JL HD 900/5 issues setting gains

So I tore back out my seat to make sure the gains were set properly.

I followed the JL manual procedure for setting the gains, specifically
pull out the speaker connections,
use a multimeter on vAC and adjust while playing sine wave on cd,
adjust gains at 3/4 volume to 20v

The highest it would go is 17v

Now it distorts bad at half volume. Looking, the current speakers are only 60w RMS, so the distortion is understandable.

BUT, WHY will gains not go to 20v measured by DMM?

I Do have a pair of Hertz I need to wire in this weekend, 80w RMS, so more there, but I'm not understanding why my amp isn't measuring up.

The subwoofer connection measured fine, at about the middle it was the 44.7 it called for, why not the front and rear?

Thanks for any input, even the obvious "that's not right", because I'm a noob and half sure I'm just somehow flubbing it lol

--alex

What are you sending it a signal from? Is your input sensitivity switch in the right orientation?

what's the input voltage switch set to? high or low? make sure that's the correct setting for your headunit's signal.

Page 9 of the manual:
http://media.datatail.com/docs/manual/119738_en.pdf

I have it set to low and am running low power from the Pioneer avh-5800 HU

Even with ohms law this makes no sense, 100watts RMS x 4ohm load = 400, sqroot of that is 20, so manual's correct.

I tried it with multiple sources, finally burning off the test tones from ummm the online site everyone kept referencing. It's Not -20db or anything, 0db.

Plus it IS going to 17, at "high" with a "low" input it would be a lot further off than that wouldn't it?

No further ideas?

Sent from my SM-G925V using Tapatalk

Do you have an actual resistive test load connected to the amplifier?

Are you driving the input voltage enough (enough volume out on the head unit before hitting the amplifier)? 3/4 volume is not exact science and is simply used as a "guessing point" to keep the source unit out of an area of clipping, but doesn't guarantee maximum output before clipping. It also doesn't consider the way in which different source unit's volume controls work. If it's a log volume control, it ramps up very considerably near the end of it's range. Meaning if your source unit has for example 4v preamp outputs (and *actually* makes that number), you might only be seeing around 1.5v out at 3/4 volume with a log volume control and need to up the volume on the source unit. This is why measuring with a DMM is just a *rough* way of setting gains and not really the best or most accurate way to go about it.

Are you trying to accurately measure the amplifiers output power or are you trying to simply set the gain structure for your system?

The best-practice method for doing this is using an O-scope and finding the clipping point of your source unit first, then keeping its volume a click below that. Then you'd also adjust each amplifier channel out using the oscope with tone(s) in the range the connected speaker will be playing up until just below the point of clipping. You can start with 0db tones for the lowest noise floor and then add some overlap by using -5db or -10db tones if you want more system output (at the sacrifice of increasing noise floor a little the more you go. Depends on the amplifier.)



-Steve

Let me know if that makes sense or not ;) Trying not to be too technical but I don't know how much experience you have with it so just let me/us know what questions you have.

At what level is the sine wave on the CD recorded? Needs to be 0dBFS to get the output you need, and then the DVM won't tell you if the headunit is clipping.

You could also check the voltage you're seeing on the RCA outputs of the head unit at whatever volume you're playing when testing with the tone. Like Chad said above though, that won't tell you if it's clipping or not. Most quality head units these days can get close to their max volume before clipping though. I would up the volume level to closer to 90-95% on the head unit and slowly up the gain as-needed starting from zero gain on the amplifier channels. Tweeters will be most sensitive to noise floor so the less you need to up gain on an amp on those channels the better.