The Octo-Booster

[jaytee]

If you want the drain of the mosfet to be around 1/2 supply voltage I make that 90mA with a 50 ohm resistor and 405mW dissipation in the mosfet. The 2N7000 is rated at 400mW max in the datasheet I have. I guess it would get pretty hot. Wouldn't it be better to use a bigger drain resistor and bias it at lower current?

[tcobretti]

You guys all make great comments.  I left off power filtering to keep the circuit as ridiculously simple as possible, but for many it will be necessary.

I based mine off the Tony Van Roon schem, and so I picked the 50R value randomly.  The mosfet gets warm, as does the resistor when running the 50R.  With the 100R, the resistor got too hot to touch.  With no resistor, you melt the mosfet.

I found the trimpot to be unnecessary with every 2N7000 I tried, so I omitted it from my Octobooster schem.

Mark, you are right, I honestly didn't know better when I built it, and didn't think about it when I just revisited it.  The end user will likely want to switch out both diodes.  I personally might do it by using a SPDT, center lug to output pot, bottom lug to the diode junction, top lug to the transformer output.

Andy, the 18v idea is interesting, and I have never messed around with running circuits at different voltages.  I'll have to try it out.

I am thinking about cascading this booster and posting a schem and layout and calling it the NO-SHO.  It's certainly not the same sound , but it's in the very general ballpark.

[tcobretti]

I made some sound clips of the last schem I posted.  This is my Les Paul Custom into my Line 6 set for Plexi.  I switch the P/Us a bit is I play, but the Octoboosted clip is mostly front P/U, first with the tone all the way up, then I turn it down, then I switch to the back P/U.

http://aronnelson.com/gallery/albums/album166/Les_Paul_Plexi_no_boost.mp3

http://aronnelson.com/gallery/albums/album166/Les_Paul_Plexi_Boosted.mp3

http://aronnelson.com/gallery/albums/album166/Les_Paul_Plexi_Octoboosted.mp3

[John Lyons]

Those sound nice Travis! I like the rolled back tone and volume ones to get that ringing Hendrix band of gypsies sound.

John

[tcobretti]

Thanks, John.  I really just realized how cool this thing can be.  I set it up for its output volume to be at about unity, then ran it into my different fuzz pedals.  It basically turns every fuzz into an octave fuzz, while introducing very little if any noise.  It sounded insane running into my Ge TB MKII, and also great into my BMP and my Axis Face.

I highly, highly recommend this pedal for someone who wants a fairly clean octave, but also has a fuzz they love that they would like to augment with an octave.

I am definitely gonna box this one and it will likely take the "octave" slot on my pedal board.  I'm really glad SGdan reminded me about this thing!

[axg20202]

I hope you don't mind tcobretti, but I took the liberty of preparing a PCB layout for the Octo-Booster, based on your schemo but also adding in some extras based on comments in this thread. Can someone give it a second pair of eyes to check that it is correct please?




Note that the 47pF cap to ground, the reverse polarity protection diode and the power filtering cap are optional.

[axg20202]

BUMP. Anyone?

[tcobretti]

I thought I had responded. It looks right to me, but in another thread someone was having trouble getting it to work, so I think adding the 100k trimpot back in might be a good idea.  I also changed the switching so you get a cleaner boost as Mark recommended.  So, check the schem on the first page for version 1.2.

Thanks for the interest, and please let me know how it works for you!

[axg20202]

Thanks. I'll add the trimmer back in. I already included pads to allow diode switching, so these should be OK. If it checks out OK, I'd be happy to share the actual PCB file with the group (as long as you are) and an updated parts layout.

[Jaicen_solo]

This might seem like a silly question, but have you tried subbing in something like a 2N3904 in place of the Mosfet??
The biasing might need a tweak, but I imagine that it would work. I don't know about the mosfets, but the 3904 can sink a lot of current before it gets hot, so it might be worth a look.

[tcobretti]

As far as the layout, I am cool with whatever you want to do.

About the transistor, I hadn't tried that because I believed the biasing was wrong for a BJT.  However, I know very little.

[predok13]

Is it possible to make octave down mod for this scheme?

[chuckd666]

Getting octave down is a little more sophisticated than this. Have a search in the forum for some more octave down projects.