You are probably right about the double insulated ground, but some of the old equipment used a floating ground. One of the most dangerous old radios was the all American five, if the polarity was reversed on the cord all the metal on the outside of the chassis would see full line voltage even if the switch was off. Some of the old stuff was somewhat safe and others were down right dangerous, but people knew these things back then.
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.
99 responses Add your response
I think Franks quote "before my Bob Carver company went down in flames, through no fault of my own" is a bit dissonant, but that seems to be his default attitude. I ended up here trying to find out if he was a sockpuppet account on Quora, because he interjects his bull$hit into tons of questions, goes out of he's way to be unhelpful and condescending while writing wacky racial junk. Moving on, his current promo/scam gig is at Alta Audio which he insists is the pinnacle of sound, every other manufacturer is now crap. BTW he just posted his business email September 29th if you need to reach him. I'm sure he will be candid if he can find the time, but wankin...posting 50 answers a day on Quora is time consuming - fmalitz@comcast.net tl;DR - Frank Malitz is a pompous ass and seemingly a pathological liar. All info presented here was sourced from Franks writing on Quora.
I registered because while Frank Malitz is a teat, this nonsense inspired me. I've personally been shocked by a two prong Princeton Reverb playing through it. It takes as little as 50mv to stop a heart unless every amp guide I've ever read is lying about putting one hand in your belt behind your back while you dig inside the guts of an amp. Maybe audiophile amps are different. I don't know, but why take the risk over a $25 fix? But whatever floats your canoe. |
What a huge waste of time this whole thread is. I know I know the OP likes to think that he save someone’s life. I especially like the story about Bob Carver started selling his amplifiers on eBay. Shake my head that is so funny eBay wasn’t even a twinkle in someone’s eye when Bob started in this business. The sad part is somebody’s gonna lose some sales over this and it’s going to be a dealer and good old Bob. this thread speaks to the bigger picture of what’s wrong with things today. People can say things and actually mean well but the problem is, they aren’t responsible for anything to do with the product. They have 1/10 of the knowledge that Bob has about these amplifiers but they can do hundreds of times more damage than they do actually helping the situation. this reminds me of that Danny guy from GR research Who takes apart other people‘s products and beats the daylights out of them to his thousands of fans. There’s just something wrong about the whole thing. Guys are out there trying to do the best they can and then somebody they don’t know , can come out of nowhere and take shots at them. Man that bums me out. Why would anybody ever wanna try and open up a manufacturing business? |
Not a tube amp situation per se (microphone, but a tube amp is potentially involved)... Les Harvey electrocuted by unearthed microphone on stage. while on stage with Stone the Crows at Swansea Top Rank in 1972, that he was electrocuted after touching a microphone that was not earthed while the fingers of his other hand were holding the strings of his guitar.
|
I know Keith Richards was shocked on stage and same with the guitarist from Kiss when their guitars created a circuit due to lack of proper grounds. Keith passed out I think, but of course he survived! He's Keith. :) But in all seriousness,I would think the number of serious injuries and fatalities might be low, yet finding you a "documented case" could be tricky. Medical histories are private. It might be just as hard as finding injuries/deaths by hairdryers. The potential for injury or death is real. What that potential equates to probability wise, who knows? |
The DC power supply in the amplifier is a separately derived power system and does not have any reference to the AC mains electrical service Equipment Ground system. The high voltage DC power supply B- for the amp is connected to the chassis. In the world of the internal circuitry of the amp the B- to chassis is the ground. No different than Class II double insulated audio equipment that doesn’t use an EGC. Looking at the wiring diagram of the amp if B+ comes in contact with the Chassis there will be a short circuit. EGC or no EGC makes no difference. (What if a power tube shorts?) It is possible the AC mains fast blow safety fuse for the amp will blow because the high voltage secondary winding of the transformer would be overloaded which would cause the primary winding to overload and cause the fuse to blow shutting off the AC power to the power transformer. The Equipment Grounding Conductor (EGC) is designed to allow unwanted fault-current to travel back to its source by way of a low-impedance (unobstructed) electrical path.
