Inside Bob Carver's Lab with Director of Operations, Jim Clark

[Ar9Jim 6,175]

Q: Bob,  How can the tubes run cooler and last for decades when most manufacturers tubes run very hot and recommend changing the tubes in their amps in 3 years.

 

A: That is a very good question! The answer is the DC Restorer. Here’s how. Most amps idle the output tubes at an average of 32 watts or so. Now the DC Restorer allows the tubes to idle at about 9.75 watts. Since tube longevity is roughly proportional to the plate dissipation raised to the 2.3 power, we have 32 divided by 9.75 raised to the power of 2.3 = 15.4. Finally, 15.4 X 3 years = 46 years.

 

Tube amplifiers are normally biased-up like they are running flat out, even at idle, to keep distortion low.

 

The DC Restorer is a dynamic bias supply. The lower idle current allows for cooler running tube temperatures and much longer tube life while maintaining low distortion. It's a circuit that was used in tube type color TVs that were very sensitive to DC voltage sag. I adapted a version for audio and It has really been a great circuit.

[ChrisTFM35 603]

The bums at ASR have their pitchforks ready for the 285.  Such insanity. I trust Carver and I trust my ears. 

[3M_Audio 942]

6 hours ago, ChrisTFM35 said:

The bums at ASR have their pitchforks ready for the 285.  Such insanity. I trust Carver and I trust my ears. 

 

Well said!

[Ar9Jim 6,175]

On 11/8/2023 at 10:40 AM, ChrisTFM35 said:

The bums at ASR have their pitchforks ready for the 285.  Such insanity. I trust Carver and I trust my ears. 

The RAM 285 is a great testing amp for comparison with tube amps. It meets it's specs and sounds wonderful.

The folks at ASR are playing a numbers belief game that what measures best, should technically sound the best. This incentivizes a numbers race well past audibility, over sound quality and a host of other priorities considered in creating a musically enjoyable design with real customer value for it's intended application.

 

Naturally, an ASR review would not recommend a RAM 285 because solid state devices can measure far better than vacuum tubes by orders of magnitude. Solid State is much lower cost to build and will measure better than vacuum tube amplifiers, unless greater complexity than is necessary for audio is added to the tube amp design, increasing the build cost even higher needlessly.

 

Some will always purchase audio products considering the best measurements as the true measure of sonic value, and that's great. There's certainly nothing wrong with that viewpoint. A tube amp at 1Khz with .2 %THD+N vs a solid state at .00002% and the choice seems perfectly clear and made really easy for some. These measurements are really simple to comprehend and to judge products by. It's scientific. It's good. These consumers would never purchase a tube amp of any brand and they shouldn't without hearing them first. This is a solid state type customer, not a tube amp customer, by nature. 

 

At the opposite end of the spectrum from ASR, you have people describing the subjective qualities of listening to multi-thousand dollar power cords. What is the customer supposed to believe in this day and age, with the hobby so polarized into these 2 camps?

 

This is why we have the Carver Amp Challenge. Our customers do not need to rely on subjective reviews or best measurement reviews at either of the extremes in the hobby. Hearing our products in their system compared to others, answers all their questions and sends many much more expensive solid state and tube designs back for refunds. 

Edited November 13, 2023 by Ar9Jim

[Ar9Jim 6,175]

• iamjohngalt11 Nov 3:32 PM

  @Ar9Jim I just got a TFM-42 restored by Greg. I've run it on my 2.5R Maggies (driven with 10 Octave LP1) and at moderate loudness on Jazz vocals the LED meters are jumping up to full height with regularity. I tested the same amp on Bill's Altec speakers and the LED's don't move off the low one at all. Full size Maggies really need some power.
• iamjohngalt11 Nov 3:35 PM

