Turn on/turn off thump solution!

**GreenBeast** · 08-12-2005, 08:29 AM

Right this is what i have done with my system to prevent startup and shut down thump.

it just uses a normal bosch 5 pin automotive relay

what happens is the relay uses (opus) molex power connection to switch the ignition feed to the amp.
this means that when you turn the key, the relay will connect the supply and turn on the amp at the same time or slightly after the motherboard.
and when you turn off (take key out) the ignition goes dead before the relay is opened which prevents shut down thump (this was the issue i had)

here is a pic:

**kbyrd** · 11-07-2005, 11:35 PM

Originally Posted by GreenBeast

what happens is the relay uses (opus) molex power connection to switch the ignition feed to the amp.
this means that when you turn the key, the relay will connect the supply and turn on the amp at the same time or slightly after the motherboard.
and when you turn off (take key out) the ignition goes dead before the relay is opened which prevents shut down thump (this was the issue i had)

Holy, thread resurrection Batman!
Seriously, I don't see how this helps. What causes thump? Is it the audio signal showing up and disappearing with a powered on amp? If that's the case the rule should be always power on the amp after the pc and shut it down before the pc:
PC On, Amp On.
Amp off, PC off.

So with your circuit, the ignition wire goes dead, the relay opens, the amp turns off. The PC turns off a little while later (mine does standby after 5 seconds). Is this right?

**sdashiki** · 11-08-2005, 10:30 AM

Amp thuds are from it receiving a signal before it has a chance to power on/off completely. usually all amps have a mute circuit that keeps this from happening as it powers up/off.

If you still have the problem, the amp is outputting a signal before it should.... I dont know what else to say that isnt said elsewhere.

**gnomad** · 11-08-2005, 10:35 AM

Personally, I think the right way to go about this is to drive the amp turn-on through one of the PC's parallel port pins. Many sound cards thump when they are activated, and some custom software could power up the amp *after* the sound card has been enabled. Another advantage is the ability to turn the amp off on-demand. For example, if you are are on the side of the road, with the engine off, doing some navigational planning, you can have the amps turn off to save battery power.

Google for "programming the pc parallel port" for scads of code and simple circuits.

-p.

**kiltjim** · 11-08-2005, 10:37 AM

Problem with th parellel port is that when the computer is coming on, several of the pins sometimes go high and low sporadically. This is the problem with some of the parellel port relay cards.