Amp Remote Turn-on via PSU?

bulgogi777 · 08-13-2004, 09:28 AM

Hey everybody, I was having some trouble with the remote turn-on function on my amp. It works fine with the switched +12V coming from my HU adapter, but I wanted it to run off of my computer PSU so that it would only be on when the computer turned on. I took a yellow +12V line off of one of the molex ends and ran it to the turn-on on the amp. But when I power up, my amp won't turn on completely, instead of the green "on" indicator, it is a red "protect" indicator. Is the +12V source different on the switched line vs. the PSU's +12V?

On a different note, I first tried to send one of the smaller 4-pin's yellow +12V line (from the power connector that would go to a floppy drive). Then I tried the thicker yellow from a molex end. Neither worked, so now I have to cut yellow ends, and in my Hardware Doctor display it says that my +5V line is running well below +5V (around +3V). Can cutting PSU wires cause this? or did I do something to blow a rail in my PSU?

Any help would be much appreciated, thanx!

rando · 08-13-2004, 09:57 AM

How far away is your PSU from your computer? You have to be careful about line resistence in low voltage signals. Suppose you are trying to pull 3A on your 5V rail. If you run enough wire such that the wire resistence is even 0.1 ohms, you will see a 0.3V drop on that rail. For typical 18G stranded computer power lines this amounts to only 8ft of wire (round trip). This resistance will increase linearly with length and gets worse if you use thinner wires.

To see a 2V drop you would need to pull a lot of current or have a fairly long run.

Get yourself an inexpensive meter to measure your voltages. That sensor inside your computer can be wrong and is worthless in any case for measureing voltages at specific points along your power distribution wires.

As for the Amp, yah it looks like something is going on there. You shouldn't have a problem running a 12v wire the length of your car to power your amp. The turn-on signal draw very little current so there isn't likely to be much of a drop there. Perhaps your supply isn't working, you have bad grounds, or some other wiring problem.

What size wire are you feeding your PSU with? Does it hook directly to the battery? Ground wires?

Imagex · 08-13-2004, 10:06 AM

try adding your pc's 12 volt ground to the cars ground, sounds like you have two 12V systems "isolated" your amp and pc grounds are not connected. Hope this helps.

bulgogi777 · 08-13-2004, 10:47 AM

Well, the amp issue I dont' think is related to the voltage issue. the voltage drop happened after I had the amp ordeal. but yea, i don't think the length issue is causing the voltage drop. I haven't extended the psu wires at all. I was just wondering if having cut molex wires could cause the voltage drop?

Oh, and that grounding sounds like a good idea. The amp is grounded to my passenger seat bolt, and the switched line is grounded to whereever... so I'll try sending the PSU +12V line and its ground to the amp and chair bolt. Thanx guys.

darkhalo · 08-13-2004, 11:07 AM

hmm.... have you tried hooking up 12v directly from say.. the cig ligter? if that works just use a 12v relay to cut the 12v from the cig lighter whenever your pc is not on.

I think this will work because we know cig lighters ground will be the same as your amps ground

Nutz · 08-13-2004, 11:10 AM

I went a different route with my amp remote turn on. A couple of times my computer crashed and sent a high pitch whine through the speakers. As I don't have control up front to shut off my computer, it was easier to run the remote turn on through a switch so that I can turn my amp off when I want.

This also was good because i use an internal sound card, and when the comptuer is booting up picks up a hum until the sound card is initialized. So I can turn on my amp after the computer is booted up. No hum and no need for an external sound card.

bulgogi777 · 08-13-2004, 01:35 PM

so, can having cut psu wires (near the molex output) cause the psu 5v rail to have a voltage drop? If not, then what could cause the PSU to drop the 5v down to 3-4v?

Alric · 08-13-2004, 02:23 PM

I use an amp relay from davidnavone.com

The amp is connected to the battery and a PSU-controlled relay controls the on/off state.

bulgogi777 · 08-13-2004, 03:00 PM

Ok, I've thought about it a little bit... as far as the grounding issue, my computer PSU is a standard ATX running to a tripplite 375w inverter. That inverter goes directly to the battery (pos and neg). So if its ground is the negative terminal on the battery, (which would mean that the PSU's ground is the same) and the amp's ground is to the seat bolts, would this cause a wiring problem?

Oh, and rando, I haven't extended any of my PSU wires. The only time I did was when I tried to run the +12v yellow wire to the amp remote turn-on. As far as wire gauge goes, I think the thicker PSU molex wires are 18awg, the thinner PSU wires (for the floppy power) are something slighty smaller like 20-22awg. And that extension wire was 18awg. I tried using both the thinner and thicker guage PSU wires to connect to the amp. Both resulted in the same "protect" led indicator instead of the green "on" indicator.

rando · 08-13-2004, 07:58 PM

Usually a 'protect' warning is caused from an overvoltage condition. This does sound like a grounding issue but could also be a faulty PSU or a number of other things. It's also possible that your ATX PSU doesn't like the output from your inverter. Inverters only mimic the 60Hz 110V mains usually with a modified sine wave output. Less expensive and/or poorly designed inverters can output something that's actually much closer to a square wave. The extra harmonics can be a source of problems. So you might try an alternate power source as well.

In any case, make a quick trip to radio shack and get yourself a $10 meter. This will be more than accurate to diagnose where your problem is. Check each of the outputs of your supply against a PSU output ground AND against your body frame as a ground. See if there is any appreciable difference. Do this for each output with no load and under load. Check for any significant variations. Report back here and I'm pretty sure we can quickly get to the bottom of your problem.

Any other approach will just be trial and error and educated guessing.

fantomas · 08-13-2004, 09:48 PM

i think you should keep the two power systems seperate (car and computer). run a small relay with the psu powering the coil and the car's powering actually turning on the amp

bulgogi777 · 08-24-2004, 09:37 AM

Well, I finally was able to work on this, and I think I have the answer to all problems... relays~!

these little guys can fix anything! so I was able to run my psu 12v into a relay which then turns my amp on, it's great... plus I was able make a relay circuit to have my computer turn on when I throw my inverter switch~! just wanted to say thanks for all your guys' help, happy carputing, hehe

Confused · 08-24-2004, 10:07 AM

The best way to do it

Garry

Nic · 08-24-2004, 10:58 PM

i dont like that method garry. i think it would be better to use the PSU to close the relay and feed the ignition through the switch, that keeps the power coming out of the PSU from being interfered with by the cars electrics, if that makes sense