Help! t-amp in car, alternator whine - diyAudio
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Old 18th February 2006, 03:06 PM   #1
ractis is offline ractis  Singapore
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Default Help! t-amp in car, alternator whine

I'm trying to use a sonic impact t-amp in my car.

Power to my t-amp is tapped directly from my pioneer in-dash receiver's black and red wires.

When I turn my key to the 'ACC' position, the t-amp works normally.

When the key is in 'ON' position, there is a slight buzzing sound introduced. This buzz is present even when my receiver is turned off. The buzz also gets louder when the volume on the amp is increased.

When the car alternator is running, I get the dreaded alternator whine. The pitch of the whine goes higher when the RPM goes up, and again this whining volume increases when the volume is turned up.

With the power supply cable removed, and the amp powered by batteries, there is no problem.

I made and used a choke + capacitor filter but it had no effect whatsoever.

Caveat is I have almost zero knowlege little electronics / electrical systems. Is there something simple that I overlooked, or was I too naive to think that the cheap t-amp could be used in a car?

Would you guys have any ideas? Thanks in advance!

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Old 18th February 2006, 06:29 PM   #2
TO-3 is offline TO-3  Peru
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Default Re: Help! t-amp in car, alternator whine

Quote:
Originally posted by ractis
I'm trying to use a sonic impact t-amp in my car.

Power to my t-amp is tapped directly from my pioneer in-dash receiver's black and red wires.

When I turn my key to the 'ACC' position, the t-amp works normally.

When the key is in 'ON' position, there is a slight buzzing sound introduced. This buzz is present even when my receiver is turned off. The buzz also gets louder when the volume on the amp is increased.

When the car alternator is running, I get the dreaded alternator whine. The pitch of the whine goes higher when the RPM goes up, and again this whining volume increases when the volume is turned up.

With the power supply cable removed, and the amp powered by batteries, there is no problem.

I made and used a choke + capacitor filter but it had no effect whatsoever.

Caveat is I have almost zero knowlege little electronics / electrical systems. Is there something simple that I overlooked, or was I too naive to think that the cheap t-amp could be used in a car?

Would you guys have any ideas? Thanks in advance!

You have a ground-loop. Check your ground connection going to the amp. If it has a good solid connection and you still get the noise, try running a return cable to your battery.
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Old 18th February 2006, 09:52 PM   #3
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If this is the amp you have:
http://www.partsexpress.com/pe/showd...number=300-952

It doesn't seem to be designed for use in a car. It is not likely to have the proper input circuitry to work in a vehicle. If that's the case, you may be able to get it to work if you use a ground loop isolator between the head unit and the amp.

If your amp is different and is designed to be used in a vehicle, you need to check the shield ground on your head unit. You'll need an ohm meter set to ohms, diode check or continuity. Unplug all of the RCA cables from the head unit. Touch one lead to the head unit's case. The other lead to the shield of the RCAs on the back of the head unit. You should get the same reading as you get when you touch the meter's leads together. If the connection between the shields and the case of the HU is open, that needs to be repaired. For a temporary fix, you can connect the shields at the back of the head unit to the case of the head unit with a short piece of wire.
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Old 23rd February 2006, 10:03 AM   #4
ractis is offline ractis  Singapore
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Argh.. i'm losing hair over this. Tried:

- Grounding amp direct to battery
- Using high-end interconnects / unshielded interconnects
- Wiring the shield RCA of HU to its casing

None of the above worked...

I found that just connecting the +12V wire to my amp is good enough to power it. The same alternator whine is heard in this case (not louder or softer). Its probably using the RCA ground return path.

Since there is ignition noise when I turn the key to 'ON', does this imply a ground loop problem? I suppose the alternator ground is added to the system when I turn key to 'ON'.

Things to try next:
1. install electronic noise filters
2. re-ground alternator properly
3. use audio isolator between RCA

Will try no.3 as a last resort since I believe sound quality will be affected unless I use really expensive audio isolators.

Anyone with any advice on whether (1) & (2) would be effective? thanks!
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Old 25th February 2006, 04:51 PM   #5
ractis is offline ractis  Singapore
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Solved the problem by using an electronic noise filter before the power supply into the t-amp.

Thanks Perry, you were right that the t-amp isnt meant to be used in a car, hence it doesnt have the usual noise filtering circuits found in car electronics. I did some research and found that these filters can be bought separately and it really solved my problem.

For anyone else that is interested, the t-amp and a noise filter can be gotten from parts express for < us$35 (excluding shipping)
I tore out the chip and installed it in my empty 2nd DIN tray below my in-dash receiver. Will get around to casing it another day
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