. |
This is absolutely true per the NEC, but the assumption made is that the incoming AC would come into contact with the chassis and trip in time. I’m not sure if this would prevent electrocution if a high voltage DC supply with lots of potential energy in the rectifier caps were to come into contact with the chassis. Lots of things could come into play here and even if the GFCI DID trip those caps may be several seconds away from fully discharging through someone’s heart or through the ground on the interconnect cables. Seriously though, not grounding the chassis of a high voltage component is hobbyist level BS. |
So this whole thing about grounding audio gear. There are millions of pieces of vintage audio gear out there without ground plugs. In fact, many don't even have a polarized two prong plug. Yet search as I may, I can't find one situation where someone was killed or seriously injured from an ungrounded piece of audio equipment. I've been in the HiFi business for over 50 years.....Never saw a recall or a warning or anything until recently. This past year I built a Bob Latino ST120 Tube Dynaco clone amplifier. I was surprised to see a lampcord power cord with no ground. When I inquired I was told by many to not ground it as it wasn't necessary and might introduce hum......Can someone show me documented case where injurie resulted from an ungrounded piece of equipment? |
Thank you @imhififan |
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. |
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? |
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. |
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… |
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:
. |
Unless I am reading the above quote wrong Bob Carver does not own Bob Carver Corporation. Bob Carver is hired on as a designer. If a refund is being offered for the amp it is being paid by the present owners of the company. FWIW, reading the first three paragraphs from the post of Frank Malitz on AUDIOKARMA, Bob Carver was not involved in the production of the Carver Crimson 275 Amplifier. That would probably included involvement in parts or parts quality.
|
@daveyf , Agreed. Personally I like the sound of the amp quite a bit through high-efficiency speakers. However, this whole thing is a dog and pony show. I really respect Bob and what he has done for the hi-fi community. However, the responses from him and others associated with this, including Bob Carver and Wyred4Sound are just bizarre. I would be quicker to believe Bob Carver and his associates, saying that the amp is safe, if they actually gave a basis as to why. Specifically I mean, just tell me why from an engineering perspective this is safe. Instead they just make a blanket conclusion that it is safe and saying that you can have a full refund if you want it. They also do say that they will ground it to the chassis if you would like. That’s good. I was just looking for a little more transparency what is going on, especially from the folks that designed, manufactured and market of the unit. |
@jbhiller So Bob offers a full refund to consumers of his product. This seems quite strange to me..as IF there is a safety hazard should he not be requiring all units in the field be recalled and corrected?? If there is no issue, why offer a refund? Plus, if there is a safety issue, why would he still want to have units in the field that could do harm ( maybe even kill?) and suffer the consequences of that action...doesn't really make any sense to me! |
I have asked EJ Sarmento of Wyred4Sound the following questions on the ASR thread where he chimed in: "Folks have raised these salient questions to which there has been utterly no response--just conclusory statements by Malitz and now Bob. Maybe you could help answer them as your firm looks to have built a good number of copies.
|
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? |
CORRECTION:
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:
Quote from owner manual. . |
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)
|
@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.
|
Not directly when the EGC is connected to the chassis. 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. (Not sure if that is the way ARC does it today.) atmasphere also does not connect the signal ground directly to the chassis. I am not sure what method Ralph uses though.
