Fender Bassman FET Preamp?

[mth5044]

Are there any schematics out there that do the Fender Bassman preamp w/o the tubes (I believe FETs are used as a replacement?). In particular, the kind with the 2x bass instrument and the 2x normal inputs? I think there is one called a Bassman 50, but other models exist.

Thanks a lot!

[electrosonic]

From http://www.runoffgroove.com/

Not exactly what you are looking for - a Princeton amp as a stompbox here - http://www.runoffgroove.com/professor.html

and some general info about simulating 12ax7s with jfets - http://www.runoffgroove.com/fetzervalve.html

Andrew.

[snyder80]

its calles "bass boy" i think and you should find in in the gallery. There might also be atopic about this preamp in this board..

[MartyMart]

Here it is, no layout but should be quite simple on perf/stripboard.
I did this in 2006 :  http://www.aronnelson.com/gallery/main.php/v/Martys-layouts-and-photos/BassBoy59V1_1.jpg.html?g2_imageViewsIndex=1

Sounds pretty darn good.

MM.

[Ben N]

Somebody also did a JFET iteration of the Alembic F2-B bass preamp, which is really just the preamp of a Fender tube amp of that era. The Alembic has a mids control for each channel, like a Twin or Dual Showman and unlike the silverface Bassman 50, but that is all to the good, and does not change the topography of the preamp at all--on its TB amps, Fender just subbed fixed resistors for the mid pot. There may be a few value substitutions to get it to match the Bassman you are after, but just go part by part through the Bassman schematic and you should be good to go. If you search the forum for Alembic F2-B you should find it.

[mth5044]

Thanks for all the recommendations. I got some of ideas off the the links posted and the ROG Fetzer thing and came up with this schematic based on the bassman 135.
Original schematic -> http://www.thevintagesound.com/ffg/schem/bassman_135_schem.jpg



But I'm not sure how to bring the two together. Should I just use a passive summing resistor? I don't think a mixer is the right idea?

[Quackzed]

looks like the differences are mainly in the tone stack, otherwise the two 'channels'  are pretty similar. i might just look closely at the differences, and see if it isn't possible to just use one channel, rather than 2 parallel channels, and incorporate the differences from one to the other via a few switches, or possibly even one 3pdt switch.... the bright switch off/on left in, the deep switch left in, and one extra switch to change the 4n7 for a 47n as well as include / exclude the extra cap+resistor at the deep switch....the  250p vs 220p is pretty negligable ... otherwise, the 2 versions are the same... depends if you want single stomp change with preset switch selections ...
if so, you could just wire in a 3pdt like a bypass switch, where instead of bypass (off) its wired to the input output of the 2nd channel
like an a/b setup... input to switch top lug to input of ch1 bottom lug to input of ch2  and next row top lug return from ch1 bottom lug return from ch2 and center lug out to jack...

[mth5044]

Quackzed,

Thanks for the response. You are right, it would be pretty easy to just put the differences on some switches and only have one. However, I didn't plan on putting this into a stompboxes; rather a preamp to put onto a recording board. So it could be possible to to get a 3 or 4PDT switch and switch between the different values, but I think it might be worthwhile to be able to jumper channels (or atleast fun to mess around with). In which case, both would preamps would need to be happening at the same time.

Another consideration I was thinking about was just having the output of each preamp avaliable, then put a dual input on a cab sim (which happens to be a 4x10 cab sim  ) and have at it like that. I am looking at the original schematic and trying to figure out how they are being summed.

[bassmannate]

Here it is, no layout but should be quite simple on perf/stripboard.
I did this in 2006 :  http://www.aronnelson.com/gallery/main.php/v/Martys-layouts-and-photos/BassBoy59V1_1.jpg.html?g2_imageViewsIndex=1

Sounds pretty darn good.

MM.

Just out of curiosity, does anyone know what this schematic sounds like on bass?

[mth5044]

Bump for any ideas on how to make the two play nicely together when the inputs played by themselves and when jumpered. Simple summing resistors? Any specific values? Thanks!

[tasos]

Thanks for all the recommendations. I got some of ideas off the the links posted and the ROG Fetzer thing and came up with this schematic based on the bassman 135.
Original schematic -> http://www.thevintagesound.com/ffg/schem/bassman_135_schem.jpg



But I'm not sure how to bring the two together. Should I just use a passive summing resistor? I don't think a mixer is the right idea?

will you make a pcb for it?