DLS A7 RCA shield voltage?

[djQUAN]

I have a DLS A7 amp on my hands. having trouble with it having whine when the engine is on.

I have tried everything and narrowed it down to the amp as the whine is present even when there is no RCA cables connected to the inputs.

besides the whine, it runs perfectly fine.

I was wondering, does anyone have experience with these or have a schematic?

the amp I have has about 3-4VDC from RCA shield to chassis ground. and sinks about 10mA if that voltage is shorted.

the leakage voltage drops to zero when the amp is turned on. when the amp is turned on, measuring with a ohmmeter, I measure ~1.3kohm from RCA shield to chassis GND no matter what polarity the DVM is attached.

there seems to be a circuit that is powered up/connects to the signal ground but I'm unsure what the purpose is for.

 

[djQUAN]

no one?

 

[Perry Babin]

I have no experience with this amp so I can't help.

 

[djQUAN]

I have no experience with this amp so I can't help.

have you fixed/tested any amp that sends a small current through the RCA grounds when off for the protection circuit or whatever?

this thing is keeping me scratching my head. when the amp is on, there is no voltage across the chassis ground and RCA ground.

everything works just fine. oh well, if all else fails I'll return this back to the owner and tell him nothing's wrong with it.

 

[Perry Babin]

I've never had this problem, as far as I can remember.

Does the amp have an active noise canceling input or does it have an isolated secondary?

If you plug RCA shunts into the input jacks, does the noise remain?

 

[djQUAN]

it doesn't seem to have any active noise canceling circuit on the RCA grounds as each pair of RCA's have a 0.01uF cap from shield to chassis at the nearest board screw point. op amps near the RCA's appear to be just preamps and filters. no differential inputs there.

I don't have any RCA shunts (ones that short the tip to the shield) so I haven't tested. noise does remain when the RCA's are unplugged. there are no shorts/damage to speaker wires.

It's been known locally that BMW cars are notorious for weird noises in audio systems and this is installed in a BMW. might have to check the DC power if hte problem is in the car and not the amp.

 

[Perry Babin]

When I used the term chassis ground, I meant the amp ground that goes to the chassis of the vehicle, not the chassis/heatsink of the amp.

Amps with active inputs, typically have the secondary transformer center tap tied to the primary/chassis ground.

 

[djQUAN]

yup. same thing I meant. the amp chassis is connected to the car ground so I thought the term should be interchangeable.

this amp's transformer secondary is not directly connected to chassis ground.