Alazira, why are you saying to not just use the resistor to isolate the
chassis ground from signal ground? BigBill now has a safe chassis ground,
or so he says, assuming he has not misunderstood what others are writing.
That's all he needs from a safety point of view.
But I agree Bill, go ahead and just connect the signal ground to the chassis
ground and if you've got no hum you're good.
Actually before that.... How this all started is you saying you were getting
shocked by the chassis. Is that still happening?
Also. That CL60 you've got - I can't tell from the photo - is that connecting
hot from the IEC socket to a fuse holder? If so, that's a diabolical piece
of kit..... there is about an inch, times 2, of hot exposed inside the chassis !!!
You should unplug the unit, desolder the CL60, put some heatshrink tubing
or some wire insulation over those exposed leads, then solder it back in.
One more thing. The wire that was connecting the signal ground to the chassis
is too thin. I can see all sorts of thick power wires in the pictures and the wire
that should be the thickest is instead the thinnest. If you don't have like 16
guage wire, you can just bulk up 2 or 3 or 4 pieces of thinner wire to connect
the IEC socket ground to the chassis, but it should be able to conduct a fair
bit of current without melting.
Clearly whoever built your amp wanted to lift the ground and of that he did a
good job. Given what I think I see in the pictures I would question why did the
person bother to connect signal ground to the chassis - it didn't help anything
and would only serve to transfer static shocks directly into the audio circuit.
Cheers all and happy new year.
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So thats hum!!! Its loud...I'll try putting something in between the circuit ground and the chassis later. Its time for NYE!!
I think that the builder was trying to prevent hum when he did it the way he did. In any case I did not touch he case b/c I turned it off as soon as I heard the hum.
Happy New Year to all.
I think that the builder was trying to prevent hum when he did it the way he did. In any case I did not touch he case b/c I turned it off as soon as I heard the hum.
Happy New Year to all.
Hi wayne325,
Although using the resistor would eliminate hum, it's not as safe a setup. Using a CL60 here is preferred.
Time to go home and watch fireworks from a safe distance (est. 350K crazy people wandering Las Vegas Blvd tonight)
Happy New Year!
Bill,
I think something is shorted to the chassis. Since you have a resistor to
use, I'd start wtih that. If the hum is gone you're good and think about
replacing the resistor with another CL60. I agree with alazira it is the better
solution.
W.
You know what? This happened me one time before on a preamp build. Exactly those problems, and also the V between chassis and neutral. Turned out to be a bad transformer. I can't remember exactly what the Tx problem was, but a buddy of mine copped it right away, said try a different transformer and problem magically dissappeared.
Grasping at straws I know, check for shorts first.
Fran
Grasping at straws I know, check for shorts first.
Fran
This was a very useful thread to read, answered so many of my questions. Not sure how I found it, probably googling something. I think it should be moved to PSU section and added to favorites.
Anyway, to recap the discussion:
1. You must use 3 prong power cable for your PSU.
2. The power cable ground pin must connect directly to the chassis.
3. Your amplifier board must have its own ground (google for 'star ground'). This ground can connect to chassis directly OR if you are getting hum, use one of these techniques:
4a. Connect amplifier ground to the chassis via thermistor (e.g. CL60)
4b. Connect amplifier ground via a pair of diodes wired back to back, with a 10R power resistor and 0.001uF cap in parallel.
4c. Connect amplifier ground via a 10R resistor of several Watts (least preferred method)
5. All ground wires must be thick enough to be able to take the live current before your fuse blows. Use 18 gauge wires at least.
6. All live wires must be insulated, regardless how short the wire is (e.g. between power inlet pin and inrush limiting thermistor).
Why do you need the tree methods to connect amplifier ground to chassis? Because ground loops could build up higher currents potentially resulting in interference with your amp circuits and generating audible noise (hum). A thermisor is the best way to deal with it because under room temperature it has high resistance and creates a barrier to the currents. If short circuit to ground happens in amp it will heat up (resistance will reduce) and will provide enough current to blow the fuses.
Please correct me if my summary is lacking or incorrect in any way.
