The Octo-Booster

tcobretti · 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.

trevize · 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)

cab42 · 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

tcobretti · 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.

idiot savant · June 09, 2006, 04:08:07 AM

Quote from: 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.

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

jmusser · 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.

tcobretti · June 09, 2006, 10:23:46 PM

I threw this together for the stripboard guys:

Seljer · 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

tcobretti · June 10, 2006, 11:08:20 AM

You're right, I fixed it. Thanks very much for checking my layout!

SGdan · July 10, 2007, 08:41:23 PM

sorry about the dumb question, but how many ohms is 50R?

tcobretti · July 10, 2007, 10:14:36 PM

50 ohms.

Dragonfly · July 10, 2007, 10:30:39 PM

A+ for you Travis.

You know I love those simple circuits.

tcobretti · 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.

rockgardenlove · 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.

YouAre · 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

tcobretti · 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.

YouAre · July 11, 2007, 09:04:22 PM

Quote from: 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.

so where would be the cutoff for the booster? is it this 100uf cap?

tcobretti · 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.

Dragonfly · 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

Mark Hammer · 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.

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