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Taming the boost on my Vox Pathfinder.

Discussion in 'Amp Central Station' started by mistermullens, May 21, 2009.

  1. mistermullens

    mistermullens Poster Extraordinaire

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    Anyone have any ideas on how to tame the boost on my Pathfinder? I love this amp, but the boost is over the top. I'd like for it to function more like a lead boost. The only way I can use it now is if I kick it in and then turn the volume way down on my guitar, which too me kind of defeats the purpose of a boost. Any and all comments are welcome!
     
  2. Joe-Bob

    Joe-Bob Doctor of Teleocity

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    Turn the boost on but the gain down. I usually leave the master volume at about 12 o'clock or more, and the gain about 9 o'clock. The boost is pretty hot, if you have a bunch of gain dialed in then it can get to be too much pretty quickly. BTW--I always have the master set pretty high and the gain pretty low, bass 10, treble 6, also, mine is a head/2 x 10 version. The speakers are loud and brite!
     
  3. jmaul

    jmaul Tele-Afflicted

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    I'm sure a well placed resistor swap would tone it down. I'm not of the mind to figure it out though, plus a cheap, small pcb board means a decent chance of ruining the amp altogether.

    Even with a toned down boost, I think there is a deeper issue with the quality of the boost tone- sort of a shrill cat in heat clawing a chalkboard sound that would probably involve diving into cutting traces and jumpering and cap changes, which would have an even higher likelihood of ruining the amp.

    My advice, forget the boost exists and add your favorite pedal.

    The Pathfinder is great at what it does, but I think at some point we need to realize that you could be better served by something else rather than committing to a total overhaul of a $130 ss amp. Loving one piece of gear too much yet constantly trying to improve it to be everything you need is an expensive and time consuming slippery slope.
     
  4. mistermullens

    mistermullens Poster Extraordinaire

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    That's a good idea, but doesn't work for what I want to use the boost for. I like the amp best when the boost isn't engaged, but if it wasn't so darn powerful, I could kick it in for that extra little boost I need sometimes. As it is right now, I'm going from blues to Metallica with a stomp of the foot switch. Too much.
     
  5. mistermullens

    mistermullens Poster Extraordinaire

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    Good point. I like the pedal idea, even though I prefer not to use them. I've pretty much given up on the boost except for occasional use.
     
  6. jmaul

    jmaul Tele-Afflicted

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  7. Cleeve

    Cleeve Tele-Holic

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    I have a bad photocopy of the schematic for the non-reverb model, it looks like the boost switches a feedback loop from a low resistance to a high one.
    I think you might be able to tack-solder an additional resistor on the high-resistance circuit which would increase the feedback and reduce the gain. I don't have the layout though to tell you exactly where to try it, maybe the resistor labels are the same on the 15R model, maybe not.
    In any case it's the resistance between pin 7 and pin 6 on the IC1 that you are interested in. I wouldn't try to solder to the IC, but to something that connects to those traces. If your amp is close to this schematic, you could try putting a resistor around 100k across c7 for example, which in my schematic is connected to pins 7 and 6 of IC1.
    To tack solder, you need to put some solder on the legs of the capacitor, then put some on the leads of the resistor, then melt the solder together with the iron. Don't try to hold the iron the resistor and the solder all at the same time. You might want to practice on some scrap first.

    I'm only guessing at the resistor value you'll need. The normal gain unboosted value is 33k, the boosted one is a 190k in series with a 470k that's parallel with a small cap, who's value I can't make out.
    That's a whole lotta resistance, for not very much feedback, thus a whole lotta gain when the boost is on.

    So I'm thinking between 100k and 500k tacked on to that C7 cap will tame things- or you could add another pot!

    If you could take a photo of the board near the IC1 I may come up with a better scheme.
    To make the low-gain setting be totally un-bothered by this mod, I need to see if R6 and R8 are the same on your amp as this drawing, as there is a more correct place to put the resistor than the way i described across C7.
     
  8. jmaul

    jmaul Tele-Afflicted

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    now THAT'S an awesome mod idea. Put a pot on the bottom of the chassis and dial in whatever boost you like. Basically a foot switchable cascading gain.

    While you are in there, swap the cap out to a sozo or something. Maybe figure out a simple FET based design to replace it.
     
  9. Cleeve

    Cleeve Tele-Holic

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    Another simple experiment to tame boost would be to find R6 and clip a jumper across it, if it's still too much boost clip a jumper across R7. Again, assuming the schematic I have applies.. R6 is a 190k, R7 the 470k...
    according to my pixilated source..
     
  10. mistermullens

    mistermullens Poster Extraordinaire

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    Good ideas here, guys. I really like the footswitch option as I'm not tampering with the amp. I'll have to open up the foot switch this weekend and see what it looks like. I might need some help with it.
     
  11. jmaul

    jmaul Tele-Afflicted

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    Unfortunately all of these ideas are amp mod based.
    I don't think a simple switch pedal will allow you to mod the boost- the pedal is not in the circuit like on the rivera designed amps, it is more like a light switch- on and off. If that was the case you could simply put some sort of in between plug that had high resistance. But that is not the case.

    If you are dead set on keeping the amp stock, I'll return to the opinion that your best bet is to forget the amp boost exists at all, and spend $40-120 on a nice external OD/Boost pedal. Again, the ebay link I gave is a great tube based boost/preamp that you should love, your amp should love, shouldn't be too expensive since it is used, and should hold value well.
     
  12. Cleeve

    Cleeve Tele-Holic

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    http://www.vintagedesign.halmstad.net/schematics/Pathfinder15.pdf

    Here's a link to the fuzzy schematic I was referring to above in case someone daring enough to make two solder connections finds this thread in the future..

    The things I mention to try above do not involve removing any components, and would be easy to reverse, leaving no alteration of the circuit.
    But I haven't seen the insides of the 15r, it could be all surface mount for all I know- which would complicate matters a little..
     
  13. Tele-Champ

    Tele-Champ Tele-Holic

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    Yeah, that over-the-top boost is the only thing I don't like about my Pathfinder. It is hard to control, definitely... I love the clean on this amp, though, and use the clean channel pretty much exclusively.
     
  14. littlericky

    littlericky Tele-Meister

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    Zombie Thread. Has anyone put a variable control on the boost?
     
  15. littlericky

    littlericky Tele-Meister

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    With the help of the good guys over at ssguitar.com forum I was able to add a 1 Meg audio pot to the board and control the "volume" of the boost. Now it can be dialed in and used with the footswitch.


    [​IMG]
     
  16. danmahoney

    danmahoney NEW MEMBER!

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    Hi,
    I`m pretty experienced with using a soldering iron but not so much with reading schematics. Can you walk me through exactly where (and how) each wire running from the 1M pot would attach to the board on the mod in the schematic? Thanks!
    Dan
     
  17. lareplus

    lareplus Tele-Afflicted

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    what an excellent concept!
     
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