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DIY Stompboxes => Building your own stompbox => Topic started by: tcobretti on June 09, 2006, 03:07:05 AM

Title: The Octo-Booster
Post by: tcobretti on June 09, 2006, 03:07:05 AM
Ok, I've been reading up on octave fuzzes trying to understand them, and it occurred to me to basically tack the transformer/diodes from a tycho octavia onto a booster in an attempt to come up with a relatively clean octave.  While I am positive that many have done this before, I hadn't seen a posted schematic for it.  What I came up with works pretty well and is riduculously simple.  It also keeps the octave even when you roll back significantly on the guitar's volume knob.  I would love any comments from you guys on how to maximize the octave while keeping the signal fairly clean and the parts count low.

(http://the23rdcentury.com/octobooster.jpg)
Title: Re: The Octo-Booster
Post by: trevize on June 09, 2006, 03:22:53 AM
you will probably hear the octave more if you roll back both volume and tone knob!

very nice btw! i'm trying a lot of octave boost/fuzzes in this period and i will try also this one.

but i'm more intested in the ones that don't use a transformer, like the rambler/cicada
(i recently did a layout for it http://www.diystompboxes.com/smfforum/index.php?topic=45990.0 (http://www.diystompboxes.com/smfforum/index.php?topic=45990.0))
Title: Re: The Octo-Booster
Post by: cab42 on June 09, 2006, 03:24:02 AM
Sounds interesting. 

I have seen an article on something almost similar to this, where the transformer part of the octavia is tacked to a Tubescreamer type circuit (Son of Screamer?) with good results. I have thought about adding it to my Tonebender NPN SI.

As far as I remember the article was called Octave Screamer by Scott Schwartz (not shure of spelling). I can check it if you are interested.

Regards

Carsten



Title: Re: The Octo-Booster
Post by: tcobretti on June 09, 2006, 03:28:00 AM
I know what you mean about the tranformer, but after building this I'm starting to think that the transformer is the way to go.  It's just so easy!

I've seen the octave screamer, but haven't built it.  It does look pretty cool.  I've been really into my Mayer Octavia.  I put off building it for a long time because I had a Scrambler, but I am really impressed with the Octavia.
Title: Re: The Octo-Booster
Post by: idiot savant on June 09, 2006, 04:08:07 AM
Ok, I've been reading up on octave fuzzes trying to understand them, and it occurred to me to basically tack the transformer/diodes from a tycho octavia onto a booster in an attempt to come up with a relatively clean octave.  While I am positive that many have done this before, I hadn't seen a posted schematic for it.  What I came up with works pretty well and is riduculously simple.  It also keeps the octave even when you roll back significantly on the guitar's volume knob.  I would love any comments from you guys on how to maximize the octave while keeping the signal fairly clean and the parts count low.


great work, nice small parts count, i'm going to have to build this one. check out tim escobedo's transformer octave circuits, in particular the psychtar has a clean octave (relatively speaking) to it, somewhat similar to your design.

http://www.geocities.com/tpe123/folkurban/fuzz/snippets.html
Title: Re: The Octo-Booster
Post by: jmusser on June 09, 2006, 03:41:58 PM
The Titan Booster with the Titan Octave attachment will get you ther, and I'm guessing so will the Octave Screamer. Your's is simpler than either one though.
Title: Re: The Octo-Booster
Post by: tcobretti on June 09, 2006, 10:23:46 PM
I threw this together for the stripboard guys:



(http://the23rdcentury.com/octobooster vero.jpg)
Title: Re: The Octo-Booster
Post by: Seljer on June 10, 2006, 03:36:39 AM
I think you're missing a cut trace there on the 2nd row up between the resistor and jumper, as +9v is shorting directly to ground
Title: Re: The Octo-Booster
Post by: tcobretti on June 10, 2006, 11:08:20 AM
You're right, I fixed it.  Thanks very much for checking my layout!
Title: Re: The Octo-Booster
Post by: SGdan on July 10, 2007, 08:41:23 PM
sorry about the dumb question, but how many ohms is 50R?
Title: Re: The Octo-Booster
Post by: tcobretti on July 10, 2007, 10:14:36 PM
50 ohms.
Title: Re: The Octo-Booster
Post by: Dragonfly on July 10, 2007, 10:30:39 PM
A+ for you Travis.

You know I love those simple circuits. :)
Title: Re: The Octo-Booster
Post by: tcobretti on July 10, 2007, 10:37:42 PM
I came up with this years ago, and I honestly don't remember how very well it worked.  I've been meaning to throw it together again and see how it worked. 

If memory serves, it was ok clean, but was nice before a fuzz or distortion.
Title: Re: The Octo-Booster
Post by: rockgardenlove on July 11, 2007, 07:23:51 AM
I think some dirt is unavoidable with a circuit using a transformer like this...due to the way it takes the wave and rectifies it so that both sides are positive and negative and a new ground reference is created.

That is, if that is actually how it works.  I kinda came up with that.  Quite possibly very faulty theorizing.
Title: Re: The Octo-Booster
Post by: YouAre on July 11, 2007, 08:12:42 PM
is it possible to isolate and remove the "boost" portion, and replace it with the AMZ mosfet boost? I already have one of those.

ALSO, how much "wiggle-room" is there on the 50 ohm resistor, cause i may not have one of those laying around.

and finally, when it comes to the transformer, is there a certain marker to know which way to orient it? i dont see the primary marked on either the schem or layout. so does either orientation work?

thanks,
murad
Title: Re: The Octo-Booster
Post by: tcobretti on July 11, 2007, 08:48:24 PM
You could try it after the Mosfet booster, I would imagine it'll be about the same.  That mosfet stage is just a super simple booster.

