Thread: Amplifier behind dash / kit amp ?

Excellent, thanks for all the info everyone.

Just going to order the AMP9 kit now

Hi Swift_gti,

The Ampctrl service raises the DTR (not DSR, sorry) on the serial port of your choice. The DTR line is Pin-4 on a DB9 serial port, or Pin-20 on a DB25.

Stop by radio-shack and pick up any simple NPN switching transistor. Like this one.
The mute switch jumper has a + side and a - side. Use a multimeter, or check the amp schematic to figure out which is which.

Transistor hookup goes like this:
Base -> Serial port DTR (Pin4)
Collector -> Mute +
Emitter -> Mute -

Transistors with a TO-92 case usually have the Base as the center pin. If you accidentally reverse the collector and emitter, nothing is likely to break or get fried, your amp just won't turn on. If that happens, reverse the transistor keeping the serial port DTR wired to the center pin.

When you start the ampctrl service, the amp should turn on. When you stop the service, the amp should turn off.

Hope this helps.

pb

Cool, thanks for that!
I've got a transistor like that laying around from another project so I will have a play once my USB > Serial convertor arrives

Hmm.. well I've tried the suggested and it works fine when the PC is on, but as soon as the DTR signal is set low by the software then I just hear fast ticking through the speakers
Any ideas?

Hi Swift,

So.. When the service starts the amp turns on, but when you stop the service you hear ticking?

What do you hear when you short the mute jumper? What happens when the mute jumper is completely disconnected?

pb

Yes thats correct.
If I short the jumper (pins 12 & 13 on the amp) I hear sound, if I disconnect the jumper then everything is silent.
However with the transistor doing this job I hear sound when the service is running but I hear ticking when the service is stopped

Hi Swift,

It's possible that the voltage on your serial port is not going low enough to fully turn off the transistor. It's also possible that the base-collector junction is building a charge large enough to switch on slightly, then as the charge dissipates along base-emitter, it switches off. This could be happening fast enough to develop a fast ticking at the speakers.

A few things you could try..
1) A different transistor.
2) A 10k resistor from base to gnd.
3) A diode between serial port DTR and J10-Pin12.

I'd try #3 first. According to the TAA4100A datasheet, the MUTEB pin requires >2.3V to unmute and <1.0V to mute. The serial port DTR should put out 12v when high. The voltage drop from the diode should prevent the amp from unmuting in the case of any leakage from the DTR pin in the low state.

Also, I saw your thread on the 41hz forums. If you think this thread is getting cluttered, we can take the conversation there.

pb

Thanks Pb, I'll give your suggesstions a try once I get home from work!

Hi Pb,

I've done some more playing around this afternoon based on your suggestions.. The diode didn't appear to make any difference (I wired it with the flow away from pin 12, I presume thats right otherwise I'd be feeding 12v into that pin )

However I did appear to have success with the 10k resistor from base to gnd.. I wired it onto gnd of my USB > Serial convertor USB casing with the 10k inbetween since I'm using a USB > Serial convertor for the DTR signal.. Is that correct or should I have gone to GND of the 41hz Board ?

I've encountered a new problem which is slightly more worrying.. when testing the various sugesstions my laptop battery began to die so I shut everything off and plugged it into the mains, when I powered everything back up I could smell burning after about 30 seconds and noticed the 41hz board wasn't powered up. I shut it off quickly and can see brown charring around R12 on the board. As soon as I pulled the power plug out of the laptop the amp was ok...
The amp still appears to be working ok, but this could present a problem in the car since i'll be powering the using the laptop for my car pc powered by an incar charger.
I presume that something is trying to ground through the amp ?? But i'm unsure how I can protect against it or what the problem might be

Cheers!