Difference between Preamp and Booster?

[phil]

I know this is a newbie question (no surprise ... I am one) - Is there a difference between a pre-amp and a booster? Is a preamp supposed to increase the input sound cleaner than a booster maybe?

The reason I as is that I have an acoustic instrument with a clip-on pickup that I want to amplify thru a Ruby amp. I think the signal the pickup generates must be very weak as the output sound is very low even with the Ruby turned up full, so I was thinking of building something to boost the signal from the pickup to the amp.

At first, I thought a booster like the beginer project (http://www.diystompboxes.com/beginner/build/npnboostbuild.htm)
would work, but then I saw a simple schematic for Don Tillman's preamp(http://www.till.com/articles/GuitarPreamp/index.html) and began to wonder whether I should build a preamp or a booster or if there is a difference between the two.

I'd really be interested in understanding the differences if anyone would be willing to explain a bit about what a preamp is for ...

Thanks!

[d95err]

The term "Preamp" is used for lots of things, and not consistently. It can mean virtually anything that amplifies something a bit.

In the guitar effect context, it means the same thing as booster. Most likely a fairly clean booster.

In the studio context, a (microphone)preamp is something that amplifies a microphone signal up to line level (the level used internally in mixers, rack effect gear etc). Such preamps also shape the sound a bit, but in general the idea is to amplify the signal as cleanly as possible.

In the amplifier context, the preamp is one of two main parts. An amplifier consists of a preamp and a poweramp. The preamp amplifies the weak signal (from a guitar, mic or other source) to a level that is better to work with internally. The preamp then shapes the sound through equalising, distortion, effects etc. Then the signal is passed to the poweramp, whose job is to add enough current (i.e power) to the signal so it can drive speakers.

[Mark Hammer]

Much of this is in the booster thread today, but consider these little tidbits.

An audio path starts out with a tiny variation in voltage in a transducer of some type, usually on the order of millivolts, and ends up being a big enough variation in both current and voltage that it can move a physical object (i.e., a speaker) and maybe even several (such as 4 speakers).  Along the way, the signal gets ratcheted up in stages, a bit like going from child to adolescent, to grownup.

The "power amp" stage will transform the signal it receives into something powerful enough to move speakers, but to do this it needs to get something which is already a significant enough voltage level that the power amplifier does not have to increase that much more to do its job.  What supplies that "almost there" signal level is traditionally referred to as the "pre-amplifier" because, lo and behold, it comes just before the amplifier, and brings the signal up to the needed level.

Here is the subtle, yet meaningful distinction between a preamplifier and booster.  The *idea* of a preamplifier is something that brings a signal up to a required or expected level.  A "booster" on the other hand, has the role of possibly bringing a signal up to some expected level, but possibly raising the level even higher than that.

Inside the box, mind you, they would be or could be entirely identical in an electronic sense.  The difference is in the role they serve.  So, build yourself an "AMZ MoFet booster".  If you place that pedal/circuit between a guitar with overwound pickups and a distortion pedal, it serves as a "booster".  The distortion pedal is already getting a hot enough signal to provide distortion, and his just adds more amplitude to that already-gnarly signal.  If, however, you plug a voice mic into that pedal, and then plug the pedal into the second channel of your amp so that the mic is loud enough that your amp can double as a PA in a pinch, you have used the pedal as a preamplifier; to bring the level of some signal up to the needed amplitude to function in a given context.  Similarly, plug that overwound guitar pickup into the same pedal, and plug that into the line-level input of a McIntosh or Crown power amp, and the pedal will have served the role of preamplifier by allowing a guitar signal to be somewhere in the ballpark of what the power amp wants to produce some audible output levels.

[phil]

Great explanation thank you! Seems like a booster would in theory perform the same function as a preamp, and could additionally add value in boosting the signal to an even higher level. I'll look at the AMZ MosFet Booster as it will be more versatile as well as do what I need it to do for now.

Thanks again for the in depth explanation! 

[petemoore]

  I forget the name but the Dyna power amp I had..each channel had two output tubes and 7199 'driver' tubes, to bring the pre-amp output to amp driving levels.
  Plugging in the amp would drive a speaker to sound.
  Using anything with a 'boost' to it including distortion could sound good, and be markedly louder.
  Using a Mosfet boost [with or without other dist/boost] would drive the amp pretty well, not as loud or driven as with a tube pre-amp.
  The mosfet boost has enough 'boost' to come to about 60% [sounding level] to 'pre-amp' driving levels.