anyone know a good clean booster circuit?

[tone_crafter]

I'm trying to find the schematic for a good, very clean booster curcuit. The only control it needs to have is volume and it only needs to have a small volume change. Needs to be unity gain at min value. It's for matching volumes of different guitars.

Someone has suggested I use channel 1 of a zvex super duper pedal but I can't find the schematic for it anywhere.

Any ideas?

[petemoore]

Mosfet Boost does that, starts at unity, cleanest booster built I have.
 A jfet'll probly do what you want real good too, checkout General Guitar Gadgets or Runoff Groove. Stratoblaster is real clean. I like the Jfets.
 4 out of 5 volume controls look the same, view some and look for a pot, near or at output, signal goes in one end, out the other, and the bottom connection to ground. You can 'throw' a variable resistance/voltage divider [pot] on any circuit to turn in down.

[idiot savant]

there are approx. 10,638,924 schematics available for a clean boost :lol:

(a very few)highlights:
AMZ
http://www.muzique.com/amz/mini.htm
http://www.muzique.com/schem/mosfet.htm

dragonfly
http://aronnelson.com/gallery/album18/SPARKLE_BOOST_LAYOUT

ROG
http://runoffgroove.com/fetzervalve.html

[Satch12879]

Non-inverting IC amplifier with gain is where it's at.

[tone_crafter]

I might try the AMZ MOSFET booster. If I wanted to decrease the maximum gain would i put a resistor in series with the 5K pot and lower the value of the pot?

Anyone know the gain difference between single coil pickups and humbuckers? Its gotta be small im sure.

[pbrommer]

You could always use a non-working EA Trem from runoffgroove as a nice clean boost

[R.G.]

Almost every time someone types in "booster" it's been preceeded by "clean". They then launch off into wondering whether the various things advertised as boosters are applicable.

There are NO "clean" boosters that involve single devices, whether MOSFET, JFET or bipolar. The best those things can get to is a few percent distortion. That may be what the requester really wants, but it may not be, too.

MOSFET boosters like the zvex SHO, the AMZ MOSFET booster, or any of that ilk are inevitably going to not be particularly clean. They do have quite high input impedance, and so they don't lose much treble. People seem to somehow mix up keeping treble with being clean.

You want clean, you use a non-inverting opamp buffer. If you also want the treble left in, you use an opamp that has a high-ish input impedance; a JFET or MOSFET input opamp works fine. JFET with a 1M or over input bias resistor does that pretty well. There are tricks with opamps to get the input impedance to well over 500M, if that's useful.

"Clean booster" is not equal to any of the several single device booster schemos.

[tone_crafter]

You want clean, you use a non-inverting opamp buffer. If you also want the treble left in, you use an opamp that has a high-ish input impedance; a JFET or MOSFET input opamp works fine. JFET with a 1M or over input bias resistor does that pretty well. There are tricks with opamps to get the input impedance to well over 500M, if that's useful.

Thats really what I want. I simply want a circuit to match pickup levels and for it to adjust the signal as little as possible (little distortion and frequency cut). It therefore only has to have a small variation of gain (depending on how pickups vary in volume).

Do u know anywhere I can find a schematic because I have seen heaps of inverting opamp circuits and they seem far too complex for what i want to do. When I first decided to build this booster or what ever you want to call it I was thinking of using opamps but im resonably new to this and have no idea what to use. If anyone has any ideas can you post a link to the schematic

[aron]

I would use an op amp circuit myself.

[tone_crafter]

I found this circuit but its designed to have 2 pickups plugged into it via a stereo plug.

http://users.chariot.net.au/~gmarts/pickcomb.htm
(see about half way down the page for the pickup compensator)

The creator said if I take out the .0056uF capacitor that will get rid of the high cut. Any ideas how I could modify this circuit so its simply a boost circut? Also where would i place the pot to adjust the level (in the feedback of the first or second opamp)? Or would I take the first one out all together?

As you can prbably tell I'm very new at this. Would this circuit after modified do what im looking for? Any suggestions?

[aron]

Try this:

http://diystompboxes.com/pedals/schems/shakaboost.jpg

Use film caps, metal film resistors and a good op amp.
The volume pot can be anything from 10K up.

[tone_crafter]

Ok that looks the best so far. Can I leave out the 220pF cap in the feedback. Doesn't that form a high pass filter? Also what does the 10uF cap do at the top? Do i connect -Vcc to ground and +Vcc to 9V?

[Khas Evets]

I want to hear more about the 500M input impedence from R.G. What's the trick, bootstraping a non-inverting opamp?

[davebungo]

Almost every time someone types in "booster" it's been preceeded by "clean". They then launch off into wondering whether the various things advertised as boosters are applicable.

There are NO "clean" boosters that involve single devices, whether MOSFET, JFET or bipolar. The best those things can get to is a few percent distortion. That may be what the requester really wants, but it may not be, too.

