radio pre out and amp gain help

[ccapital83 10+ year member]

i have a prs80 head unit and mb quart q4.150 both are supppose to be designed for sq.the reason i asked about the volume knob is my friend one day day woah you only use your volume at 19 when it will max out at 60. i said yesa i let the amp do the work he said big mistake other way around you have a prs series with 5v preout use that more dont overwork the amp and get muddier sound. at that time i thought he was insane. but now im thinkin maybe i should go to about 50 percent the 30 mark and turn the gains down. i have made the mistake of using gains for volume control i alweays used gains for when i hear distortion id back off just a tad but maybe i should first set my radio to 30 then slowly turn gains up till i get distortion

 

[calebkhill 10+ year member]

true, but by definition, voltage has a linear relationship with impedance and current... //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif good catch, i suppose i should have read more into the question... it was late.
also, it's not possible to know exactly how your HU volume behaves without metering it because they can buy accurate or cheap audio taper potentiometers.

This shows plots of various potentiometers. We want the blue line, but some head units use cheap pots and have the red line.

my concept still holds true - assume voltage is linear when setting gains and you will always be safe... it also makes math easy.

What is the rotation axis describing

 

[maylar 10+ year member]

my concept still holds true - assume voltage is linear when setting gains and you will always be safe... it also makes math easy.

Safe, yes. At 75-80% volume where we typically set gains it's safe to assume 75-80% of preout voltage. But at 1/2 volume there's nowhere near 1/2 voltage. Unfortunately there's no way to predict exactly what will be there.

What is the rotation axis describing

An analog volume control is a potentiometer (variable resistor) that usually has 270 drgrees of rotation. The graphs show the relationship between resistance and the position of the control for different types of "tapers" available.

Of course modern HUs are digital and the volume control is a rotary encoder, not a pot. The volume control function is part of the DSP firmware.

 

[calebkhill 10+ year member]

An analog volume control is a potentiometer (variable resistor) that usually has 270 drgrees of rotation. The graphs show the relationship between resistance and the position of the control for different types of "tapers" available.

Of course modern HUs are digital and the volume control is a rotary encoder, not a pot. The volume control function is part of the DSP firmware.

I see. You say "modern". When about did they do away analog pots?

Also, I did a little wiki search on potentiometers, my understanding is that its a mechanism in a device that controls the amount of voltage, and voltage is obviously what determines volume, how voltage determines this I have more reading to do unless you answer this for me lol.

Also thinking about it on the way home I figured if my thinking is true then this must be the very reason for using a dmm or oscope, correct me if I'm wrong.

And do you have any good links about this subject?

If I'm wrong in anything just correct me.

 

[maylar 10+ year member]

I see. You say "modern". When about did they do away analog pots?

Analog pots are still used for the frequency controls in LPF/HPF circuits and as volume controls in simple devices or where size is a concern. But devices that have digital signal processing usually use a rotary encoder instead. They work like a fancy multi-pole switch that puts out pulses that the processor can count. Easier for a computer chip to count than measure resistance or voltage.

Also, I did a little wiki search on potentiometers, my understanding is that its a mechanism in a device that controls the amount of voltage, and voltage is obviously what determines volume, how voltage determines this I have more reading to do unless you answer this for me lol.Also thinking about it on the way home I figured if my thinking is true then this must be the very reason for using a dmm or oscope, correct me if I'm wrong.

And do you have any good links about this subject?

If I'm wrong in anything just correct me.

Here's a reference that might explain some things:

Hi-Fi Amplifiers

 

[calebkhill 10+ year member]

Analog pots are still used for the frequency controls in LPF/HPF circuits and as volume controls in simple devices or where size is a concern. But devices that have digital signal processing usually use a rotary encoder instead. They work like a fancy multi-pole switch that puts out pulses that the processor can count. Easier for a computer chip to count than measure resistance or voltage.


Here's a reference that might explain some things:

Hi-Fi Amplifiers

That does explain more. So let me ask, considering that hu pre-out voltage is much smaller than the voltage found at the amplifier stage, how much more beneficial is it to have a higher pre out voltage. Say from 2v to 4v, or 4v to 8v, and in what ways?

 

[maylar 10+ year member]

That does explain more. So let me ask, considering that hu pre-out voltage is much smaller than the voltage found at the amplifier stage, how much more beneficial is it to have a higher pre out voltage. Say from 2v to 4v, or 4v to 8v, and in what ways?

The advantages of higher preouts have been debated here ad nauseam, and don't relate to anything other than sending signals down a wire to an external device. Signal to noise ratio and the ability to match amp gain sensitivity are the (alleged) things at stake.

 

[calebkhill 10+ year member]

The advantages of higher preouts have been debated here ad nauseam, and don't relate to anything other than sending signals down a wire to an external device. Signal to noise ratio and the ability to match amp gain sensitivity are the (alleged) things at stake.

I see.

 

[keep_hope_alive Premium Member]

Good dialog.

Basically, potentiometers just vary resistance. That resistance is seen in a feedback loop of an amplification circuit, usually with op-amps. Change resistance and you change gain. Change gain and you change voltage.

Amplifiers perform two main functions.

1. Act as a current source for low impedance loads.

2. Act as a voltage amplifier.

Provide more voltage to the amp input and less amplification is needed by the amp, which usually means less noise.

 

[ccapital83 10+ year member]

25 on head unit and 70% on gain did the trick it sounds absolutely incredible clean no distortion no clipping perfect.

 

[calebkhill 10+ year member]

Good dialog.
Basically, potentiometers just vary resistance. That resistance is seen in a feedback loop of an amplification circuit, usually with op-amps. Change resistance and you change gain. Change gain and you change voltage.

Amplifiers perform two main functions.

1. Act as a current source for low impedance loads.

2. Act as a voltage amplifier.

Provide more voltage to the amp input and less amplification is needed by the amp, which usually means less noise.

So let me ask, would you half the voltage at the amp if voltage at the pre-out was doubled?

 

[maylar 10+ year member]

So let me ask, would you half the voltage at the amp if voltage at the pre-out was doubled?

Not sure what you're asking...

What we call the "gain" control on an amp is it's input sensitivity adjustment (a potentiometer, suprise lol). It works exactly like a volume control for the amp in that it adjusts the power output for a given input level. It's purpose is to match the preout voltage to the amp's input circuits. If you have a 2V preout, you set the gain control to 2V which means the amp will (should) deliver full power when the HU is putting out it's max signal. If you have a 4V preout, you set the gain to 4V etc. Higher preout voltage means you turn the gain control down (CCW) to match.

Set your system to aux input sometime without a source connected and turn the volume all the way up. You'll likely hear some noise like a hiss. That's what happens when the preamp circuits (like a gain control) are at full bore. The higher the source level, the less gain you need and the less noise the preamp circuits make.