Ar9Jim

Measuring with the back EMF output from speaker vibrations. Back EMF is the force used in Bob Carver's "listening to the room" feedback loop in his tube amplifiers.

Welcome to TCS Sir. Enjoy!

This morning we tested 16- un-matched tubes and 8 (2 matched quads) for 24 in all. All the tubes test strong on the basic tube test given on a restored Knight 600B. This is not a pro grade device, but is good for checking for shorts, gas, filaments but it's not an emissions type tester. We normally buy matched quads and let the factory do the sorting. The next test was using a Crimson 275 to check the bias current at full plate voltage, using the 275 power supply providing 685 volts to the plates of each tube individually. The matched quads bias current came in the same with the 4 tubes drawing the same bias current within 5mA on both quads. (100mA, 100mA, 100mA, 95mA) and (75mA, 75mA, 75mA, 70mA) respectively. The 16 unmatched tubes had variation from 55mA to 110mA in this test as described below. It's simple and informative under actual voltage. Matched quads are really the way to go in push pull stereo tube amps, imho.. Using your Bob Carver amp as a Tube Tester: The front panel meter may be used to test the tubes. • Remove all the power output tubes • Plug the amp into the AC wall socket with the main rear panel power switch OFF. • Insert the tube you wish to test into socket four (the far-right large tube socket). Turn the bias control fully clockwise, then turn the main power switch ON. With a watch, time the warm-up period for exactly one and a half minutes and note the current reading. Turn the amplifier OFF. • Remove the tube and insert the next one. You can hold the tube with your bare fingers — it will not be too hot after only a minute and a half, provided it was cool to start with. • Keep track of each reading, and repeat until all tubes have been checked. If any single tube does not bias up or “runs away” with its cur-rent climbing substantially higher, ≈200% than the others, then it must be replaced. • It is okay to turn the amp on and off at will. • Return the BIAS CONTROL to its original position and put all the tubes back into their sockets. This completes the tube testing operation. Enjoy the Music!

Over the past few years some experience with tubes and some observations may help you. Years ago having a KT-120 flash on start-up after being shipped with the same tubes as used during burn-in was an issue. There were impurities that could move around and then get vaporized and collected by the getters (those shiny mirror disc inside the tube), this rare occurrence would blow the B+ fuse in the amp.. After the fuse was replaced all was well again. The Carver design doesn't require matched sets of tubes. That being said, if we ordered matched quads of tubes the issue occurred much less often. The matching process seemed to provide another level of quality control and longer burn time for matching sets. The days of tube flash were effectively solved my buying matched quads and hasn't been an issue in 2-3 years. The quality issue at the factory went away in the mean time. There is another reason to buy matched tubes. The unmatched tolerance allows a wide variability in tubes. If you don't buy matched sets (at least pairs) it's a bit of a crap shoot as to how far apart the tubes may be. Although technically the DC Restorer circuit eliminates the need for matched power tubes, without specifying matched tubes, the mismatch can be so far off to cause bias instability in rare cases. You may want to consider this, even if you need just one tube, if you can buy 2 and get a matched pair with measurements included, rather than just a pass/fail inspection, the quality control seems better than buying unmatched. The matching charge is well worth the extra quality control it provides from our experience with quantities. Enjoy the Music.

Here is another Q & A session from 2008. Thanks James Sauter. Here is the first video in the 08 series.

This video series from 2010 has many good questions and answers. There are about a dozen of these videos in this session that you can click on in progression after this 1st video ends. Thanks to James Sauter for posting these videos on Youtube.

Conventional wisdom seems to dictate that audio power supply designs should be highly regulated and stiff, keeping the voltage regulated within tight parameters. This type of stiff design is common and is considered an advantage in most applications for dealing with voltage variations under load. Bob Carver Philosophy - Power supplies will experience voltage sag. In the case of tube amps, they all experience DC voltage sag, pulled down from the average of 450v DC produced by the power transformer and supplied to the vacuum tube plates, bias, etc.. Rather than a heavier transformer to try and stiffen the voltage, Bob Carver increases the power supply operating voltage from 450v average to as high as 785v. The 19lb Crimson and Black Magic 275 design leverages the higher operating voltage (685v) to enable smaller transformers, lighter weight and lower cost. Bob was asked, how do you design a supply to be bouncy and springy as you explain sounds the best? " Well, In the 275 design I started with higher voltage than any other design I know of at 685v, so that is more than 200v above most other deigns." "The bouncy and springy action is enhanced by use of a physically smaller power transformer that will experience some voltage sag under load, then spring or bounce back." "My designs operate at much higher operating voltages so the sag never pulls the voltages down too low." "After many years of work and study, I've determined this approach to sound the best." Bob Carver.

