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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. 

 

jbhiller
jea48
4,785 posts
 
jbhiller's avatar
jbhiller OP
1,115 posts

Hi @jea48 , can you explain the takeaway for us from this observation?  Are you saying the B- is properly handled so we do not have to worry about other means of chassis grounding? 

No I am not saying that at all. There are two grounding systems involved. One is the "Circuit Ground". (Internal electronics circuitry ground). The other is the AC mains power Safety Equipment Grounding. (Connection to the AC mains Equipment Grounding System at the main electrical service panel).

Both are connected to the chassis. Though some manufacturers will employ a Ground Lift switch that will lift the signal ground from the chassis when an EGC is used and there is a ground loop hum problem.

If the Carver amp was CLASS II wired, using double insulated power wiring, the only ground connection to the chassis would be the "Circuit Ground". Therein power supply B- and signal ground. The metal chassis has to be connected to them to work properly.

This from the late Charles Hansen:

The only way that the case can provide any shielding for the audio circuitry is if it is connected to the signal ground. In addition, if it is left unconnected from the signal ground, then it will create unwanted capacitive feedback loops (both positive and negative) between various parts of the circuitry. Refer to Morrison's books for additional details.

.

daveyf's avatar
daveyf
3,076 posts
 

Reading the article posted on ASR would indicate that this amp is really a POS..particularly for the money asked…

But it would be more acceptable if it was advertised as a 15 watt amp with a design by Carver at a more appropriate price to its quality. Instead, the company seems willing to risk liability and damages, with the full expectation that enough profits will accrue to off-set the risk. A common business practice these days…

daveyf's avatar
daveyf
3,076 posts
 

OTOH, could it be possible that the amp discussed on the ASR forum is in fact a fake?? Or that the issues about safety are not in fact part of the design at all...and are not a factor...?? Only real way to know is for Carver, or one of his employees, to rebut the issues and design..and clear the air. Probably not a bad idea to see if this is forthcoming, before any more conclusions are arrived at! 

I'm off this thread now.

jbhiller's avatar
jbhiller OP
1,446 posts
 

Team Audiogon,  

Trying to put this into perspective...

If the amp measures 15W continuous at 4ohm with <1% distortion, it might be fair to say that when driving 8ohm nominal Klipsch Cornwall IVs at 102dB efficiency, the amp sounds or can sound sublime.  Wasn't it David Manley who said that distortion under 1% is not really audible? 

The facts remain though that they likely misrepresented its power (by a bunch) and it has a wonky, outdated grounding scheme. 

Finally, would a GCFI outlet/plug truly make the unit safe? 

imhififan's avatar
imhififan
2,231 posts
 

would a GCFI outlet/plug truly make the unit safe?

Same as a fuel cut off switch that shuts off the power supply for the fuel pump if the vehicle is in a collision. Thus, it prevents fuel from being pumped in case of fuel line damage during an accident. Although a ground fault circuit interrupter (GFCI) can’t prevent short circuits and other electrical faults, it help prevent electrocution. If a person’s body starts to receive a shock, the GFCI senses this and cuts off the power before a person get injured. Also, GFCI is a suitable replacement for two prong outlets without a grounded wire.

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