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Micro Qtron, anyone done the volume mod?

Discussion in 'Effects [BG]' started by bass349, Nov 17, 2010.

  1. Hey guys,

    Was hoping someone could point me in the right direct here, or pass on some advice if you've done it.

    I've been using the micro q-tron for a while now (probably 2+ years).. straight out of the box it had the famous volume spike issue, making it almost completely redundant for live use. As a quick fix at the time, i threw an old boss odb3 after it, dialed it completely clean and used the volume on that to knock down the level of the q-tron to an acceptable level. Well, fast-track a few years and the odb-3 is still there.

    I literally just completed a mod for the dod fx25b, fixing the opposite problem (massive volume drop). It worked a treat, this is gonna be a killer pedal now!

    Anyone, as i was re-arranging my new pedal setup, it got me thinking about my old qtron problem, and decided i'd do some searching about for a mod for this to fix this pedal once and for all.

    I've found this thread - somebody did it here with the q-tron+ http://www.talkbass.com/forum/showthread.php?t=570171&highlight=qtron+volume+issue with some good info here also http://www.diystompboxes.com/smfforum/index.php?topic=7354.0

    I was hoping for some info, as it seems like a fairly simple fix. From what i can gather i need to insert a pot in the FX output from the switch, and then back to the switch. The problem i have is figuring out which lugs on the switch to do this to. I can post a photo later if that helps? The switch is mounted on a PCB, so i guess i may need to cut through some of the tracks.

    Any help, advice, or encouragement is appreciated!
  2. BrandonBass


    May 29, 2006
    Why dont you add a compressor after e qtron like I did? It has worked pretty fine for me
  3. Hi Brandon, i'm not interested in adding another pedal to the equation.. i basically want to do the complete opposite - do the mod to eliminate the need for another pedal.

    Would it help if i post a pic of the insides? also, if anyone knows where i could find the schematic of this pedal, it would be much appreciated at this point (just to clarify, i have the "Micro Q-Tron", not the mini)
  4. Ok, so i found a schematic of the "mini qtron" - the "micro qtron" (the one i have) is supposed to be the exact same pedal, but squashed in a smaller box. It's been a little confusing (the switch, from what i can tell was laid out differently on the Micro, and the circuit is laid out rather differently), but i think I've figured it out by tracing the capacitor and resistor values on the pcb.

    I'm going to head into the electronics store this arvo and pick up the pot i need. Is anyone actually interested in this? i'm really surprised that i couldn't find any info on this mod, seeing as there are a pile of threads about people complaining about the volume issue on the Qtron's, but not much about fixing the problem fixing the problem. Aside from the stock standard reply "put a compressor after it".

    Anyway, let me know if you're interested, assuming this actually works (fingers crossed) i can probably post up some photos and diagrams on how to do it.

    Either that or i'll be back in a few hours extremely frustrated :)
  5. bugger.. i soldered the pot from the switch to the output, the volume works great, but unfortunately it affects the clean sound as well (probably should have seen that one coming).

    So... Help! anyone out there that can help talk me through this? I need to get the volume control only affecting the the effected output, not the clean signal when the effect is switched off.
  6. ..and the saga continues.

    I moved the pot into (i think) the correct place - where the signal returns from the circuit to the switch (pole 7).

    Now something very strange has happened, the pedal no longer powers up off the 9v input - when the power is plugged in, the with the pedal switched off (clean) it is as normal, with the power plugged in, nothing - sound mutes, led doesn't light up - completely dead!

    However, there is a slight upside - the pedal works perfectly with the battery powering it rather than an external power supply. I mean, the mod is successful, the volume only affects the effected signal! fantastic!

    But this power thing is a serious issue - i don't want to use batteries, so i really need to fix it.

    I assume i've blown something in the circuit, the pedal did power up when i first turned it on. Any ideas here?

    Another option is to power the pedal off the 9v daisy chain, with an adapter to the battery plugs. But i'd prefer to fix this properly.

    Again, if anyone is reading this, please feel free to shoot through some suggestions or thoughts if you have any.


    Ok, upon closer inspection, the 9v power plug casing has a snap in it (like a tear along the plastic). I don't think i have a spare one of those lying around, so i'll have to wait until i can get to the shops again (saturday) to see if this is what's causing the issue. . in the meantime, please throw your thoughts in.
  7. I was going to do it to mine (I've long since sold it), but the surface mount nature of all the parts scared me off.

    One thing I can tell you is that detailed pictures would help those interested in doing the mod as well as those interested in fixing your power issue.
  8. i've never encountered a high-resonance envelope filter that didn't require a compressor, mod or no mod. sorry.
  9. Thanks for the replies.

    Cheapbasslovin - yep, they sure are crammed in there! i'll upload some photos in a bit.

    RCCollins - gonna have to respectfully disagree with you there mate. the dynamic nature of envelope filters is what i like about them. unfortunately, seems a lot of them don't even get close to unity gain when engaged. Regardless, i'm not a huge fan of compressors for live use.

    The mod was a success.. Volume pot installed, only affects the level when the pedal is engaged. Works a treat! exactly what i was after :) i drilled a spot and installed the volume pot on the top (bit below and to the right of the LED) - was hard to find a spot, because of the nature of the design, and how close the pcb sits to the top.

    I'm pretty sure i must have snapped something in the 2.1mm power socket (theres a crack in it); i've just ordered some new ones off ebay, so will have to wait and see. In the meantime i'm gonna hook up an adapter to connect the power to the battery leads.

    Maybe i'll post up photos and a how-to (if anybody is actually interested in this) when all is completed and i get the power working again!
  10. TheFantod

    TheFantod #5 of the Pentaverate. Took Col. Sanders' spot.

    Aug 7, 2009
    Eastern N.C.
    I'd be very interested in pictures/diagrams on where to put a volume pot!
  11. Limiting is really the point of a post-filter compressor, and I find that defeating the drastic volume spikes can actually bring out the dynamics of your playing by making everything more audible
    MichaelT likes this.
  12. ZoBass


    Jun 20, 2014
    very interested, do tell
  13. I agree with this. My BOSS LMB-3 (limiter enhancer) is after my envelope filter and it makes the quieter parts of the filter effect sound louder while also controlling large peaks

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