Some of Bob's SS designs also failed to use an earth ground bonded to the chassis. This caused hum when using SE connections due to a difference in ground potential between components.
Owners of Carver Crimson 275 -Caution/Warning--Potential Increased Risk of Electric Shock
What's going on?: If you own a Carver Crimson 275 amplifier there is a real potential that your amplifier does not have a proper chassis grounding scheme inside. There is a type of grounding system involved, but the third prong of the IEC socket (the actual electrical socket on the inside of the amplifier) is left wide open on my amplifier and and at least one other amp that I have virtually confirmed (not firsthand--only through another owner).
What does this mean?: If one of the hookup wires carrying power/B+ came loose from its soldered weld and touched either the chassis or something conductive to the chassis and the user then touched the chassis/unit with the power on they could get a significant electric shock. There are some seriously high voltages in this tube amp (like many amps of its topology) and the result could be lethal.
Carver Corporation's Response to Status on Grounding: I have notified Frank Malitz of the Carver Corporation about this problem. He responded to me in writing saying the following, exact quotation, nothing more or less:
"the design is under review with engineering and I'll contact you tomorrow." (F. Malitz)
In the interim, users may be at an increased risk of shock and bodily harm. I would encourage you to check with an electronics expert or the Carver Corporation for further guidance, as I'm not qualified to say more than there's no confirmed chassis ground in the unit that I have and at least one other unit.
Finally, unless you are qualified in working with high voltages do not open your unit to check for the ground wire running to the ground prong on the IEC. Please note that doing so with or without a chassis ground should only be done by someone experienced with electronics--i.e. caps must be discharged and care taken to cause an issue. Seek professional help.
I'm just a music lover and hobbyist. I'm merely relaying this information out of concern for the safety of fellow humans. I'm not an expert and perhaps an expert will rule out this identified potential increased risk as non-existent. For now, I can say that it is my opinion that there is a real reason to believe that grounding scheme might be deficient and I will not be using my amp until this is sorted out.
I'll report any response from the Carver Corporation as soon as I hear back. For now, my amp will sit unplugged.
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I found it out by looking at it--literally opening the unit up. Also, the folks at AudioScienceReview.com saw it too. To be honest, I wasn't quite sure upon initial discovery whether the grounding scheme had some other means of protecting users because I don't have the true education, training and experience in the field. I've also confirmed this is a problem from at least one electrical engineer. And, Carver Corp. has not denied it. Instead, the amp is under engineering review after I emailed them. By "wide open" I mean the ground post on the IEC is not attached to anything at all. |
@daveyf , Yes, and I have read books that cover the subject. Most authors are very serious about this and seem to say what you say here--that many designers get it wrong. Bob Carver has a PhD in physics so maybe he can explain how it is safe. |
I would be surprised if the B- is not connected to the chassis as well as the circuit signal ground. Question is how are they connected to the chassis? Directly or through a low wattage resistance resistor? Or how. If B+ were to short to chassis it would not matter one way or the other if the chassis was connected to the AC mains wall outlet equipment ground. There is not any electrical reference to the wall outlet equipment ground and the secondary windings of the power transformer. I would hope the designer added some type of protection in the high voltage DC power supply to save it from seriously being damaged, If there was a B+ fault to the chassis B- of the high voltage DC power supply. / / / / The problem with the equipment ground contact, of the IEC inlet connector not solidly connected by a wire to the chassis, is there is not any protection from a possible electrical shock hazard if the HOT AC mains conductor came into contact with the chassis. Or it could be a bared spot in the primary winding of the power transformer to the iron core. FWIW I looked up the amp. It looks like it was made in 2019. I though maybe it was wired using Double Insulated AC power wiring. I didn’t see any evidence that it is. Also worth noting a two prong IEC power inlet should have been used. . |
Poor design... I bet the B- and signal ground was connected directly to the chassis. A 1/4 watt 10 ohm resistor connected in series between the B- and circuit signal ground to chassis would have more than likely solved the ground loop problem. The 1/4 watt rating of the resistor works as a fuse if the B+ is shorted to the chassis. . |
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You bet @jjss49 I’m hoping, but not optimistic, there is an explanation for this situation that explains away the potential problem. Time to unplug and let this unfold. |
Perhaps in the electronics industry there is a thinking that so long as no harm has occurred then no foul. This is common ( unbelievably enough) in a number of industries and occupations...and only luck has caused no immense damage, or death! Pathetic (criminal?) on a number of levels...but quite common!!! |
@jea48 years ago when I first joined the forum, I bought a Sunfire 300 1st generation which had a 60Hz hum. Almarg was able to help diagnosis that there was no earth ground. Jim, I don’t expect you to remember, but you instructed me how to test this with a multimeter for which I’m grateful because now I’m fanatical about proper grounding. Anyway, our measurements confirmed there was only a functional signal ground. I sent the amp to Carver service, now owned by one of Bob’s techs and asked for a mod to the grounding scheme. The tech said that this was Bob’s design and he wouldn’t change it. I subsequently learned that later Sunfire generations had a functioning earth ground using a resistor connected to chassis. |
@wfarrell, Bill, you are welcome. I debated posting something at all on the issue. Then I thought--you know, even though it would probably be unlikely that a wire would come lose from its solder weld, it’s possible. Not to mention that the build quality on these amps varies. Amir at ASR has a copy of the amp that has like 26 gauge wire going to the speaker terminals, whereas mine has heavy duty wire. His had a lose screw rolling around the chassis and the power transformer loose. So, I thought: How do I know the welds in these amps are solid? There could be owners who have units where things were rushed in assembly. No one deserves to get zapped in 2022 from just touching the machine in operation!