Anyway, to recap the discussion:
1. You must use 3 prong power cable for your PSU.
2. The power cable ground pin must connect directly to the chassis.
3. Your amplifier board must have its own ground (google for 'star ground'). This ground can connect to chassis directly OR if you are getting hum, use one of these techniques:
4a. Connect amplifier ground to the chassis via thermistor (e.g. CL60)
4b. Connect amplifier ground via a pair of diodes wired back to back, with a 10R power resistor and 0.001uF cap in parallel.
4c. Connect amplifier ground via a 10R resistor of several Watts (least preferred method)
5. All ground wires must be thick enough to be able to take the live current before your fuse blows. Use 18 gauge wires at least.
6. All live wires must be insulated, regardless how short the wire is (e.g. between power inlet pin and inrush limiting thermistor).
Why do you need the tree methods to connect amplifier ground to chassis? Because ground loops could build up higher currents potentially resulting in interference with your amp circuits and generating audible noise (hum). A thermisor is the best way to deal with it because under room temperature it has high resistance and creates a barrier to the currents. If short circuit to ground happens in amp it will heat up (resistance will reduce) and will provide enough current to blow the fuses.
Please correct me if my summary is lacking or incorrect in any way.
4c. does not work.
4b. As NP has stated the POWER Diodes must be in inverse parallel (4b).
The Disconnecting Network (" OR if you are getting hum, use one of these techniques:
4a. Connect amplifier ground to the chassis via thermistor (e.g. CL60)
4b. Connect amplifier ground via a pair of diodes wired back to back, with a 10R power resistor and 0.001uF cap in parallel.")
must be able to pass the FAULT Current until the mains fuse ruptures and the arc has extinguished. This Fault Current can easily exceed 1kA for a few microseconds.
N.Pass,
have you tested the CL60 you show in some of your diagrams to pass Fault Current?
I note that your more recent diagrams show instead the Power Bridge Rectifier as the Disconnecting Network, between Chassis and Main Audio Ground (MAG).
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As I am now building the XONO/ONO, the grounding scheme becomes very important. And honestly, this will be my first time using the XLR interconnections all the way from the preamp to the power amp. I wasn't clear about connecting the signal ground and the chassis ground, and it seems that people in this forum are suggesting kind of "Try this... if it doesn't work, then try that".
I found that this article is very helpful, and helps me a lot to understand the grounding problem (especially for the signal vs chassis ground):
Grounding and Shielding Audio Devices
From this article, it is very interesting to learn that the balanced and unbalanced audio equipments are *NOT* compatible (in terms of grounding interconnection shields).
Hope this helps!
I found that this article is very helpful, and helps me a lot to understand the grounding problem (especially for the signal vs chassis ground):
Grounding and Shielding Audio Devices
From this article, it is very interesting to learn that the balanced and unbalanced audio equipments are *NOT* compatible (in terms of grounding interconnection shields).
Hope this helps!
Did you conclude that the correct way is to connect Pin1 at both ends to the enclosure/chassis?As I am now building the XONO/ONO, the grounding scheme becomes very important. And honestly, this will be my first time using the XLR interconnections all the way from the preamp to the power amp. I wasn't clear about connecting the signal ground and the chassis ground, and it seems that people in this forum are suggesting kind of "Try this... if it doesn't work, then try that".
I found that this article is very helpful, and helps me a lot to understand the grounding problem (especially for the signal vs chassis ground):
Grounding and Shielding Audio Devices
From this article, it is very interesting to learn that the balanced and unbalanced audio equipments are *NOT* compatible (in terms of grounding interconnection shields).
Hope this helps!
Great link, Sianturi!
All my stuff is unbalanced, but I still learned a lot. (For instance, the practice of only terminating one end of cable shielding has become endemic, even inside chassis. I suppose that's not so bad since most of them are also incorrectly tied to signal ground, but tying both ends to the chassis ground seems highly preferable.)
Cheers,
Jeff.
All my stuff is unbalanced, but I still learned a lot. (For instance, the practice of only terminating one end of cable shielding has become endemic, even inside chassis. I suppose that's not so bad since most of them are also incorrectly tied to signal ground, but tying both ends to the chassis ground seems highly preferable.)
Cheers,
Jeff.
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