  Didn't you demo those MGIIIa's with a Carver 275 regularly in your sales listening room?
•  
  Hello JG.. Yes, have used 275s on the Maggies alot. Also with the ALS line source and those are not an easy load running about 50 drivers in one pair of speakers.
•  
  Maggies really like the high voltage side of the V x A = W math.
•  
  Easiest analogy is water. Physics are fundamental. The garden hose will flow current well, but you can stop it with your thumb. Now crank it up to 1000psi (pressure / electromotive force in electrons) of a pressure washer. Now you do not want to put your thumb on it. "Current needs to be enough" Bob Carver.
•  
  If your design priority is testing well with resistive load drain test, then you will be distracted from the application and that's ok. It's a good way to get good reviews, but of limited value to the customer looking for a powerful, musical and accurate reproduction of music.
•  
•  
  People are so smart but yet the basic differences between reactive loads and resistors are beyond understanding.
•  
  Voltage swing moves loudspeakers.
•  

  Car battery has huge current and will smoke low resistance loads right. But you can put your hands on the post and nothing happens.
•  
  That's good for low impedance drain test. But how does the power supply respond with the impedance (AC resistance) goes up?
•  
  "My design increases voltage with increased impedance." Bob Carver.
•  
  Can see it in the designs. 685, 740, 800. At 800v custom capacitors get expensive.
•  
  At the 285 voltage the 1000v B+ fuses for a littelfuse can cost $10 each. They have some for $5
•  

  Fun stuff. 
•  
  One of the 285 customers owns a company that rents sounds systems for concerts to bands. He is in the Hollywood area.
•  
  I was telling him how the 285 was built heavy and makes excess current. He says "I don't care about that, how does it punch?"
•  
  This is in his home stereo, but his mindset is dynamics.
• Or voltage swing in other words.
   
  So the RAM 285 is built for both high voltage and high current at a shipping weight of 60lbs and Bob took the voltage even higher. It's awesome. At full power output it doesn't start to roll off in frequency response until below 18Hz.. 
   
  https://www.ap.com/technical-library/measuring-power-amplifiers-with-reactive-loads/

Edited November 12, 2023 by Ar9Jim

[Ar9Jim 6,175]

RAM 285s moving along. In person the copper finish matches the color of fresh copper wire or a new copper penny. Customers are calling it "captivating", "stunning", "beautiful", "the anodize is nicer than paint". We are very happy with the initial feedback about sound, fit and finish.

 

[Ar9Jim 6,175]

Q. What is the finish used on the RAM 285? Is it painted? Will the copper tarnish?

 

A. Great question. The entire chassis is CNC machined from thick 6061 aluminum. The copper cover portion is 6mm thick. The black and copper colors are anodize finishes, not paint. Anodize provides a nice even, sealed, durable finish as used in high end aluminum automotive and aircraft parts (commonly blue or gold in color) we use copper and black.

https://www.anodizing.org/page/what-is-anodizing

Edited November 13, 2023 by Ar9Jim

[BobTFM35 1,666]

@Ar9Jim Thanks for the post on anodizing. It got me looking at how it was done and if I can do something like that at home.

 

My search came up with this, https://caswellplating.com/

 

This looks like a match in color?

 

https://caswellplating.com/anodizing-products/anodizing-kits.html

 

Looks interesting and they have several other coating systems to explore.

 

Thanks Jim 

 

 

[Ar9Jim 6,175]

2 hours ago, BobTFM35 said:

@Ar9Jim Thanks for the post on anodizing. It got me looking at how it was done and if I can do something like that at home.

 

My search came up with this, https://caswellplating.com/

 

This looks like a match in color?

 

https://caswellplating.com/anodizing-products/anodizing-kits.html

 

Looks interesting and they have several other coating systems to explore.

 

Thanks Jim 

 

 

Yeah, that's a good color match. It's difficult to get right in the pictures. This is a good photo. The luster in the light is nice!

