Marshall Plexi / Fender Bassman Fet preamps?

[dan6896]

hi, i am looking for a fet preamp version of a Marshall Plexi or Fender Bassman, like the ones of runoffgroove.com. i have had look around the interweb and done many google searches but nothing great has come up. So if anyone knows of any could you post a link to the schematic.

Thanks.

[DIRO]

 hi,,,,,i  ever looking for marshall plexi, and i found  @ this web
[url http://www.ultimate-guitar.com/forum/showthread.php?t=968411]

[spud]

Hi,

I've built the Plexizer that Mojotron developed but I'm still DEBUGGING it.  It's on DIYSTOMPBOXES (search for Plexizer or Plexi or Mojotron Plexi).  I created my own layout with DIYLC (also at DIYSTOMPBOXES). 

Here is a link to the thread at DIYSTOMPBOXES: 

http://www.diystompboxes.com/smfforum/index.php?topic=50207.0

And here is my Layout - still debugging it as it squeals and buzzes with very low output.  Mojotron built it and posted clips with it in the above thread.  Here's my layout (not quite verified): 

http://s252.photobucket.com/albums/hh7/spudjds/Public/Builds/PEDALS/Plexi-izer/

The first is closest to what I actually built - still need to finish debugging it and update the layout if needed.

I was planning to use this as the preamp in combination with a chip amp power amp (one of: LM1875? or TDA2005? or LM3886? or ) and stick it into a car sub-woofer box I got for next to nothing (like $5.00) at Parts-Express (closeout sale).  It takes a 8" speaker so I figured the Jensen Mod 8 or even a Weber 8" of some kind.  Run it from either a wall wart or build the PS into the cab - that part I'm still deciding.

The Sub-cab is one of the grey carpet covered wedge things with the speaker on the slanted front.  There is about a 2-2.5" panel on the font where I figured I'd put the controls and input.  On the back there is a speaker in jack on a round panel.  There's plenty of room on the inside as the speaker sits at an angle and most of the interior is empty.  Only issue is where to put a handle but it's no biggie really. 

Oh, there's also the JCM800 emulator that I have a schematic for somewhere and I did a layout but it was really close to the plexizer overall - I think it adds 1 extra JFET.  I can post it but need to find it first. 

Jim

[dan6896]

thank's for the information spud. that plexitizer looks great but its a bit complicated for a n00b like me maybe one day in the future i will build it. i got lots of other projects going on at the moment.

[spud]

Hey, I haven't gotten it to work either but I'm the type that gets frustrated easily so I've not much patience for debugging.  I will get it working though, just need some period of continuous free time to sit down quietly and go to it.  Just not easy to get that. 

Best of luck and keep posting your results - I like to get ideas from people on my builds.  I ended up here so I could try to build a decent sounding SS guitar amp and I'm hoping to pick up some tips and ideas from you all.   

Jim

[J M Fahey]

If in doubt/beginner/easily frustrated , start by the plain vanilla version, the one that's published in sites such as GGG, Runofgroove, etc., and which has already been built by many.
That way, if you have any problem  ( we all do), you know it's something small, such as miswiring, putting a polarized part the wrong way, misreading some color code, different Fet pinout, whatever.
If you add to that designing your own board, you'll always be in doubt.
Once you got it to work, and have built a couple other projects, yes, then start drawing your own.
Good luck.

[spud]

Well, this one didn't have a layout for perf - it did have PCB etch mask but I haven't done that kind of stuff yet.  Kind of leary of the chemicals -    There was only the schematic so I decided to make my own perf - I've done it before with other pedals so I'm pretty confident I did it right but yeah, you're right, this way I have a lot more possible issues - build errors plus possible layout errors.  Proven designs are always quicker/easier to get up and running - but this is how I learn, doing stuff like this on my own.  Just need the stretch of time (and patience) to go through an end to end debug - I think it's got to do with the pots cuz when I wiggle some of the pot leads, it sounds ok for sec or 2 then starts back buzzing, etc.  Probably something shorted out there.  Hopefully something simple -

Jim

[J M Fahey]

Unfortunately I think it's a grounding->(in)stability issue.
All I can tell you is that in the beginning *all* my projects buzzed, picked the radio, motorboated, *transmitted* interference, you name it, although I used shielded wire everywhere, used right-angle-bent, perfectly parallel paths solid wire á la Hiwatt, etc. and today I build "sloppily", use regular, not shielded wire for signal ... and have no RF, oscillations, hum, very little hiss .....
I think it comes together with experience.
Practice makes better, so build, mod, test, as much as you can   8|