To ground or not to ground the OPT secondary, that is the question - Page 2 - diyAudio
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Old 13th November 2010, 02:39 PM   #11
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Default My speakers require it....

I have a pair of vintage Polk SDA 1's (with the umbilical interconnect between speakers) and they require that the speaker common terminals be grounded (or at least connected together in a stereo amp), especially with monoblocks, so all of my amps have grounded speaker common leads. The alternative is to put an isolation transformer in the umbilical between the speakers.
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Old 13th November 2010, 05:43 PM   #12
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Smile The green wire is safety ground!

Hello All,
I use a pair of Electra-Print 8000 : 300 headphone transformers with a grounded secondary center tap. If the secondary was not grounded the headphones would not go on my head.
DT
All just for Fun!
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Old 13th November 2010, 06:48 PM   #13
tomchr is offline tomchr  United States
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Quote:
Originally Posted by tubelab.com View Post
There are emotional responses on both sides of this debate, and some have been posted on these forums over the years. Some claim it "clouds the sound".

I always ground one side of the secondary because I found a guitar amp with 300 volts on the speaker leads about 30 years ago.

[...]

I ground the chassis at one point, usually near (or at) the input connectors. I run a direct wire from that point to the center pin on the power (IEC) connector, and a wire to each negative speaker connector.
I'm all about sound quality, but this is a safety issue. I shall ground my secondaries. Thanks for confirming my suspicion.

Quote:
Originally Posted by aardvarkash10 View Post
two really good articles on grounding, earth and common by regular posters on this site. Shorter one here, longer one here
I openly admit that I didn't look at the "long one" in detail. But the "short one" seems like a good primer on signal grounding. I.e. what ground loops do and how to avoid them. For that kind of material, I actually find Ralph Morrison's book, Grounding and Shielding.... to be the authoritative guide on the topic.

In my case, it's more of a safety/earth grounding issue. I'm trying not to kill the cat (or myself) here... I wasn't exactly clear on that in my original question.

Thanks for bringing those links out in the limelight, though. That Valve Wizard site has a lot of easy-to-approach information on it.

~Tom
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Old 13th November 2010, 06:54 PM   #14
tomchr is offline tomchr  United States
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Quote:
Originally Posted by THD+N View Post
I always ground my secondaries as other people have noted. Not only for safety, but some test equipment may not give you accurate results unless the secondary is grounded.
I've seen that on my HP8903A as well. In my case, easily mendable by flipping the GND switch on the front panel to ground the (-) input, thereby, the secondary.

Note that having both the input and output ground referenced may also give you inaccurate readings on your test gear as it can set up a ground loop. I've seen THD+N figures drop by a couple of dB when the ground loop was broken.

~Tom
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Old 6th May 2011, 04:24 AM   #15
rsdio is offline rsdio  United States
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Safety grounding requires a metal chassis with the green ground wire attached to it. The chassis serves as a protective barrier between you and any hazardous potential in the circuit, e.g., loose wires. If something bad happens, the safety ground conducts back to the circuit breaker. It really is the circuit breaker that saves your life, and the safety ground that makes the circuit breaker trigger as quickly as possible when there is a fault (well, except for a safety ground fault). You really should not need to ground anything but the chassis.

Headphones might be an exception to this, since they conduct voltages from inside the chassis to outside. I have not heard any opinion on whether grounding the headphone cable shield would be enough to protect against electrocution.

In other words, it's unclear to me why grounding the secondary would be absolutely necessary, unless the headphones could specifically conduct serious current away from the amplifier.
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Old 6th May 2011, 08:15 AM   #16
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Amps with a reasonable wattage output, especially those with 16 ohm outputs, can have speaker voltage levels that exceed certain safety limits (eg. 32Vrms). This situation is seen as much worse in the eyes of some safety standards if the voltage is floating, compared to referenced to PE (protective earth). This is a simplistic comment - as anyone who has had to navigate product compliance through a variety of safety standards can attest.

If safety is an aim, then I suggest reviewing whether you can ground a ct or tapping on the secondary, which has the benefit of minimising the voltage level on the speaker wires wrt ground.

Ciao, Tim
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Old 6th May 2011, 10:10 AM   #17
rsdio is offline rsdio  United States
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Quote:
Originally Posted by trobbins View Post
Amps with a reasonable wattage output, especially those with 16 ohm outputs, can have speaker voltage levels that exceed certain safety limits (eg. 32Vrms). This situation is seen as much worse in the eyes of some safety standards if the voltage is floating, compared to referenced to PE (protective earth). This is a simplistic comment - as anyone who has had to navigate product compliance through a variety of safety standards can attest.
Excellent point. I recently learned at an AES meeting that speaker wires are treated just like 120 VAC power wiring when it comes to codes for conduit or other built-in wiring runs. Makes sense. I've certainly been shocked by the speaker wires on a guitar amp.
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Old 6th May 2011, 12:00 PM   #18
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Which I suspect is why most manufacturers are/have transfered to Speakon connectors. Yet another change to make for those who have an aim for safety first - especially at the speaker end.
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Old 6th May 2011, 08:57 PM   #19
rsdio is offline rsdio  United States
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My impression has always been that speakON connectors make a higher quality connection anyway. Seems like safety, reliability, and performance are all improved by using speakON.

I've certainly modified some of my speaker cabinets to take speakON instead of any of the other standard connectors, partly for the biamping capability. The manufacturer even provided a blank panel since there really was no room left on the standard panel.
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Old 7th May 2011, 12:25 AM   #20
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Checking the Neutrik Speakon spec shows a 250VAC rating (to IEC 61984), and although no un-mated IP rating was given, it probably meets IP3x. A titch better than a 6.5mm phono jack ;-)
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