Polk C400.4 Amp Question

mrmsudawgs

I have a C400.4 and have a question about setting the "input signal" to either "Low" or "High" on the amp. The manual says that if I have a head unit that puts out a 4V or 8V signal to the amp that I should set the "input signal" selector switch to "High". My Alpine CDA-9831 puts out 4V so I did this and immediately noticed that my volume dropped to about half of what it was. Specifically, my volume ranges from 0 to 35. Normally, I listen to it on about "19". Now that I have changed my input settings on my amp to "High" I have to turn the volume up to "30" to get the same effect. It is like the amp setting has cut my volume in half.

I have not changed the gain settings on the amp nor changed anything on the head unit. I have since switched the settings back to "Low" which goes against the user's manual directions but now the volume level is up where it should be.

Does anyone have any idea what is going on? What are other owners of this amp doing with this setting?

Thanks,

Mike

exalted512

the volume is half as low because the voltage is half as low. Try moving your gain up. I'm not familiar with that particular dial on the 400.4. Maybe try looking in the manual and see what it recommends?
-Cody

1996blackmax

Try to readjust your gains with this setting to see if you get good results.


I am not famliar with that particular model, but Alpine has been known to put out HU's that do not put out their 4V ratings. This happened to me with 2 different CDA-7998's. Every time I switched between the 7998's and my older 4V Alpine setup (CDA-7949/PXA-H600), there was always some tweeking to do with the gains on my amps. This meant turning the gains down when I put in my older Alpine stuff, and turning them back up when the 7998's went it. The subwoofer outputs seemed to be effected more.

mrmsudawgs

I went out and tweaked my gains. All is better now. Thanks for the advice.

I did notice that the sub sounded cleaner when set on "high" instead of "low". Maybe a cleaner signal is reaching the sub now. Hmmm. Guess I'll just leave it alone for now.

I'd like to just add one coment about the C400.4 amp - GEE FREAKING WIZZ THAT THING IS STOUT!!


Mike

1996blackmax

I'm glad it worked out for you .

MacLeod

The gain is not a volume control. What it does is matches your h/u's output with the amps. In other words you want to amp to be at 50% when your h/u volume is at 50%. If you set the gain to near max then the amp will be at 100% when your volume is at 40% and youll likely overdrive your amp, clipping it and killing your speakers possibly.

When you switched to the "high input" the gain lowers on the amp to match your intput signal. Ideally your volume will be maxed before the amp is so its normal to have to turn it up to 20+ for normal listening. I have an Alpine too and for normal listening with windows up Im at 20-24. However, having to go to 30 is a little much. That should be the level for windows down crankin'.

Either way, sounds like you got it worked out. Just remember to be careful with the gains and save your speakers and SQ.

PoweredByDodge

Unless alpine has changed their designs... most if not all alpine head units volume knob ranges from "zero" to "35"

just so that you are aware of this... the head unit's pre-amp output (the red and white RCA wires) will CLIP (read as "distort, play dirty, give **** signal to the amp, which means after the amplifier boosts it, its even more **** to the speakers") at about 23-25

I've scoped 4 alpine heads, from various model years, all were in the 350 to 500 dollar retail price range, and they all showed some form of clipping (when playing common recently produced music cd's) between 22 and 23 -- very noticeable clipping by 25. I try to keep my alpines "maxed out" at 22.

this means that i dial the deck up to 22, put in a "normal" cd that i listen to, and then dial the amp up until it is either a) producing audible distortion to the speakers, or b) until the speakers are at a volume that i feel is "well balanced" to the other speakers/amplifiers in my system.

what i mean by a "normal" "Recently recorded" cd is this...

modern cd's utilize better recording quality and devices... this produces a clean, consistent "source level" of sound, for the deck to read and amplify (a very little) into pre-out voltage (say 4 volts or so).

but if you have an older cd... or even a re-mastered new cd of an old recording... for example, "The Doors Greatest Hits" - that was recorded in the 1970's on dual 4-tracks... then they remastered it digitally and made cd's of it... so the original "volume" of the information on the cd was only about 70% or so (i'm just guessing) of what it would be for something Eminem just recorded last week on an original digital master.

i hope u sorta follow me here - i've lost my eloquence of speech these days... got my foot in my mouth half the damn day.

neomagus00

are you referring to the tendancy of older recordings to be quieter? cause i agree as far as sheer volume goes, but you also have to take into account the massive amount of compression on CDs today...

MacLeod

I didnt think passive signals could clip.

Ive got mine set to where my normal listening is between 20-25. Maybe I should turn my gain up some.

PoweredByDodge

the preamp output isn't exactly passive.

the original recorded information is passive, but once its read by the "laser eye" or whatever, it is then transmitted at some voltage, however small or large is irrelevant... it is - from that moment forward - no longer passive. that voltage that it's transmitted at is dependant upon the head unit and its internal components.

some companies had "4 volt non-clipping preouts" ... all that meant was that you'd get a deck that had true 4 volt RMS preouts - in all reality you probably had a 6 or 8 volt preout that was just "clean" to 4 volts.

now you get decks that are "4 volt preout" and they friggin clip after 2.25 volts (commonly observed ****).

there are several ways to "find the sweet spot" - but as an alternative to what i stated in the earlier post, you can just do this...

dial your gains down to the floor (almost nothing)... then juice the deck up... and really really really listen... when it starts to sound "different", even if its not what you'd normally consider as distortion or clipping... then that's most likely your pre-out clip point.

my old alpine was odd to figure out - i did the "gains to nothing" trial and i couldn't figure out where between 22 and 25 it was... but i knew it was in that range... i just couldn't nail it down. dicked around a little more and got it.

---

as far as my comment about "old recordings" and "sheer volume" - yup - that's what i meant. they're just plain quieter. a good way to "check" this is to rip an old classic rock cd or something of that nature and view the waveform of a track in something like goldwave. do the same with a newer cd... then dump one waveform over top of the other and view the relative size of the waveforms to each other.

1996blackmax

You are right about the older recordings. Whenever I play my CD of a little mix of the Stones/Doors/ & Animals I have to give it more volume than with the newer stuff. This is also where the remote amplifier controller comes in very handy .

AustinKP

I scoped my 9815 with a 1KHz and a 50Hz 0dB test tone. It didn't clip even at full volume (35/35). This was, of course, with the speakers unhooked. This is how I set my gains, so even after the amp, I had no clipping.

PoweredByDodge

cda-9815 is a nice piece of equipment - i remember when it had just come out it was retailing for $550, and all i could do was drool over it in envy.

i sooooo need a new deck.

AustinKP

I paid $360 for it 1.5 years ago. Bet it's a ton cheaper now.

MacLeod

Hmmm. I did crank mine up today to about 27 listening to The Police Syncronicity and it did sound worse. I think I will dial my gains up a smidge.

mrmsudawgs

I started this thread (initial post) because I had set my input on my amp to "high" and noticed a reduction in volume. As far as clipping goes, I was able to run my Alpine CDA-9831 to 35 (max volume) and no clipping occured. It was clean as a whistle. Of course, I've since adjusted my gains to accomodate for the reduction in volume so 35 would be much, much more than I could stand in the cab of my truck. It is still clean up to 27 which is about as much as I can take.

You can see my installation here

Mike

1996blackmax

Nice install .

neomagus00

the 'high-low' switch changes the input range, to compensate for high-power HUs... so on low you're adjusting for say a 0.2 to 2 Volt input, but on high that changes to 2 to 8 volts (i just made those numbers up, but they get the point across)...