Spectral amps and lifting their grounds

ack

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This is a subject I've discussed with the dealer a number of times, and the bottom line is this:

The way to lift the ground for the amp is to use a 3-2 adaptor into the wall socket. If you'd like to do something more elegant then I could order you a Nordost QRT QB8 MARK II. They also make smaller ones namely the QRT QB4 MARK II or QRT QB6 MARK II. If you use the Nordost then everything is floated (without using cheater plugs) except for one socket where the preamp is plugged in.

I am pretty sure there are no safety concerns, and I know that Nordost know what they are doing as well.

Sonically, this is something I have experimented with extensively with the older 400RS and current 500AR monos, and the results have been interesting:

1) With the amp grounds in place and everything connected, I've always had a very faint hum from the speakers, audible only if you stick your ear to the woofer and it was barely audible. It's unclear where the loop is, considering that all cords and interconnect lengths are respectively identical and the same respective brands

2) With the amp grounds lifted, the hum is gone, even if I lift one amp's round, but prior to recent power-management changes I am not sure I heard real sonic differences either way

3) With my current full loom of 13 Shunyata Venom NR & XC cords plus Denali 6000/S V2, and a much cleaner signal all around (from source to speakers), the difference and improvement WITH GROUNDS LIFTED is fairly easy to discern and appreciate. There is incredible fidelity to string tone, even from FM radio, and timbre all around is really a notch higher. That tiny hum seeping through the ground connections can be a killjoy. I would love to be able to figure out where it's coming from, but my efforts so far have been fruitless.

Just my experience, and obviously, proceed carefully if you were to entertain this type of experimentation.

-ack
 

dan31

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Are you using a cheater plug for your amps on the Denali?

Let me know if you demo the Nordost QRT QB8 or other model. I have been curious about the products ability to isolate the ground. I would consider the product but the price per contents is a little on the high side. If it works and the system is happy then perhaps its worth the price of admission.
 

ack

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Yes I am using cheater plugs, and the fundamental question with all of them is whether they affect instantaneous current delivery. I experimented with a number of them from various sources, there are no heavy duty ones that I could find, and ended up with these JACKYLED https://www.amazon.com/gp/product/B071FFHQNC/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1 for a firmer fit (and like all of the ones I could source, they are folded metal - not ideal).

If anyone has better suggestions, I am all ears. I could not get away with wrapping the ground prong with electrical tape, with the Denali (it worked with the previous MIT Z-Strips).
 

Kingsrule

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Cut the ground lug off ur pc of choice or disconnect the ground at socket Anything better than cheaters.....
 

ack

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Aren't I glad I did not spend too much money on cords ;)
 

ack

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Success. Found thin electrical tape that works well to cover the ground prong. Time to drink and listen...
 

Whbgarrett

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I have always (for DMA 360, DMA 360 Series 2, DMA 400RS and now DMA 500AR) as suggested above, simply disconnected the ground at the socket. Works like a charm, and sounds quite good to my ears.
 

ack

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Thanks. You mean you disconnect from inside the chassis?
 

Whbgarrett

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Yes. Remove the ground lead, enclose it with electrical tape and bend it backward out of the way.
 

DonH50

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Unless the manufacturer states the component is certified to be used without the safety ground ("double insulated") then removing it is a shock risk. The risk may be minimal in normal operation but if something in the line or power circuit fails the chassis could go "hot" and shock or electrocute someone as well as damage itself and/or other components.

There are numerous aftermarket solutions, and you may be able to install a series resistor (small value, but usually 5-10 W) in the internal ground to break a ground loop and reduce noise. That should not be done without the manufacturer's approval.

A "cheater plug" is a convenient way to test for ground noise issues but should be considered a temporary troubleshooting device used with strict precautions and not a permanent solution.
 

bazelio

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Yes. Remove the ground lead, enclose it with electrical tape and bend it backward out of the way.
This is what I'd do too. The ground connection to the IEC won't be soldered... Or probably won't be. :)

Note: I'm not endorsing the floating of an amplifier. I wouldn't do this at all. BUT, if you're dead set (poor choice of words?) on it, then that is how I'd do it. :)
 
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DaveC

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Hmm... I'd bet the increase in SQ is from noise that isn't necessarily audible, but hum indicates there's a ground loop.

Do you get the hum with only the amp on and no IC cables connected? With the ins shorted? Are the amps on their own circuit?