[Ar9Jim 6,175]

RAM 285 after burn in and line test. Final step is arriving here for listening test. The amps stay on their cart through the process. Listening test are normally performed on Tuesdays and Thursdays. Demo's are also available on Tuesdays and Thursdays in Rockford, IL. by appointment. You are welcome to participate in listening test of the RAM 285s and Black Magic products before they ship out.

 

[Ar9Jim 6,175]

The color of these pictures are close. 

We updated the site with better pictures and closer viewpoints.

 

In sleep mode all power supplies are off.

In stand-by, the low voltage supply is on and the tubes glow and stay warm.

On- Activates the high voltage supply together with low voltage supply.

Light- Simply activates the meter light while under power

 

Edited November 15, 2023 by Ar9Jim

[Ar9Jim 6,175]

Here is a quick pic of the RAM 285 transformers. Some will be added to the site. More nudes coming today. These 100watt Hammond transformers are matched pairs and the frequency response stays flat below 18Hz beyond full rated power.. The chassis is a full 17 inches wide. The amps weighs 56lbs.

 

[Ar9Jim 6,175]

Customer in California received his RAM 285. Thank you, Watt. Enjoy your trip to Bangkok. 

 

Dear Jim and Lerma:  I got the Ram 285 tube amp yesterday. I hook them up and enjoy playing for couple hours. The unit is very pretty and very heavy. Thank you for beautiful product.

Thank you,  Watt 

Edited November 16, 2023 by Ar9Jim

[Ar9Jim 6,175]

Ram 285 transformers from another view. For scale, the bottom portion of the chassis is 3-1/2 inches high and 17" wide. The transformer section is 5-1/2" high. The copper color shows accurately in this picture. Same amp in the previous picture but the previous picture looks too orange. Customers are really liking the copper. Note the CNC machining on the top cover. Note the copper chassis is chamfered where the wire pass though. All of the exposed outside corners are radiused. The copper anodized top plate is almost 1/4 in. thick (6mm) 6061 alum..

 

 

 

Edited November 16, 2023 by Ar9Jim

[BobTFM35 1,666]

@Ar9Jim Checking in to see what the progress is on the Phono Preamp?

 

 

[anatech 40]

I've worked on Carver equipment and Bob's earlier designs for a very, very long time.  All kinds of gear for MI and consumer use.  Nearly 50 years now being paid for what I do.  I also have a test and measurement background and use HP / Agilent / Keysight equipment mostly.

 

Resistive dummy loads.  Yes, they are there so you can make claims that are reproducible by others with standard, industry agreed upon equipment characteristics.  This is for starters.  Early on, Marantz had us connecting capacitors in parallel with the load resistors.  You can also use inductors and capacitor-inductor networks, but then you are not on any standard.  This is useful for internal design direction so you can drive real loads well.  However I draw the line at stupid loads.  Unhappy amplifiers will not perform at their best, so why design a speaker that puts amplifiers in this position???  (Infinity and Ohm come to mind).

 

Anyway, before any of you criticize testing with the standard industry resistive loads, stop and consider why this is done.  Those tests are valid.  Mine are those 250 watt, Dale 1% non-inductive 8 ohm things, I have three sets mounted on heat sinks.  Some folks use heating elements and claim they are valid (ahh - no).  You can get a base comparison and weed out the junk so you can focus on equipment that is designed well by looking at those tests.  We look at spectrums these days, not a needle pointing at a number.

I find Bob's designs inspired and frankly I see him as a very gifted engineer with a flair for promotion.  Also, the lower the distortion, the better something does sound.  I do feel the music and commonly run things at very high SPL.  Bob designed some very fun products, although people who blew woofers in LaScalas driven by M 1.5 and PM 1.5 amps make me wonder (did Klipsch warranty too).

 

I do have one burning question for Bob and others in design.  Why the devil would you use a 4136 quad op amp?  Not great performance and a non-standard pinout.  Low current draw sure, but who cares?  It forced me to use an adapter PCB (I designed decades ago, others have them now) and install better power supplies in some products.  Just asking ....

