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This is a quick overview of how to properly set up a system using a preamp to control pre-distortion peak volume in car audio systems.


system layout example:

head unit to
preamp/EQ to (acting as crossover as well)
4 channel amp and sub amp to
2 subs, and front/rear components

pretty normal setup, with a preamp tossed in.

most head units (just about any under $500 or so) will show a sharp increase in distortion at the pre-out signal as you get close to peak volume (say vol goes to 40, we'll say this unit distorts on an oscilloscope at a volume of 30 although the actual volume distortion point varies widely from unit to unit.)

A preamp usually has a master volume, fader, balance, and a few EQ bands on it, and mounts below the head unit, or near it, in a half-DIN format.
The preamp acts as both a master control and a line-driver for the system.

The idea here is to set the volume of the head unit to just before distortion. In our case, a volume of "30." Then, you'll want to set the line driver voltage of the pre-amp to your desired voltage using a scope, with the preamp volume at maximum. This is usually about 4 volts for most systems, as 4 volts is the peak input voltage for the majority of amplifiers and signal processors.
After setting this voltage, you'll want to connect the preamp to your amplifiers, and set their input sensitivities accordingly, to match the preamp line voltage.

At this point, if your speakers are matched to your amplifiers moderately well, and you've set crossover points and slopes wisely, you should have a system that can reach peak volume on the preamp volume knob, without any audible distortion caused by the source. If you do have speakers bottoming out, you can decrease the ehad unit's volume further until all audible distortion is gone. At this point you will no longer use the head unit volume control, and use only the preamp for volume, fade, and balance. The preamp generally has cleaner EQing as well, being at the line driver stage of the signal processing, so you will get a very clean boost at say, 40Hz if that's one of your EQ frequencies on the preamp.

Hmmm...... I alway assumed it was best to keep things in the digital realm as long as possible and that utilizing a "good" head unit's DSP was the way to go.

-Fishy

In a perfect world, yes :) . I think most head units have to sacrafice too much for "features". I would personally prefer dedicated units.

and how much would a good preamp cost...

and what sort of "gain" can you even expect out of it?

I think thats more important to address.

IMO... this is a bunch of wasted time and money, just keep an eye on the volume control.

And what for recordings that are recorded "quiet"... it happens, and I have a few cd's and a few songs that I have to turn up 5-6 volume levels higher than others to get the same volume as "typical".

What do you do when that happens in the preamp setup?

William from NOLA wrote:In a perfect world, yes :) . I think most head units have to sacrafice too much for "features". I would personally prefer dedicated units.

What about this one?

http://www.clarion.com/usa/products/sou ... Z9255.html

Its a dead-head with DSP functions that consist only of a 5 band PEQ, 4 way Xover, and 8 channel time alignment. It doesn't even have a removable faceplate.

:)

-Fishy

have a few cd's and a few songs that I have to turn up 5-6 volume levels higher than others to get the same volume as "typical".

What do you do when that happens in the preamp setup?

Temporarily turn up the volume on the h/u?



-Fishy

Fishy wrote: have a few cd's and a few songs that I have to turn up 5-6 volume levels higher than others to get the same volume as "typical".

What do you do when that happens in the preamp setup?

Temporarily turn up the volume on the h/u?



-Fishy

so, whats the point of the preamp..?

I dunno.

In the other thread we talked about how my frx456 seemed to improve imaging......

and I read somewhere about a guy that took the high end pot out of some old school PPI processor to use as a master line level volume control......

plus 1/2 din preamps just look cool mounted in the dash.



-Fishy

Fishy wrote:I dunno.

In the other thread we talked about how my frx456 seemed to improve imaging......

Which was probably more because of the further amount of tweaking you could do.

+, placebo? probably a lil some of that too!

and I read somewhere about a guy that took the high end pot out of some old school PPI processor to use as a master line level volume control......

plus 1/2 din preamps just look cool mounted in the dash.



-Fishy

looking cool and having a purpose are 2 different things.

I just can't justify using the volume control on the deck, then the volume control on the preamp... the preamp is 100% not needed.

Not like ADDING things in the signal chain will magically increase SQ, especially just another volume control

I just want to know why this is so much better than just using the head unit's volume control?

well let's see.. a preamp can cost between $100-$400 on average depending on brand and style.
less if you go used. I see the Orion 300PRQ and 300PSW on eBay fairly often, and they go pretty cheaply.

as for the recording levels of the CDs, you use a reference CD. dynamic range is limited on a CD. You can only get so loud, thus you use a test tone CD with high but pre-distortion volume tones to set the preamp. you should know this. If you're playing a CD that was mastered at a lower mean level, you turn the volume up on the preamp a bit.. I've never had to use full volume on my systems. I've always made sure to have ample power so I don't have a problem with my system being too weak to handle any volume I want to listen to.

as for digital signal path, it's good as long as you can keep the entire path digital. The instant you go to analog though, you may as well stay analog because when you go back and forth from DA to AD to DA you're just re-sampling the data over and over and losing quality from the initial source. Very few product lines offer pure digital signal path from head unit to amplifiers. Alpine's F#1status is one of the few, and you pay dearly for it.

Another reason I prefer a preamp is the analog volume knob. I despise digital volume +/- buttons, and digital rotary knobs are just below that in my dislike list.

If you don't want to use a preamp, then don't. I didn't write this to convince you of anything. I wrote this as the title says, because someone asked me to.