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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. 

 

128x128jbhiller
gktaudio's avatar
gktaudio
22 posts
 

@jea48 Yes, on reflection you are correct and I didn't express those thoughts clearly. But as I said, there are many grounding schemes for signal grounds. Also, I have seen and have used loop breakers for power supply grounds, but the concern here was the complete lack of an AC safety ground from the IEC connector.

I am unsure if you are suggesting that the lack of the IEC ground connection is acceptable in this example, and if so, why. That was one of several concerns raised by the OP and others.

ARC used to make the signal ground connection to the chassis through a 10 ohm resistor. Same for connecting the B- of the power supply to the chassis. Here ARC used a 1/4 watt 10 ohm resistor from the B- rail to the chassis. The resistor works as fuse in the event of a short from the B+ to chassis.

gktaudio's avatar
gktaudio
22 posts
 

If this topic hasn’t bored everyone already, here are a few informative resources. I have no affiliation and haven't read through every word, but they may be of interest to you:

https://www.aikenamps.com/index.php/grounding

Shock Hazard and Grounding (peavey.com)

PowerPoint Presentation (hifisonix.com)

IMPORTANCE OF GROUNDING TECHNIQUES (celectronics.com)

 

 

 

imhififan's avatar
imhififan
2,205 posts
 

Plug it into a GFCI adapter.

https://dfarq.homeip.net/gfci-without-ground-wire/

fiesta75
1,378 posts
 

Another excellent solution.

jea48
4,451 posts
 

@jbhiller 

CORRECTION:

 

jea48
3,741 posts
 
 

@jbhiller ,

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+.

The B+ rail is not fused! 

B- is bonded, connected, directly to the chassis. IF the B+ ever came into contact with the chassis there would be a loud big bang...

The DC fuse on the back panel:

The (rear panel) vacuum tube cathode fuse
(B+) is a 1.0 ampere and should be replaced with
the same type and rating. If the fuse blows during
bench testing, it may be temporarily replaced with
a 1.25 or 1.5 ampere fuse. Do not, under any cir-
cumstances, use a "slow-blow" fuse here

Quote from owner manual.

.

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