Amplifier Gains and Preouts

[MKader17 332]

Ok, so lets take for example the Sundown SAE-1200D. 1200W @ 1ohm and an input sensitivy ranging from .153V to 5.6V. For everything in this post lets assume no clipping of the audio signal from the source unit and say the source unit is putting out 3V from the pre-outs.

What is going to happen if you turn the gain knob "up" (as in toward the .2V) after you have matched the gains of the amp to the sensitivity of your source? I assume it will not put out more power. Will it begin to send the amplifier into clipping?

[dbjunior 0]

the amp will produce more current= more power but in the form of heat and the wave will be flat on top not pointy like it should be, causing the extra heat to spend more time heating the coil. you could have 1200w of clean power and 1200w of clipped power the coil will remain a lot cooler with the unclipped signal. just because you have the gains matched doesnt mean you wont clip either a highly eq'd cd can throw off your signal and cause it to clip. is this some sort of test figured a super mod would know this.

Edited January 8, 2009 by dbjunior

[MKader17 332]

the amp will produce more current= more power but in the form of heat and the wave will be flat on top not pointy like it should be, causing the extra heat to spend more time heating the coil.

Wouldn't the wave being flat on top be clipping? I also don't think that sin waves are "pointy"

just because you have the gains matched doesnt mean you wont clip either a highly eq'd cd can throw off your signal and cause it to clip.

That is why I said to assume the signal coming from the source is not clipped

is this some sort of test figured a super mod would know this.

Nope, no test. Sometimes Supermods don't know everything despite what our spiffy title might lead you to believe , but I was looking for a good techinical answer and I figured I'd make it public on the forums for others to see.

[dbjunior 0]

not pointy exactly but not flat more rounded i guess. and the flat is clipping. yes you can get it to produce more power but it can easily harm you speaker or sub this way. if the gains are set correctly i wouldnt turn them up any more. how did you set the gains turn the know to where you think the voltage of the preouts would be? a hu with 5v preouts might not produce 5v before clipping. an o scope is the best way to set gains so you know you are getting the most power without clipping.

[topgun 262]

is this some sort of test figured a super mod would know this.

I've never claimed to know anything

[MKader17 332]

not pointy exactly but not flat more rounded i guess. and the flat is clipping. yes you can get it to produce more power but it can easily harm you speaker or sub this way. if the gains are set correctly i wouldnt turn them up any more. how did you set the gains turn the know to where you think the voltage of the preouts would be? a hu with 5v preouts might not produce 5v before clipping. an o scope is the best way to set gains so you know you are getting the most power without clipping.

Rounded sounds a lot better

And again I know there are plenty of ways to make your HU (source) signal clip, but for the sake of the discussion it is an unclipped signal

And for my question there was really no gains set. It was just making a theoretical question and decided to use an actually amp to make it easier to relate to.

I remembered ///M5 saying a long time ago that getting a new HU soley for higher voltage pre-outs was not going to make your system any louder it will only make you turn down the gains on your amp. All of what we discussed proves that theory...

Could this quite possibly have been a test?

[dbjunior 0]

what is the use for higher voltage preouts? im not sure but i thought it had to due with noise inductance.

[NB50 206]

I'm in search for answer for this, I have an idea of how it works just not really sure on how to explain it. I am sure 95Honda can explain it.

My guess is the input sensitivity works with the preouts in an op amp configuration producing gain for further amplification. Now there is multiple ways an op amp can be wired producing different results but it seems to me that a non inverting configuration would be the one used.

looking at the diagram

Input = the RCA line left or right (there will be one circuit for each line)

R1 = is the sensitivity knob (a potentiometer)

R2 = is a resistor that sets how much gain is produced.

R1 is set to drop as much voltage as Vin is producing so that 0V is across the + & - inputs. When R1 is set to a low resistance the voltage across the + & - inputs increases creating to much gain from the amplifier and driving it into saturation (clipping). This is just for the preamp stage the signal then goes on for further amplification

That is how I assume it works but I could be wrong.

[seanbw 1]

are you talking about a constant sine wave or music? i guess you can send the amp into clipping which means the sine wave will be cut flat at the top and bottom and cause distortion. with music i guess it would just start to distort when the music reached peaks that would cause the amp to clip, but that would vary a lot based on what you were listening to. the further you crank the gain the more distortion you would get. all of this at the expense of your speakers and ears.

[KU40 173]

the amp will produce more current= more power but in the form of heat

How would an amplifier send heat down the speaker wire?

The amp does put out more power when it is clipping due to the area under the sine wave curve increasing. Think of a sine wave. Actually, draw one. Well, here, I'll draw one for you.

