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WakeWorld Discussion Board » >> Boats, Accessories & Tow Vehicles Archive » Archive through April 21, 2006 » 2 Pre-amp Voltage Questions « Previous Next »
By jon bassham (texasbear08) on Tuesday, March 21, 2006 - 5:30 pm:    Edit Post Delete Post
One, is there any way to measure the preamp voltage that mine three.1 linedriver is running to my amps?

Two, how risky is it to run a high pre-amp signal from my three.1 to my 3 amps - ED 9.1, Orion 8004, Clarion 480. Can i damage them with a high volt signal?

 
By Sound_Illusions (grant_west) on Tuesday, March 21, 2006 - 5:55 pm:    Edit Post Delete Post
Sorry I dont know how to test the RCA voltage signal at the Pre Amp/EQ. IMO the best way to test signal voltage is at the amp. Most amps like to see between 4-7 volts at the amp. That way you can adjust your signal voltage via a line driver or the gain on your EQ.

The way the you test or adjust your line voltage at the amp (check your owners manual) With JL amp's You test the output from the speaker leeds on the amp with a volt meter and a testing CD that has a solid straight signal and your deck at 3/4 volume your amp will produce a sertan voltage (check your owners manual for exact voltage) and you can adjust up or down with the gain at the am or the Eq or line driver, Sorry I can be more specific. To answer your second question running any amp with 2 much imput signal will create a distorted signal, You should be able to hear that. Running anything with distortion at high volumes is bad, Your not gonna blow up your amp right away so dont be worried about that. Do you have anything that has a clip light that you can use as away of letting you know you have a a clipping /to much line voltage situation. Example you see the clip light blinking you need to back it down so that its only flashing on a heavy note

 
By Mikeski (mikeski) on Tuesday, March 21, 2006 - 7:15 pm:    Edit Post Delete Post
Jon,

You might want to send an e-mail to the technicians at Audio Control or just give them a call. It's a real company with real people to give advice. I talked to a couple of thier engineers on the phone when I was working with Grant setting up some dockside audio repeaters.

As far as I know you would need a scope to measure the pre-amp signal. Even then it might be difficult to isolate the variables so you get a decent measurement. As Grant hinted sometimes your ear is your best meter.

You can overdrive the input audio section of any amp, in fact my ipod's headphone output can overdrive my truck's audio input. You might also just be trading gain for attenuation with amps and preamps. I would expect good performance as long as nothing is below 25% and nothing is over 75% on the dial. One clear sign of an over driven input is raspy distortion at low or medium volume ranges.

Put 4 sound engineers in a room with this topic and you are likely to get 4 different opinions (pretty much applies to all engineering issues).

 
By Psyclone (cyclonecj) on Tuesday, March 21, 2006 - 11:18 pm:    Edit Post Delete Post
Mike, opinion #1 :-) If you wanna do it....
It's actually pretty easy to measure the output of your preamp, given that you have or know someone with an o'scope. A cheap one is fine for audio. You can take an old RCA cable, split it in the middle and strip the wires so that you can attach the probe to the hot and the ground lead to the shield of one channel. Make sure they don't touch! Then, play a test CD with a 1khz test tone. Set the scope up to measure the output signal of the head unit, turn up the output until the sine wave starts to flatten out top and bottom (clip) then back it off until it is at the max undistorted output. It is pretty obvious. THen, using the gradient on the scope (or a true RMS voltmeter) measure the size of the AC signal. (.707 * the peak voltage) (1/2 of the signal) is the RMS voltage output before clipping. Once you've found the max undistorted output of your head unit, do the same for the output of the preamp.

I would say that the bigger problem you would have would be matching a high output preamp to multiple amps from different manufacturers, they each are probably designed to handle a slightly different range of preamp input voltage levels. You will have to back down the preamp output until the amp with the lowest voltage handling capability does not clip at it's minimum sensitivity setting, then set the other amps to match. Good reason to use the same amps or ones from the same manufacturer. The "voltage" gradients on the input level pots of most amps are usually not accurate.

I used a six channel preamp so that I have three independent pairs for my three different amps.

Clipping LEDs usually don't flash until the signal is heavily clipped, you will hear it in the speakers before you see the clip light flashing.

Measuring the output signal and clipping of the amps requires BIG dummy loads that will get hot, but that is the only accurate way to see if your amps are clipping. You measure it exactly the same way. If you have a two channel scope, you can have both the input sine wave from the RCA and output sine across the dummy load. On the scope, you can put them right on top of each other, to look for any distortion (output not shaped like input in some way)

Still, use your ears, but if you measure it you have a reference instead of just tweaking until it sounds OK.


 
By Mike Snyder (rem_pss308) on Wednesday, March 22, 2006 - 2:04 am:    Edit Post Delete Post
You can always use speaker-level to preamp-level adapter to hook the wires to the Amp.
 
By jon bassham (texasbear08) on Wednesday, March 22, 2006 - 9:50 pm:    Edit Post Delete Post
I emailed audio control and they said based on the clarion's 1-2V output the three.1 at 75% gain should be putting out 5-6V... So i would assume that will be fine.

If none of the amps are clipping and no noticable distortion... can i assume i am not running to high of pre-amp voltage?

Also, does any one in dfw have an o-scope i could use in exchange for some pulls???

Thanks

 
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