Sadowsky Schematic?

[Fiorenza2]

Hey all,

I'm contemplating installing one of these, as they sound great, but cost too much.
I've done a search on Google, and apart from a couple of people claiming they have the schematic for the circuit, I haven't been successful in actually obtaining one. As far as I can tell, the circuit itself looks simple, and seems to be a JFET design, as there are a couple of JFET's on the PCB and there are no IC's.

Here's a picture of the board (albeit epoxied) to illustrate the matter:



Any help with regards to a schematic would be great, as building one from scratch would be a fun alternative to buying an off the shelf preamp.

Cheers!
Phil

[Matt P]

this also interests me, i'd love to fit a pre into one of my basses but don't have the cash at the moment (but have some soldering skill)
i'd be incredibly surprised if anyone has the schematic for the sadowsky pre though (or any of the other aftermarket pre's). I'd guess that the exact specs of these are a closely guarded secret (hence the black epoxy over the circuit).

but if anyone has a generic design for a preamp (2/3 band) then a link would be great, i'm prepared to have a go with building and tweaking and if i get anywhere i'll happily share my findings

matt

[Fiorenza2]

[quote name='Matt P' post='1338575' date='Aug 13 2011, 11:07 AM']this also interests me, i'd love to fit a pre into one of my basses but don't have the cash at the moment (but have some soldering skill)
i'd be incredibly surprised if anyone has the schematic for the sadowsky pre though (or any of the other aftermarket pre's). I'd guess that the exact specs of these are a closely guarded secret (hence the black epoxy over the circuit).

but if anyone has a generic design for a preamp (2/3 band) then a link would be great, i'm prepared to have a go with building and tweaking and if i get anywhere i'll happily share my findings

matt[/quote]

Hey Matt, from what I've heard the Sadowsky pre is based on an old Bartolini design, possibly a TCT. Can't find schematics for that either though... The best preamp I can find that is DIY friendly is this:

[url="http://www.albertkreuzer.com/preamp_onboard.htm"]Albert Kreuzer[/url]

but it's got a single "tone" control, as opposed to an actual EQ section. I'm sure someone with some electronics know how could adjust the design to accommodate this? Also being a FET based design, it may be close to a Sadowsky in sound.

[Pollinator95]

Schem for an Alembic F-2B (it has JFETs)


Perf layout


Vero layout



Some bass preamp (I don´t think it´s commercially available. It also has JFETs)



And a Fender tone-stack (it has a low output, so you might want to add a booster)



You can ask in the DIY thread in the Effects subforum, maybe someone will have a better answer.

Edited August 20, 2011 by Pollinator95

[ubersam]

[quote name='Pollinator95' timestamp='1313850410' post='1346413']


Some bass preamp (I don´t think it´s commercially available. It also has JFETs)



[/quote]
Hey all, first post here, anyway... fancy seeing my schematic posted here. I know this is an old topic but I just wanted to chime in. For anyone interested, this is essentially the FET-2B project posted at a DIY forum, but with modifications.

First, I designed my version to run on 18V for higher headroom (clean signal before clipping), also, higher output voltage (volume). The output of my version can drive the input of a power amp.

Second, I'm using J305 jfets instead of J201. The J305 has a higher V[sub]gs(off)[/sub] than the J201, which means the J305 can take a larger input signal before clipping.

Third, the tone stack i'm using is based on the Marshall tone stack topology instead of the Fender topology.

Fourth, instead of trimmers to set the fets drain voltage, the required drain and source resistor values are calculated for each fet for optimal biasing. This biasing method is based on the Fetzer Valve project at runoffgroove and Dimitri Danyuk's Triode Emulator paper.

So there you have it. BTW, I have since taken this schematic down as I have made some changes to it.