The black is the maximum unclipped signal that the amplifier can put out. The thinner black lines represent the limit. When you turn the gain up too far, the signal wave does get a higher amplitude, as seen by the red sine wave (poorly and quickly drawn). However, because the amplifier has reached it's signal amplitude limit (thin black lines) it has to cut off the peaks and valleys of the sine wave. It cuts it off along the blue dotted line. So the red line/blue dotted line is what is sent to your speaker. Notice the area under the red/blue curve is greater than the area under the black curve. That extra area is extra power being sent.

A fully clipped, square wave has twice the power as a normal sine wave of the same amplitude.

Read this thread: http://www.soundsolutionsaudio.com/forum/i...showtopic=19001

Actually the first link in djjdnap's post at the bottom explains all this better.

[dbjunior 0]

what i ment was yeah there is more power but not really more out put due to limited amplitude the sub or speaker is getting more power but instead of turning into sound its turned into heat on the coil. a 1000w square wave (clipped sine wave) and a 1000w sine wave will sound diffrent and create diffrent amounts of heat in the coil the unclipped signal will also be louder. proof termlab. i have competed many times and seen lower volumes on hu work much better than higer volumes in same exact app. due to clipped signals.

[95Honda 486]

The speaker doen't cae if it is a clipped signal or unclipped, power is power and heats up the voicecoil the same. 100 watts of any signal is 100 watts. I have tested this. Thoroughly.

The gain knob is simply there for matching H/U voltage drive and decreasing the system noise floor. The gain setting of an amplifier simply sets the voltage gain, nothing else.

If you have a 1200 watt amp, it can put out 1200 watts, reguardless of gain setting. If it puts out say, 1200 watts at a certain setting, and you increase ANYTHING ANYWHERE in the signal chain, you will drive it into clipping.

It is much simpler in every aspect than everyone makes it out to be.

[NB50 206]

Whoops thought you wanted a technical explanation on how the gain setting worked.

[MKader17 332]

The gain knob is simply there for matching H/U voltage drive and decreasing the system noise floor. The gain setting of an amplifier simply sets the voltage gain, nothing else.

Would you mind elaborating on that more?

[christobear 0]

The speaker doen't cae if it is a clipped signal or unclipped, power is power and heats up the voicecoil the same. 100 watts of any signal is 100 watts. I have tested this. Thoroughly.

this is how i have always had it explained to me, the idea that the speaker "doesn't care" what quality of sound it is producing.

yet, i have heard many say that they can "blow" a 1000 watt speaker with only 100 watts....does this claim have anything to do with a clipped signal or are there other factors involved?

[Adrian_D 520]

The gain knob is simply there for matching H/U voltage drive and decreasing the system noise floor. The gain setting of an amplifier simply sets the voltage gain, nothing else.

Would you mind elaborating on that more?

The way I understand is that the amplifier achieves maximum output for a certain input voltage so the gain knob only reduces the input voltage to that level. Higher gain = more voltage to the input and if it is over the voltage needed for maximum output, you get clipping.

I know from first hand experience that you don't need an awful lot of input voltage to send an amplifier into clipping. Just using the headphone output from an Ipod was more than enough in my case.

The speaker doen't cae if it is a clipped signal or unclipped, power is power and heats up the voicecoil the same. 100 watts of any signal is 100 watts. I have tested this. Thoroughly.

this is how i have always had it explained to me, the idea that the speaker "doesn't care" what quality of sound it is producing.

yet, i have heard many say that they can "blow" a 1000 watt speaker with only 100 watts....does this claim have anything to do with a clipped signal or are there other factors involved?

I think that blowing it up has something to do with mechanical stresses. Considering the case of a coil rated at 1000w, and a box that can keep the cone motion withing the mechanical limits at that power level I can't see how you will "blow" the subwoofer with 100w, square wave or sine wave.

Otherwise, that claim is rather stupid. Does a speaker connected to a 100w amplifier always receive a 100w input ? We would blow speakes all the time when listening to music ar low levels.

By integrating the function which represents the waveform you obtain the area under it's graph which, iirc, represents power (rms, but I may be wrong). Integrate only half a period. Because half is positive and half negative, if you integrate a whole period you will get zero.

[KU40 173]

The speaker doen't cae if it is a clipped signal or unclipped, power is power and heats up the voicecoil the same. 100 watts of any signal is 100 watts. I have tested this. Thoroughly.

this is how i have always had it explained to me, the idea that the speaker "doesn't care" what quality of sound it is producing.

yet, i have heard many say that they can "blow" a 1000 watt speaker with only 100 watts....does this claim have anything to do with a clipped signal or are there other factors involved?

This simply cannot be done. At least not thermally, as we are talking about here. If you build a ported box and tune it really high then play a 5 hz note at full blast, it may be possible to reach the mechanical limits of the speaker with 100 watts and damage it that way.

