What is actually happening when the gain on an amp is turned up and
down? Is it throtteling down the power of the, amp, reducing the
preamp signal?

"Sub_Lover" wrote in message
oups.com...
What is actually happening when the gain on an amp is turned up and
down? Is it throtteling down the power of the, amp, reducing the
preamp signal?


It is decreasing the sensitivity of the amplifier, with it turned way down
the amp can still make full power, it just takes more input to do so.

Chad

On 16 Mar 2005 12:42:17 -0800, "Sub_Lover"
wrote:

What is actually happening when the gain on an amp is turned up and
down? Is it throtteling down the power of the, amp, reducing the
preamp signal?

Adjusting the gain control adjusts the level of the input signal.
This allows you to adjust the amplifier so that it can be driven to
full volume regardless of what your head unit's preamp voltage is.

"Gain" is just the ratio of the output voltage divided by input
voltage. So, let's say that an amp's maximum output is 20V, and it
can achieve this output with an input of 1V. This amplifier would
therefore have a gain of 20 divided by 1, or 20.

You could also describe this amplifier as having a gain of 13 dB,
using the formula (10 * log (output/input)).

Now, let's say that instead of a 1V input, we give the same amplifier
a 4V input. The maximum rated output of the amp is still 20V, so we
have to reduce the gain from 20 to 5 to keep from overdriving the amp.

Now, a 4V input and a gain of 5 still gives us 20V at the output, so
the amp is still being driven to full volume, even though we've turned
the gain knob "down".

So, the only purpose for the gain control is so that you can match an
amplifier to a variety of head units. The only reason you don't see
very many gain adjustments on home stereo amp is that almost all CD
players, VCR's, DVD players, and receivers use a standard pre-amp
voltage. Since the amplifier manufacturers know what the preamp
voltage from the source will be, they don't need to include a gain
adjustment on the amp. (Some do anyway, just to give you more
flexibility).



--
Scott Gardner

"Evolution is a harsh mistress."

The amps power is the same regardless of the gain.
The main function of that control is to match it with the head units output.
I remember years ago (10 maybe) Kenwood head unit had a very low output and
it was hard to match different brands with them.
Other brand amps you had to turn the gain all the way up to get descent
volume out of them. on the flip side, Kenwood amp's played louder with
different brands and you had to turn the gains down. I don't know if that is
still the case with ken, but I don't recall any problems like that recently

--
The Clown Prince of Car Stereo


"Sub_Lover" wrote in message
oups.com...
What is actually happening when the gain on an amp is turned up and
down? Is it throtteling down the power of the, amp, reducing the
preamp signal?

On a related note, my Nakamich CD-35 head unit's preamp out has fairly
low output which feeds my Rocford Fosgate 4600x 4-channel amp. I have
to turn the amp's gain up quite a bit in order to drive the amp to near
or full power. I do have some room to spare on the gains, but when I
turn them up, more engine whine noise is introduced, so I compromise
and lower the gains a bit to where the engine noise is still there but
very tolerable when listening at normal volumes.

What would happen if I put a line level controller in front of the amp
and raise the gain on it so that the amp is getting a higher level
signal than the head unit normally outputs, and then lower the gains on
the amp slightly to allow a lower volume on the head unit to drive the
amp to the same volume as before at a higher head unit volume? I'm
hoping that by lowering the gains on the amp, that less engine whine
noise will be there.

I think if your moter noise is coming from the head unit, then the line
driver is not going to help much.
If the noise is coming from the Amp, then the line driver will help.

--
The Clown Prince of Car Stereo


"Bob" wrote in message
...

On a related note, my Nakamich CD-35 head unit's preamp out has fairly
low output which feeds my Rocford Fosgate 4600x 4-channel amp. I have
to turn the amp's gain up quite a bit in order to drive the amp to near
or full power. I do have some room to spare on the gains, but when I
turn them up, more engine whine noise is introduced, so I compromise
and lower the gains a bit to where the engine noise is still there but
very tolerable when listening at normal volumes.

What would happen if I put a line level controller in front of the amp
and raise the gain on it so that the amp is getting a higher level
signal than the head unit normally outputs, and then lower the gains on
the amp slightly to allow a lower volume on the head unit to drive the
amp to the same volume as before at a higher head unit volume? I'm
hoping that by lowering the gains on the amp, that less engine whine
noise will be there.

Isn't the reason for having higher pre out voltage is to be able to
drive the amp cleanly before the source starts to distort?

On 16 Mar 2005 14:09:01 -0800, wrote:

Isn't the reason for having higher pre out voltage is to be able to
drive the amp cleanly before the source starts to distort?


