Mosfet

[schotness]

quick question or 2 for you all

I've heard a couple of mentions about a mosfet clean boost pedal

1 if I boost the volume, does that make the breakup from clean to driven later/louder too

2 does anyone know where i can buy one of these pre-made, I'm cack handed & a bit dangerous with electrics & soldering irons

[ricach]

The idea of a clean boost pedal is not to inject an already distorted signal into the amp - but more to allow the amp (tubes) to start breaking up earlier with a clean signal - thus less headroom, but louder. At least this is my interpretation since I've never really used one myself.

 

I do remember seeing one of those available via custom made, but can't recall where. But I'll look around.

[rafaelh]

Don't know if this is the one you're referring to.

 

http://fulltone.com/stpframe.html

 

( Have to click on the "FullDrive 2 MOSFET" )

 

I had one for a couple of weeks before taking it back....over priced and over rated IMO.

 

Anyhow pretty much what ricach said as far why use, or how, an OD pedal...at any rate, LOL...right or wrong, the way I use one.

[ricach]

No its not the one I was thinking of, and neither is this I just came across

 

http://www.proguitarshop.com/product.php?ProductID=929&CategoryID=15

 

but probably worth checking out.

[Robo]

A clean boost is just another gain stage. They can be used to boost volume or to overdrive the frontend into even more preamp distortion, which can also be used to hit the power stage harder for more power tube and output transformer saturation. FETs are nicer than most SS gain as they react more like a tube than TTLs and other transistors. Because of this their distortion characteristics are superior to other transistors, diodes and such. They have other advantages too, especially MOSFETs, tho MOSFETs are sensitive to damage from static charges.

[m-theory]

Fulltone doesn't make a clean boost. They make a "fat boost," which is the same as Jack Orman's "minibooster." It uses JFET transistors to boost the signal, but in doing so, it also introduces some distortion, which is why it's NOT a "clean boost." A clean boost does nothing but boost. The Fulldrive pedal, including the latest version with mosfets, is a modified tube screamer. In the mosfet version, mosfets are used as clipping diodes, instead of the standard 1N914 or 4148 signal diodes.

 

The homebrew pedal on the posted link is PROBABLY Orman's mosfet boost, Catinbread's Super Chili Picaso is definitely a commercial offering, and the zvex super hard on is very similar as well. Interestingly, zvex merely cascaded this circuit for the super duper, and added another stage of cascade (along with a tone stack) for the box of rock.

 

That said, it's an incredibly simple circuit and a snap to build on your own, especially when using a ready-made PCB, such as those available from generalguitargadets.com, muzique.com, or tonepad.com. buildyourownclone.com also sells a complete kit that combines three different boosts into one pedal. If you build a mosfet or minibooster yourself, you can do it for about $40 or so.

 

As for what a clean boost will do, it simply boosts the guitar signal into the amp. In the case of the mosfet boost, that boost is about 35db, which is more than sufficient to send any tube amp into overdrive. If you run it at minimum setting, it becomes a very potent buffer. Slight throttle increases will result in volume increases, BUT, at some point, you'll also be driving the preamp tube into distortion.

 

I use a clean boost and/or a minibooster for leads. Both give significant boost and make the amp burst and bloom, but the minibooster will fatten things up as well, as it adds some distortion to the signal. Both react very well to guitar volume levels, so you CAN crank the pedal and ride the guitar volume to go from a hairy clean to seering, singing lead tones, with the twist of the guitar volume. However, you WILL get some hiss, because the signal is being boosted significantly even with the guitar volume rolled back, and you will likely NOT get a pristine clean.

[Robo]

Fulltone doesn't make a clean boost. They make a "fat boost' date='" which is the same as Jack Orman's "minibooster." It uses JFET transistors to boost the signal, but in doing so, it also introduces some distortion, which is why it's NOT a "clean boost." A clean boost does nothing but boost. The Fulldrive pedal, including the latest version with mosfets, is a modified tube screamer. In the mosfet version, mosfets are used as clipping diodes, instead of the standard 1N914 or 4148 signal diodes.

[/quote']

I'm a little confused by this, are they using the MOSFETs for amplification, and distortion, by overdriving the FETs for the distortion, or using them like diodes, LEDS, for the voltage cutoff distortion, by just using the emitter and collector and disregarding the gate? I would think using MOSFETs for voltage clipping over regular diodes and LEDs would be quite expensive in the end, but I may be confused by the way that's worded. I'[m easily confused!

