Quest Z stator earth is also AC power earth

[Krazikiwi]

Folks,

I thought it was time to get into the swing of things and share a problem I uncovered when I set up my system years ago.

I ended up frying the output transistors on my 6 month old Jeff Rowland Model 8 that were connected to my Quest Z's.

To cut a long investigation short, I found that the Rowland is fully balanced, this means the negative speaker signal output has no connection what so ever with the chassis or power earth. However, the Quest Z negative signal speaker post is also tied to the AC power earth. Ouch! This means the poor output transistors were driving to ground and eventually gave up the ghost!

I now run the Quest Z's without AC power earth and have never had a problem since. Jeff Rowland was incredibly helpful and stood by his product with absolute superb customer service.

I recall a Japanese client ran into similar difficulty.

Are ther any other amps out there that run fully balanced operation through to the output stage?

Has anyone had this kind of challenge with the common signal and power earth on their MLs?

Jeff

 

[persson]

hello

well i think i am getting this problem to but i have not blown the amps i got two monoblocks acoustic reality ear one mk 2 but i gotspeaker outputs are both hot with 40 volt. did jou disconect a cable from the panel :rocker:

 

[Krazikiwi]

Hi,

No, I run my AC power cables into the MLs without an earth pin on the plug.

Has been working for 15 years perfectly.

Jeff

 

[persson]

hi

ok thank jou

 

[slowGEEZR]

Interesting post. This is the first time I've heard of an amp blowing with MLs for this reason! You would think that ground is ground, but I guess not. The usual problem with grounds and equipment is ground loops, causing noise in the speakers. I also solved this problem (ground loop noise) with my phono amp the same way you did, I used a cheater plug to eliminate the ground on the phono amp power cord. Strangely, I didn't have the problem when using my MLs, but first noticed it when I switched to the Wilsons in my main system.

 

[Krazikiwi]

Hej Persson and Steve,

I think the problem is only when using an amp that is fully balanced right through to the speaker outputs as Jeff Rowland and Acoustic Reality are.

Traditional speakers have no AC ground involved but the ML Request Z's do and they couple this AC ground to the speaker ground ( black negative binding post) which of course is upsetting to such an amp design as it has been designed to not do this.

Think of it as balanced versus single ended signaling, putting them together in the same signal path is a challenge on the earth side of things.

Are other MLs built like this with the common earth?

Se Dig. Cheers

Jeff

 

[tsv_1]

Are other MLs built like this with the common earth?

Se Dig. Cheers

Jeff

CLXs don't even have the third (earth ground) prong in the IEC receptacle.

The Quest Z manual doesn't include picture of someone being electrocuted with giant bold font exclaiming the horrifying results of connecting a balanced amp??? If not, that's unforgivable. There are many, many stereo amps out there that allow for bridging and even small inverter/adaptors that allow people to gang two monos together to create one massive bridged mono. These would all become smoke generators with a grounded negative binding post.

 

[GDSA]

Hi Krazi,
I have run Krell FPB amps into CLS (neg post has E pot.) for ages..No Problem.
My understanding is "fully balanced output" has no chassis earth involved in the output signal and no potential to seek E unless it is given that potential further back up the interconnect wiring chain.
HOWEVER
Pin Wiring on XLR is not universal from manufacturer to manfufacturer (and cables can be cocked up too) .. maybe some combo left the amp output with a potential to seek earth via interconnect wiring missmatch?? Just a thought!

 

[Speedskater]

Interesting post. This is the first time I've heard of an amp blowing with MLs for this reason! ...

No, actually "ground" is nothing more than a common reference point.
You can have:

Audio ground.
Digital ground.
Circuit ground.
Chassis ground.
Safety ground for AC power.
Mother Earth ground.

These are not all (or always) the same thing. How of they are connected to each other can and does change in different situations.

For instance the Safety Ground only connects to Mother Earth one specified way.