Floating Ground

[Jamier]

I’m working on an amp that, by design, has a “floating” ground.I’m thinking I should Earth ground the input shields since tying them to the circuit ground will probably not accomplish what I want ( noise rejection). Is this correct?

Jamie

[Paul Birkeland]

You should consider providing a whole lot more info about what you're working on.  Connecting shield grounds to audio ground does tend to defeat the purpose of the shield in the first place.

[Jamier]

I was given a pair of K-501 boards by a friend. I built chassis for them with the intention of mounting the inputs off board. I have mounted RCAs on the chassis which require an input cable run of about 4 inches. The connection for the inputs,on the board, is about 4 inches from the PT. I concluded, possibly erroneously, that I should use shielded cable to connect the RCAs to the board. The circuit ground floats so I figured, possibly erroneously, that grounding the shield to the circuit ground would have no effect. At this point I intend to ground the shields at the ground on the IEC, but I do have concerns that they will pick up noise from the adjacent AC input.

Jamie

[Paul Birkeland]

At the IEC, connect the ground straight to the chassis.  Wherever you have cable shields, connect them at the load end to the chassis.  I would either connect the audio ground to the chassis right where that signal cable enters the board, or use a pair of anti-phase diodes to tie the audio ground to the chassis.

[Jamier]

PB, I don't have any 2A diodes but I have a crapload of 1A uf4007s. Can I parallel 2 of those in each direction, or is that a  no go?

Jamie

[Paul Birkeland]

You want the diodes to be able to blow the fuse if the SHTF.  I suspect a UF4007 would still blow a 1A fuse without trouble.

[Jamier]

PB, So should I parallel 2 uf4007s in each direction, or just use 1 in each direction?

Jamie

[Paul Birkeland]

You could try it both ways.

If there's a local electronics shop, the diodes don't have to be anything particularly special.

[Jamier]

What about a 2A fuse?

Jamie

[Paul Birkeland]

What is the current fuse value?

[Jamier]

In don't know. I'm away from it at the moment. Do you have formula for calculating the diode rating.

Jamie

[Paul Birkeland]

Yes, you look at the datasheet for the diode and read the number for forward current.

[Jamier]

Peak or average? I figure your going with average, right? So if I do have a 2A fuse, I probably need to use 4A diodes in anti-parallel to insure that the 2A fuse will fail if the SHTF?

Jamie

[Paul Birkeland]

I would stick with average.  You don't want the diode to blow with the fuse!

[Jamier]

So, am I correct? Or?

Jamie