JMP 50W Lead/Bass Build

[neikeel]

I wanted the screens and PI separate for two reasons, one being such that I can easily try different values in each location, but more importantly, so I could separate the grounds for proper Larry Grounding. It worked too, because I used 32uF for the PI and this thing is dead quite.

As it should be -what did you use for screens (I use 32 on a JMP as well, so a 32/32uF can, use the PI node as grounding point for presence circuit)?

[bbaug14]

I used 50uF for the screens, for now. I'll almost undoubtedly change the filtering a time or two. I like a nice tight response, so I may try 50uF in the PI too just to see the pros and con's. Right now the bottom is a little flubby, but that very well may be my cab. Greenbacks aren't the tightest in a straight 4X12.

Yeah, PI and presence to the same ground node. The grounding scheme is perfect. This thing is dead quite.

[bbaug14]

Got her buttoned up this morning. Now I just need to break in the OT and coupling caps. I don't see that happening anytime soon with how often I get a chance to play at home. Oh well...

[kdmay]

Congratulations on the build!

Glad you got your issues sorted. I'm sure it sounds killer. I miss my Plexi!!

[bbaug14]

Congratulations on the build!

Glad you got your issues sorted. I'm sure it sounds killer. I miss my Plexi!!

Thanks so much for the help with the questions you answered for me on your build. Yours was definitely my inspiration.

Amp sounds awesome. I'm finding I really dig the bass spec. The lead sounds great too, but there's something about the richness of the bass spec.

[neikeel]

Bass spec often sounds best with a T1221 cab at home, the Lead spec and T1281 cabs come into their own when playing out with a band, you can hear yourself better in the band mix (although cranking presence, mids and boosting treble will help if you don't have a switch

[bbaug14]

Bass spec often sounds best with a T1221 cab at home, the Lead spec and T1281 cabs come into their own when playing out with a band, you can hear yourself better in the band mix (although cranking presence, mids and boosting treble will help if you don't have a switch

Couldn't agree more, though I don't have those nice vintage greenies. Luckily for me, I play in a band where the other guitar player plays a Mesa MKIV combo, and he doesn't like mids for whatever reason. So, I have no problem being heard in the mix... at least with my Wizard MCII. At our last show, a buddy of mine was telling me how much more my rig cuts through. I'm looking forward to trying this one out at practice and seeing how it compares in the mix.

My Mather 4X12 has a quad of WGS Green Berets and my oversized 2X12 has a WGS Liberator/Reaper HG mix (wanted 100W for the 2X12). I find the 2X12 has a lot more clarity and tighter response, whereas the 4X12 is a little darker/warmer and a little more muddy. I might have to swap out a couple Green Berets for some Reapers in the 4X12 in the future and try that on. If you can't tell, I really dig WGS speakers. They sound great and don't break the bank (no affiliation).

[bbaug14]

Here's a few minute clip of my noodling through some riffs this morning. Gives you sort of an idea how it sounds, though the quality is not that great. I chopped out some of the video here and there so it wouldn't be so long, so pardon that.

http://youtu.be/WGAcNY_WT10

[bbaug14]

Here's a quick clip of the Bass side. Same settings as the Lead clip, just on the bass settings. Sorry about the flubs (might be a bit out of tune in the cold basement) and don't mind the occasional sound of kids in the background if it made it on the video. I ran downstairs to throw something together...

http://youtu.be/8Ri4ZeKBVIY

[bbaug14]

So when I finished this build, on the Lead setting there was some scratchiness in the BMT pots only on the Lead setting. I figured the Tone Stack cap I was switching in was leaking a little DC. I finally decided to fix it and swapped both Tone Stack caps out for completeness. I experienced no change in the scratchy pots though. On the Bass setting there is zero noise. So I lifted the V2a cathode cap (0.68u) that I switch in to see if that was the cause. Nope, no change. I'm at a loss for what to try next. Some how, DC is getting onto the BMT pots only in the lead settings. I know the 2 250p caps I'm using in the Tone Stack are good now and I know that V2a bypass isn't the issue. I wouldn't think it would be the V2a 2.7k/0.68u arrangement as the Volume pot is clean. I'm looking for some suggestions here. I've read that bad grounding can cause this, but I'm using the Larry grounding method and it's dead quite in the Bass setting. The only things that change in the Lead setting are split cathode, V2a bypass cap added, and a resistor/cap added in parallel to make 33k/500p. Anyone have any suggestions? Pictures are earlier in the thread of the amp. Thanks!!!!

[axeman]

Got her buttoned up this morning. Now I just need to break in the OT and coupling caps. I don't see that happening anytime soon with how often I get a chance to play at home. Oh well...

Were did you get the head cab from?

[bbaug14]

Cab came from Valvestorm but its a Mojo cab.

[danman]

Nice looking build! I really like the option to switch between lead/bass spec that you installed! My first build, several years ago, started as lead spec but I found that I preferred the bass spec more for home playing. I have recently installed a switch to open the NFB circuit and I find that I really like the looseness and extra growl that running no NFB provides. I am at a loss as to why you are getting the scratchiness on the T/M/B pots in lead spec mode only. Is it possible that the noise is also there while in bass spec mode but with the reduction in the highs it goes unnoticed? Possibly the higher frequencies introduced with the lead spec cap are causing the noise to show up. Have you checked all the coupling caps around each stage for DC leaking through?