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Electrocuted Gamma3

gamma3, gamma24 (plug-in for the γ3)

Electrocuted Gamma3

Postby Balcmeg » August 3rd, 2017, 8:44 pm

Hi, yes it's me and my Gamma3 again.

I need some help in chasing down a new problem. Short story: I was listening to some music using my Gamma3, Tempel power amp and Raspberry Pi 3/KODI setup when my wife decided it was time for lunch and switched on the kitchen fan. A loud pop from the switch and since then I get no music, only LOUD humming from both speakers. I flew up from the sofa and switched off pretty fast!
Anyway, as I remember the humming was unbearable loud with Gamma3 powered on (I won't turn it on again to listen again) With Gamma3 powered totally off, the humming is loud on the edge to unbearable. To be sure I also tried with the RCA connectors unplugged from the Power amp and its no noise then so it seems it's the Poor Gamma3 that got hit again.

Any tips on how to move on and find the fault? Any obvious part to check first?

-Stefan
/Stefan
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Re: Electrocuted Gamma3

Postby amb » August 3rd, 2017, 10:32 pm

Are you saying that your γ3 produces a loud hum at its output even when turned off? That's implausible.

Disconnect all external cables except the AC power cord and umbilical cable. Power up and check all voltage test points (as described at the γ3 website). That should hopefully help to narrow down which area to look at.
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Re: Electrocuted Gamma3

Postby Balcmeg » August 4th, 2017, 12:14 am

Ok, thanks Ti - i re-checked and measured as you advised.

First of all. With unbalanced output connected to my power amp:
    with γ3 power cable UNPLUGGED - very weak hum in the speakers.
    with γ3 Powercable plugged, but γ3 power OFF - Quite loud noise/hum
    with γ3 Powercable plugged, and γ3 power ON - Louder noise/hum

Set your multimeter to DC V mode and measure the voltage between the following points (with red probe on the first point and black post on the second). The expected result is shown:
    LVDD (backplane J7 pin 3) and G (backplane) → +4.97V
    VREF (backplane) and IG (backplane) → +3.25V
    VRXTX (backplane) and IG (backplane) → +3.31V
    V+ (α24 L) and IG (backplane) → +9.98V
    V- (α24 L) and IG (backplane) → -10.05V
    V+ (α24 R) and IG (backplane) → +9.98V
    V- (α24 R) and IG (backplane) → -10.05V
    AVDD (γ24) and IG (backplane) → +9.98V
    AVSS (γ24) and IG (backplane) → -10.05V
    GVDD (γ24) and IG (backplane) → +5V
    +3.3A (γ24) and IG (backplane) → +3.3V
    +3.3B (γ24) and IG (backplane) → +3.29V
    +3.3C (γ24) and IG (backplane) → +3.3V
    +1.8A (γ24) and IG (backplane) → +1.8V
    +5.0A (γ24) and IG (backplane) → +4.99V
    +5.0B (γ24) and IG (backplane) → +4.98V
    G_RESET (γ24 board connector pin 35) and IG (backplane) → +3.3V
    G_PCMDSD (γ24 board connector pin 2) and IG (backplane) → 0V
    ZVDD_5V0 (ζ1 board connector 28) and G (backplane) → +4.89V
    ZVDD_3V3 (ζ1 board connector 2 and 27) and G (backplane) → +3.3V

Set your multimeter to DC mV mode and measure the voltage between the following points (with red probe on the first point and black post on the second). These are the analog output DC offsets. They should be be near 0V (less than ±4mV).
[list=]OUT+ (α24 L) and OUT- (α24 L) → minimal
OUT (α24 L) and G (α24 L) → minimal
OUT+ (α24 R) and OUT- (α24 R) → minimal
OUT (α24 R) and G (α24 R) → minimal[/list]
/Stefan
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Re: Electrocuted Gamma3

Postby Balcmeg » August 4th, 2017, 12:38 am

Ok, so now all is ok again...
Not 100% certain what had happened, but it seems like it was just a coincidence that the noise started when the power broke.
After moving γ3 at some extremes I suddenly discovered that the noise stopped at some points. Not making much sense but after testing a bit it seems it MIGHT be when the RCA cable ground doesn't get in full contact with the RCA chassis female.
I'm still a bit uncertain that this is the real cause, and why it suddenly popped up like this, but it's the best explanation I have right now.
/Stefan
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Re: Electrocuted Gamma3

Postby amb » August 4th, 2017, 2:34 am

Hmm, so it works fine now? No more hum?

By the way, if the analog output interconnect cable has poor contact (especially the ground), there would definitely be a loud hum.
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Re: Electrocuted Gamma3

Postby Balcmeg » August 4th, 2017, 3:37 am

Yep, been listening to it since my last post with no incidents. I switched from this type of RCA with only a single sided ground connector, to a homemade cable with neutrinos spring-loaded ground connection and there has been no problem even when moving the stuff.


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/Stefan
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Re: Electrocuted Gamma3

Postby hagak » August 10th, 2017, 10:59 am

The outputs of the Gamma 3 float when no power is applied to the Gamma 3, if the power amp is on and the Gamma3 is off you could get a pretty loud hum
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Re: Electrocuted Gamma3

Postby amb » August 10th, 2017, 12:50 pm

hagak wrote:The outputs of the Gamma 3 float when no power is applied to the Gamma 3, if the power amp is on and the Gamma3 is off you could get a pretty loud hum

As long as the interconnect cable is shielded and intact (i.e., no disconnected ground), there shouldn't be significant hum heard in this scenario.
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Re: Electrocuted Gamma3

Postby hagak » August 10th, 2017, 1:03 pm

hmm, now i need to recheck my gamma 3. Cause with it connected to my balanced Beta22 I get a hum if I power off the gamma3 first before the beta22. Cables are good, but maybe the jack is not properly grounded.
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Re: Electrocuted Gamma3

Postby amb » August 10th, 2017, 1:12 pm

If you power off the γ3 while the power amp is on (assuming γ3 connected to power amp directly and not via a preamp), you'll get a thump, but not a hum afterwards.
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