 

-Chris

[Ar9Jim 6,175]

Hi Chris,

Excellent post. Thanks!

I could not agree more about the use of non-inductive resistors as a useful tool for objective standard measurements. We perform resistive load QA test of every amp that goes out the door at Bob Carver and a serialized report is included with the unit for the customer.

They are great tools of the designer and quality control, but not ultimate design goals as some sites would imply in their ranking of state of the art. Here's something from earlier on FB.. Your thoughts are appreciated. I'll ask Bob about the op amp choice.

 

There's an interesting disconnect from reality in audio today. The science of audio designers is reproducing the best sound in audio possible, after higher education and decades of study and experimentation in most cases.

Men like Carver, Curl, Pass, Hafler, King, Rowland and other real scientist, decide what parameters are most important to the sonic objectives they are working to achieve. This is the real audio science. Analyzers and test equipment are the objective tools of the designer.

 

These same often highly educated men have focused intently for decades to design the most musical products. These men are world famous for their work, for good reason.

Several sites exist today for the purpose of measuring audio products. Some even use the word 'science' in their titles, while others recognize the limitations of their measurements to describe sound quality and admittedly refrain from the science title.

 

There is a disconnect between real audio science, that has provided wonderful music for generations, by truly advancing the state of the art in audio (and becoming world famous for doing so), even when compared to other designers found world wide.

 

Compare this to the science of measuring audio equipment with higher resolution and better numbers as the goal of the science on some sites. The scientist listed above have long been using analyzers as tools of their trade.

I've read discouraging reviews for products designed by all of these men, largely due to the fact that they know enough to not go down rabbit holes chasing measurements over their priority of improving sound quality for their customers.

 

The best audio designers on earth use analyzers as objective tools but not as their primary design goals.

To imply that the best audio designers on earth (Americans seem to be the target, all of them) are not state of the art, based on a lowest measurement like SINAD is absurd.

Analyzers are great slaves but I wouldn't expect the best designers on earth to make them their master. The real audio science of sound quality will take priority with these world class designers, over pursuing the best measurement rabbit holes, that beyond a point, offer no sonic value to the customer. Customer value is why we have a trial offer. The customer always wins.

Edited December 5, 2023 by Ar9Jim

[Ar9Jim 6,175]

On 11/27/2023 at 3:51 PM, BobTFM35 said:

@Ar9Jim Checking in to see what the progress is on the Phono Preamp?

 

 

Hi Bob,

After the SH.. Hopeful for this Summer. 

Edited December 6, 2023 by Ar9Jim

[AndrewJohn 8,249]

Hi Jim @Ar9Jim,

 

There's a discussion (slight dispute) about whether the Coffee Can amp was real, or not..., 

 

Could you ask Bob to confirm?  Someone is actually saying that they heard Bob Carver say he really never made an amp in a coffee can.

 

When you were in Snohomish, did you happen to see it in Bob's museum?  I can't imagine this piece ever leaving his personal archives..., but you never know.

 

This is over on the Phase Linear FB group.  I'll post your answer from Bob.

 

 

[Ar9Jim 6,175]

On 12/6/2023 at 7:39 AM, AndrewJohn said:

Hi Jim @Ar9Jim,

 

There's a discussion (slight dispute) about whether the Coffee Can amp was real, or not..., 

 

Could you ask Bob to confirm?  Someone is actually saying that they heard Bob Carver say he really never made an amp in a coffee can.

 

When you were in Snohomish, did you happen to see it in Bob's museum?  I can't imagine this piece ever leaving his personal archives..., but you never know.

 

This is over on the Phase Linear FB group.  I'll post your answer from Bob.

 

 

I'll ask later today, AJ..

 

[Ar9Jim 6,175]

Question: What types of patch cords are commonly used for amplifier testing? Are they high end audio cables?

