Remove IEC connector from Super 70i?

oneinthepipe · « **on:** 7 Jul 2008, 05:28 am »

I read the five page post about adding an IEC connector to AVA equipment, but I have the reverse situation, except that the component is not a modern AVA product. I recently acquired a Super 70i. Based upon the schematic, it appears to be true to the design, except the builder 1) installed a three prong plug and 2) did not wire the amp for 16 ohm speakers (although the yellow transformer leads are connected to a terminal strip and then to the correct circuit board eyelets).

Regarding the IEC connector, the ground prong wire is connected to the Super 70i frame. Should I remove the IEC connector and install a two prong plug? The amplifier is currently connected to a dedicated isolated ground circuit.

avahifi · « **Reply #1 on:** 7 Jul 2008, 01:41 pm »

In general, a three wire AC cord, with the ground wire attached to the chassis, invites ground loop hum in the system as there are now two ground paths between components; the signal ground side of the interconnect cables and the second chassis ground path through the power cords. I cannot recommend the fix for your particular unit without seeing it here on the bench as there is no guarantee the three AC wires are correctly connected.

Regards,

Frank Van Alstine

oneinthepipe · « **Reply #2 on:** 7 Jul 2008, 06:11 pm »

Thank you for your response.

Do other components that have grounded plugs also invite ground loop hum? For example, my CDP, a JoLida JD100, has a three-prong plug, and I assume (but I can disconnect it and confirm) that the ground pin is attached to the chassis.

markC · « **Reply #3 on:** 7 Jul 2008, 09:01 pm »

Never had the lid off your JD 100? The ground is definitely attached to the chassis.

oneinthepipe · « **Reply #4 on:** 7 Jul 2008, 10:01 pm »

Quote from: markC on 7 Jul 2008, 09:01 pm

Never had the lid off your JD 100? The ground is definitely attached to the chassis.

Yes, I've owned it for a few weeks, but I've never looked at anything other than the tubes.

rustneversleeps · « **Reply #5 on:** 8 Jul 2008, 12:00 am »

I've always thought that the 3-prong plug is a safety feature that if the hot connection somehow touches the chassis, then it would immediately trip the breaker at your electrical panel. So you wouldn't be shocked by 120Vac when you grab the chassis.

In the case of my Eico HF-85, the power transformer is not isolated, because it was made in the stone age of audio. I have to mark the two prong AC plug's hot prong, and making sure it goes into the + side of the AC outlet, if I reversed it, I actually measured 120Vac from the chassis to ground. Before I found that out, I was shocked a couple of times when I was disconnecting my patch cables. I still have to install a polarized two Prong AC plug to eliminate the problem.

As far as I know, three prong is for safety, but it will generate something called "ground loop", not an audio upgrade.

markC · « **Reply #6 on:** 8 Jul 2008, 02:26 am »

Yes, the ground to chassis is referred to as a Safety Ground. But if implemented correctly there are ways to do without it and still maintain safety. As long as one does not tinker...
My personal opinion, however, is to implement safety ground and Not have it cause any audible issues.

rustneversleeps · « **Reply #7 on:** 8 Jul 2008, 01:24 pm »

Quote

to implement safety ground and Not have it cause any audible issues

How would you do it? I built a Super Amp signature kit, it has a three prong AC plug. It's RCA jacks are isolated from the chassis, because it has audiophile jacks, which have plastic isolators separating the RCA jack ground from the chassis. Their audiophile jacks are designed for the godzilla cables, not that I need the godzilla cables.

For the AVA equipment, the RCA jacks are grounded on the ground plane, putting the safety ground on the chassis would also put it right on the signal ground.

Wayner · « **Reply #8 on:** 8 Jul 2008, 02:26 pm »

That, gentelmen is why there are fuses. A short has zero resistance (which is very bad) and it means that in a very few micro seconds, thousands of amps of inrush current happens. A short circuit in AVA equipment will take out the fast blow fuse almost instantly.

Wayner

rustneversleeps · « **Reply #9 on:** 8 Jul 2008, 04:42 pm »

We all know from basic electronics that fuse doesn't protect everything, even fast blow fuse, it only protect the circuits, but it's not a sure thing. What if the side before the fuse touching your ungrounded chassis, it rarely happens, but it could.

Even the hot side after the fuse touching the ungrounded chassis, the fuse wouldn't protect you from being shocked. The only way to protect you would be ground the chassis, then the circuit breaker in your power panel would protect you.

avahifi · « **Reply #10 on:** 8 Jul 2008, 05:04 pm »

In new AVA units the fuse is first, ahead of everything on the hot side. Thus any short or failure in the equipment will blow the fuse and protect the user. All that is ahead of the fuse is the simple power cord connection hard wired and soldered to the input side of the fuse block itself, with an almost zero failure potential.

