I'd be interested in hearing what they say. I understand Carver sold the company.
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. . |
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