On Thu,6/1/2017 10:23 PM, Dukes HiFi wrote:
Sorry Jim, ground loops are real. That is why many high end audio components are sold with
IEC cords that do NOT have the grounds connected. In fact, there is a version of the
“standard” IEC three prong chassis connector that has no ground post at all.
Nope. Wrong analysis. First, that gear with no third pin is double
insulated, so there's no possibility of a short between AC and exposed
metal. Such equipment is identified by electrical codes as Class II
equipment. "Regular" stuff is Class I. Read about it on page 17 of this
tutorial that I was hired to write for pro audio and video contractors.
http://k9yc.com/SurgeXPowerGround.pdf
Second, the power line buzz we have erroneously blamed on "ground loops"
is really leakage current from the AC power line to the chassis, which,
by law (if it's Class I gear) MUST be connected to the green wire. AND
all the chassis must be coupled together.
The best analysis I've seen of how leakage current causes buzz is by
Bill Whitlock, a superb audio and RF engineer who owns Jensen
Transformers. I've borrowed it for the tutorials on my website. It's
part of this slide set for talks I've done for several ham conventions.
http://k9yc.com/GroundingAndAudio.pdf Fact is, it's NOT a loop, and the
REAL solution is bonding every chassis in the station together, and to
all other grounds in the home/building. This Power Point formed the
basis of most of N0AX's new ARRL book on Grounding and Bonding.
I have three Paragon Audio examples in my own living room, two rear channel
powered surround speakers and a very nice center front channel powered speaker.
They came from the factory that way and are NOT illegal.
Right. They're Class II products. Home audio products are built that
way BECAUSE the double insulation minimizes leakage current, and BECAUSE
the green wire connection can legally be eliminated.
Ground loops DO cause hum. That is the sole reason for what is known as “Star grounding” in
sophisticated electronic components. Every competent electronic designer employs “Star
grounding” for just the purpose of eliminating ground loops, especially in products that involve
audio.
The purpose of "star grounding" is really proper bonding. See my
tutorial. Bonding is critical for killing buzz.
I personally corrected the design of a very costly high voltage regulated 60 Hz AC power
supply from a prominent vendor because I identified that they had depended upon a PAINTED
hole as the electrical connection for their well-intended star ground. They forgot that paint
is an insulator and this “AC” power supply suddenly became immensely polarity
dependent as a result. An AC supply should NEVER be polarity dependent!
Every Astron I've opened has paint between the lug where the AC green
wire is soldered and the chassis it's mounted to. :) And that same
paint-insulated lug is used as the point where V- is bonded to the chassis.
A prominent high end audio equipment manufacturer, Audio Research, made the same mistake in
their D115 vacuum tube power amplifier, only it this case, the hole they were using for
“Star” was anodized. Different cause, same result, hum.
Yep, I see that set of mistakes a LOT. Paint as an insulator also a HUGE
problem in vehicles.
This is also the reason why several companies sell a useful device (of which I own
two) that isolates the cable company’s coax shield from electrical ground -
these DO eliminate ground loop hum that arises from the multiple grounds that are
involved with a massive cable system and a home audio system.
Such devices are unsafe and illegal if they interrupt the proper
grounding and bonding of that CATV cable. Jensen Transformers sells a
good quality RF transformer that can be placed between a properly bonded
CATV (or antenna) cable and a home entertainment system. The purpose is
to eliminate an uncontrolled path for AC power leakage current.
This is not theory or legal mumbo jumbo written by lawyers, this is personal
experience with hum elimination and some very solid science.
Electrical codes (like NEC) are written by a bunch of EXCELLENT
electrical engineers, and are based on solid engineering. Codes are
written to take a VERY wide variety of conditions into account --
everything from lightning protection, electrical safety, to the
interconnection of all sorts of low voltage systems (like home
entertainment systems, telephone, CATV, alarm and security systems,
etc.). Anyone who thinks they're wrong needs to learn some more
engineering, or to learn more about those multiple systems types. And
anyone who thinks there is a difference between theory and practice
needs to learn more about one or the other.
73, Jim K9YC
With all due respect,
Gary
W0DVN
PS: I did not say eliminating the ground pin on the C21 WOULD resolve the hum, only that it
COULD solve the problem. It seems that it did not so there must be another path to ground or
another mechanism of 60 Hz coupling that is the offending root cause of the hum in the C21 In
question. The fact that the gentleman was able to worsen the hum by moving his hand near some
capacitor suggests that there is a high impedance “antenna” for 60 Hz in this
radio, and a source of significant 60 AC energy within. I say this because operating this
radio with the ground pin removed is the electrical equivalent of operating the radio from an
external 12 volt DC supply ELECTRICALLY. Something else is coupling 60 Hz AC into the audio
line of the radio. There is NO Way that he could affect power supply 120 Hz ripple by moving
his hands around some capacitors inside the radio. He is only affecting coupling of 60 Hz
energy into the audio line, not power supply regulation.
It is even possible that the hum coupling is magnetic, coupling from the
magnetic transformer core, which is inside the C21 cabinet, directly to the
audio circuit, and thus the use of an eternal supply would most likely
eliminate this. This was the exact reason why Counterpoint Audio chose to put
the power transformer for their esteemed SA-3000 preamplifier in a separate
case from the main electronics cabinet. Even though Counterpoint still sent the
AC power from the transformer into the preamplifier cabinet to be rectified,
filtered and regulated there, the magnetic coupling aspect of hum generation
(by the transformer) was totally eliminated by 6 feet of separation between the
transformer and the electronics.It may well be that the C21 audio circuit has
so much gain (for the dual direct conversion design to work) and such high
impedance, combined with the possibility that the transformer has so much
magnetic leakage that this presents itself as the hum that is reported. A
simple piece of Nickel foil between the transformer and the rest of the radio
would fix this.
I still contend that there is no reason why operation of a C21 should require
an external supply. I assume Ten Tec felt that the amount of coupling was
acceptable for most users and that headphones would only be used with an
attenuator.
On Jun 1, 2017, at 10:42 PM, Jim Brown <k9yc@xxxxxxxxxxxxxxxxxxxxx> wrote:
On Thu,6/1/2017 8:02 PM, Dukes HiFi wrote:
The internal supply is pretty good. If it is introducing hum of the ground loop
type, why not just lift the ground (green wire). That should eliminate ground
loops.
NO, NO, NO. This both illegal and unsafe. NEVER do this.
Ground loops are a myth.
73, Jim K9YC
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