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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
10229's avatar
10229
41 posts
 

So just to play devils advocate, and to potentially obtain some useful knowledge, I own both a Marantz NR1200 and a Cambridge AXR85…both amplifiers house in metal casework and neither have a ground pin on their power cords…why is the Carver amp any different?  
 

Matter of fact after further inspection, I have lots and lots of electrical devices that don’t have 3 pin power cables plugged directly in to outlets…should each of these devices also get dedicated threads publicly telling everyone that they are potentially deadly and to contact their makers for comment otherwise?

jea48
4,323 posts
 

@gktaudio

As for changing the incorrect AC Power wiring it would be an easy fix for someone with a soldering iron and basic soldering skills.

Note, the schematic wiring diagram for the amp. Carver shows the correct wiring sequence. Fuse >> switch >> transformer.

Note, the R57 4.7M resistor from the neutral conductor to the chassis.

Also note, "CIRCUIT GROUNDED TO CHASSIS" I think there he is referring to the circuit ground of the amplifier. Therein B- and signal ground.

Schematic wiring diagram of the power supply for the amp.

 

 

As for the EGC, (Equipment Grounding Conductor), I agree with what you said in your post. But... My point that I was making, my post, is that user doesn’t know the EGC pin on the 3 pin IEC connector is not connected to the chassis. It should be the users choice if he/she wants to lift the EGC with a ground cheater.

From what I have read Carver doesn’t like the EGC. It does nothing for the sound of the equipment. If anything the EGC can harm the sound. Especially if the signal ground is connected directly to the chassis. And it appears Carver did on this amp. That can leads to ground loop hum if an EGC is connected to the chassis.

There are things carver could of did in his design to solve the problem and connect an EGC to the chassis for electrical safety. But apparently he chose not to...

Here is the schematic wiring diagram for the amplifier section. Note the RCA jack ground is grounded directly to the chassis.

 

 

jea48
4,323 posts
 

@10229

The AC power wiring inside the equipment is double insulated. (NO safety EGC , Equipment Grounding Conductor, is needed)

Look on the back of the units. It should say Class ll wiring and or may display a square inside of a square.

It costs more to make Class ll equipment, than it does to make equipment that uses the EGC from the AC mains wall outlet.

CLASS II power wiring

 

 

jea48
4,323 posts
 

@gktaudio

 

Here is the schematic wiring diagram for the amplifier section. Note the RCA jack ground is grounded directly to the chassis.

EDIT: Go to page #13.

 

erik_squires
15,966 posts
 

This sounds like a hot mess.

If the gear is in fact double insulated (which I'm not sure applies JUST to the power supply) then why use a 3 prong IEC connector?  Use a 2 prong like other gear which is double insulated uses.

And ... why oh why would you connect the chassis ground to signal ground directly?

Being a tube power amplifier we have lots of high voltage wiring besides the power supply.  In case of a high voltage short to the chassis that high voltage and current gets carried by the delicate ground in the interconnect wiring, which is then a fire hazard, or upstream equipment risk.

Really quite a messy set of choices.

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