what is 'unity gain'?

[StevieStingray]

As posted in a previous thread of mine, I ordered a SansAmp Bass Driver DI programmable recently

In anticipation, I downloaded the owner's manual and had a read through.

A couple of sections that really stumped me were:

"...you can run SansAmp PBDR into the front input of an amp. Be sure to keep the Level of SansAmp close to unity gain, so as not to overload the amp’s input, which could result in undesirable distortion. "

"To minimize noise going into SansAmp PBDR, we recommend active electronic instruments have the volume set at unity gain/maximum and tone controls positioned flat."

As an EBMM owner, I took note, but what the heck is "unity gain"?!

I Googled it, and after reading a few lines of a few articles, my head starting hurting.

Since I am neither an electrical engineer nor a physicist, can someone explain in lay terms what "unity gain" is?

Are they talking about the bass' controls? Or the amp's controls?

Either way, how do you determine when unity gain is achieved?

 

[adouglas]

No boost. Same volume engaged as disengaged.

The SansAmp is a preamp, the important part of that word being "amp." You can use it to boost the level of (increase the gain of) the signal being fed to it.

Unity gain means that whatever comes out is the same level as what's going in. 1/1=1=unity.

They're talking about the SansAmp, not the bass.

The way you tell is to set the knob on the SansAmp, play and hit the bypass button. If the signal coming out of the SansAmp with it engaged is louder, then it's not unity gain. If it's the same volume, then it is unity gain.

Make sense?

The whole point of this is to keep the signal going to whatever you've got the SansAmp plugged into from being too hot, which causes distortion.

So...think about it. You can turn your bass down and the SansAmp up and get the same end result, right? But that's kind of pointless. Just take the SansAmp boost out of the equation.

There's room to fiddle here. Most of the things you're going to be plugging into have enough headroom available that you're not going to overdrive the input even if you don't have unity gain. Go ahead and play with it....you won't hurt anything.

What they're really concerned about is plugging into a bass combo or head (as opposed to just plugging into a power amp). Bass combos and heads by definition have preamps already that are designed to take an instrument-level input, not a boosted line-level input. So the input on such an amp is usually more sensitive than one on a power amp would be.

 

[StevieStingray]

The way you tell is to set the knob on the SansAmp, play and hit the bypass button. If the signal coming out of the SansAmp with it engaged is louder, then it's not unity gain. If it's the same volume, then it is unity gain.

This is exactly what I needed to know

Thanks! Much appreciated

 

[Colin]

unity gain = 0db