Some observations setting the gain
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=50810
Printed Date: May 21, 2024 at 8:12 PM
Topic: Some observations setting the gain
Posted By: Fat4free
Subject: Some observations setting the gain
Date Posted: February 25, 2005 at 12:35 AM
My amp is a Audiobahn A8002T running with 2 12" Kicker CVRs 4ohm DVCs at 400wx1@4ohm. My HU is a Kenwood that is a few years old. According to the formula, I am supposed to set the gain to 40 volts. However this can only be achieved by turning the head unit up to 30/35. At my normal highest listening volume, the head unit is at 28 but the output cannot even reach 40v even all the way up with a max of about 36v. I am testing the output with a test cd with 50hz. Whats up with this? Now for the Remote Bass Boost Controller. Once I have the output set to 40v with the HU at 30/35 I try and plug in this remote controller. The first thing is that it does not light up like it should as in the blue circle around the knob. Secondly, without the bass boost turned on, the max output i can get is 30v with the remote turned all the way up. Thirdly, if I turn the remote all the way down, the protection light + the power lights are lit up. Any reason for these. Just so u know about the system completely, the subsonic filter on the amp is all the way up at 50hz, with the LPF turned to around 100hz in addition to an external crossover at 100hz with the gain turned to MAX on it. The whole system is securely grounded and wires are perfect so no need to worry about that. Basically, I would like to know the following: 1) Why can I only get the output of the amp to be 40v when the HU is at 30/35? 75% of max volume as recomended is 27-28 which is the max i practically listen to it at. 2) Why wont my remote bass controller light up? 3) Does Bass Boost have to be turned on in order for the remote to work correctly? 4) Why does my amp go to protection when the remote is turned all the way down? 5) Why can I only get a max of 30v with the remote plugged in with a max of 40v with it unplugged? Thanks alot guys for taking the time to read this long post. Any help/experience you guys have with this is greatly appreciated.
Replies:
Posted By: kklagge
Date Posted: February 25, 2005 at 6:26 AM
If you have (2) 4ohm DVC subs and your amp will put out 400x2 @ 2ohm why aren't you running it that way? The A8002T is a 2-channel amp...or do you actually have an A8000T which is a mono amp?
You are correct in having the volume at 27-28. With the amp set up to run at 400x2 @ 2ohm you would set the gain so that the voltage is about 28.
The bass boost needs to be on in order for the controller to work (this should fix the problem with it not lighting up...if not then it's either defective or the wire is bad or the plug-in on the amp is bad...I'm guessing it will work fine with the bass boost on).
With (2) Kicker CVR's why do you have the subsonic turned so high? I'd set it to the minimum or somewhere around 25-30 at the most.
If you're using the Xover on the amp for your subs why are you using an external one also?
Set the Xover on the amp to about 80Hz and forget the external Xover and it should sound a lot tighter.
That of course is just my 2 cents and my experience with my Audiobahn amps (which I've had nothing but good luck with...stay away from their subs & speakers though).
Posted By: haemphyst
Date Posted: February 25, 2005 at 9:29 AM
DO NOT USE A METER TO SET YOUR GAINS! IT IS ONLY ACCURATE IN TEST TONE SITUATIONS AND THAT ACCURACY GOES OUT THE WINDOW WHEN PLAYING MUSIC!!!!
Turn all gains down. Turn you bass knob up (actually, get rid of it completely - those things are bad news) With a fairly loud CD playing, turn HU up, JUST until you start to hear distortion - whatever that number is (BTW, those numbers MEAN nothing, they are just reference points). Back it off a TINY bit. Remember that position, cause that's the LOUDEST you will ever want to turn your HU up to ever again. Go to the amp, and start to turn it up until you hear distortion again. (This is where the amp runs out, or the woofer is getiing all it can take.) This is properly matched gain settings.
