Transistorized Fender twin pre amp section

[Pat F]

Ive seen a schematic for this on line- it seems pretty straight forward, but I'm not skilled at translating schematics  to strip board yet. The schem shows it powered by 18-30v so it could be powered by a wall transformer- avoiding high voltage mains work
It uses 4 2n3819 n channel FETs, 8 resistors and 8 caps so it should be fairly compact.
If this request is a possibility I would be very grateful and would try to build it for verification straight away.
Thanks,
Pat

[IvIark]

Have you got a link to the schematic?

[Pat F]

Its on www.redcircuits.com/pg 120

It's actually not specifically a twin but a fender black face which is fine
I actually want to build it to replace my failing fender 75 head
Thank you very much for the quick reply and consideration
Pat

[IvIark]

This should cover it.  Let me know how it sounds and if it's worth adding I'll put it on the main blog.

[Pat F]

Wow that was quick,thanks!
I'm not clear on the the way the bass pot is wired in, would it be possible for you to diagram the tone stack wiring?
I've got all the parts but the transistors-are there  any common subs for 2n3819?
Also do you think that 250k Lin pots will sub for the 220s?
Thanks again for your time and this layout
I'm going to get started right away!
Pat

[IvIark]

Bass 2 and 3 needs to be linked to Treble 1, Bass 1 needs to be linked to Mids 2 & 3. Just daisy chain the wires, so you will have two wires soldered to Treble 1, one will do to the Treble 1 connection on the board, the other will go to Bass 2 & 3 (just take the wire to either Bass 2 or Bass 3 then wrap it round the other lug or make a small link from a resistor cut off or something similar so both lugs are connected).

Try any JFETs you have in there.  J201, 2N5457, 2SK117, 2SK170 etc but watch the pin order and twist the pins over if necessary.

[IvIark]

Incidentally this is quite similar to the Catalinbread Formula No 5, but that one has a simplified tone control and an added gain control.  Check that one out if you want something similar.

[Pat F]

Sorry never mind about the bass pot connection, I see your description.
Thanks. Again
Pat

[Pat F]

Hello again, I finally built this after getting the last few correct parts. It works!, but not quite as well as I had hoped. The tone stack works as expected but the bright switch doesn't seem as effective as the one on my Fender 75. The gain is really low unless the input is buffered, and even still not what I was hoping for. I did try it w/ a booster between it and the power amp, which brought it up to passable living room volume.
 It doesn't seem to like a booster in front of it though. Maybe I need a booster with more gain than the stratoblaster i tried to use. Also the schem called for 18-30v, but this layout uses 9v, would it help to use a voltage doubler daughter board or ganged 9v batteries?
Thank you again for creating this layout for me to try, I was elated when I plugged in and it even worked at all!
Any suggestions or comments are totally appreciated, my goal is to use this to drive a 100W SS power amp into 2x12 @ 8 Ohms