It is fuse, switch, and then the transformer on the polarized hot AC connection to protect the user.

Regards,

Frank Van Alstine

TomW16 · « **Reply #11 on:** 8 Jul 2008, 05:10 pm »

The problem with the short and fuses argument is that a chassis could inadvertently go "live" and a person could be the path to ground. The person who creates a path to ground would be shocked for a few microseconds until the fuse blew. This, of course, assumes that the person doesn't offer adequate resistance preventing the fuse from blowing.

A safety ground would allow the chassis to "see" ground and trip the circuit breaker before anyone touched the chassis.

I agree with MarkC that one should not tinker with the main voltage lines without adequate knowledge. I was thinking about purchasing a transformer from Kevin Haskins at DIY Cable since they are on clearance to build a Balanced Power supply but due to the AVA amp not having an electrical ground made things more complicated and I eventually abandoned the idea.

Cheers,
Tom

Wayner · « **Reply #12 on:** 8 Jul 2008, 05:54 pm »

Tom,

You don't need a ground wire to trip a circuit breaker. The breaker has a spring loaded mechanism that is connected to an inductor element and when the heat of the material reaches trip temperature, the spring breaks the contact. A breaker can actually take longer to trip then a fast acting fuse to burn.

Second point is that the person operating any electrical equipment is assumed not to be standing on a wet surface that has a copper pipe or something like that to present full potential to ground. That is why many HIFI manufacturers warn about using their equipment in unfavorable, wet envirnmonts. That basically goes for anything that runs on electricity.

If you want to be really safe, install a GFCI outlet ahead of your ungrounded equipment. Any unaccounted for current will trip the GFCI.

Wayner

Wayner · « **Reply #13 on:** 8 Jul 2008, 06:00 pm »

By the way, death can occur with as little as 6 milliamps at about 70 volts and up. All it has to do is freeze your heart muscle.

Just an interesting little tid-bit.

Wayner

TomW16 · « **Reply #14 on:** 8 Jul 2008, 06:32 pm »

Quote

By the way, death can occur with as little as 6 milliamps at about 70 volts and up. All it has to do is freeze your heart muscle.

Hey Wayner, no more little tidbits like that or I'll never break out my soldering iron again. I have a tough enough time getting up the courage to open up tube equipment never mind worrying about milliamps

Cheers,
Tom

rustneversleeps · « **Reply #15 on:** 8 Jul 2008, 09:45 pm »

Wayner, a person doesn't have to stand in a puddle of water to get shocked. I bet you will get shocked by just sticking your finger in the hot side of the outlet. I am not suggesting that you should try it, but if you do, it's your business, it's my disclaimer.

AVA has polarized AC plug and it should provide adequate protection. Why people would put a three prong there it's beyond me.

How fast a breaker will trip? The idea is an grounded chassis would trip the breaker before you grab it.

Wayner · « **Reply #16 on:** 9 Jul 2008, 12:02 am »

Rusty,

Everything in the world of electricity works where charge likes to find neutrality. This is the balance of the universe. Tesla understood it. Einstein kind of understood it. Most do not. Some day, the universe will come to rest as that is the ultimate battle, between charge and anti-charge. Everyone just wants to go home.

aa

Listens2tubes · « **Reply #17 on:** 10 Jul 2008, 01:20 am »

Ah yes

oneinthepipe · « **Reply #18 on:** 21 Jul 2008, 06:07 pm »

Not to beat a dead horse, but I have been thinking (therein lies my problem) about my Super 70i's power cord, which is currently a three-prong IEC connector that is grounded to the chassis.

Would this theoretically be problematic, assuming that everything else is operating correctly, to: 1) attach the hot lead of a polarized two-prong power cord to lug 2 of the on/off switch, 2) attach a jumper from lug 1 of the on/off switch to lug B of the fuse post, 3) attach a power transformer lead to lug A of the fuse post, and 4) attach the common lead of the power cord to the other power transformer lead (by way of a terminal strip)?

avahifi · « **Reply #19 on:** 21 Jul 2008, 08:30 pm »

Inasmuch as I cannot be certain that the IEC connector is properly wired in the first place, I cannot advise you as to how to rewire it without seeing the unit on our test bench. There are more ways to do it wrong than do it right.

Regards,

Frank Van Alstine