|Setting gain controls is one
of the most important things in making a great system sound great. It
has always been something I love to do, and something I always do well.
But, there is so much bad
information and VOODOO going around the internet about how to set
car audio amplifier gain controls that I thought I better write this paper.
Gain controls on an amplifier are basically
just small potentiometers (variable resistors) or volume controls if you
will, that allow you to adjust the incoming signal to the amplifier so
the amplifier works well with your headunit of choice or to match the
level of other amplifiers in your system.
Its not rocket science to set the
gains. Gains are like little volume controls, (I don't know why so many
installers are taught that gains are NOT volume controls, when in fact
that is EXACTLY what they are!) its super simple to just set them
where the level sounds good to you.
With one amplifier its desirable to
have a nice swing on your headunits volume control. Let me try to clarify
this a little.
If we hook up a head unit with a 8volt
(or more) output to an amplifier, then the volume will get loud very
fast when we start to turn it up...In other words if our digital volume
control goes from 1-30, then a HIGH VOLT output to an amplifier might
make the amplifier reach full power at 5 on the volume scale... That
kinda sucks cause it would be nice if you had a little more swing in
your 1-30 range!
And by the same token a headunit with a
LOW VOLT output might have to be turned up all the way to 30 and might
still not quite drive the amplifier to full power... That sucks too!
A gain control in this case will allow
you to adjust the amplifier so it allows the volume of a headunit to
control the amplifier so it will get loud at a desirable point in the
1-30 swing... Usually about 3/4 the way up. We don't want it to get loud
too fast as we wont have a good control as music levels differ. And we
don't want it to have to be turned up all the way to get loud either,
because since different music may be recorded at different levels if we
set the gains for max output with one music source it might not get loud
with a music source recorded at a lesser level.
So, by setting the gains so 3/4 turn of
the headunits volume knob gets it LOUD gives you plenty of control and
some extra above the 3/4 mark in case you get some music that's recorded
at a lesser level...
To do this its easiest to do it by ear.
No need to drag out the TEST TONES and OSCILLOSCOPES! They will do
you absolutely no good.
One MYTH is how the gain controls will
help to prevent amplifier distortion and amplifier clipping... That's
simply not true, UNLESS you set the gains at a level where the headunit
cannot possibly drive the amplifier to full power.. And even if you were
to find this magic spot for your gain controls then (A) you would have
to turn that volume control FULL SWING to get your system loud and (B)
since many music sources (or disks) are not all recorded at the same
level, its likely that if you have a disk recorded lower then you cant
get it loud at all! and if you have a disk recorded louder then you can
still surpass your magic spot... So in reality searching for this magic
spot is fruitless! Dont waste your time...
In the early 80s when high fidelity car
amplifiers were just starting to make the scene I worked with a pretty
crazy installer that was kind of legendary around these parts... I wont
mention his name but he was pretty highly respected at the time.. Well
anyway, this crazy installer had heard that the amplifier gain control
was to prevent amplifier clipping.. (still widely heard today)..
Well this crazy installer set up EVERY CAR WE DID to the point where the
gain control was so LOW that if you turned the head unit all the way up
the amplifier WOULD NOT DISTORT.. And of course if you did turn the
headunit all the way up the system would just be getting loud...
Customers would find that some
cassettes would be recorded at a lower level and the music just wouldn't
get loud enough... The Crazy installer would FLIP OUT and tell the
customer that a "REAL AUDIOPHILE" doesn't want his music to distort or be
that loud! The customers were NOT HAPPY and came to me to say
"Gee Eddie, I don't want to make the other guy mad but can you
adjust my system so it sounds good and please dont tell the other
guy?" Of course I said yes, and some of those customers from back
in the early 80s are still my customers and they are sending sending their
children to me for work as well.
SO, you see the only way the gains can
be used to eliminate clipping or distortion will also limit your top end
volume! And for most of us it is NOT DESIRABLE to do so.
As long as this is not done, it is just
as possible to turn your system up to FULL power and beyond to clipping
no matter where the gains are set....
Now, on to another reason to adjust a
gain control. A MULTI AMP SYSTEM!
If there is more than one amplifier it
is possible that one set if speakers plays louder than another! This can
be because of mounting location in the car, it can be cause the speakers
are different sizes or different brands or maybe your two amps are
different brands with different sensitivities, either way, with the
amplifier gain controls you can set the radio fader in the middle (if
you have one) and then make the adjustments to the amplifiers so the
levels are the same. Good thing those gain controls are there...
This multi amp adjustment is pretty
easy to do by ear, simply have someone sit in the listening area and
tell you as you adjust them when the sounds are equal. Simple!
Same kind of think with gain adjustments
on subwoofer amps, just turn them up or down till they sound good with
the rest of the systems sound.
All the VOODOO about watching an oscilloscope
and looking for a clipped signal is a waste of time and wont get you
what you want anyway! Do it by ear, its simple. Don't let
adjusting the gains scare you, they are simply volume controls...