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@jea48 , THANK YOU for the education. Seriously.
Note: the photo above is from AudioScienceReview.com. My amp is built a bit better than this one, which is also odd and slightly disturbing. But, the lack of ground on the IEC and grounding scheme looks similar if not identical to mine. It looks like the power supply side of things is grounded to the fuse holder. |
@jea48 , it makes total safety sense that proper grounding would require a mechanical connection--not just a solder connection--because that wire to the chassis could still come lose. I think I get it. |
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@carlsbad, I would ask you to re-read my post. I talk about an "increased risk". I cannot quantify it, but I would agree that a good strong weld should not come loose. But they can and do come loose. While it may not be probable, it is entirely possible. Not to mention, Carlsbad, there are questionable things going on in the amp. I actually did have the line running to the meter come lose and I re-worked and resoldered that. In my amp, some of the welds (not many) could have been better so I touched them up. The other thing to note is that the DC Restorer circuit and its PCB are mounted vertically and some of it appears to be glued into place as opposed to being bolted or connected with a standoff. If that glue were to come loose due to heat, age, etc., that vertically mounted board carrying many hundreds of volts of power (per Carver’s own schematic available on their forums) could touch the chassis or other component parts. The hookup wires holding power have bare leads exposed before they attach to the solder welds. So I don’t think I’m exaggerating the risk. I say numerous times its a potential increased risk. |
Carlsbad, I would think that any tube power amplifier using power transformers, output transformers, which has 600+ volts going on in some sections must use a grounding scheme that grounds to chassis and to earth prong so that if something happens the current goes into the 3rd prong and your wall wiring and trips a breaker. Stuff happens. People drop amps. Wires age, And so on. Maybe an electrical engineer can chime in on this. Disclaimer: I am not taking the position that this amplifier is a "Widowmaker" or "Widowermaker". Could it be? Yes. That's the sole point. |
What a mess. Sell it and never look back! Good news don’t worry about the DC power supply B+ inside the amp. On the back of the amp is a fuse for the B+. Bad news, from what I see the AC power wiring violates electrical safety standards that have been in effect for at least the last 30 years... The AC power fuse is connected to the neutral connection on the IEC inlet connector. That’s a no no... You don’t fuse the neutral conductor. The Hot connection on the IEC inlet connector is connected to the on/off power switch. The guy got that right. Except he should have went to the fuse first then to the switch. Will the AC fuse blow in the event of an overload condition? Yes... Will a blown fuse kill the HOT energized AC conductor inside the amp? NO! IF for what ever reason, your fault my fault anybody’s fault if the fuse blew due an overload and it was caused by a short in the primary winding of the transformer and the insulation on the winding got hot enough and bared the conductor, and the bared conductor came into contact with the iron core of the transformer, the metal chassis of the amp would be energized... HOT...
Scroll down page to photos . |
@czarivey , Thank you for your courtesy. Lovely. |
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I’ve always been a big fan of Bob Carver. Maybe there was a mistake made maybe not. All consumer-electronics need to have her UL approval. I don’t understand how some of the guys on this forum are taking the screws to Good ole Bob.