MOSFET boosters like the zvex SHO, the AMZ MOSFET booster, or any of that ilk are inevitably going to not be particularly clean. They do have quite high input impedance, and so they don't lose much treble. People seem to somehow mix up keeping treble with being clean.

You want clean, you use a non-inverting opamp buffer. If you also want the treble left in, you use an opamp that has a high-ish input impedance; a JFET or MOSFET input opamp works fine. JFET with a 1M or over input bias resistor does that pretty well. There are tricks with opamps to get the input impedance to well over 500M, if that's useful.

"Clean booster" is not equal to any of the several single device booster schemos.

One could argue that any booster no matter how it is made will not be particularly "clean" if all you are running off is a single 9V supply.  If it's clean it probably aint boosting very much. (Well, probably not much more than 10-15dB - I've measured close to a volt pk-pk out of my guitar and I suspect humbuckers will produce more than this quite easily).

...and if you are boosting by quite a bit, you are probably into pre-amp overdrive mode anyway (typical MXR Micro-amp into JCM800 territory I imagine).  So does it really need to be that clean??

[R.G.]

I want to hear more about the 500M input impedence from R.G. What's the trick, bootstraping a non-inverting opamp?

Yeah, FET input, bootstrapped. It's possible to bootstrap an inverting input, but it's trickier. As a practical matter, any input impedance over a few megohms is going to make almost as many problems for you as it solves in terms of noise pickup, sensitivity to dust, and amplifying piezoelectric and triboelectric noise from the insulators that connect to the input. You can easily begin to sense noise pickup from microphonic guitar cords.

One could argue that any booster no matter how it is made will not be particularly "clean" if all you are running off is a single 9V supply. If it's clean it probably aint boosting very much. (Well, probably not much more than 10-15dB - I've measured close to a volt pk-pk out of my guitar and I suspect humbuckers will produce more than this quite easily).

In fact, one would *have* to argue that. Fact is, a 12AX7 tube input is only linear for about 1.7V peak input as they're biased in most guitar inputs.

But I believe that what most people like about boosters is not the distortion the booster produces (that's why they always say "clean") but rather the distortion of overdriving that 12AX7 grid.

Triodes have a trick that most people don't know about consiously, but use unconsciously. When the grid is driven positive WRT the cathode, the grid conducts. A 12A?7 tube goes from megohms down to around 5K or so. If your driving impedance is high, that looks like a brick wall, and the signal flat-tops right there.

However, the triode can still conduct more in the plate circuit if you can drive the grid more positive. It's softly nonlinear there.  So the trick is to drive that super-high-impedance triode input from a low impedance driver. What that does is to pull the grid more positive than the cathode, even if it doesn't want to go. The distortion is much softer than a high impedance drive flat-topping when Vgk = 0.

And that's what a solid state booster really does when it drives an amp input. That's what's under most of the primal urges to have high gain effects chains driving a triode input that can only go about +1.5V peak.

[vanhansen]

As always, R.G.  Great info.

My favorite booster right now is one I made up similar to the Fetzer Valve but based it off the Marshall front end.
http://aronnelson.com/gallery/albums/vanhansen/marshavalve1_1.gif

What I like about it is it's simple to put together, sounds really nice and full, has mild boost or boost from hell.   The 1M Volume pot can be as low as 100K.

[petemoore]

Wire this thing up.   http://diystompboxes.com/pedals/schems/shakaboost.jpg
 Using an existing V Divider from the Splitter Blend made sense, and it took only minutes to have the Shaka Boost working.
 It sounds very clean with a 1458 OA in it, I used slightly smaller value box metal films for the input or output output is 68n.
 Sounds "Clean' to me, until I overdrive the OA, I'm using a 100k pot for the moment as gain setter.
 I haven't yet installed the 220pf.
 I'm thinking I'll use the other unused half of the OA for a Shaka Boost, one for each side of the Splitter Blend.
 But I'm wondering if 'cross-interference' [word?] would be an issue with this application.

[bwanasonic]

For the purpose stated by the original poster ( balancing perceived output between guitars) the AMZ Mosfet booster works superbly. From an EE stand point it may not be *clean*, but from a practical gigging guitarist's POV it is *perceptually* clean if you have enough headroom ( and don't crank the gain all the way up). I use the Mosfet boost for clean jazz tones all the time and it works well to compensate volumes between humbucker guitars and single-coils. I don't know how it looks on an oscilloscope, but in subjective terms, it's a very musical and relatively neutral boost that has a very good *feel*. The Fetzer and related boosts are nice, but color the tone of your guitar a bit more.

Kerry M

[aron]

Thanks Pete!!!!!

Yep, go ahead and use the "other side" for a stereo boost.

[aron]

R.G. said:

Code Select Expand

So the trick is to drive that super-high-impedance triode input from a low impedance driver.

Pete,

Try changing the fixed 100K output resistor (from signal to ground) to a trim pot (100K?) see if it sounds or feels different when you reduce it to as low as 5K or 10K. I seem to recall someone saying 10K was the ideal value for going into a tube input... I forget.....