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texgrind
05-13-2008, 05:01 PM
Hello -
I have an '83 Marshall JCM 800 model 4010 (which is the combo version of the 2204) that I use as a head. It's almost identical to the 2204 except that it has a capacitor across the middle tone pot. Apparently Marshall did this to revoice the heads as a combo. I'm not sure exactly what it's removing, but the amp does sound a bit darker/thicker with it. In fact in it's current form I actually prefer having the stock brite caps in place.
The cap on the mid pot is a 4n7 cap - so that's 4700pF. I removed it to hear what it sounds like in "head" form and it was a little bright for me...I definitely prefer having a capacitor there. I always get confused about how going up/down in value affects tone. If I'd like to still keep a cap on the mid pot but have it split the difference between the current sound and the sound with no cap what value should I use? Is it as simple as trying something around 2400pF to get right between 0 and 4700?
Thanks.

jay42
05-13-2008, 05:24 PM
If I'd like to still keep a cap on the mid pot but have it split the difference between the current sound and the sound with no cap what value should I use? Is it as simple as trying something around 2400pF to get right between 0 and 4700?Yup. Get a few values like 1000, 1500, 2000, 2200, 2700, and 3000pF. Is it mica (looks like a brown chiclet) ? (Those are actually a bit pricey.) Polyester film is fine in that range. www.mouser.com (http://www.mouser.com) for M150's at .001, .0022, and .0033uF. Search on 539-150102J630AA or look for page 818.

Clip off the 0.001uF on the PREAMP volume pot first, assuming it's still there.

texgrind
05-13-2008, 08:37 PM
Thanks Jay! It actually looks like a big ceramic disc cap. Here's a picture...

http://i55.photobucket.com/albums/g121/pixpicspictures/Marshallpresencebassmiddlepots.jpg

Thanks for the suggestions on where to find the caps. Would going with a different type of cap produce any noticable improvement or should I simply stick with the stock type?

jay42
05-13-2008, 11:28 PM
Thanks Jay! It actually looks like a big ceramic disc cap. Here's a picture...

http://i55.photobucket.com/albums/g121/pixpicspictures/Marshallpresencebassmiddlepots.jpg

Thanks for the suggestions on where to find the caps. Would going with a different type of cap produce any noticable improvement or should I simply stick with the stock type?
Even cheaper...yes, the type of cap will change the quality a bit. It's worth a few bucks to try film and ceramic caps. It's impossible to know which you'll prefer. You just tack them on without cutting the leads, then listen.