Home Forums GuitarPCB Build Support Re: PURP Questions

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    I was asked, awhile back, to build a “stock” PURP (I used Barry’s suggestions for C2 / C6 22N, and did not populate C4) for a guitar player acquaintance of mine. The pedal seems to be hissing like crazy now, so when the PURP boards come back in I’m planning on doing a rebuild (including C4). He’d like me to do a MOD, and I’m posting to see if it’s even possible. Instead of treb / mid / full spectrum boosts, he’d like treb / mid treb /mid boosts. I’m assuming I need to adjust cap size to get the boost frequencies higher, but I’m not sure where to tweak. Again, IF the board was made to function with certain size components then it is what it is…

    Thanks All!!


    You simply cannot boost frequency with any passive tone control on any circuit. Only cut.

    Same as your passive Guitar Tone Control. It only cuts frequency. See this excellent video:

    If you wanted to boost you would need to add an active tone control like our Tone TwEQ.

    Most guitar pedal tone controls are passive like the Muff, SD-1 or TubeScreamer etc…

    Important: Adding an active tone control can boost unwanted sounds like the Hiss you describe or other unwanted artifacts so it is important to pick the right circuit and make sure it is performing to its potential before considering that option.

    As for the Hiss we should have a good look at the pedal to be sure there is not an error or bad solder joint and I suggest testing your transistors with a proper testing rig like the DCA-55 Peak Atlas. A typical DMM tester will never provide accurate results nor show leakage. If you do not have access to a DCA-55 Peak Atlas and decide to order a new transistor I would only buy from a “Very Reputable” dealer like Small Bear. Never eBay!!

    Incidentally there are many other factors which could create hiss in a HIGH GAIN Circuit like the Rangemaster. Bad Solder Joint: Re-flow entire project, always do the battery test on every pedal (attach a battery strap to a 2.1mm Negative Tip (paying mind to polarity). Do not use a Positive Tip rigged battery strap that may come included with 1-Spots! This will rule out any power supply and a bad wall receptacle. Move on to checking cables, re-flow ground wiring, be sure the pedal is properly grounded, etc…

    Remember our Rangemaster uses a charge pump (so be sure to use the recommended version) and likewise only use a Negative Tip power supply (so you can use with other pedals in chain). Many people associate Rangemasters with a Positive Tip (which includes people who buy from you) which can ruin your pedal.


    Thank you, Barry. I’ll look for the PURP boards, and get a few when they come in…hopefully soon.

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