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previous: Mark Buckingham >Marshall 0.68uF>cap will start... -- 6/22/1998 7:45 AM View Thread

Re: guitar frequencies

6/22/1998 8:21 PM
Steve A.
Re: guitar frequencies
    I have e-caps going down to 0.33uF, but for the lower values a mylar cap works even better (e-caps are used because they are much cheaper).  
    My print for the PR shows a 1k5 cathode resistor so a 1.0uF cap would simulate the freq response of a Marshall with their 0.68uF cap and 2k7 cathode resistor.  
    The universal mod I do to practically all of my amps is to put in a center-off DPDT mini-toggle switch to allow me to select the Ck for the initial preamp stage between 25uF (stock Fender) 0uF (unboosted with more clean headroom) and 0.47uF to 1.0uF (Midrangy Marshall-like response). Of course if your PR is vintage you might not want to drill out holes in your amp for the switch (but could use a p-p pot for the volume to select between 2 of those values). For Clean channels I'd wire the p-p switch for 25uF or 0uF (that's like the "Fat" switch on a Fender Blues Jr. amp). For OD channels I'd wire it for 25uF and 0.47uF-1.0uF. (In my Pignose there wasn't a lot of room for many mods so I put in a 6 position rotary switch: 0uf 0.33uF 0.47uF 0.68uF 1.0uF 22uF. I had tried a 0.047uF cap instead of the 0.33uF cap for awhile which worked like a bright switch, but it sounded pretty nasty with OD settings and I wanted to "idiot-proof" the design. I may add it back in because there's not much difference between 0.33uF and 0.47uF)  
    If you go with a switch, add a bleed resistor between the switching contacts to eliminate "pops". For a 22uF cap try 220k; for the 1.0uF range of caps a 470k resistor works great. The game plan is to have the resistor bleed off any dc charge building up on the cap.  
Steve Ahola

Mark Buckingham Thanks again. I've already got a p... -- 6/23/1998 11:19 AM