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.
Showing 5 responses by lowrider57
@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. |
Bob started this venture by building these amps and some monoblocks and selling them on Ebay. Of course there was a lot of interest. With each hand-built amp he would make improvements and describe the design elements. I was closely following him on Ebay because these amps were beautiful. At some point he started the new Carver Corp. offering the high power monoblocks first which were in the $9000 range I believe. The affordable 275 came later. When Bob decided to retire, a deal was brokered with Wyred 4 Sound to assemble the Carver amps.
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The 275 is the entry-level amp. It would be interesting to see the schematic of the Raven 350 monoblocks. https://www.bobcarvercorp.com/crimson-raven-features-specs Btw, I'm a Bob Carver fan. |