McCormack DNA 1 DLX Monoblocks Speaker Hum

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jmdesignz2

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McCormack DNA 1 DLX Monoblocks Speaker Hum
« on: 12 Dec 2016, 07:01 pm »
I switched the operation of My McCormack DNA 1 mono blocks from balanced mode to unbalanced and there is a much more audible Hum/buzz through the speakers Now.

There is an internal switch in the DNA1's to enable one to use XLR OR RCA inputs and I believe that using them in unbalanced mode has introduced this hum somehow.

The amps are connected to a 4kva isolation transformer on a separate dedicated line. I suppose I could try to connect all connected components to the isolation transformer to see if that eliminates any ground loops.
Trouble-shooting: Disconnected all components from power and it seems that the amps are making this noise all by themselves.

Should I use rca to xlr to eliminate this? Or would I be better to use a Jensen di box?
Anyone else run into this?

Chris Adams

Re: McCormack DNA 1 DLX Monoblocks Speaker Hum
« Reply #1 on: 12 Dec 2016, 08:33 pm »
Call Steve. He's a great guy and will know what to do.  http://smcaudio.com/contact/

Stercom

Re: McCormack DNA 1 DLX Monoblocks Speaker Hum
« Reply #2 on: 13 Dec 2016, 12:40 am »
I assume its grounding. A balanced cable is better in reducing hum because its grounded around the hot lead in addition to the "ground" lead. You could also try grounding the chassis of the amps by simply running a piece of wire from a screw on the chassis to a common ground.

jmdesignz2

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Re: McCormack DNA 1 DLX Monoblocks Speaker Hum
« Reply #3 on: 13 Dec 2016, 11:16 pm »

The DAC is an Exasound e28 and it does Not have a grounded plug...so it's likely not the issue.

I unplugged everything on that dedicated circuit - still have hum.
Since unplugging everything still results in a hum from the speakers- there must be an issue with the grounding of the house or of the amps themselves?

Ground loop between the different circuits in the house?

Should I run a grounding wire directly from the amps to the main grounding wire of the house?

What risks are involved there? I suppose if there is ever a short, the amp's grounding wire could start a fire if it was not sufficiently large enough gauge or insulated properly ?

Probably the easiest thing is to get a passive Di Jensen box to convert the unbalanced signal to balanced and run balanced XLR to the amps?
Would this work?

Steve called me and he believes that Di box would work. But this was over the phone and I hope I communicated all the troubleshooting and there was no misunderstanding

jmdesignz2

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Re: McCormack DNA 1 DLX Monoblocks Speaker Hum
« Reply #4 on: 14 Dec 2016, 01:34 am »
Anyone run an active or passive DI box to their XLR inputs on a McCormack DNA amp ?
Would be interested to know how that impacted your sound

jmdesignz2

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Re: McCormack DNA 1 DLX Monoblocks Speaker Hum
« Reply #5 on: 17 Dec 2016, 04:26 am »
OK - more info.

It seems this hum chase has lead somewhere finally!

First, I tried grounding an amp chassis screw to house ground in the dedicated circuit. Found that modulated the hum to very slightly higher frequency but did not reduce or elminate it much.

Grounding the DAC chassis screw to dedicated circuit ground did nothing.

The 4kVa isolation transformer has a power cord running to a duplex connector where each mono block power cord plugs in.

We'll call that the iso duplex power cord.

Then there is a power cord running from the Isotrans to the dedicated 20A outlet.

Well - I went behind the unit to re-organize things and noticed that when I touched the iso duplex power cord, there was a change in the hum.

Well - I then rearranged the mono block power cords and the isotrans power cord so that they did not cross each other and were further apart.

The amount of hum decreased by at least half!

I now believe I may need to use shielded power cables?

Thoughts?

paul79

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Re: McCormack DNA 1 DLX Monoblocks Speaker Hum
« Reply #6 on: 17 Dec 2016, 05:19 am »
What preamp are you using? What interconnect cables are you using?

jea48

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Re: McCormack DNA 1 DLX Monoblocks Speaker Hum
« Reply #7 on: 17 Dec 2016, 01:29 pm »
OK - more info.

It seems this hum chase has lead somewhere finally!

First, I tried grounding an amp chassis screw to house ground in the dedicated circuit. Found that modulated the hum to very slightly higher frequency but did not reduce or elminate it much.

Grounding the DAC chassis screw to dedicated circuit ground did nothing.

The 4kVa isolation transformer has a power cord running to a duplex connector where each mono block power cord plugs in.

We'll call that the iso duplex power cord.

Then there is a power cord running from the Isotrans to the dedicated 20A outlet.

Well - I went behind the unit to re-organize things and noticed that when I touched the iso duplex power cord, there was a change in the hum.

