JL Audio 500/1v1- Low Output

[gsxtasy]

Alright, so I have this JL 500/1, and I just put in a new 8w7 and hooked it all up and it was pretty quiet, it sounded clean and clear, just quiet. So I went to adjust the input sensitivity as described by the manual.

So I get it all setup, and even with the gain all the way clockwise, while running a 50hz sine wave at 0db, I am still only getting around 5.5v on the sub output terminals. It's supposed to be up to 38.7v for a 3 ohm sub.

I'm using an Alpine CDE-126BT headunit, with all EQ's off. Subwoofer out is on with it turned up 3/4 of the way.

Voltmeter was set to AC.

Amp Settings:

Infrasonic Filter: Off
Bass EQ: Off
Low Pass filter: 24db ; knob at 85 ----Also tried with this off.
Input Voltage: Low

[Perry Babin]

Measure the AC voltage on the RCAs feeding the amp. Place the black probe on the RCA shield and the red probe on the center conductor. Do this with the 50Hz sine wave and the volume set to ~80%.

[gsxtasy]

Hmmm, doing this test I only get about 86mV from eeach RCA. This is with the 50hz sine wave playing with volume at 30 out of 35. That doesn't seem right.... this is pretty much a brand new headunit though.

[Perry Babin]

Measure the resistance from the shield ground on the head unit to the case of the head unit (no RCAs plugged in).
RCA Shield Repair

[gsxtasy]

Does it matter if the head unit is on or off, and which lead goes to which point?

Here is what I found:

Head unit off; red lead on case/black on RCA shield = .6 ohm
Head unit off; red lead on RCA shield/black on case = 0 ohm
Head unit on; red lead on case/black on RCA shield = 0 ohm
Head unit on; red lead on RCA shield/black on case = 2.6 ohm

Probably made that way more complicated than necessary, but thought I'd share the results... thanks

[Perry Babin]

You should not read anything different no matter the probe orientation or the head unit on of off. Did you disconnect the RCA cables from the head unit?

It's probably not important.

Go back and measure the AC voltage on all of the RCA outputs.

[gsxtasy]

Originally Posted by Perry Babin

You should not read anything different no matter the probe orientation or the head unit on of off. Did you disconnect the RCA cables from the head unit?

It's probably not important.

Go back and measure the AC voltage on all of the RCA outputs.

Yes I had them disconnected. Maybe a problem with my dmm? It was definitely reading differently.

Measure the AC voltage on RCA's on the head unit itself with the sine wave playing? Thank you for your help so far, I appreciate it!

[Perry Babin]

Yes. Check both front and rear outputs.

[gsxtasy]

Doing this, I get 137.5mV for the front RCA outs, and 97mV for the Subwoofer RCA outs.

This is with the same volume and tone that was previously measured.

[Perry Babin]

It appears that the head unit is not working properly. Do you have a different head unit that you could try this with?