I am trying to connect an after-market DSP to my OEM head unit. The issue is that the signal is not always being output by the head unit. When the system is first turned on with everything connected, the signal is off, but when the RCA is unplugged from the DSP, the signal immediately turns on and stays on after being plugged back in. Actually, just disconnecting the negative side of the signal from the DSP causes it to turn on. I know that the signal from the head unit is not turning vs an issue with the DSP because I have a scope connected to the head unit's output and can see when it switches on.
My first thought was that it is either some load sensing circuit to ensure the expected load is connected, or some kind of protection circuit when it senses too much current being drawn. I measured the OEM amplifier input impedance and it measures at either 500 ohms or 50 ohms, depending on the resistance used to measure it (another mystery perhaps). I tried putting dummy loads of 50 and 500 ohms between the head unit and DSP, but it still only turns on when you disconnect from the DSP. I also tried loads of 47, 250, 1k, 5k and 10k for good measure, and still no luck until I unplug from the DSP and plug back in. What could be going on here?
My first thought was that it is either some load sensing circuit to ensure the expected load is connected, or some kind of protection circuit when it senses too much current being drawn. I measured the OEM amplifier input impedance and it measures at either 500 ohms or 50 ohms, depending on the resistance used to measure it (another mystery perhaps). I tried putting dummy loads of 50 and 500 ohms between the head unit and DSP, but it still only turns on when you disconnect from the DSP. I also tried loads of 47, 250, 1k, 5k and 10k for good measure, and still no luck until I unplug from the DSP and plug back in. What could be going on here?
You should be aware that it can be very expensive to repair an OEM head unit if the manufacturer won't sell you the parts to repair it.
If you have 6v on all of the speaker terminals, the head unit may be going into protect if your DSP doesn't have a balanced input.
If you have 6v on all of the speaker terminals, the head unit may be going into protect if your DSP doesn't have a balanced input.
Thank you for the guidance. They do all measure around 6v, so I assume that you are correct. I did not consider that they were balanced outputs because it appears that there are only 2 wires per channel.
I may attempt to convert the outputs to unbalanced. Would there be any risk to the head unit in doing so?
I may attempt to convert the outputs to unbalanced. Would there be any risk to the head unit in doing so?
PAC, METRA... ? Make safe converters.
If the output is designed to drive speakers directly (not balanced preamp), a 'high power' Line Output Converter will do the job since they have transformers that will convert the balanced output to a standard RCA output.
Line Output Converters
If the output is designed to drive speakers directly (not balanced preamp), a 'high power' Line Output Converter will do the job since they have transformers that will convert the balanced output to a standard RCA output.
Line Output Converters