madmanmax3000

So I'm in the process of putting a new system in my car and am faced with a dilemma. The amplifier that I really want to use doesn't have a remote gain control available for it (on the subwoofer channel specifically). I was considering making one, and was wondering if anybody had some experience.

I figure there are 2 options. The first would be to split my signal through a "Y" cable, and make some sort of an inline potentiometer on one end of the cable. I could then run this end into my subwoofer channel, and be able to control the voltage that channel receives.

The second option would be to fabricate a mount for a small servo to sit on the edge of the amp, and manually control the "input sensitivity" knob on the amp itself.

Either of these solutions would include a wire to the front for control.

Does anybody have some idea how to do what I want?

a much simpler approach would be to pick up a universal remote gain control knob that ran off of an RCA pass-through, but I can't seem to find any online. Does anybody know of one?

lensam69

If it's the same system you've been discussing in other posts, you need one of these:

http://mobile.jlaudio.com/products_c...hp?prod_id=446

You need to be careful with what components you use because you're using differential-balanced output from the head unit (You're going to be using mercmans harness right?), so you need an unit like this one with balanced inputs. It may not be cheap, but it's definitely the ideal product for your needs.

madmanmax3000

Wow, that looks great. So if I understand properly from the drawing, it will essentially turn my 4 RCA outputs from Mercman's cable into 6 RCA outputs, with one pair remote-level-controlled?

The 5ch amp I am considering has 3 sets of inputs, channel A, channel B, and channel Subwoofer

This would enable me to plug into each input and have a level control on just the "channel Subwoofer", correct?

97BlackAckCL

iTrader: (6)

lensam69

You got it...

madmanmax3000

I checked out the PDF manual and it says the inputs are differential-balanced and the outputs are unbalanced. What is the significance of that?

Does this essentially do what mercman's balun does and also acts as a remote gain control?

And more importantly, an unbalanced signal will still work properly with a balanced amp, correct?

lensam69

What amp are you getting exactly?

madmanmax3000

it's a Next 5.500

they don't have a website but the closest thing to it is this...

http://ampguts.realmofexcursion.com/Next_VRz_5.500/

Is this what I want for this amp?

And thanks for all of your help lensam, if this works out it could save me tons of money!

madmanmax3000

For those of you who don't feel like clicking, here's a picture of the inputs:



As you can see there are 3 sets of inputs, and right now I only have 2. I am hoping to use the JL splitter to split the front channel into "A" and "Sub" so that I can have remote gain control on the sub.

Think it'll work? There are more pictures and specs of the amp if you follow the link above.

wong05tsx

iTrader: (6)

seem to be pretty settled on a gain knob o_O

could easily just Y-split and fade forward :\ to turn down sub if you wanted to. yea yea i said it before, bored b4 school!

madmanmax3000

Well I ordered it, $59 with free shipping from Crutchfield so I figure if it doesn't work I can always just return it.

It's certainly cheaper than getting a JL 250/1 (which would give the same power) and now I get a Class A/B subwoofer amp with gain control (hopefully). Exactly what I wanted!

lensam69

The only "problem" you may find, is that you'll have to set the gains differently for each input, since one set of speakers will use a balanced signal, while the other two will be receiving and unbalanced signal. Place the controller as close as possible to the amp to avoid line noise over the unbalanced section of the wire run.

You mentioned that amp in the other post and had come to the conclusions that it can receive balanced inputs right?

It's easier to connect unbalanced signal to balanced equipment than the other way around.

madmanmax3000

Yes, the amp seems to be balanced, but how should a balanced signal's gain setting differ from that of an unbalanced signal?

I was under the impression that the proper gain was to be calculated using only watts and ohms. What else should I be taking into consideration?

Reach

Why do you need splitters? Your amp has an "A+B" button for the sub section.

madmanmax3000

Basically because I'm picky. I know that I can get a signal to the sub channel no problem without using a splitter, but I really want to have control over the subwoofer's level. I listen to mostly classic rock, but often put on some rap or techno. I don't want to have to run to the trunk to turn up the sub output when I really want some bump

Also, I often get a pretty full trunk, so any way to save room in my trunk is great. Without this cable I would have to get a second amp and lose valuable space.

lensam69

You have to read up a bit on Balanced and Unbalanced connections.

