Owners of Carver Crimson 275 -Caution/Warning--Potential Increased Risk of Electric Shock

@jbhiller

What year did you buy the Carver Crimson 275 amplifier?

As for ’ your ’ Carver Crimson 275 amplifier did you remove the bottom cover and actually look inside the amp? The photo you posted was not of your amp.

It is possible your amp may be wired differently than the one shown in the photo.

(Note: The photos I posted were from the same Web Site as the one you posted)

From what I have read Bob Carver only designed the Carver Crimson 275 amplifier. He had nothing to do with its production. I doubt if Carver had any say in the quality of components used in the amp.

I doubt if Frank Malitz did either.

Who knows who actually assembled(s) and wires the amp. Is it farmed out?

It would help to know for sure if ’your’ amp is wired the same as the one in the photo. Good chance the IEC ground pin is not bonded, connected, to the chassis. Carver’s schematic wiring diagram only shows the AC source symbol. Typically a picture of an AC plug, be it a 2 pole only, (no EGC), or a 2 pole with ground pin for a EGC will be shown. Carver may not have wanted an EGC to be used. But that doesn’t mean he wanted a 3 pin IEC inlet connector installed on the amp. A two pin IEC would have been the correct IEC connector to use. Carver was out of the loop...

Who owns and runs Bob Carver Corporation.

What I would like you to look for is how the IEC power inlet connector is wired. Is it wired exactly as the amp shown in the photo you posted?

FYI, Before you remove the bottom cover, for your safety, unplug the amp from the wall outlet. If the amp was on before you start removing the bottom cover then wait about an hour before removing the cover. That will allow the electrolytic caps to bleed off the high B+ DC voltage.

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.

Set aside who designed the amp and look at it from a design standpoint. I’m not an EE but have built about 22 tube amps and repaired many others, and have built and repaired a lot of solid state gear. I rely on current information on safety from books and qualified engineers either in person or online.

First, as has been said before, proper installation of the fuse is in the hot (line) leg of the primary winding of the transformer along with the power switch. In years past, the neutral was fused but this is incorrect because it could blow, leaving the hot connected to the circuit through the switch, waiting to complete a circuit through the operator or internal mechanical failure. This is a strange holdover from early tube amplifier and radio designs that I’ve run across, and it gets replicated to this day, which is incorrect.

Second, I don’t see how the unit can be classified as Class II, where it is double-insulated. Even if it had a completely non-conductive outer shell, the circuit, which is connected to the chassis per the schematic cited earlier, could be connected through the input/output jacks, exposed screws, etc. That means the unit should have a safety ground connection - a dedicated, short piece of green or green/yellow wire connecting the ground lug on the IEC jack directly to a dedicated nut/bolt through the chassis.

This is so that if any hot part of the wiring comes into contact with the chassis, it will blow the fuse and/or the service panel breaker. In the US, neutral is tied to the ground buss bar in the service panel, so hot leaking or making direct connection to neutral or ground trips the safety devices.

Some manufacturers consider the transformer to be a safe isolation between AC wall power and the circuit and chassis, but that does not account for a potential failure at the primary side of the transformer, or the transformer itself which could short internally (some output tube failures can cause this), coupling the circuit with AC and the chassis.

Hard to tell from the photo, but if I read the comments properly, the rectifier board is glued to the chassis? If that is correct, it’s really bad design/construction. That is a high voltage part of the circuit with lots of current and should be very well attached to the chassis.

It will be very interesting to hear what the company provides in response to the questions by the OP!

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.

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?