Thanks for the reply BYRTT, that is the sort of cable I use, built after that exact diagram. I guess I can just leave the ground connector of the power86 disconnected from the chassis. Safety wise only the PE absolutely must be connected to the chassis, I guess.
Think if power amp have dual PSU as for pure mono blocks and/or if pre amp have dual PSU then often it can work without lifted ground at far end of cable. Agree if PE is connected to chassis then care for safety area must be okay, and a lifted ground at far end of cable is a hole lot cheaper 🙂 than add more PSUs or use Tom's balanced THAT driver to convert single ended preamp.
The mains ground should go to the chassis. That's the safety ground. You can lift any other ground to your heart's desire. The only caveat is that the input common-mode voltage to the MOD86 should be within ±15 V of its local ground. If you're having issues with hum due to a ground loop, you'll be fine lifting the Pin 1 ground off the MOD86 chassis and connecting it to the source using the pseudo-differential cable.
Stuff like this is why I use differential inputs. Use them with differential outputs and all the ground issues go *poof* away. 🙂
Tom
Stuff like this is why I use differential inputs. Use them with differential outputs and all the ground issues go *poof* away. 🙂
Tom
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That's certainly an option, although it is really quite rare that anybody has hum issues with the Modulus-86. Certainly less than 1% of builders experience hum from ground loops - or if they do, I don't hear about it. So for me, it falls in a category of "if it ain't broken, don't fix it". Or perhaps as Red Green would say, "if it ain't broken, you ain't trying". 🙂
Thanks for pointing to the F5, though. I'll keep that in mind for the future.
Tom
The amplifier is really good, wasn’t really expecting much of an improvement over my old gainclone, but, wow!
Oh, nothing. Just a li'l protection board. 🙂
Guardian-86 is in and works well. I have boards in stock. You can find the circuit description here: Guardian-86: Speaker protection board for LM3886-based amplifiers (and others).
Oh, that other board? That's the Intelligent Soft Start. Description here: ISS: Intelligent Soft Start
My mom let me know a couple of hours ago that my dad has suffered a major stroke, so I'm heading out of town ASAP to be with family. Thus, don't expect me to stick around for Q&A.
Sometimes life throws you a curveball. This is one of those times. I'll respond when I can.
Tom
Guardian-86 is in and works well. I have boards in stock. You can find the circuit description here: Guardian-86: Speaker protection board for LM3886-based amplifiers (and others).
Oh, that other board? That's the Intelligent Soft Start. Description here: ISS: Intelligent Soft Start
My mom let me know a couple of hours ago that my dad has suffered a major stroke, so I'm heading out of town ASAP to be with family. Thus, don't expect me to stick around for Q&A.
Sometimes life throws you a curveball. This is one of those times. I'll respond when I can.
Tom
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I actually went ahead and ordered the differential driver 🙂 I don’t feel confident in this lifting grounds stuff, I don’t understand what the root cause is. I will try another preamp, maybe the old Linn has some issues.
Tom sorry to hear about your fathers misfortune. A couple of years back my own father suffered a major stroke. I wish all the best for you and your family.
On the preamp, the rca shields are grounded to the chassis. So the rca shield is also connected to the poweramp chassis over PE. Could that be the groundloop causing hum?
I have now left the shield connection on the modulus86 disconnected, and the hum is gone.
I have now left the shield connection on the modulus86 disconnected, and the hum is gone.
Guess you right, also that both L and R channels have each their own shield gives in principle three paths for return to pick as its route back
and probably the reason why gear with true separate PSU for L and R channel often have less of these problems.
I suggest reading Bruno P's (Hypex) article on grounding. If I recall correctly, it's called "The G Word". In a single-ended setup, the various pieces of equipment basically arm wrestle over what ground is. The ground current is shared in the parallel impedances formed by the various ground wires and shields. You will always have some current flowing and it will always cause an error term.
The issue with single-ended signalling is that this error term is added to the signal as the transmitter and receiver will have a different understanding of what ground is.
Differential signalling solves this beautifully by moving the ground connection out of the signal path. A differential receiver only cares about the voltage difference between the two signal lines. Ground is irrelevant (as long as the input common mode voltage spec of the receiver is not violated).
Tom
The issue with single-ended signalling is that this error term is added to the signal as the transmitter and receiver will have a different understanding of what ground is.
Differential signalling solves this beautifully by moving the ground connection out of the signal path. A differential receiver only cares about the voltage difference between the two signal lines. Ground is irrelevant (as long as the input common mode voltage spec of the receiver is not violated).
Tom
Thanks for the suggested read, and your explanation,I am beginning to understand better.
Still, I can’t seem to grasp why It is a good to connect the ground of the power86 to the chassis directly at the mains safety ground. Why is it not enough with the connection from the modulus86 boards shield (I measured 0 ohm between the Power86 ground connector and the shield connector on the Modulus86) to xlr pin one which in turn is connected to the chassis? If I arrange it thus, the hum goes away AND the RF filter works and all is great, right?
I believe that the problems with hum and noise I am having stems from the fact that my electrical house installation lacks a dedicated PE. Especially since Tom says only few builders get this hum problem. Neutral connects to PE in the wall outlets.
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I am sorry to hear about your dad Tom. My hopes are with you for the best possible outcome.
Matt
Matt
Hi Tom,
All my best wishes for your father. I really wish him a good outcome.
Take care, Chris
All my best wishes for your father. I really wish him a good outcome.
Take care, Chris
Tom, I assume Guardian could be used for other power amplifiers too. What would be max. amplifier power or PSU voltage, that this nice circuit would have confident work?
P.S.: Keep finger crossed for your father.
P.S.: Keep finger crossed for your father.
±100 V would be the max rail voltage the switch MOSFETs can handle.
My dad died Sunday from a massive stroke. I arrived about 20 minutes after he died and was able to say my goodbye. It was peaceful and a good goodbye. Thanks to all for your well wishes. I really appreciate it.
Tom