In a *very* simplified nutshell, what the balanced connection does, is sending the signal on the + wire, and the opposite signal on the - wire (Hot and Cold wires). The amp measures the difference between the two signals, and calculates the actual signal it wants to reproduce.

For example (Remember this is very simplified), if it wants to play "6" it would send "+3" on the hot wire, and "-3" on the cold wire.

The unbalanced connection simply sends the full signal on the +wire, and uses the -wire as a ground reference ("0"), so if the unbalanced connection wanted to play "6", it would just send "+6" on the hot wire, and "0" on the ground wire.

When you interconnect balanced to unbalanced, you're only taking the signal that's coming in through the +wire, so if the source is trying to play "6", the unbalanced amp will think it's trying to play "3", since it only uses the "+3" signal coming through the +wire. You would need to adjust your gain on that channel to compensate (catch up with ) the other channel that's receiving the full balanced signal.

Again, very simplified, but it kinda sums it up.

You would set your gains the usual way. (You are setting the gains the right way right?)

madmanmax3000

I'm actually in EE school so that makes a fair amount of sense to me. So since my amp is seeing both sides of the wave, it doesn't matter that it's only on the positive side, right?

I can set everything as the site tells me to? Just do sqrt(P*R) = V ?

K25LOL

http://www.aaroncake.net/circuits/volume.asp

mercman

You’re over complicating this,

The gain setting and voltage levels don’t change.
If you feed a balanced differential amp with an unbalanced signal you just loose CMRR (Common Mode Rejection Ratio), the ability for the amp to reject noise picked up on the interconnect line. You do however gain Ground loop isolation so that is a benefit of differential input amps and pre amps and why JL and others are using it.

The problem arises when you attempt to feed a balanced differential signal into an unbalanced amp.


Max, as I explained in my PM you have to watch your levels and you might not be able to play the HU at full volume (40) without distorting your rmt level control. Also, the extra 10dB of boost on the sub channel will have to be accounted for when setting the sub amp. You don’t want to cause the sub amp to clip.

I don’t think you will play the HU at 40 with the sub cranked but you never know.

jeff

K25LOL

Can't he just use this formula?

lensam69

I would assume that the way the RCA cable is built you will be using the hot wire for your unbalanced signal input anyways.

By the way Jeff, I received your harness, but hadn't had time to unpackage it. I just opened it today, and WOW. Top notch quality, money well spent.

Thanks!

madmanmax3000

My remote gain control from JL came in yesterday and I installed it but am having issues with it.

I then decided to split the front channel RCAs. So I ran my front channel inputs, and sub channel inputs to the amp from the JL unit, and I ran the rear channel directly from the amp.

I turned on the system and got a loud high pitched whine from the rear speakers. The car was idling, and I noticed the whine to be in tune with the RPM fluctuations. I decided to turn the gains all of the way down on the rears and fade the sound to the front. this effectively muted the rear speakers.

After doing that everything sounded great! The front channels sound as good as before, and using the knob I am able to go from hard hitting bass to a full mute of the subwoofer.

There is one thing I did that may not have been correct, but shouldn't have produced this problem. There was one wire that wanted "ignition switched" power, which I powered with the "remote" wire. However, if that wasn't correct I would assume nothing would work.

What do you guys think is causing the rears to do this?

EDIT:

I also have plenty of pictures of the unit at home that I can upload later if that would help. There is also lots of info about the unit if you follow the link from lensam up top.

lensam69

Just to see if I understand correctly, both outputs from the gain controler are producing good sound, but the one that's connected directly to the amp is the one causing issues?

madmanmax3000

mercman

You’re amp is not balanced differential. You also have to move your ground and power connections to the JL box as I explained in my PM. You can pick up another JL for the rears or wait a few more days for my 4 ch interface converter.

Jeff