it’s funny how this subject never comes up when we’re talking about the latest power cord from some dude in his basement that claims it brings out more highs in the soundstage. Also I just wandered do fuses need to be UL approved? How many of you guys don’t think twice about sticking a fuse that you have no idea who manufactured it or tested it for safety all because some goofball says it’s moves out the soundstage. This really bums me out. What did Bob do to deserve this? |
@raysmtb1 What Bob did to deserve the attention is apparently exactly what he failed to do...oversee a product that has his name on it and could very well prove to be deadly to the consumer. This has not happened so far, at least that we are aware of, BUT the OP is trying to expose a potentially deadly fault in Bob’s design..and as such, IMO, it needs to be disclosed. PERHAPS Bob will be pleased to realize this potential issue and instruct his manufacturer to remedy the problem, or if there is no issue to rebut the issue and clear the air. Either way, perhaps Bob ( or one of his crew) will be more than pleased to have the opportunity to correct a potential disaster in the making...or not?? |
@carlsbad The amp came from the distributor with a loose screw rattling around. Say that screw rolled against the power switch and rested against the chassis, which is 100% plausible, now you have a chassis at 120V and you would be relying on having interconnect cables connected to the 275 in order to provide a path to trip your circuit breaker. |
@raysmtb1, many of us respect Bob and love what he’s done for hifi. He’s a legend in my book. Go read my posts about this amp. You’ll see we’ve given him the benefit of many doubts. But anyone saying the lack of proper grounding on this amp is not a problem, is incorrect. There’s no room for accepting this grounding scheme as acceptable in 2022. I used to take electricity less seriously than I do today. I’ve incidentally rubbed up against a beefy Lundhal power transformer. I’ve touched a 120v AC line. I cannot imagine what 300, 400, 500 or more volts would feel like. If an amp design has issues with ground loops, this is not the way to handle it. Paulbottlehead is spot on here. Also, maybe it’s not so bad that the meter and the big electrolytic caps on the DC restorer circuit are literally held in place with glue--with no mechanical bond. But that method coupled with heat and a terrible, or shall we say non-existent grounding scheme, makes it utterly foreseeable that the amp could result in injury. I think if anyone makes a post that says this isn’t an issue or it’s being exaggerated should have to take a basic electronics test before posting. If you’re reading this post, please make your decisions on the side of caution. The voltages in tube amps are seriously high. Some caps can hold super high voltages hours after power is shutdown. On a lighter note...Maybe the shocks I have taken have caused my hifi Gear Acquisition Syndrome. :) |
All electrical products should be UL tested, I work for a large construction company and have read to many spec's, all of the electrical products are specified as UL tested. It's interesting that the Crimson 275 did not test well but sounds so good. Bob Carver is a great designer and respect his genius, but I want to turn on my Crimson 275 and not get zapped. Hope we here from Frank soon. Take Care
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The power wiring is correct. From the switch there are two wires, each of which goes to one of the dual primary 120V windings of the mains xfmr. Coming out of the transformer are the two neutrals that tie into the fuse, which then goes out of the IEC neutral. That is okay, but I prefer to wire the primary from the fuse. What I think Carver is relying on is the acrylic paint providing insulation against a fault condition. While it may provide protection, paint is not considered an appliance insulator in double insulation schemes. Even if there was a loose wire, it could land on a screw which comes in contact with bare metal, resulting in the chassis being live. The danger lies in you touching a screw or the valve base or even the screw on the power switch. Once upon a time tube amps were built without a chassis ground and IEC plugs were just to ensure correct AC polarity. But looking at those pictures gives me pause: the high tension circuit board is glued to the chassis in the upright position, I wouldn't trust that at all. If it was me, I certainly would not question Carver -- I would be asking for a refund. |
All it takes is the switch shorted to chassis and you can have a problem. That could happen easily in shipping. OTOH If the wiring is set up properly, if the product is plugged in with a shorted switch and turned on it will simply blow the fuse. As best I can make out that is not the case here. |
So, the 3rd prong on the ac connector is not grounded ( Crimson 275 ) ? Can someone, with the technical knowledge, explain how this is different to the hot wired 2 prong wire / plug we used to have on older components, before the iec inlet and the power cables war ? I was told by an electrician, the 3rd prong was developed as a 2ndary ground. I do not know....... |
I would be willing to bet you do not fuse the AC mains neutral conductor in your equipment. The correct way is Hot from the IEC inlet connector to >> fuse to >> switch... Fuse as soon as possible inside the equipment. The 3 pin IEC power inlet connector on the Carver amp falsely leads the consumer to believe the chassis is grounded when plugged into grounded wall outlet. |
A neutral is only a neutral when it is electrically connected to the electrical service grounded conductor neutral bar, in the electrical panel. Open the neutral up stream on a load connected to a live HOT conductor and the lead, wiring, from load is HOT. At that point it’s no longer a neutral. It is a HOT conductor and can be lethal. Never fuse a neutral conductor. Just because it was done in audio equipment over 35 to 40 years ago is no excuse... . |
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Here are just a few examples. https://robrobinette.com/Widowmakers.htm You had a 50/50 chance of plugging the radio into the wall outlet with the chassis grounded conductor plugged in the wall outlet grounded neutral conductor. In the radios defense the chassis was installed in a wood or plastic case. Plastic or wood knobs with an insulated back cover. . |
