DC from INPUT! - Page 2

Bakmeel · 9th March 2009, 07:19 PM

agi,

Can you explain exactly how you are measuring the DC on your inputs? A small drawing would help. Also, what kind of measuring device are you using? (I guess a multimeter).

Try adding a resistor to ground before your capacitor, to bleed off any residual DC voltage. If still the DC remains, there is something else at work...

agithegreat · 9th March 2009, 07:32 PM

Yes, I'm using a multimeter across the termainals of the socket pins (the none normally visible side of the RCA socket.)

The voltage is present only when i plug in my HU into the amplifier, but i tested the HU for the voltage on the output and got nothing......

The voltage flows form the ground to the centre pin too......
I got -10volts... ish when i put the red connector onto the centre pin and the ground (of the RCA) onto the black connector.
So put a resistor across from the centre pin to the ground then? Leave that in there all the time? Or just a one off?

Later i'll test for a voltage difference when the RCA's are plugged in between the ground of the RCA's (shield or whatever its tech name is :P) and the ground of my amplifier (cars common ground (chassis)).

agithegreat · 9th March 2009, 07:41 PM

Ok, just checked and the voltage difference from the amplifiers ground ( The cars chassis ) to the RCA's output and it is 12.whatever my batts floating at's voltage)
So 12.56 right now on my UPS batts....

So maybe I need to change that Capacitor so that its on the ground instead of centre signal pin. Also whats the harm in putting a cable directly from the RCA earth to the earth of my car? I hope that would fix it, yeh?

Bakmeel · 9th March 2009, 08:30 PM

Wait... let me get this straight... Your HU is your signal source yes?

When you measure the output with nothing attached, there is no DC between center pin (signal) and shield (ground) right?

If you measure the input of your sub amp, there is no voltage between signal and ground?

But.... when you hook the two together, a DC voltage between signal and ground appears equal to your battery voltage.

Then the next important bit of info is that between car chassis and RCA signal pin is <battery voltage>... Or is that between car chassis and RCA ground (signal ground)?

If you have a voltage between RCA ground and car chassis then maybe there is a miswiring in your setup.

agithegreat · 9th March 2009, 08:59 PM

No,

When i have the amp wired up corectly as i never had this problem with my old amp, or any of my other 2 wired in the same way...

I get about 8v difference across the RCA plug when i put the cap inline of the RCa signal. ONLY WHEN RCA's are pluged into HU! When caps not in i get 12ish volts here!

When HU not plugged in i get 0v between the rca gnd and signal.
When off i get a 12v FROM the RCA earth to the common earth (amps earth) This may also be the case when on i haven't checked yet...

agithegreat · 9th March 2009, 11:04 PM

Ok, I bridged the RCA's gnd to my amplifiers gnd.
Tut tut, blown a track inside just by the edge of a toroidal!
Will pull out the iron and fill her back in though

As this was a part to blow I noticed this... hmmmmmmmm.........
What looks like a capacitor which was definatly added on after the construction of the board.

So what this doing there?
Should I remove it? It appears to be connected one side to the track I blew... which leads ultimatly to the RCA's ground....
The other side goes onto a resistor then through another cap one way but god knows where then. I might remove this cap then see what that says???
What you guys think?

9th March 2009, 07:19 PM	#11
Bakmeel diyAudio Member Join Date: Jan 2002 Location: The Netherlands	agi, Can you explain exactly how you are measuring the DC on your inputs? A small drawing would help. Also, what kind of measuring device are you using? (I guess a multimeter). Try adding a resistor to ground before your capacitor, to bleed off any residual DC voltage. If still the DC remains, there is something else at work... __________________ More Power Igor! More Power!

9th March 2009, 08:30 PM	#14
Bakmeel diyAudio Member Join Date: Jan 2002 Location: The Netherlands	Wait... let me get this straight... Your HU is your signal source yes? When you measure the output with nothing attached, there is no DC between center pin (signal) and shield (ground) right? If you measure the input of your sub amp, there is no voltage between signal and ground? But.... when you hook the two together, a DC voltage between signal and ground appears equal to your battery voltage. Then the next important bit of info is that between car chassis and RCA signal pin is <battery voltage>... Or is that between car chassis and RCA ground (signal ground)? If you have a voltage between RCA ground and car chassis then maybe there is a miswiring in your setup. __________________ More Power Igor! More Power!

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9th March 2009, 07:32 PM	#12
agithegreat diyAudio Member Join Date: Jun 2008	Yes, I'm using a multimeter across the termainals of the socket pins (the none normally visible side of the RCA socket.) The voltage is present only when i plug in my HU into the amplifier, but i tested the HU for the voltage on the output and got nothing...... The voltage flows form the ground to the centre pin too...... I got -10volts... ish when i put the red connector onto the centre pin and the ground (of the RCA) onto the black connector. So put a resistor across from the centre pin to the ground then? Leave that in there all the time? Or just a one off? Later i'll test for a voltage difference when the RCA's are plugged in between the ground of the RCA's (shield or whatever its tech name is :P) and the ground of my amplifier (cars common ground (chassis)).

9th March 2009, 07:41 PM	#13
agithegreat diyAudio Member Join Date: Jun 2008	Ok, just checked and the voltage difference from the amplifiers ground ( The cars chassis ) to the RCA's output and it is 12.whatever my batts floating at's voltage) So 12.56 right now on my UPS batts.... So maybe I need to change that Capacitor so that its on the ground instead of centre signal pin. Also whats the harm in putting a cable directly from the RCA earth to the earth of my car? I hope that would fix it, yeh?

9th March 2009, 08:59 PM	#15
agithegreat diyAudio Member Join Date: Jun 2008	No, When i have the amp wired up corectly as i never had this problem with my old amp, or any of my other 2 wired in the same way... I get about 8v difference across the RCA plug when i put the cap inline of the RCa signal. ONLY WHEN RCA's are pluged into HU! When caps not in i get 12ish volts here! When HU not plugged in i get 0v between the rca gnd and signal. When off i get a 12v FROM the RCA earth to the common earth (amps earth) This may also be the case when on i haven't checked yet...

9th March 2009, 11:04 PM	#16
agithegreat diyAudio Member Join Date: Jun 2008	Ok, I bridged the RCA's gnd to my amplifiers gnd. Tut tut, blown a track inside just by the edge of a toroidal! Will pull out the iron and fill her back in though As this was a part to blow I noticed this... hmmmmmmmm......... What looks like a capacitor which was definatly added on after the construction of the board. So what this doing there? Should I remove it? It appears to be connected one side to the track I blew... which leads ultimatly to the RCA's ground.... The other side goes onto a resistor then through another cap one way but god knows where then. I might remove this cap then see what that says??? What you guys think?