This is a JFET version of one of the Benson amps, which is I think why the pedal doesn't really have a proper name.
It's hard to find a B2M pot for the bass control, but you can use a dual B1M pot and gang the two sides together to reach 2M. Check the Pedal PCB 'Son of Ben' build docs to see how.
Or you can change somme values and use a 1M pot instead, see this post for values.
Like any pedal using J201 FETs, make sure you get proper ones, or it just won't work very well (I naively tried cheap J201 FETs once - it sounded awful).
There's a thread on Freestompboxes where Mr Benson jumps in with advice too. Nice guy... note: the schematic on freestompboxes has a 330pf cap listed instead of the 250pf cap on the Pedal PCB schematic. The 250pf value was supplied by Benson.
BENSON PREAMP - POINT TO POINT LAYOUT
Hey Andy - Planning to build this tomorrow. Do you know if it's been verified? Many thanks
ReplyDeleteTony - Preston UK
Hi Tony. I haven’t built this version myself. Let me double check against the schematic. This is based off a working vero layout, but I will look again just to be sure.
DeleteHave you done point to point before? This will be a bit fiddly
Hey - I went over the schematic again. It looks fine to me.
DeleteUsual J201 warning for through hole parts. If yours don’t come from a reputable source, there’s a good chance that they will not behave as expected. Confirm pin out before soldering.
Hi - Thanks for your response
ReplyDelete. I've done a few vero but never p2p so I am looking forward to the build experience. I'm prepared for fiddling things, sourced some legitimate jfets and a 2M pot (Mouser) So good to go. How come there is not trim pot for the first stage? Will offer a build report when done - Many thanks again.
Tony
Great. I did the layout without a trimmer on the first JFET as that’s what the original schematic on FSB listed. The first stage is basically a straight boost, so not much to really to tune there.
DeleteI would recommend testing the bias resistor before really committing to soldering in properly. If you don’t have a breadboard, maybe just tack it on lightly with a bit of solder first.
Good luck, hope it goes well.
Ta - I built a sweet decade resister a few years ago that will come in really useful biasing it / them all. If I can find the right fet and resistance combo I might do away with the trim pots. Set and forget. I suspect dailing in that right spot might be different when I apply a fixed resistor. Will experiment a little before I commit.
ReplyDeleteYour a cool guy - thanks for your support and work with the builder community.
Happy to help where I can.
DeleteHi Andy - Your schematic worked first time - absolutely brilliant !
DeleteTo my ears it's ready to be boxed up but to an audiophile maybe not.
There is a high pitched whirling going on seemingly around the volume pot. Turn all pots ACW apart from the volume. When I now turn the volume anywhere between centre point the whirling occurs. Louder the further away from mid point you are either direction.
It's a very background thing. Likely my build quality. Consider it verified .
The old ladies at church will love this !
Regards
Tony
Glad that it fired up straight away.
DeleteUnusual that you have that sound though. It may be picking up external noise and amplifying it as it’s not insulated in a box.
Usually I’d see if it does the same thing running off a battery, if it doesn’t it’s probably related to power supply
Also does this only happen with guitar plugged in, or no signal source (sometimes things only make noise in either circumstance)
Single coils or humbuckers?
Andy
https://www.pedalsnake.com/blog/category/the-noise-manual/
DeleteThis is really handy - despite the look of the website, the guy is an expert on noise. NASA level expert….
Morning - Just noisy psu's! Once boxed up it will resolve I hope. This is a brilliantly dynamic pedal. Going to have some fun! That website was really useful. Thanks.
DeleteTony