Actually, high pre-out voltages in car audio have turned into nothing
more than a marketing gimmick.

The theory is that the higher pre-out voltage will raise the
signal-to-noise ratio, assuming the noise floor remains constant. If
you keep the amount of noise constant, then each doubling of the
pre-out voltage will raise the signal-to-noise ratio by 3 dB.

In reality, the signal-to-noise ratios for modern equipment are
already so high that an extra 3, 6, or even 9 dB is completely
undetectable, by *anyone*. This is why you don't see this kind of
silliness in home audio, even with high-end gear. I think the
standard pre-out voltage for home gear is still something like 0.7
VRMS, and that works just fine.

Here's an example with numbers, to put it into perspective.

90 dB signal-to-noise, with 1V output:

Noise voltage equals one volt divided by antilog (90/10), or
..000000001V (That's one part noise in a billion parts signal)

Now, keep the noise voltage the same (.000000001V), and raise the
total pre-out voltage to 8 volts:

signal-to-noise ratio = 10 * log (8V/.000000001V) = 99 dB

So, the signal-to-noise ratio has gone from 90 dB to 99 dB, which will
make the marketing people happy, but the reality is that the noise has
gone from being one part in a billion to one part in eight billion.
Think you can tell the difference?

There was a time when typical signal-to-nioise ratios were a lot
lower, like around 30 dB or so, that you might have been able to tell
the difference from a few extra dB, but not anymore. Now, it's like
damping factor - all of the modern components have gotten so good that
the differences in signal-to-noise ratio and damping factor are
undetectable.


--
Scott Gardner

"Computers are useless. They can only give you answers." (Pablo Picasso)

Ok gotcha.

Scott,

Excellent information!

Tony


--
2001 Nissan Maxima SE Anniversary Edition
Eclipse CD8454 Head Unit, Phoenix Gold ZX475ti, ZX450 and ZX500 Amplifiers,
Phoenix Gold EQ-232 30-Band EQ, Dynaudio System 360 Tri-Amped In Front and
Focal 130HCs For Rear Fill, 2 Soundstream EXACT10s In Aperiodic Enclosure

2001 Chevy S10 ZR2
Pioneer DEH-P9600MP (Just gettin' started)

On Wed, 16 Mar 2005 19:06:45 -0800, "Tony F"
wrote:

Scott,

Excellent information!

Tony


Thanks, Tony. I wish there were a better way to express mathematical
equations in newsgroups posts. It gets to be kind of a pain in the
ass not having subscripts, superscripts, or all of the right symbols.
I should probably do all of the equations in Word or Mathematica, save
the results as web pages, and just post links to them.

It really opens people's eyes when they find out what a S/N ratio of
90 dB or 100 dB really MEANS, and just how insignificant the
difference between the two is.

I think the pre-out voltage hype started with the original Alpine 7909
CD player. It was one of the earliest "high-voltage" preout models,
with 2V or 4V pre-outs (I can't remember which right now). Anyway, it
wa considered at the time to be a good-sounding unit, and was very
popular, but the sound had nothing to do with the high-voltage
preouts. They could have made it with standard-voltage preouts, and
it would have sounded the same.

In the typical car audio "more-is-better" style, it's now typical to
have at least 2V pre-outs, and 4V or 8V pre-outs are becoming more
common as well. The only real effect is that it makes it harder to
use new head units with older amps. Have you ever tried to use a head
unit with 8V pre-outs and an amplifier that was only designed for a
maximum of 2V inputs? You can make it work by adjusting the gain on
the amp, but with an input that high, the usable range on the gain
knob is about ten degrees of rotation. *Very* annoying.



--
Scott Gardner

"A government that robs Peter to pay Paul can always depend on the support of Paul." (George Bernard Shaw)

Scott, thanks for the great info. I have a question maybe you can
answer...or maybe not as it is a little odd.

My Nak CD-35 head unit's specs say the preamp's output voltage is 0.8V.
If I add a line level controller that adds up to 8 dB of gain to the
signal, what would that same gain be expressed in volts?

Thanks,
Bob

On Thu, 17 Mar 2005 04:08:24 +0000 (UTC),
(Bob) wrote:


Scott, thanks for the great info. I have a question maybe you can
answer...or maybe not as it is a little odd.

My Nak CD-35 head unit's specs say the preamp's output voltage is 0.8V.
If I add a line level controller that adds up to 8 dB of gain to the
signal, what would that same gain be expressed in volts?

Thanks,
Bob


Not an odd question at all. A line driver is just another kind of
signal booster or amplifier.