Well - I then rearranged the mono block power cords and the isotrans power cord so that they did not cross each other and were further apart.

The amount of hum decreased by at least half!

I now believe I may need to use shielded power cables?

Thoughts?

For starters just focusing on the 4kva power transformer.

I assume you wired up the primary and secondary windings of the transformer. Does the secondary of the transformer have one output winding or two?
IF two secondary windings how did you configure them for the 120V power feeding the ISO power duplex outlet?

How did you ground the secondary winding to the main grounding system of your home's electrical service? From what you described above in your post it sounds like you left the secondary of the transformer floating above earth ground. The secondary of the transformer is a separately derived power system and must be converted/wired making it a grounded power system.
.

jmdesignz2

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Re: McCormack DNA 1 DLX Monoblocks Speaker Hum
« Reply #8 on: 17 Dec 2016, 01:55 pm »
Thanks -this is a Topaz unit

I was told to wire it this way  -

> So the side that you attach to the wall voltage is the "H" side. The output side should be is the "X" side.
>
> Incoming:
> Hot wire connect to "H1"
> Common wire connect to "H3" (assuming your wall power is 120V, which it should be)
> Ground connect to "Chassis"
> On this model I am not 100% sure the best way to attach the shield (S1). You could try it either connected to "Chassis" or to "H1", as I have seen both used on other Topaz (the units with 120/240 set ups) but I am not sure on this dedicated voltage unit how best to do it. You can try playing with it and see what works for you.
>
> Outgoing:
> Hot wire connect to "X1"
> Common wire connect to "X2"
> Ground connect to "Chassis"
> Same advice on the shield S2 as from S1 above.
> I usually mount a 3 plug dual wall outlet on the output side.

I forget what I did with the Shield (S1 and S2) as I wired this up with instructions from a e-audio buddy in early 2012

I could take it apart and check/experiment but it's much quieter right now

Here is the wiring diagram



and input and output physical connections






jmdesignz2

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Re: McCormack DNA 1 DLX Monoblocks Speaker Hum
« Reply #9 on: 17 Dec 2016, 02:13 pm »
I should add that while the low frequency hum is greatly reduced - there is still a bit of a high frequency buzz. Very faint but still there that was not there when I used the amps in Balanced mode with a balanced output DAC

jea48

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Re: McCormack DNA 1 DLX Monoblocks Speaker Hum
« Reply #10 on: 17 Dec 2016, 03:07 pm »
Thanks -this is a Topaz unit

I was told to wire it this way  -

> So the side that you attach to the wall voltage is the "H" side. The output side should be is the "X" side.
>
> Incoming:
> Hot wire connect to "H1"
> Common wire connect to "H3" (assuming your wall power is 120V, which it should be)
> Ground connect to "Chassis"
> On this model I am not 100% sure the best way to attach the shield (S1). You could try it either connected to "Chassis" or to "H1", as I have seen both used on other Topaz (the units with 120/240 set ups) but I am not sure on this dedicated voltage unit how best to do it. You can try playing with it and see what works for you.
>
> Outgoing:
> Hot wire connect to "X1"
> Common wire connect to "X2"
> Ground connect to "Chassis"
> Same advice on the shield S2 as from S1 above.
> I usually mount a 3 plug dual wall outlet on the output side.

I forget what I did with the Shield (S1 and S2) as I wired this up with instructions from a e-audio buddy in early 2012

I could take it apart and check/experiment but it's much quieter right now

Here is the wiring diagram



and input and output physical connections




Because you are using a cord and plug, to feed the transformer that is plugged into a 120V wall receptacle.

The Hot wire of the cord should connect to H1.
The neutral wire from the cord to H3
The safety equipment grounding conductor, wire, from the cord connects to the metal chassis/enclosure, of the transformer. ALL other grounds will connect to this point.

* Both S1 and S2 connect to the equipment ground chassis ground point.

Secondary winding.

* X2 needs to be connected to the equipment chassis ground point. This makes X2 winding lead the neutral conductor. (The grounded Conductor) This will also connect to the silver color screw on the output duplex receptacle.

* X1 becomes the HOT (The ungrounded Conductor) and connects to the copper/brass color screw on the receptacle.

* The green color safety equipment ground screw of the receptacle connects to the equipment ground chassis ground point.

//

Test for proper AC polarity.

Measure for voltage from the Hot contact of the output duplex receptacle to the neutral contact. You should measure 120Vac, nominal.

Measure from the Hot contact to the safety equipment ground "U" shaped ground contact. You should measure 120Vac, nominal.

Measure from the Neutral contact to the "U" shaped ground terminal. You should measure zero volts.

In the world of your new separately derived Grounded AC power source/system the equipment ground chassis ground point is the system ground for the ISO transformer.

