Howdy all,

In tinkering with my Rockford TM400x4ad I constantly ran up against the problem of the SS PN4.1000d in the fairing running the four speakers up front stomping all over it. The Rockford just didn't get loud enough to keep up. It sounded great, especially with the EQ adjustments, it's just that once you got rolling it was MIA.

When Lefty told me he installed one in his fairing and said it didn't get very loud that got me to thinking. He has the same head unit I do, the pre-Rushmore HK with preamp outputs installed by Iron Cross Audio. I had boosted the gains a bit to get the sound I had and noticed I could hear white noise coming out of the speakers when the volume of the head unit was turned down, so that implied that the amp just wasn't getting a fat enough signal voltage wise.

I did some searching on Ebay for line drivers and found the PAC LD-10. PAC had come through for me every time in the past when I needed a gadget to mate my OEM head unit to aftermarket equipment, so I thought I'd give it a try since I found one for only $15. I got out my old Tenma CRT oscilloscope and put in the Rockford test CD on the 1 KHz track looping and ran the volume all the way up on the head unit and backed it down one notch (with the speakers unplugged). I recall this was how high I could turn the volume up before the input clipping light lit up on the TM400x4ad. The reason I used the scope is most DVMs can't display such low voltages accurately and definitely will not show clipping of an audio signal. On the preamp output I measured 4 volts peak to peak. I bumped the volume up to the highest notch and just barely saw the peaks of the sine wave flatten out a bit. I thought that was really cool because that means the clip indicator light on the amp was dead accurate.

I then plugged up the LD-10. Since the turn on lead for the amp was fed by a PAC TR-4 I was able to use it to power it. The TR4 delivers a couple of amps of current so that was more than enough. I then put the scope on the output of the LD-10 and saw it was about nine volts peak to peak but the sine wave was clipped noticeably. The adjustment pots were turned all the way up so I backed them down until the flat spots on the peaks of the sine wave rounded out properly meaning no clipping was present. At that point I knew I had a clean nine volt signal to feed the amp with. The specs of the amp from RF say it can take a twelve volt input signal so I figured that would work fine.

I then turned the gains down on the amp, plugged in the inputs and began adjusting them back up. Now the output clip lights both came on at about 1 o'clock, which is a good bit sooner than they did originally. Next I turned the volume back down and put in a music CD and had much more volume than before. I didn't have to run the fader nearly as far towards the back to have things balanced out.

Here is the LD-10:



Since I wanted the ability to tweak it if necessary without pulling the fairing cap off I mounted it in the bag with the amp for now:






I figured I'd throw this out there in case someone needed a fatter signal but didn't want to spend the money for a DSP. With all the different head units and amps out there it stands to reason that some combos wouldn't match up as good as others and this little doodad helped me out in my situation.

 

Thanks for the update Hoyt!! Guess I now know what I need.

 

You're welcome Lefty.

One thing I just discovered when I got back from a ride is the amp seems to run a little cooler. I had never encountered an amp that ran as hot as this one before. I guess now with the gains turned down a bit it isn't working as hard as it was originally.

 

This is interesting..... I just installed a system in my Road King and was waiting on an Oscilloscope to come in to get everything set properly. I had set the amp based on calculations but had no idea whether it was really clipping or not. Well, got the handheld in yesterday and set to checking the source first to see about clipping(my Android connected to a JL Audio MBT-RX Bluetooth Receiver) and found that with the phone turned all the way up I am only getting around 1.5v of input from it. I am interested to find out if something like this would help me get a little more juice to the amp, allowing me to turn the gains down on it a touch just so that it might run a little cooler since it's stored in the saddlebag? I was contemplating using a DSP device(and still may do that) to get more tuning ability since I don't really have a head unit to tune with...

 

I have read about folks using this device for phones as well. It should work fine. I imagine you could compare the wave forms from your phone as is then pipe it int the LD-10 and put the scope on the output and set the dials on it to get the sinewave you want, then patch that into your amplifier and adjust the gains on it.

All you would need to get in addition to the LD-10 would be a 3.5mm to RCA male patch cable. If you like the volume levels you are getting then you might feel safer spending the money on a DSP.

 

Here is a short clip I made before installing the LD-10 on the rears. You can really hear the hiss from the gains having to be turned up so high. For some reason the SS PN4.1000d in the fairing likes the same signal just fine. I don't know a thing in the world about YouTube so I may have buggered it up but here goes:

 

Well, I looked up the specs, as I have the PN4.1000D as well, and saw that it take 600mV-6V input wise..... so I'm just gonna go for a DSP so that I can control more EQ wise, Levels wise, and Crossover wise. I just feel like it should be a little louder, but I may just be being picky. I went full Pro Audio speaker wise and I can at least turn my source(cell phone) all the way up without distortion. Then I have my gains set on the PN4.1000D at about 10:30(clock face) on each channel without distortion. Just got a handheld oscilloscope in yesterday to verify. I was able to dial both channels up to around 22.0v with the bike cranked, which was a little less than what the formula was. I tested it with a SPL and hit 108dB fully cranked out of 2 PRV 6.5's and 2 Cadence Xpro 6x9's. Maybe I'm just being too picky, lol.

 

Hey ssmorga, I run the gains on my SS at about 12:00 with no distortion. Maybe try that and look at the output with your scope and see if the peaks of the wave form flatten out. If they don't that may be all you need to do. If you aren't getting white noise with no source input and the amp on then I don't think a line driver is what you need.

 

No, not getting any white noise out of it at all. I went out last night and tested it out again with the scope and around 22.0-22.5 was all I was able to get out of the SS amp without the peaks flattening out.... which put the dials aiming at just about 10:30. Any higher than that, with a 1000hZ track at 0dB I downloaded from JL Audio, and those peaks flatten out something fierce. Not really sure how you are getting Noon on your dials without distortion though? You running your headunit at 2/3rds volume or max volume? That could be the difference, as I am maxing out the volume on my Android to make sure that I can get max volume out of it and not have to remember to not go over a certain point. I figured that was a good way to set it once I tested it out and made sure that it didn't clip if I had it at full volume.

 

ssmorga my head unit is the stock HK with preamps installed by Iron Cross Audio. It puts out a little lower voltage on the low level outputs than most aftermarket head units do, so I suspect that is the difference. If I remember correctly with a 1Khz test tone I can turn the head unit up to one notch from wide open before I get clipping. Some head units will go wide open with no clipping. The 2/3 volume recommendation is really not applicable if you can test properly. It is just a setting some folks use if they do not have access to an oscilloscope. I had a similar discussion with Iron Cross a while back. Each head unit is different so there is no one size fits all volume setting when tweaking gains.

Maybe put the scope on the output of your phone to see what your peak to peak voltage is with a 1 KHz test tone. If it is down around 4 volts or so maybe the LD-10 would be worth a try. It boosted the 4v output of my stock head unit to almost 9v peak to peak with no clipping at all. If I turned the adjustments of the LD-10 higher the voltage didn't increase but the wave form definitely clipped. I was definitely pleased with the increased volume from my rear speakers after taking the time to set the LD-10 properly.