes.
     
  8. MrClint

    MrClint Tele-Meister

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    @V52S, Thanks for sharing. Heckuva rig!
     
  9. V52S

    V52S TDPRI Member

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    Thanks, and a quick update too from message #6.
    Did another tube swap.
    Changed V1 to a Mullard Long Plate 12AX7 and move my 12AT7 to V2.
    More volume now with the gain still at 2 and the volume at 6 and V2 sweetened up the reverb.
    It's got a bit more depth and sounds spacial. :D

    -v-
     
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