FWIW: As for Bob Carver not liking to use an EGC, neither did the late Charles Hansen, Manufacture of Ayre Acoustics. Do a search on AA under Charles Hansen posts with the word "ground". .
|
@10229 Two-prong plug devices are usually either double-insulated, or there is a SMPS that has additional isolation that protects the chassis from potential AC faults. I have several CD players like this, but I also have 30 year old preamps that only had 2-prong plugs but had low voltage transformers. @jea48 Grounding schemes have been a matter of debate for many years in the audio world. Some builders believe grounding the chassis to earth causes hum, others do not. I agree that a Class II device with no need for chassis earth ground should have a 2-prong jack. I agree the schematic shows signal and circuit grounds go to chassis, and that the sequence shows fuse, switch, and transformer. It would have been nice to show the jack connection first, rather than just the source AC symbol. Also, RCA jacks and speaker jacks are generally connected to the chassis, would you agree? @erik_squires The photo shows me nothing to believe this is a Class II double-insulted circuit on the primary of the transformer (or anywhere else). It is also fused incorrectly as described previously. The power supply has a primary side at incoming AC voltage which is what is being discussed here. The secondary side of the transformer is the other part of the power supply. If the AC side has a short, for example the power switch as atmasphere has stated, or a broken line (hot) connection, etc. touches the chassis, there should be a low resistance path to ground, but sometimes designers rely on the neutral connection at the service panel to provide that ground. However, properly connected, the fuse will blow. This is true of solid state gear as well, which can have much higher current draw but lower voltages. On the secondary side with the HT voltage going to the tubes and circuitry, if there is a short, it will blow the fuse(s) or in circuits with virtual center tap connections through 100 Ohm resistors to ground, the resistors. Properly designed and fused, the unit is unlikely to damage the interconnects. High-gain signal grounds (preamp, VAS, driver, etc.) are kept separated from high-current grounds (output tubes, output transistors) in most amps to minimize hum or there is some sort of star grounding scheme. Signal grounding schemes are quite varied and hotly debated as well, but they are not safety grounds. There is ample information available that details the need for proper chassis AC safety grounding, but there may be some particular reason why this unit was considered to be safe without it - I just don’t see it based on the schematics. I’m not pro or con Carver, just commenting on the photo and the schematic. Again, it would be very nice if Carver would provide their reasoning which may answer all these concerns. |
@erik_squires Tube amp or not, if the power switch were to be damaged (such as in shipment) and shorted to the chassis, if wired correctly the main power fuse would blow the instant the unit were plugged into the wall. |
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. |
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
|
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.
|
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? |
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. |
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! |
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.
|
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. |
@jea48 You are correct.
@aberyclark UL is not required for sales in the US. Overseas it isn't a thing. In the EU, the equipment must bear the CE mark which shares many of the same requirements needed to meet UL approval. UL isn't required, but if you don't have it things can go south bad if there is a lawsuit. If you meet CE though its no worries.
|
Why is the schematic wiring diagram for the AC mains connection to the switch and fuse connection to the power transformer in the manual different than the unit shown in the photos of the amp in your thread? Also note the schematic wiring digram in the manual shows a switch to change from 120V AC mains to 240V AC mains. Was the amp also sold as kit?
|
@jea48 , I wish you were in my town and I could take a class from you. Thank you. It seems we may be seeing an update from Carver Corp. on this soon per Jim Clark. However, @jea48 , if Carver Corp.'s offer is to chassis ground the scheme would you say that is not enough? Specifically, they must remove the neutral to fuse connection too? That would be my understanding. Still no response from Frank Malik. I would think that knowing they have a loose bolt rolling around in an amp with a loose power transformer (the one ASR bought), they would want to issue a statement sooner than later. They have now been alerted (they have actual knowledge) that there's a grounding scheme problem that could result in serious injury/death. All this raises the question: Wouldn't Wyred4Sound see the wonky design issues that relate to grounding, securing the meter and the DC restorer circuit PCB, etc., when they build these things? I'm not trying to be critical. I'm just thinking if Jea48 and others can see this so simply, would W4Sound? Something is off here. And we wait.... |
Here are just a few examples. https://robrobinette.com/Widowmakers.htm You had a 50/50 chance of plugging the radio into the wall outlet with the chassis grounded conductor plugged in the wall outlet grounded neutral conductor. In the radios defense the chassis was installed in a wood or plastic case. Plastic or wood knobs with an insulated back cover. . |
