Most impactful mods to a Monoprice 15 W amp?

Discussion in 'Amp Tech Center' started by kmckenna45, Sep 20, 2021.

  1. kmckenna45

    kmckenna45 TDPRI Member

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    I have a Monoprice 1/15W Stage Right amp with the stock Celection speaker. I've upgraded the reverb tank, but found little improvement.

    I've watched a few YT video's on mods to this amp, but none seem to really make a difference.

    Can anyone make a recommendation to upgrading mod for this amp that is worth the additional $ investment?

    I'd really like to improve the crunch sound - I"ve thought about buying a diff amp (Peavey Delta Blues, if I could find one) - but this amp really does so much for the money - I'd hate to throw money away just for marginal improvement.

    The Gain knob is close to worthless - I can get a decent distortion by cranking it all the way up, but it seems more like an on/off than a pot.

    Would it be worth it to change out the tubes? The Speaker? I don't want to throw money away for a tiny improvement (like I did for the reverb tank - but it was only $40).

    Thanks.
     
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  2. stormsedge

    stormsedge Poster Extraordinaire Gold Supporter

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    I've rolled the preamp tubes in mine a couple of times and succeeded in making minor changes. I ended up with V1 Golden Lion ECC83; V2 EHX 12AX7; V3 Mullard 12AX7...which produced a cleaner sound to me and was what I was looking for at the time---the wrong direction for what you want to do. The V1 tube makes the biggest difference if you were to pick one more towards what you want based upon the tube description...probably no reason to mess with V2/3. I've had good luck with various pedals on this amp...you might consider trying a couple of different distortion pedals to get the sound you seek--it would probably get you there quicker.
     
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  3. kbold

    kbold Friend of Leo's

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    Trying some old/NOS 12AX7 tubes will often improve any amp.
    5751's would also be a suitable 12AX7 replacement to try.
    Targeting V1 (preamp) and V3 (inverter) would give you the best improvements IMO.

    This would be the easiest as no circuit modification is required. (No chance of damaging yourself or the amp.)
     
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  4. VintageSG

    VintageSG Friend of Leo's Silver Supporter

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    Buy an extension cab to put a better speaker in. Even with a better speaker, it's still a slightly crappy cab. A plywood baffle will help, even with the stock speaker.
    If you do go down the route of a ply baffle, make two; one for a 12" and one for a 10" Try a 10" in that cabinet, on a ply baffle.
    Cabs are great, because it's an excuse to buy/build amp heads. Heads take up less space, so more amps :)

    Speaker wise, I was a Jensen MOD fanboi. Then I tried a Jet Falcon 12" in a build.

    Use an amp stand and get the speaker pointed at your head.

    For crunch, use an EQ pedal. Boost the front end, but lower the bass via the EQ pedal.

    Get it biased properly. I have yet to see a modern production, adjustable ( fixed ) bias amp that isn't biased cold. Fun things happen when the valves are properly warm. I have the circuit diagram with bias test points for the Laney donor which match, but better results come from using a probe and monitoring the voltage too rather than the ( still conservative ) fixed value given on the sheets. If that means nothing, get it biased by a techie.

    V1 is the money valve. It effects the largest change. A 5751 ( The JJ is a good modern production example ) will give some sweep back to the gain control.
    Leave V2 alone. The Shuguang/Ruby will do a good job.
    V3, the inverter, may benefit from a Sovtek 12AX7LPs, the Long plate 12AX7 or a JJ ECC803 ( similar )
    V4+5 are the EL84. Old Soviet 6p14p-EV are the dogs danglies, but the Sovtek and JJ are good enough. There's not much wrong with the Sino EL84 valves fitted, they just need biasing properly to come alive.
     
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  5. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    The schematics for the Stage Right are sketchy. Most say to look at the Laney. The Laney shows a 300V B+. If this is true for the Stage Right, it is a limiting factor for what I think you are wanting.

    Since I don't know the true numbers for voltages and parts, it makes it too difficult to suggest mods. It would also be informative to know the specs and size of the Output Transformer (probably another limiting factor). Ime, more info is needed.

    I like the earlier post that suggests pedals. Best bang for the buck, imo.
     
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  6. drew1d

    drew1d Tele-Meister Silver Supporter

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    My friend uses one of those with his cover band. I think it sounds great. It started making a little noise...perhaps it was always there. He retubed it with JJ's and it sounds even better. It could have been dirty tube sockets. To be honest, a good servicing with some deoxit and cleaning the connections is probably the best place to start. Even if brand new.

    I know it's not a mod, but would give you the best baseline to compare.
     
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  7. LightningPhil

    LightningPhil Tele-Meister

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    Fairly sure there's a huge thread on this.

    Anyhow, to improve crunch, as in crunch made by valves, there's a mod to the cathode bias you can do. Very much depends exactly what you're after as to how to tune it and best to expect a little tinkering. Very inexpensive parts and reversable.

    In essence, massively lower the cathode resistor value. This lowers the gain of the low frequencies and stiffens the bass, also making it less farty when a gain stage does break up. The highs will still be bypassed and keep their gain. However, the step is quite steep, so bypass the whole lot with a second capacitor with a resistor in series with it (like a snbber). That capacitor should be twice the size of the new small bypass capacitor and the resistor the same as the cathode resistor. Should be a good starting point for progressive gain.