Edit- whoops, didn't see Adrian's post on page 2 where he got into mechanical limits already.

[95Honda 486]

The gain knob is simply there for matching H/U voltage drive and decreasing the system noise floor. The gain setting of an amplifier simply sets the voltage gain, nothing else.

Would you mind elaborating on that more?

OK, and dammit sticky this or something because this is getting ridiculous these days... LOL...

The voltage gain of an amplifier is the ratio of voltage applied to the input vs. the voltage produced at the output. This is expressed in db. An average voltage gain for a high power sub amplifier is somewhere in the vicinity of 30 db, or 5x the voltage doubling. This would mean that if the amplifier was presented with 2V on the input, it would present 64V on the output.

You need to remember that audio amplifiers are voltage sources, they attempt to maintain a fixed voltage level into different impedances. Try not to forget this, it is important. This is why amplifiers have different power ratings at different impedances, because the rails will always try and swing the same voltage with the same input, and then the output stage will source the differing amounts of current required to maintain the constant voltage into the varying impedances.

Ok, so we understand that amplifers are a voltage source. So now, lets look at an amplifier without a gain knob, like many older amps and most home audio amps. They have a fixed voltage gain (this is published when usable specs are actually given by manufacturers) and if we know what the voltage gain is, we know exactly what input drive will produce full ouput power into any impedance. We know this because if the amplifier is rated at say 100 watts at 8 ohms it has 29VRMS output capabilty before the rails are exhausted and clipping sets in (square root of W*Z) And we know if the amplifier is rated with 30db of voltage gain that roughly 900mv on the input will produce 29V on the output and is the maximum power (900mv * 30db = Apr. 29V)

Now lets look at the amplifer with a gain knob. I has adjustable voltage gain. They usually give you around 10-15db of adjustment in overall volatge gain of the amplifier. Why isn't it expressed as db on the knob? Because most people wouldn't understand how db relates to voltage (a 6b increase doubles the voltage). So instead, they do the math for you and write a voltage level that cooresponds to the gain amount (like 200mv to 8V) and put that on the amp so you can set the voltage gain of the amp.

Why do they do this? #1 so you can match multiple outputs of multiple channels/amps. #2 to increase the S/N ratio. #3 as a marketing gimmick.....

#1 is easy and needs no explanation.

#2 is also easy, but I will explain. The more voltage gain an amp has, the more it amplifies everything. This includes alternator whine, white noise (hiss) and everything else. The less volatge gain the amp has, the less it amplifies everything, including all of these noises. So, the lower you set the voltage gain while still being able to get the power you need out of the amp (you have sufficient voltage drive from your source) the less overall noise the system will have. This is also where matching the H/U output to amplifer gain comes into effect.

#3 Would most people on here buy an amp with a gain knob or without one, if everything else was exactly the same? Think about it....

The most expensive amplifiers in the world do NOT have gain knobs. Look at any Krell, Mark Levinson, Pass Labs, etc and you will see this.....

AND DAMMIT, speakers don't care about clipping.... If you are listening to any Jimi, Metalica or G-n-R, you are listening to clipping, and alot of it.... And I bet your speakers are doing just fine.... Speakers don't like too much power, that is what kills them. It kills them thermally if the enclosure alignment permits, and kills them mechanically if the enclosure alignment permits... That's it... That's all...

[topgun 262]

It is now pinned. Some good info here.

[dbjunior 0]

i thought a clipped wattage compared to unclipped same wattage signal would cause more heat due to a stall in signal amplitude and less cone movement compared to unclipped. but i guess you learn everyday.

[justin smith 0]

i legitimately think i learned something usefull today thank you no v8's for me

[SaxMan 2]

ill probably get yelled at but w/e, so if i buy lets say the SAZ-1500D for one subwoofer, lets say the 12" FI BTL, the gain would mean nothing, i could just leave it alone and not worry about hurting the subwoofer?

so basically gain would be used to match another amp to the SAZ?

[jcarter1885 995]

You use your gain to match your pre-out voltage or signal of your head unit. With 1500 watts on a BTL you should be fine, make sure you listen for distortion and you should be fine if you set the gain correctly.

[SaxMan 2]

You use your gain to match your pre-out voltage or signal of your head unit. With 1500 watts on a BTL you should be fine, make sure you listen for distortion and you should be fine if you set the gain correctly.

i was just using those subs as a reference, i would be getting the 1000 and the BL, so if the H/U is a 40 watt pre-out, i just match the amp?

[jcarter1885 995]

Dont use the wattage output that is for the speakes hooked up to it (that 40 is max anyway, so pretty useless). You use the pre-out voltage, most headunits are 2 volts, 4 volts, 5 volts or 8 volts. The voltage signal of the rca outputs.