 

Answer from Jim: At Bob Carver's lab in Snohomish and in Rockford the most common test cables are made by Pomona. The stackable banana plugs are very handy for piggy backing loads and test instruments. They make several BNC adaptors as well. On most test benches you will find Pomona. High end audio cables are generally absent from test benches. 

These stackable bananas are very handy when measuring loudspeaker / amplifier interactions like Bob does in development.

 

https://www.pomonaelectronics.com/products/patch-cords/banana-plug

 

https://www.digikey.com/en/products/detail/pomona-electronics/B-36-02/737939?utm_adgroup=&utm_source=google&utm_medium=cpc&utm_campaign=PMax Shopping_Product_Medium ROAS Categories&utm_term=&utm_content=&utm_id=go_cmp-20223376311_adg-_ad-__dev-c_ext-_prd-737939_sig-CjwKCAiAmsurBhBvEiwA6e-WPLPgfpiCd0_9DncUvRJlZPRmJob0HopBWPGvtguafGdVycBROOIFBxoCWeQQAvD_BwE&gad_source=4&gclid=CjwKCAiAmsurBhBvEiwA6e-WPLPgfpiCd0_9DncUvRJlZPRmJob0HopBWPGvtguafGdVycBROOIFBxoCWeQQAvD_BwE

 

 

 

Edited December 8, 2023 by Ar9Jim

[radtraveller 222]

On 11/12/2023 at 3:18 AM, Ar9Jim said:

• iamjohngalt11 Nov 3:32 PM

  @Ar9Jim I just got a TFM-42 restored by Greg. I've run it on my 2.5R Maggies (driven with 10 Octave LP1) and at moderate loudness on Jazz vocals the LED meters are jumping up to full height with regularity. I tested the same amp on Bill's Altec speakers and the LED's don't move off the low one at all. Full size Maggies really need some power.
• iamjohngalt11 Nov 3:35 PM

  Didn't you demo those MGIIIa's with a Carver 275 regularly in your sales listening room?
•  
  Hello JG.. Yes, have used 275s on the Maggies alot. Also with the ALS line source and those are not an easy load running about 50 drivers in one pair of speakers.
•  
  Maggies really like the high voltage side of the V x A = W math.
•  
  Easiest analogy is water. Physics are fundamental. The garden hose will flow current well, but you can stop it with your thumb. Now crank it up to 1000psi (pressure / electromotive force in electrons) of a pressure washer. Now you do not want to put your thumb on it. "Current needs to be enough" Bob Carver.
•  
  If your design priority is testing well with resistive load drain test, then you will be distracted from the application and that's ok. It's a good way to get good reviews, but of limited value to the customer looking for a powerful, musical and accurate reproduction of music.
•  
•  
  People are so smart but yet the basic differences between reactive loads and resistors are beyond understanding.
•  
  Voltage swing moves loudspeakers.
•  

  Car battery has huge current and will smoke low resistance loads right. But you can put your hands on the post and nothing happens.
•  
  That's good for low impedance drain test. But how does the power supply respond with the impedance (AC resistance) goes up?
•  
  "My design increases voltage with increased impedance." Bob Carver.
•  
  Can see it in the designs. 685, 740, 800. At 800v custom capacitors get expensive.
•  
  At the 285 voltage the 1000v B+ fuses for a littelfuse can cost $10 each. They have some for $5
•  

  Fun stuff. 
•  
  One of the 285 customers owns a company that rents sounds systems for concerts to bands. He is in the Hollywood area.
•  
  I was telling him how the 285 was built heavy and makes excess current. He says "I don't care about that, how does it punch?"
•  
  This is in his home stereo, but his mindset is dynamics.
• Or voltage swing in other words.
   
  So the RAM 285 is built for both high voltage and high current at a shipping weight of 60lbs and Bob took the voltage even higher. It's awesome. At full power output it doesn't start to roll off in frequency response until below 18Hz.. 
   
  https://www.ap.com/technical-library/measuring-power-amplifiers-with-reactive-loads/

Amazing Line Source loudspeakers = excessive drooling