One possibility to alleviate the electrocution issue would be to install ground straps from the grounded chassis to the other chassis.
 
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ack

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Hmm... I'd bet the increase in SQ is from noise that isn't necessarily audible, but hum indicates there's a ground loop.
Yes, I agree, it's more than the faint hum seeping in, which is why I did not consider in-series resistors
Do you get the hum with only the amp on and no IC cables connected? With the ins shorted? Are the amps on their own circuit?
No, no hum if I remove the interconnects. There is a small loop somewhere. Everything is star-grounded at the Denali (or MIT Z-Strips before it)
One possibility to alleviate the electrocution issue would be to install ground straps from the grounded chassis to the other chassis.
Yeah, and they would need to be fat wires
 

ack

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So I decided to open up my amps and do some dusting, and given the opportunity, take some pictures.

First the ground wire, from the socket (thin black, running against the grey transformer case) to the star-grounded screw. @Whbgarrett Did you remove your ground from that screw?

IMG_4339.JPG IMG_4340.JPG


Next, anyone know what that red On/Off switch on the top-left of the power supply board is all about? I've been told it lifts the ground, others have said it's for testing purposes

IMG_4337.JPG
 

ack

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BTW, during a fault, it's possible for 150A to flow through the ground connection for a brief period of time - there is no way that thin wire is going to withstand such current. Am I wrong?
 

DaveC

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So the IEC is directly connected to the chassis, this may be an issue. You could try using one of these in series with the ground wire:


Ground strap(s) between amp and preamp would also likely reduce noise, and they would need to be at least 14g to act as a safety, and a braided strap would be best as it'll have less impedance at higher frequencies. You could test it with a regular round wire though. The heavier the gauge the more it'll reduce noise, and braided straps or litz wire will have less impedance at higher frequencies. I do have 14g UPOCC copper litz wire, a double run is 11g, this would make an ideal ground cable...

The ground wire inside the component should be at least 14g imo, and while faults can be high current they will also be short duration. Code is the safety ground should be the same size as the hot and neutral conductors. I'm not sure what gauge the wire is in your amp, but it's short enough there probably isn't enough resistance that the wire will heat up before the breaker trips.

Also, still not sure if you're using more than one circuit? If so, try plugging everything into a single line, via a distributor that connects all of the grounds together. Or you can check the voltage difference between the grounds of the receptacles the amp and pre are plugged into if they are different receptacles, there should be very little difference in voltage between these grounds.
 

DonH50

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BTW, during a fault, it's possible for 150A to flow through the ground connection for a brief period of time - there is no way that thin wire is going to withstand such current. Am I wrong?
The idea (hope) is the breaker blows due to the fault since the current is sourced from the main power line. If you are on a GFI circuit it takes only a tiny leakage to trip it. Codes vary, but around here new homes are required to put GFIs (and often arc-fault interrupters) pretty much everywhere.

I started to say it might be tough to tell which is worse, being electrocuted or having many thousands of dollars in equipment get fried, but realized in my case it does not matter. Even though my system pales in comparison to most here, if I survived and the equipment died, my wife would kill me for being stupid and killing the gear anyway. :D
 
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ack

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Also, still not sure if you're using more than one circuit?
Yes, I mentioned earlier everything is star-grounded at the Denali, meaning they are all plugged into it (and an MIT device in the past). The Denali also has a ground bolt which I have not used yet.
 
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ack

VIP/Donor & WBF Founding Member
May 6, 2010
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Boston, MA
The idea (hope) is the breaker blows due to the fault since the current is sourced from the main power line. If you are on a GFI circuit it takes only a tiny leakage to trip it. Codes vary, but around here new homes are required to put GFIs (and often arc-fault interrupters) pretty much everywhere.

I started to say it might be tough to tell which is worse, being electrocuted or having many thousands of dollars in equipment get fried, but realized in my case it does not matter. Even though my system pales in comparison to most here, if I survived and the equipment died, my wife would kill me for being stupid and killing the gear anyway. :D

So I have to ask the obvious question: The Nordost power distributor floats the ground in all but one outlet, which is labeled "Primary Earth" with a preamp connected to it. The intention obviously is to star-ground everything at the preamp, via the interconnects, with a single path to earth ground from the preamp.

Why would they be comfortably selling it?
 
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dan31

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I thought the Nordost strip increased the impedance to ground on all but the preamp. I thought all the lines are still connected to ground just designed to make the preamp ground the path of least resistance for noise.
 

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