The equation for expressing gain in dB is:

Gain = 10 * log (output voltage/input voltage)

Re-arrange to solve for the ratio between output voltage and input
voltage:

(output voltage/input voltage) = 10^ (8/10),
which gives us a gain of 6.30. This means that with a gain of 8 dB,
the output voltage will be 6.30 times higher than the input voltage.

Since the input is 0.8V, the output would be about 5.0 V.

Hope this helps,


--
Scott Gardner

"It's easy to get a Friday off when you're unemployed."

In article ,
Scott Gardner wrote:
:On Thu, 17 Mar 2005 04:08:24 +0000 (UTC),
Bob) wrote:
:
:
:Scott, thanks for the great info. I have a question maybe you can
:answer...or maybe not as it is a little odd.
:
:My Nak CD-35 head unit's specs say the preamp's output voltage is 0.8V.
:If I add a line level controller that adds up to 8 dB of gain to the
:signal, what would that same gain be expressed in volts?
:
:Thanks,
:Bob
:
:
:Not an odd question at all. A line driver is just another kind of
:signal booster or amplifier.
:
:The equation for expressing gain in dB is:
:
:Gain = 10 * log (output voltage/input voltage)
:
:Re-arrange to solve for the ratio between output voltage and input
:voltage:
:
output voltage/input voltage) = 10^ (8/10),
:which gives us a gain of 6.30. This means that with a gain of 8 dB,
:the output voltage will be 6.30 times higher than the input voltage.
:
:Since the input is 0.8V, the output would be about 5.0 V.
:
:Hope this helps,
:
:
:--
:Scott Gardner

Thanks again, Scott. That helps tremendously. Now I am faced with the
possibility that this 8 dB gain might be too much for my amp. The
specs for it say the input sensitivity is 250 mV = 1 V.

Bob

On Thu, 17 Mar 2005 04:30:50 +0000 (UTC),
(Bob) wrote:

In article ,
Scott Gardner wrote:
:On Thu, 17 Mar 2005 04:08:24 +0000 (UTC),
Bob) wrote:
:
:
:Scott, thanks for the great info. I have a question maybe you can
:answer...or maybe not as it is a little odd.
:
:My Nak CD-35 head unit's specs say the preamp's output voltage is 0.8V.
:If I add a line level controller that adds up to 8 dB of gain to the
:signal, what would that same gain be expressed in volts?
:
:Thanks,
:Bob
:
:
:Not an odd question at all. A line driver is just another kind of
:signal booster or amplifier.
:
:The equation for expressing gain in dB is:
:
:Gain = 10 * log (output voltage/input voltage)
:
:Re-arrange to solve for the ratio between output voltage and input
:voltage:
:
output voltage/input voltage) = 10^ (8/10),
:which gives us a gain of 6.30. This means that with a gain of 8 dB,
:the output voltage will be 6.30 times higher than the input voltage.
:
:Since the input is 0.8V, the output would be about 5.0 V.
:
:Hope this helps,
:
:
:--
:Scott Gardner

Thanks again, Scott. That helps tremendously. Now I am faced with the
possibility that this 8 dB gain might be too much for my amp. The
specs for it say the input sensitivity is 250 mV = 1 V.

Bob

That means that the amplifier is designed to be used with inputs
ranging from 250mV up to 1 V. Since the 0.8V from your Nak head unit
falls in that range, your head unit and amp seem to be pretty
well-matched. What were you wanting the 8dB boost from the line
driver for? It doesn't sound like you need it.


--
Scott Gardner

"I've been accused of vulgarity. I say that's bull****." (Mel Brooks)

In article ,
Scott Gardner wrote:
:On Thu, 17 Mar 2005 04:30:50 +0000 (UTC),
Bob) wrote:
:
:In article ,
:Scott Gardner wrote:
::On Thu, 17 Mar 2005 04:08:24 +0000 (UTC),
:Bob) wrote:
::
::
::Scott, thanks for the great info. I have a question maybe you can
::answer...or maybe not as it is a little odd.
::
::My Nak CD-35 head unit's specs say the preamp's output voltage is 0.8V.
::If I add a line level controller that adds up to 8 dB of gain to the
::signal, what would that same gain be expressed in volts?
::
::Thanks,
::Bob
::
::
::Not an odd question at all. A line driver is just another kind of
::signal booster or amplifier.
::
::The equation for expressing gain in dB is:
::
::Gain = 10 * log (output voltage/input voltage)
::
::Re-arrange to solve for the ratio between output voltage and input
::voltage:
::
:output voltage/input voltage) = 10^ (8/10),
::which gives us a gain of 6.30. This means that with a gain of 8 dB,
::the output voltage will be 6.30 times higher than the input voltage.
::
::Since the input is 0.8V, the output would be about 5.0 V.
::
::Hope this helps,
::
::
::--
::Scott Gardner
:
:Thanks again, Scott. That helps tremendously. Now I am faced with the
:possibility that this 8 dB gain might be too much for my amp. The
:specs for it say the input sensitivity is 250 mV = 1 V.
:
:Bob
:
:That means that the amplifier is designed to be used with inputs
:ranging from 250mV up to 1 V. Since the 0.8V from your Nak head unit
:falls in that range, your head unit and amp seem to be pretty
:well-matched. What were you wanting the 8dB boost from the line
:driver for? It doesn't sound like you need it.
:
:
:--
:Scott Gardner

