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Npn Boost Pedal


mattdowney

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hello, i am thinking about building a NPN boost from the diy stompbox fourm. i want a clean boost to turn on for lead work so i dont get drowned out. i dont want a overdrive. i know the NPN is a boost but will it be fairly clean? if i put it through my effects loop will it work as a clean boost? i dont mind it if boosts my gain a tiny bit as well. also can anyone tell mo how many dB's of boost it has? i have posted an searched all over the diy fourm and i cant find the information i am looking for.

thanks, matt

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Don't have an answer for you on the amount of boost in terms of dB, but most boosters are capable of overdrive IMO. Just keep the gain control down and the volume up and you will get as clean a sound as possible. Keep in mind that any booster can cause your amp to overdrive more/easier because the signal going to the amp is larger in amplitude than without the boost. That means the signal will get clipped if it goes over a certain threshold, which is dictated by your guitar, your pedals, your amp, etc.

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Maxed out, that circuit will give you over 40dB of boost at 1KHz, dropping to about 30dB at 100Hz. That means if you feed it much more than .5 volts P-P, it will clip, which I'm assuming is what you mean by overdrive. It probably won't work in your F/X loop, at least not the way you want it to - the voltages there should be line level (~2Volts?), and it will probably clip constantly. If any of that isn't clear, take a look at this:

Boosters, Gain and Distortion

Hopefully that will clear it up for you.

<edit>Oops, make that about 42dB at 1KHz and 36dB at 100 Hz (I told you my math was shaky) - and I should have specified, that's with a 2N5088. Sorry if that caused any confusion!

Edited by lovekraft
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Maxed out, that circuit will give you over 40dB of boost at 1KHz, dropping to about 30dB at 100Hz. That means if you feed it much more than .5 volts P-P, it will clip, which I'm assuming is what you mean by overdrive. It probably won't work in your F/X loop, at least not the way you want it to - the voltages there should be line level (~2Volts?), and it will probably clip constantly. If any of that isn't clear, take a look at this:

Boosters, Gain and Distortion

Hopefully that will clear it up for you.

<edit>Oops, make that about 42dB at 1KHz and 36dB at 100 Hz (I told you my math was shaky) - and I should have specified, that's with a 2N5088. Sorry if that caused any confusion!

i dont quite understand what you mean. will this pedal work as a clean boost or not? if i put this pedal in my effects loop or infont of my amp and have the pot on the right setting will it give me a clean boost like a seymour duncan pickup booster or a mxr micro amp? or will it just add some distortion? i will be using with a already overdriven amp. if it wont what will it do?

also if this isnt the right pedal can anyone direct me to a schematic to a step by step clean boost?

thanks, matt

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ive been told its exactly like a volume pedal so you can switch from rythm to leads but instead of pedal form its stombox form. it should be a clean boost but if you have your volume all the way up and the the stompbox knob all the way up, you may get overdrive/distortion.

-Jamie

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mattdowney-

On virtually any booster, if you have your gain and your volume all the way up and you have it in an FX loop or going straight into your amp, it will clip your signal. You can make most boosters give a "clean" boost by setting the gain and/or volume controls low enough to avoid obvious clipping yet still give a modest boost.

EDIT: I did forget to mention that the power supply has an affect on the clipping as well. If your circuit clips at 9V, it may be pretty clean at 18V, if its components can handle the higher operating voltage.

lovecraft-

Just how do you calculate dB anyway?! :D

I need to learn how to do that...

Edited by Paul Marossy
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Just how do you calculate dB anyway?! 

Simple - I CHEAT!! :D

I just model the simple stuff in Circuitmaker at several different input levels and frequencies and use the AC analysis plots to figger out what's about average. I'm sure there's a simple way to do it with the transistor's Hfe and the currents, but I'm no EE, I'm just a circuit hack! If I need more definite answers on more complicated circuits, I have to holler for RG, or Jack Orman, or another one of the real experts! B)

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Seriously, Paul, if you've got the time and the interest, you (and everybody else, too! :D ) should download Circuitmaker 6 Student - it's got some limitations (the most irritating is a limit of 50 total devices), and the learning curve is moderately steep, but it works great for estimating DC operating points, clipping thresholds, and AC response curves. You can't trust it completely, but it'll get you in the ballpark, and then it's off to the breadboard. It's available here:

CircuitMaker Student Version

It even has some vacuum tube models, and there are some more available from Duncan Munro's Spice pages - thus far I've been too stupid/scared/lazy to download and install them, but it's on the to-do list. Take a look - you might like it.

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i don't suppose there are any Mac programs out there for this sort of work?

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Thanks lovecraft, I'll download that when I get home tonight. :D

EDIT: If you can figure out the approximate voltage gain of the circuit, then you can plug that number into this nifty little calculator:

http://www.muzique.com/schem/decibel.htm

Edited by Paul Marossy
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