There are a couple equations to understand the physics Bob has leveraged. I'm not a designer but have asked Bob many questions in an effort to understand how and why he does what he does, to make products that produce a powerful, musical, accurate performance, often lighter in weight at fair prices over the years. Here are facts Bob refers to for reference: W = V squared / R Here is a calculator - http://www.csgnetwork.com/ohmslaw2.html V X A = W. Here is a calculator - https://convert-formula.com/a-v-w Power increases to the square of voltage. It's a big deal. Here is an example: If amp A can produce 100v at 8ohms its wattage is 1250w If amp B can produce 30% more voltage 133v at 8 ohms, its power goes up by 90% to 2211w and the amp doesn't necessarily gain weigh or cost. As the physics work, increasing voltage can have benefits in weight reduction. This is why the high voltage power lines overhead run up to 765,000 volts and carry huge power over long distances on small wires with minimal losses. At lower voltage the lines would be the size of oil pipeline in diameter and run hot with high losses flowing massive current. Voltage equals pressure. You can think of Bob's designs as 'high pressure' for a bit easier understanding of what Carver leverages and what he feels sounds best after decades of study at the physics level of electronics, sound and the ear brain interface. Bob has a long studied philosophy of using higher voltage power supply designs than normally found in solid state or tube amplifiers. Carver designs power supplies that act springy and bouncy, as he has determined these design types to sound the best. More about springy vs stiff power supplies in another post, 'Bob Carver Power Supplies - Stiff vs bouncy and springy.' What sounds best?

Welcome to The Carver Site. Enjoy!

The RAM285 is being reviewed by Steve Guttenberg at this time. One of the speakers used in the review is shown here. The high voltage design of Bob Carver should provide a great performance. They recommend 100watts. The 285 is actually 105watts but punches way above its class. I'm guessing there will be no shortage of power. Bob's high voltage design runs this type of speaker at their best.

December 12 2023. UPDATE: After the closing of the company that owned license to Bob Carver's designs and products from 2019 to 2021, I asked Bob if he was willing to take one more swing at audio together, to combine our strengths and repair the damage to his legacy from the previous attempt. In Feb 2022 Bob Carver LLC was founded as the IP holder and BC Audio was founded as the manufacturer. A start-up while facing headwinds from a typhoon of negative feedback related to the Crimson 275 has been tough to say the least. Seeing the legacy of a brilliant man who has given his life to improving our listening experience, tarnished by the previous attempt was gut wrenching for me personally. I know Bob Carver the man vs the unfair insinuations and allegations being made about his intent and design of the Crimson 275. Bob is all about customer satisfaction as the main reason for doing this work. Bob offered refunds for 30 days at that time in 2022 and then extended it to 90 days. Bob also offered to change the chassis ground at no charge for those who wanted the change. We still offer that change at no charge if the customer sends it in. Bob profited nothing from the previous attempt but stood behind his name like the good man that he is. What I've learned about the Crimson 275's produced from 2019 to 2021, after having many come in for the updates: The grounding on the Crimson 275 is actually quiet safe. Similar to the audio components you own from the 1980s without safety grounded plugs (sometimes not even polarized) and metal chassis, or the millions of tube amplifiers made before the 3 prong plug was even invented. A full short potential was 6 volts at only mA of current Not even a tingle. Very few Crimson 275s had a polarity issue. Maybe one builder on one day. The vast majority had no issue, judging from the build dates on either side of the poor review specimen that have came in for ground changes. The transformers used are the exact parts Bob specified for the 275. The 15w Edcor are a Carver design from over a decade earlier. The 275 is a type of performance to weight ratio experiment. Building a great sounding 75w @ 1K tube amp weighing less than 20lbs for less than $3K, being serviced and Made in the USA was the target. The previous license owner did not change the Bob Carver designated parts. The Black Magic 275 uses the same parts with a few manufacturing updates.. Specs gone wrong As a dealer, I had no doubt about the power output of the Crimson 275 from experience. Customers had positive feedback comparing to others of 3 times the 275s power rating. If you notice, tube amplifier power ratings by most any company, you will generally find the power rating stated at 1Khz as standard practice, in comparison to solid state specs that generally state a 20Hz to 20Khz bandwidth quantifier in the spec.. The reasoning for this is the older tube amp designs being soft on bass. Still today, many tube amps tend to roll off in low frequencies, so they state power at 1Khz.. The Crimson 275 power spec should have been stated as 75w @ 1Khz like a tube amp, not 20Hz to 20Khz like a solid state. I suspect this was a salesman spec error but I was not involved and can't say for sure. The RAM 285 is one of few tube amps that can make it's full power to below 20Hz, so the power rating on the RAM 285 is not an error, but instead of 19lbs it weighs 56lbs. Bye for now.

Plug your Carver designed power amplifiers directly to the wall without conditioners per Bob Carver. "Those devices can not help, but may hurt."

Made several of these mistakes myself over the years.

Safest way to buy is to arrange for a trial period of an audio product in your system at home, without charging you a restocking fee if the product is not the best in your system. All new Bob Carver products come with a 30 day trial offer with no restocking fees. If a company won't waive their restocking fees for your home comparison with a Bob Carver product, you might ask them why?

In the forums and YouTube Bob Carver videos, there's talk of the ear-brain interface. What's that about and don't all companies do this?" If they do, they are unknown to us and likely to be accidental. Dr. Carver has a background in physiology, as well as electronic design and engineering and his doctorate is in physics. He developed monoclonal antibodies to fight cancer and infections and established a facility to manufacture the antibodies as well. Every product we make takes the ear-brain interface into consideration. For example, without providing proprietary details, Bob's research is consistent with that of Frank McIntosh, Stu Hegeman, the BBC, the Crown Corporation and Seigfried Linkwitz despite minor differences in application, but Bob has made more products following those precepts than all other companies combined. The goal is the reduction of listener fatigue, imprecise imaging and a small tight soundstage lacking envelopment, depth and openness. All our amplifiers use this technology as did the loudspeakers he's manufactured in the past.

Hi Jeff, Welcome to The Carver Site. Enjoy!