Scott, here is another post I made to this thread that you probably
missed. I should also add that my head unit only has a single set of
preamp outs so I am splitting them with y-splitters in order to feed
the 4 channel amp's inputs (front and rear).

On a related note, my Nakamich CD-35 head unit's preamp out has fairly
low output which feeds my Rocford Fosgate 4600x 4-channel amp. I have
to turn the amp's gain up quite a bit in order to drive the amp to near
or full power. I do have some room to spare on the gains, but when I
turn them up, more engine whine noise is introduced, so I compromise
and lower the gains a bit to where the engine noise is still there but
very tolerable when listening at normal volumes.

What would happen if I put a line level controller in front of the amp
and raise the gain on it so that the amp is getting a higher level
signal than the head unit normally outputs, and then lower the gains on
the amp slightly to allow a lower volume on the head unit to drive the
amp to the same volume as before at a higher head unit volume? I'm
hoping that by lowering the gains on the amp, that less engine whine
noise will be there.

As someone responded, if the noise is coming from the head unit, that
noise would be amplified by the line driver, but if it's coming from
the amp, lowering the amp gains might help lower the noise level. I
guess I need to troubleshoot the origin of the engine whine noise and
take corrective action there. I get the feeling though that the noise
is coming from the amp because it is wired into the factory power and
ground wires for the now not being used, factory external amp in my '96
Ford Explorer.

Bob

On Thu, 17 Mar 2005 04:49:56 +0000 (UTC),
(Bob) wrote:


As someone responded, if the noise is coming from the head unit, that
noise would be amplified by the line driver, but if it's coming from
the amp, lowering the amp gains might help lower the noise level. I
guess I need to troubleshoot the origin of the engine whine noise and
take corrective action there. I get the feeling though that the noise
is coming from the amp because it is wired into the factory power and
ground wires for the now not being used, factory external amp in my '96
Ford Explorer.

Bob

Ah, yes. I remember the post - I just didn't put the two posts
together as being from the same person.

I would **definitely** try to resolve your noise issues before you
start getting into things like line drivers, noise filters,
ground-loop isolators, or things like that.

I really, really HATE engine noise, especially alternator whine. No
matter how quiet it is, the first time I accelerate during a quiet
part of a song and hear the whining, it's like nails on a chalkboard.

The one technique that has *always* worked for me is to make sure that
all of my components are grounded to the same exact spot. That
includes the head unit, amplifiers, signal processors, changers,
everything. The easiest way to do this is to run a big honkin' ground
wire directly from the battery back to a ground distribution block
near where your amps and processors are. Ground all of your stereo
equipment to that distribution block. Don't forget to run the head
unit ground wire back there as well - don't rely on the factory ground
in the behind-dash wiring harness.

Replace the ground wire under your hood that connects the battery to
the chassis, and replace the ground strap that connects the engine
block to the chassis. 4-gauge or 1/0 gauge works well for this. This
is because depending on how old your car is and what model it is, some
of the factory ground wires may be undersized and/or corroded.

Don't mount your amplifier chassis directly to the metal car body. I
mount my amps to a wood or MDF board, and then bolt the board to the
car's body. This will insulate the amp chassis from the car body,
eliminating another possible ground path. Same goes for CD changers
and signal processors.

If you do all this, it will almost certainly eliminate your engine
noise, unless some piece of your equipment is actually damaged. This
single-point "star" grounding method might be overkill, but I really
dislike chasing down engine noise, and I've found that if I do it this
way from the start, I just don't have any problems.



--
Scott Gardner

"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return." (Leonardo da Vinci)

Scott,

Excellent information!

Tony



Yeah, Scott posts something worthwhile every once in a (long) while.

(kidding!)

I get the feeling though that the noise
is coming from the amp because it is wired into the factory power and
ground wires for the now not being used, factory external amp in my '96
Ford Explorer.

Bob

The noise is most likely because you are using the factory power wires. Run
your own Power and ground wire. your battery is the best noise filter in the
car.
--
The Clown Prince of Car Stereo