[m-theory]

You're mixing two different circuits up. The FULLDRIVE is a tube-screamer-based circuit that utilizes clipping diodes and an op-amp. The FATBOOST is a transistor-based booster.

 

In a tube screamer-type circuit, diodes are used to do the clipping, not the amplification. The amplifying is done by an op-amp. The typical TS used small signal diodes, such as 1n914 or 4148. You can also use Schotkey diodes, LEDs, the diode side of mosfets, or just about any other diode that you want. They all produce slightly different clipping tones, because they all have different specs and react differently to signal input.

 

The reason mosfets are used sometimes is because they tend to sound and feel very tube-like when they clip. Yes, mosfets are higher in cost than standard signal diodes, but you have to remember that we're talking about pedals that run anywhere from $150 to $300 in a market in which hype sells. If a mosfet version of your TS design costs you a quarter more to build, but can be sold for dollars more, and will sell far more due to internet chatter and hype, that's what it's all about.

[Robo]

You're mixing two different circuits up. The FULLDRIVE is a tube-screamer-based circuit that utilizes clipping diodes and an op-amp. The FATBOOST is a transistor-based booster.

 

In a tube screamer-type circuit' date=' diodes are used to do the clipping, not the amplification. The amplifying is done by an op-amp. The typical TS used small signal diodes, such as 1n914 or 4148. You can also use Schotkey diodes, LEDs, the diode side of mosfets, or just about any other diode that you want. They all produce slightly different clipping tones, because they all have different specs and react differently to signal input.

 

The reason mosfets are used sometimes is because they tend to sound and feel very tube-like when they clip. Yes, mosfets are higher in cost than standard signal diodes, but you have to remember that we're talking about pedals that run anywhere from $150 to $300 in a market in which hype sells. If a mosfet version of your TS design costs you a quarter more to build, but can be sold for dollars more, and will sell far more due to internet chatter and hype, that's what it's all about. [/quote']

Ok, I was confused! I'm not familiar with Fulltone pedals. I am familiar with diodes and transistors. When I was going to community college for electronics and computers, one of my electronics classes had a semester project where we had to build any electronic device. I started out just building a simple transistor clean boost, then went with FETs for distortion, started adding gain stages, then diodes for clipping, then added LEDs. Kinda got carried away, all kinds of different distortion, switches and pots all over. Started adding power transistors. Constantly looking for bigger and bigger cases. Added more circuits with different FETs, TTLs for clean. Towards the start of the year we had to show a schematic of what we were going to build, at finals when we showed him what we had, he looked at mine, looked at my schematic, told him I should have updated it, but he was quite impressed. A bunch of different colored LEDs for different sounds. But I really liked the sounds from the different FET circuits. Didn't cost much to build. Made a decent little battery powered amp too, tho I eventually took that part back out. Don't even know where it's at anymore.

[Dr_Satan]

look at the HAMPTONE JFET amp

 

http://www.diyfactory.com/projects/fetboy/hamptone_fet_scan.jpg

[shartom]

Mosfets are sometimes used in the output stage of power amps. They are also used in the rotor control circuitry of xray machines. I actually saw one selfdestruct with rather dramatic results.

If you want a clean boost, there are many JFET circuits out there. The circuits are pretty simple, sort of along the lines of the EH LPB1.

I have a couple of DOD preamps that work well between my Tele and a Twin. It will definitely push the twin into overdrive.

On the other hand, it can be used between an acoustic that doesn't have a preamp built in and an acoustic amp or board.

They add very little color to you sound. You can drive long cables with them withou losing your highs.

[m-theory]

Not to take anything away from JFETs (or, in the case of the LPB, NPN transistors) as signal boosters, because they do boost signal very effectively, but they really don't do it very cleanly. They add grit, in a very pleasing way. Some of the most convincing solid state distortion circuits use cascading JFETs.

 

For CLEAN boosting guitar signal, I don't know of a better basic circuit than Jack Orman's "AMZ mosfet boost."

 

I'm not sure what your DOD box is, but if it's the 250, it's virtually identical to the MXR distortion +, which is an op amp-based (741) distortion/boost circuit.