    Every time I've done this to a gain stage, I've always liked the crunch sound once it's driven. There's a bit more sustain and volume on the highs too, but not excessively.

    Capacitor values not given as not looking at circuit and depends on taste. Have done the mod to several amps and added schematics of them here. Faff to link as typing answer from ipad.
     
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  8. naveed211

    naveed211 Friend of Leo's

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    What speaker is in it? I ask because my Monoprice cab came with a Vintage 30, which was the selling point as to why I got it. That’s one of my favorite all-around speakers.

    But, speaker will have the biggest effect on tone almost assuredly. You can change the sound pretty radically. Do you have a favorite speaker to try with it?

    Also, don’t sleep on the notion of an EQ pedal. That’ll open up a lot of tonal options, too, without having to swap anything out.
     
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  9. LightningPhil

    LightningPhil Tele-Meister

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    Found a plausible-looking schematic:
    https://www.vguitarforums.com/smf/index.php?topic=21220.0

    Shame these aren't sole in the UK as I'd love to play with one. Ages ago when people were getting enthusiastic about Monoprice, I poked them with a stick (email) and asked. Apparently, it's on the cards one day.

    Anyhow, seems R19 and C11 are the cathode resistor and bypass capacitor for the input tube respectively. Suggest tinkering there. Leave R19 alone, but desolder C11. And in place of C11, add something like a 330 nF film cap, leaving some of it's legs exposed to add components onto. Then across the film cap, add 666 nF of capacitance (or close-ish) in series with a 2k2 resistor.

    What this should do is, decrease the gain of the low frequencies by about 6 dB, but keep the highs the same, with a fairly flat 3 dB per octave slope in between. I find this evens out the volume across the fretboard nicely. And when the gain is turned up a bit, allows for the highs to break up about the same time as the lows. Makes for a fairly controlled progression into mild dirt. Then when driven more, always find the crunch and sustain pleasing.

    This is similar to the bass blocking and attenuating going on in a lot of high gain pedals. Though generally, they use a 6 dB per octave slope which always feels too steel and obvious. In an amp, where there's mild gain, the mild 3 dB per octave change in gain between the lows and highs is transparent.

    This is just a starting suggestion, it'll cost a little time and about $1 to accomplish it. I'm convinced it'll have much more of a change than any speaker swap. On the latter front, I've tried everything from Celestion over the years. Generally prefer the G12H55, modified with a foam surround in place of it's original tight paper one for a much lower resonance. Faff to do, but gets the boomy bass of speaker resonance away from the guitar's vocal range and sounds wicked with a bass too. Might have gotten carried away...
     
  10. bettyseldest

    bettyseldest Friend of Leo's

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    I believe that this is the same amp;

    upload_2021-10-3_13-18-2.png
     
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  11. Addnine

    Addnine Tele-Holic

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    First off, I do prefer the sound of their 5w model, which is perfect as it is. Even the Asian Celestion is really good.

    The sound of the 15w is a little dense to me, no sparkle or space. I swapped in a 12ay7 to get more clarity/headroom. Made a little difference. I like the amp, but I like his little brother better. Maybe it's the el84's.

    [​IMG]
     
  12. GreatDaneRock

    GreatDaneRock Tele-Afflicted

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    The speaker will be the biggest change and improvement in the sound, if you feel that it needs to be improved. Decide on American or British style sound, modern or vintage, then look at your typical manufacturers like celestion, Eminence, and wgs.

    I truly like Eminence's Swamp Thang. Big, loud, more sensitive than your average speaker (loud), and very articulate and balanced in it's sound character.

    I actually put a 12AY7 on my five watter as I use my amps as pedal platforms, sounds stellar through a bigger cab and not bad at all through the little speaker if the tone is turned almost fully down.
     
    Last edited: Oct 3, 2021
  13. jvin248

    jvin248 Doctor of Teleocity

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    Speaker swapping.





    .
     
  14. EsquireOK

    EsquireOK Poster Extraordinaire

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    Yup.

    I would treat the amp as a head. I would use it through an external cab 80 percent of the time, or more.

    But I would also replace the stock speaker, with the only real consideration for the speaker being light weight. That way, I would have a very lightweight grab-n-go combo when convenience was wanted, and tone could be compromised.
     
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  15. LightningPhil

    LightningPhil Tele-Meister

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    It does look similar. Onto the Christmas list it goes..
     
  16. LightningPhil

    LightningPhil Tele-Meister

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    If you want to meddle with the speaker...

    Most of the stiffness, especially in Celestions, comes from the surround. Very careful application of a razor blade to remove it and some glue to install a foam one slackens it massively. Well worth doing if the old driver is going to be junk anyhow. Here's a link to the surrounds:
    https://www.ebay.co.uk/itm/163606695515?hash=item2617b80e5b:g:fBcAAOSwslJckig2

    It'll deop the resonance, like the most broken-in driver ever, and increase the efficiency a wee bit. In theory, it could allow the coil to move more and end up with more distortion as it operates in slightly the strong bit of the gap some of the time. Meh...

    You're £7 and an evening away from a unique speaker.

    Eminence has made custom guitar speakers with foam surrounds. At least 4 of them, they're awesome. Rich, Bassey, and much versatile than paper surround ones.
     
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