I think the 50R could be replaced with 100R with no problems.

The primary is toward the output side.

Title: Re: The Octo-Booster
Post by: YouAre on July 11, 2007, 09:04:22 PM
You could try it after the Mosfet booster, I would imagine it'll be about the same.  That mosfet stage is just a super simple booster.

I think the 50R could be replaced with 100R with no problems.

The primary is toward the output side.



so where would be the cutoff for the booster? is it this 100uf cap?
Title: Re: The Octo-Booster
Post by: tcobretti on July 11, 2007, 10:23:32 PM
Yes, the booster ends after the cap.  All you would have to do is tack the transformer and two diodes on the end of your booster, but the booster's volume control might screw things up, so it would be better to put it directly after the booster and put the volume control after the diodes as in the schematic above.  You might want to change to a large output cap on the booster as well; you want as much signal as possible to reach the transformer.

I just breadboarded this, and updated the schem.  I am really surprised at how much I like it.  It does a decent octave, and sounds not unlike the SHO when being used as a booster.

However, I tried the 100R resistor on the drain of the Mosfet, and the resistor got very hot, so I think a smaller value is a good idea.  Maybe 50R to 22R.
Title: Re: The Octo-Booster
Post by: Dragonfly on July 12, 2007, 03:32:50 PM
Yeah, the booster circuit works really well as a standalone booster...it has nice tone, and a reasonably good amount of boost. Ive built it in one form or another over the years, and hacked it into various circuits. I like a output cap between 1uf and 10uf, and an input cap from .022uf to .1uf for basic booster usage. I add a small (47pf) cap to ground at the beginning of the circuit to A) shave some extreme high end off, and B) send stray radio signals to ground, and add a 47uf - 100uf cap from +9V to ground in case you hook it up to a noisy power supply. As a standalone boost, I havent had any issues using a 100 ohm resistor from +9V to drain, but smaller certainly wouldnt hurt. I would also suggest adding a 9.1V-12V zener diode for mosfet protection, as in the AMZ mosfet boost.

Further, heres a suggestion for the octave circuit....try running the boost at 18V and see if that helps give a better, cleaner octave. I havent tried it, but it may help a bit.

Here are some related schematics of interest....Basically the same schemo....also, a page that has a few interesting things, including a "mosfet proximity sensor circuit".

http://www.uoguelph.ca/~antoon/gadgets/mostest.htm

(http://diyaudioprojects.com/Solid/ZCA/sch_ZCA.png)

(http://img.villagephotos.com/p/2006-11/1226934/CLASSAMOSFETAMPLIFIER.GIF)



Title: Re: The Octo-Booster
Post by: Mark Hammer on July 12, 2007, 03:42:39 PM
I would think the booster-alone setting would sound less than optimal with the diode in the signal path.  Maybe the smarter thing to do is to wire up a SPDT switch with the common going to the input of the volume pot.  In one position, the switch makes the connection to the "upper" diode.  In the other position, the switch breaks the connection to that diode and shunts the remaining diode such thatthere is a straight wire path between the transformer and the volume pot.
Title: Re: The Octo-Booster
Post by: jaytee on July 12, 2007, 04:11:35 PM
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?
Title: Re: The Octo-Booster
Post by: tcobretti on July 12, 2007, 10:41:37 PM
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.
Title: Re: The Octo-Booster
Post by: tcobretti on July 15, 2007, 04:09:11 PM
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_no_boost.mp3)

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

http://aronnelson.com/gallery/albums/album166/Les_Paul_Plexi_Octoboosted.mp3 (http://aronnelson.com/gallery/albums/album166/Les_Paul_Plexi_Octoboosted.mp3)
Title: Re: The Octo-Booster
Post by: John Lyons on July 15, 2007, 06:58:46 PM
Those sound nice Travis! I like the rolled back tone and volume ones to get that ringing Hendrix band of gypsies sound.

John

Title: Re: The Octo-Booster
Post by: tcobretti on July 15, 2007, 07:10:29 PM
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!
Title: Re: The Octo-Booster
Post by: axg20202 on August 04, 2007, 09:40:12 AM
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?

(http://i204.photobucket.com/albums/bb75/axg20202/Octoboosterpartslayout.jpg)


Note that the 47pF cap to ground, the reverse polarity protection diode and the power filtering cap are optional.
Title: Re: The Octo-Booster
Post by: axg20202 on August 06, 2007, 04:20:07 PM
BUMP. Anyone?
Title: Re: The Octo-Booster
Post by: tcobretti on August 06, 2007, 11:00:28 PM
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!
Title: Re: The Octo-Booster
Post by: axg20202 on August 07, 2007, 02:58:39 AM
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.

Title: Re: The Octo-Booster
Post by: Jaicen_solo on August 07, 2007, 03:04:29 PM
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.
Title: Re: The Octo-Booster
Post by: tcobretti on August 07, 2007, 07:12:38 PM
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.
Title: Re: The Octo-Booster
Post by: predok13 on August 20, 2016, 04:00:39 PM
Is it possible to make octave down mod for this scheme?
Title: Re: The Octo-Booster
Post by: chuckd666 on August 22, 2016, 11:37:41 PM
Getting octave down is a little more sophisticated than this. Have a search in the forum for some more octave down projects.