Some of Bob’s SS designs also failed to use an earth ground bonded to the chassis. This caused hum when using SE connections due to a difference in ground potential between components.
Poor design... I bet the B- and signal ground was connected directly to the chassis.
A 1/4 watt 10 ohm resistor connected in series between the B- and circuit signal ground to chassis would have more than likely solved the ground loop problem.
The 1/4 watt rating of the resistor works as a fuse if the B+ is shorted to the chassis.
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@jbhiller
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.
I would be surprised if the B- is not connected to the chassis as well as the circuit signal ground. Question is how are they connected to the chassis? Directly or through a low wattage resistance resistor? Or how.
If B+ were to short to chassis it would not matter one way or the other if the chassis was connected to the AC mains wall outlet equipment ground. There is not any electrical reference to the wall outlet equipment ground and the secondary windings of the power transformer.
I would hope the designer added some type of protection in the high voltage DC power supply to save it from seriously being damaged, If there was a B+ fault to the chassis B- of the high voltage DC power supply.
/ / / /
The problem with the equipment ground contact, of the IEC inlet connector not solidly connected by a wire to the chassis, is there is not any protection from a possible electrical shock hazard if the HOT AC mains conductor came into contact with the chassis. Or it could be a bared spot in the primary winding of the power transformer to the iron core.
FWIW I looked up the amp. It looks like it was made in 2019. I though maybe it was wired using Double Insulated AC power wiring. I didn’t see any evidence that it is. Also worth noting a two prong IEC power inlet should have been used.
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@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+.
Bad news, from what I see the AC power wiring violates electrical safety standards that have been in effect for at least the last 30 years...
The AC power fuse is connected to the neutral connection on the IEC inlet connector. That’s a no no... You don’t fuse the neutral conductor.
The Hot connection on the IEC inlet connector is connected to the on/off power switch. The guy got that right. Except he should have went to the fuse first then to the switch.
Will the AC fuse blow in the event of an overload condition? Yes... Will a blown fuse kill the HOT energized AC conductor inside the amp? NO!
IF for what ever reason, your fault my fault anybody’s fault if the fuse blew due an overload and it was caused by a short in the primary winding of the transformer and the insulation on the winding got hot enough and bared the conductor, and the bared conductor came into contact with the iron core of the transformer, the metal chassis of the amp would be energized... HOT...
Scroll down page to photos
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@atmasphere
I would be willing to bet you do not fuse the AC mains neutral conductor in your equipment.
The correct way is Hot from the IEC inlet connector to >> fuse to >> switch... Fuse as soon as possible inside the equipment.
The 3 pin IEC power inlet connector on the Carver amp falsely leads the consumer to believe the chassis is grounded when plugged into grounded wall outlet.
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The power wiring is correct. From the switch there are two wires, each of which goes to one of the dual primary 120V windings of the mains xfmr. Coming out of the transformer are the two neutrals that tie into the fuse, which then goes out of the IEC neutral. That is okay,
A neutral is only a neutral when it is electrically connected to the electrical service grounded conductor neutral bar, in the electrical panel. Open the neutral up stream on a load connected to a live HOT conductor and the lead, wiring, from load is HOT. At that point it’s no longer a neutral. It is a HOT conductor and can be lethal.
Never fuse a neutral conductor. Just because it was done in audio equipment over 35 to 40 years ago is no excuse...
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So, the 3rd prong on the ac connector is not grounded ( Crimson 275 ) ? Can someone, with the technical knowledge, explain how this is different to the hot wired 2 prong wire / plug we used to have on older components, before the iec inlet and the power cables war ? I was told by an electrician, the 3rd prong was developed as a 2ndary ground. I do not know.......
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.
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@jbhiller
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?
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@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.
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@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
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@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.
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@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.
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@gktaudio
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?
Also, RCA jacks and speaker jacks are generally connected to the chassis, would you agree?
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".
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@jbhiller
CORRECTION:
@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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With Bob getting older, it was time for him to focus on what he loved-- his family, his hobby, and designing audio gear. So I recruited EJ Sarmento of Wyred 4 Sound and we bought the rights to the brand keeping Bob as our chief designer-- effective January 2020 . I demoted myself (thankfully) from CEO to VP so I could no longer worry about logistics or paying the bills. Instead, I could focus on product development and building the dealer network as well as dealing with the public directly, something I love dearly. We closed our facilities in Washington state, moving everything to my office in the Chicago area and to our new factory in central California.
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.
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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.
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GFCI is a suitable replacement for two prong outlets without a grounded wire.
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.
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.
https://www.ecmweb.com/national-electrical-code/code-basics/article/20886140/behind-the-equipment-grounding-conductor
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Most of the older two prong corded equipment is double insulated
No it was not. When there was no internal AC faults the equipment was safe to use.
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