* Next test. 

Because you are using AC power from your main electrical service to power other audio equipment in your system, that is connected to the power amps by wire ICs you want both 120V power systems to be in phase with one another.

Measure for voltage from the Hot contact of the transformer's output duplex receptacle  to the Hot contact of the wall duplex receptacle that the other audio equipment plugs into.

If the 120Vac output of the transformer is in phase with the mains 120Vac power feeding the wall receptacle you should measure zero volts, nominal.
IF the two 120Vac power sources are out of phase with with one another you will measure 240Vac, nominal.

If out of phase post back and I will tell you what you need to do to so both will be in phase with one another.

Are both wall receptacles that feed the transformer and the other audio equipment fed from the same Line, leg?

 I will need to know if both branch circuits, feeding the wall duplex receptacles feeding the transformer, and the one feeding the other audio equipment, are fed from the same same Line, leg, from the main electrical service electrical panel. You can easily find out by measuring for voltage from one hot contact of one duplex receptacle to the hot contact of the other duplex receptacle. If both are fed from the same Line you will measure zero volts, nominal. If one is fed from one Line and the other from the other Line you will measure 240Vac nominal.

.   

jmdesignz2

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Re: McCormack DNA 1 DLX Monoblocks Speaker Hum
« Reply #11 on: 17 Dec 2016, 03:26 pm »
@jea. Thanks I will check

From your screen name Any chance you're in Jax?

jea48

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Re: McCormack DNA 1 DLX Monoblocks Speaker Hum
« Reply #12 on: 17 Dec 2016, 04:13 pm »
@jea. Thanks I will check

From your screen name Any chance you're in Jax?

Quote
From your screen name Any chance you're in Jax?

?? 

srb

Re: McCormack DNA 1 DLX Monoblocks Speaker Hum
« Reply #13 on: 17 Dec 2016, 04:24 pm »
??

JEA is a Northeast Florida non-profit community owned electric utility company with headquarters in Jacksonville, FL (JAX is airport code for Jacksonville International Airport)

jea48

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Re: McCormack DNA 1 DLX Monoblocks Speaker Hum
« Reply #14 on: 17 Dec 2016, 04:40 pm »
JEA is a Northeast Florida non-profit community owned electric utility company with headquarters in Jacksonville, FL (JAX is airport code for Jacksonville International Airport)

Thanks srb.

That's not me. I live in the Midwest where it is REALLY cold today.  :( :(

jmdesignz2

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Re: McCormack DNA 1 DLX Monoblocks Speaker Hum
« Reply #15 on: 17 Dec 2016, 05:03 pm »
@JEA - anytime you want to visit Jacksonville LMK - good fishing here and I know some great areas

jmdesignz2

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Re: McCormack DNA 1 DLX Monoblocks Speaker Hum
« Reply #16 on: 17 Dec 2016, 05:06 pm »
The amps run off a dedicated 20A line I had run to the living room.

There is a second 20A dedicated line - I run other equipment on. However, I unplugged everything except iso trans, amps, speakers and there was hum.

the voltage I'm getting checking all the outlets is 119V

Going to check the Iso trans etc in more detail shortly

paul79

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Re: McCormack DNA 1 DLX Monoblocks Speaker Hum
« Reply #17 on: 17 Dec 2016, 05:14 pm »
DAC direct I assume, to the amps, and since you are now using RCA Cables, you are humming? DAC is not AC Grounded, so 2 wire power? Hook your DAC back up to the amps, and unplug one amp power cord, leaving the other powered up. Still hum?

jmdesignz2

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Re: McCormack DNA 1 DLX Monoblocks Speaker Hum
« Reply #18 on: 17 Dec 2016, 06:12 pm »
DAC direct - it has 2 wire power, not grounded.

Yes- DAC hooked up, on channel powered up - still had strong hum (before I re-arranged the power cables)

I am now taking apart the iso trans to re-wire per JEA48 instructions :) will report back soon

jmdesignz2

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Re: McCormack DNA 1 DLX Monoblocks Speaker Hum
« Reply #19 on: 17 Dec 2016, 07:02 pm »
@jea. Thanks I will check

"* X2 needs to be connected to the equipment chassis ground point. This makes X2 winding lead the neutral conductor. (The grounded Conductor) This will also connect to the silver color screw on the output duplex receptacle."

Just want to triple check - I just grounded the shields to Chassis ground

Now - we ground X2 AND the White wire to the same Chassis ground?

see pic

Can I leave the white wired to X2 and I just run one wire from X2 to chassis ground
OR
do I need to run Wire X2 to Chassis ground
AND White wire to Chassis ground

Then I will probably need to install spades to get all those wires to fit on one chassis ground screw lug

see pic