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.
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.
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.
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!
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.
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.
This is not theory or legal mumbo jumbo written by lawyers, this is personal
experience with hum elimination and some very solid science.
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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