-----LEAVE ALL OF THE BASS BOOSTS OFF!-----
Now... If you are using a 50Hz test track, and your subsonic filter is set to 50Hz, then you are NEVER going to set your system correctly. You want to set your subsonic filter to the F3 of your enclosure (what's F3? What's your box tuned to? THAT's F3)
Also 100Hz is WAY too high of a crossover point for a 12 inch driver - kklagge said it right - it should be around 75 to 80 Hz.
-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
Posted By: Fat4free
Date Posted: February 25, 2005 at 9:49 AM
kk the amp is an 8002 but it would run 200x2@4ohm in stereo and i prefer to ha-ve it 400x1@4ohm in mono. I cant wire the speakers to 2 ohm. The light on the remote still does not come on when bass boost is on but im not gonna mess with it. How should it be 28v when the sqrt(400x4)=40? Any external crossover is better than a amp crossover which is why I use it, it cleans up the sound real nice. Haem- How do I know what the box is tuned to? Its a sealed box i didnt know it was still tuned?
Posted By: stevdart
Date Posted: February 25, 2005 at 9:52 AM
One problem in using a test tone and meter to set the amp gain is that you have to rely on the published specs to be true and accurate. If you set voltage to what the specs say it should be, you may be into a clipped signal if the amp REALLY won't give that much.
Posted By: Fat4free
Date Posted: February 25, 2005 at 10:01 AM
True Stevdart but what I have it set at now (30/35 40v) the amp is turned a bit more than 1/2 way up which is where I had it by just temporarily tuning it by listening to it. It sounds good right where its at with no distortion so I dont think the numbers are off that much.
Posted By: stevdart
Date Posted: February 25, 2005 at 10:20 AM
Probably not. And it's usually common and necessary to do some minor tweaking from time to time as you listen to various music sources. If the system ever seems fatigueing to listen to, you'll know that a tweak is in order.
Posted By: kklagge
Date Posted: February 25, 2005 at 10:22 AM
You said you had 4ohm DVC woofers....correct? If so, then why can't you wire each one to 2ohm?
Actually the A8002T will put out 800x1 @4ohm mono so I suppose it's the same as running them @ 2ohm.
I set my gains the way haemphyst says to do them and have never had any issues ever doing it that way.
I've never owned an A8002T but I'm currently running an A1504DP in my truck and an A6004T in my wife's Xterra (and used to have 2 A4002T's in my other truck) and never turned the gains up past halfway...all my HU's were Alpine's with 4v preouts.
I would set your gains the way haemphyst said to do it and I'd be willing to bet that your gains will be a little LESS than halfway when you're done with it (assuming you have 4v preouts).
Posted By: stevdart
Date Posted: February 25, 2005 at 10:32 AM
kklagge wrote:
Actually the A8002T will put out 800x1 @4ohm mono so I suppose it's the same as running them @ 2ohm.
Yes, it's exactly the same impedance on each channel. A 4-ohm load bridged across two channels places half the load onto each channel. Preferred way to wire DVC subwoofers: coils in series, subs in parallel, bridged across the two channels or connected to a one-channel amp. 
------------- Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Posted By: kfr01
Date Posted: February 25, 2005 at 10:44 AM
I like Haemphyst's advice here. Very clear post. However, I'd bet that many of you do not know what distortion sounds like. I'm not talking about severe mechanical noise / unloading / or close to square wave clipping - I'm talking about distortion a little more subtle than that. Get the gain setting CD from Autosound 2000. It has examples of various levels of distortion on real music tracks. Learn how to identify the beginnings of distortion. Use this same track when setting gains. Apply Haemphyst's advice. Also, Stevdart's point re the problem with gains via a meter identified the issue - to be successful with that method the manufacturer needs to be honest. Easier with Zapco; laughable with Audiobahn. ------------- New Project: 2003 Pathfinder
Posted By: DYohn
Date Posted: February 25, 2005 at 10:55 AM
I always use a meter to set max voltage per specs first, then back it off from there if clipping is still evident. Doing this by ear is effective if you understand what to listen for. I suggest using an O-scope for critical setups. ------------- Support the12volt.com
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