Nocentelli's JFET boost with Baxandall  [documentation]

Original effects with schematics, layouts and instructions, freely contributed by members or found in publications. Cannot be used for commercial purposes without the consent of the owners of the copyright.
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Nocentelli
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Post by Nocentelli »

A simple boost/preamp circuit I put together recently. The JFET starts to clip in a pleasingly smooth manner if you really dig in so the gain control allows you to set how hard you need to play to make this happen. The simple active two band EQ gives a nice range of tones for not many parts.
FETBoost_schem_nocentelli.bmp
FETBoost_schem_nocentelli.bmp (63.19 KiB) Viewed 5188 times
modman wrote: Let's hope it's not a hit, because soldering up the same pedal everyday, is a sad life. It's that same ole devilish double bind again...

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roseblood11
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Post by roseblood11 »

Nice. Do you see an advantage of this circuit over the Boss FA-1? The parts count is similar.

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Nocentelli
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Post by Nocentelli »

I think the JFET gives a certain je ne sais quoi that an op amp booster doesn't, i.e. mainly a little bit of distortion/compression on the edge of the notes when you hit the guitar hard. Apart from that, I had one single decent spec J201 left in my stash of through-holes that I wanted to make into something useful :lol:

Since posting the schematic, I have attempted to design a small and efficient veroboard layout and have (re)discovered that single op amps are terrible for efficient use of space. I've done another schematic for a transistor-based baxandall stage, which should be much easier to lay out nice and small. I'll post the new schem when I'm happy it works properly and sounds as good as the one above.
modman wrote: Let's hope it's not a hit, because soldering up the same pedal everyday, is a sad life. It's that same ole devilish double bind again...

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Nocentelli
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Post by Nocentelli »

FETBaxBJT_nocentelli.bmp
FETBaxBJT_nocentelli.bmp (53.94 KiB) Viewed 5038 times
modman wrote: Let's hope it's not a hit, because soldering up the same pedal everyday, is a sad life. It's that same ole devilish double bind again...

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Nocentelli
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Post by Nocentelli »

Verified, and I'm quite pleased with the result: A 1kC gain pot is highly recommended for smooth transition from totally clean to pleasantly gritty throughout the whole rotation. If i played a strat/tele all the time I might be tempted to omit the gain pot (jumpered flat-out) and just use the volume pot to adjust the grit. I'm going to try it out again in the near future with some other FETs as I still have some decent spec'd thru-hole 2N5457s left.
FETboost_vero_nocentelli.gif
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modman wrote: Let's hope it's not a hit, because soldering up the same pedal everyday, is a sad life. It's that same ole devilish double bind again...

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poiureza
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Post by poiureza »

Thanks a lot

May I ask what makes a JFET "decent spec'd" ?
Is it a matter a resistance value ?

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brobri
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Post by brobri »

Building this from the second schematic. Just a heads up, the 100nF cap is missing from the layout, and the 47uF electrolytic off of the BC109 is labeled as 22uF on the layout. Cheers!

~bb
Last edited by brobri on 03 Mar 2023, 22:08, edited 1 time in total.

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roseblood11
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Post by roseblood11 »

Logarithmic pots in a baxandall?

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brobri
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Post by brobri »

I'm reading that Baxandall = active = log pots, where James = passive = lin pots, but I don't know enough to know if the BC109C at the end makes this active or just buffered output or not. And, I'm seeing more schematics with lin (or no taper defined) than log. Can anyone add any clarity?

-bb

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bajaman
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Post by bajaman »

should be linear pots ;-)
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Post by brobri »

Thanks! These 9mm pots are a pain to wire and I didn't want to breadboard it again. Any idea where the idea of logs in a Baxandall might've come from? The active vs passive story sounded like a plausible narrative to me.

-bb

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