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|previous: Mark Buckingham >Marshall 0.68uF||View Thread|
|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.
|Mark Buckingham Thanks again. I've already got a p... -- 6/23/1998 11:19 AM|