To Float or not to Float...

weebeesdad OP
54 posts                                                                            09-12-2017 12:48pm


Thanks for all of your responses. Cleeds triggered the solution when he (or she) wrote "a properly grounded power cord", which reminded me that I was having intermittent problems with the connecting plug of the preamp’s power cord. Swapped out the power cord and problem solved. I also have a pair of DeHavilland mono block amps with the same ground/float switches, and in the manual it states that leaving the switch in the "float" position may result in a "cleaner sound". At any rate, a fully functioning grounded power cord has done the trick...

Cleeds triggered the solution when he (or she) wrote "a properly grounded power cord", which reminded me that I was having intermittent problems with the connecting plug of the preamp’s power cord. Swapped out the power cord and problem solved.

It may have stopped the buzzing but it, just my opinion, is only a band aid that stops the buzzing. Just a guess on my part you may have a cold solder connection internally with the return signal ground output jacks on the preamp. When you close the ground lift switch the signal ground connection is being completed through the power cord equipment ground wires. There in the signal ground of the equipment is connected to the chassis of the equipment. The safety equipment ground is connected to the chassis. (If designed properly the signal ground does not connect directly to the chassis. May be through a resistor). When you close the ground lift switch on the preamp you completed the signal ground circuit from the preamp to the power amp through the power cords equipment ground wires. Preamp power cord >> to the wall receptacle "U" shape equipment ground contact >> to the power cord of the power amp.

Jim

Cleeds wrote:

This is extremely dangerous - interconnects are not intended to carry safety grounds. Following this practice means that a component's chassis could be energized with lethal voltage. Safety grounds should be "earthed" only through a properly grounded power cord, or a chassis that is itself directly connected to a safety ground.

This is absolutely correct, and it amazes me that audiophiles will accept a potentially lethal component in their house.  Interconnects are not designed to carry a safety ground.

There are several techniques for eliminating ground loops while at the same time having every component's SIGNAL ground connected to the SAFETY ground (i.e. the chassis and ground lug of the mains outlet) .

Look at section 15.10 of the document downloadable on this page for one sample solution:  http://www.valvewizard.co.uk/Grounding.html

It would be easy to retrofit the above suggested circuit (4 parts) into a vacuum tube component (especially one that's hard-wired).

Cheers,
Thom @ Galibier Design

What if all the AC powered audio equipment uses two pin mains plugs?

Then this is lethal, there must be always a ground.
Look at most CD players, tuners, phono stages ect, they mostly have a figure 8 mains plug on the back yes just two pin, and yes it get's it's earth ref from the next stage, the pre if it's earthed, via "guess what" the interconnects.

Cheers George  

georgehifi

Look at most CD players, tuners, phono stages ect, they mostly have a figure 8 mains plug on the back yes just two pin, and yes it get’s it’s earth ref from the next stage ...

I thought we were talking about components manufactured in this millennium, which typically use IEC connectors and either have safety grounds or special construction to insulate the chassis. It’s rare for modern equipment to use figure-eight, two-prong AC connectors.

You might still be relying on obsolete knob-and-tube wiring in your house, too. But most of the world has moved on from that.

No matter how you to try to twist this discussion, @georgehifi , interconnects are not intended to carry a safety ground. And there is no inherent risk in having a system with multiple safety grounds. The goal is to have equal electrical potential of each ground - rather than to bypass safety grounds.

georgehifi
2,764 posts                                                                       09-13-2017 11:20pm

What if all the AC powered audio equipment uses two pin mains plugs?

Then this is lethal, there must be always a ground.
Look at most CD players, tuners, phono stages ect, they mostly have a figure 8 mains plug on the back yes just two pin, and yes it get’s it’s earth ref from the next stage, the pre if it’s earthed, via "guess what" the interconnects.

Cheers George

No, an earth ground is not needed when the equipment is Class ll (Double Insulated) power rated.

If a piece of audio equipment is Class ll rated the power cord will be two wire. In the US and Canada at least the NEMA 5-15P or 5-20P plug will be polarized so it can only plug into the wall receptacle in one direction.

For detachable power cords there are of number of IEC connectors available.
The C17/C18 15 amp combo is widely used.
https://en.wikipedia.org/wiki/IEC_60320

Picture of power cord with a C17 female IEC connector.
http://www.yunhuanelectric.com/Clkj_Images/upfile/image/IEC-60320-C17-Power-Connector.jpg

Picture of the IEC C18 inlet connector.
http://usr.audioasylum.com/images/1/14409/C18_IEC_Inlet.jpg

Where the inlet IEC is a C18 a 3 wire power cord with a female C13 connector can be used. (Though NO earth connection is made to the equipment.)
https://www.kenable.co.uk/images/RB-291_i1.jpg

Here is a picture of the back of a Marantz PM8005 Integrated amp. Note the inlet connector is non earth grounding.
http://www.us.marantz.com/us/Products/Pages/ZoomImage.aspx?img=/Assets/images/products/PM8005/XL_pm8...

Here is a picture of the back of a Marantz SA8005 player.
http://www.us.marantz.com/us/Products/Pages/ZoomImage.aspx?img=/Assets/images/products/SA8005/XL_sa8...
Note the inlet connector is a 2 wire non grounding type.

NO earth ground connection is used.

~ ~ ~ ~ ~

As for using the small gauge signal ground wire of an IC for a safety equipment grounding conductor.

First the IC cable is not approved to be used as an equipment grounding conductor by any recognized third party testing laboratory. NONE.

IF a ground fault event, from the hot conductor to chassis on the load side of a small amperage value fuse were to occur it is possible the small gauge signal ground wire might carry the current long enough to cause the fuse to blow. Might.

If the ground fault event happened on the line side of the fuse, NO WAY. In the USA the typical 15 amp branch circuit breaker could pass 100 amps before it would react to the ground fault event and trip open. NO way the small signal ground wire of the IC can handle that kind of current. What will happen the small wire will blow, burn, itself free at one end or both where it connects to the connector. If the IC jack on the back of the audio equipment is soldered directly to a circuit board it may melt the solder and the arcing that follows may cause damage to the small circuit trace.

Now what if a ground cheater is used on a big honken Krell power amp that uses a 15 amp magnetic breaker to protect the amp. Do you think the small signal ground wire in the ICs will carry the high ground fault current and cause it to trip open?

Jim