Audio opinions needed on Krell CAST & Current Mode technology

[ShadowZA]

I'm looking for any opinions (based on personal experience) out there on audio comparatives on Krell systems between utilising Krell's CAST & Current Mode technologies and not using them (and rather going with balanced connections).

For information purposes, the following information explains these technologies (taken from the Krell Evolution 505 SACD/CD Player Owner's Reference Manual):

CAST Basics

Here is how a CAST audio system works: Internally, each CAST source transfers, or amplifies, current using Krell Current Mode circuitry. This current signal is then output using CAST circuitry. When the signal is received by a CAST input, Krell Current Mode circuitry again takes over until the signal reaches the loudspeaker. By maintaining the musical signal in the current domain from beginning to end, an entire CAST system behaves as if it is one component. With CAST, circuit board properties and signal transmission aberrations between components are eliminated. Cable impedances and their effects on the transmitted signal are non-existent.

How CAST and Krell Current Mode Interact: While CAST is a new method of transferring the musical signal between components, its origin stems from Krell Current Mode, the technology developed to transfer the musical signal within a component. CAST combined with Krell Current Mode takes circuitry signal transmission to the next evolutionary level.

In essence, Krell Current Mode maintains the integrity of the signal within the component and CAST preserves the transmitted signal between components. Together, CAST and Krell Current Mode technologies unify separate Krell components into a single global circuit. Krell Current Mode technology enjoys bandwidth increases up to an order of magnitude greater than their voltage based counterparts.
This dramatic increase in circuit bandwidth delivers near perfection in the audible band that typically suffers from phase distortions in voltage circuits.

[Victor]

ShadowZA,

I have absolutely no experience with Krell’s CAST transmission method nor do I have any experience with Krell’s current mode topology. That is to say that I do not own any of the Krells components that feature those technologies.

I tried however to read the technical explanation of those technologies that you posted. It was very difficult to understand in spite of my familiarity with audio engineering. It seems that Krell does not want you to understand what exactly they do with those CAST things and Current-mode electronics.

Let me tell you what Krell actually does, - in a word it is nothing new, nothing truly revolutionary here and certainly nothing worth paying for in my opinion.

Current-Mode method of signal processing is many years old. Krell implements it in a totally symmetric balanced mode, which is very nice. The symmetric mode implementation is the only remedial feature here.

The best example of current mode amplifier that comes to mind was published by Mark Alexander back in 1991 when he worked for Analog Devices. The complete description of that amp can be found here

http://www.analog.com/UploadedFiles/Application_Notes/492001115525484056221917334AN211.pdf

If you read this note, you will understand all the benefits of current mode processing that Krell does not tell you in their flowery pseudo-engineering description. In fact I build Mark’s amp back in late 1980’s and it did exactly what Krell says the current mode amp should do, - it can deal with input signals in excess of 1 Megahertz. All I can say is WOW! But what are the benefits of such technology when it comes to audio signals with typical bandwidth of less then 20 KHz, - I do not know.

Rest assured that all that talk that bandwidth extended to those heights somehow results in better sound is a complete nonsense from the engineering point of view. Furthermore rest assured that all that talk about amp acting as one component is also nonsense along with the claim of less noise and implied freedom from phase loss or distortion. Those mechanisms are still there, but they are somewhat diminished relative to more mundane designs.

When it comes to power amps, it is the output driver that contributes the lion share of distortion and that driver is there no matter what topology you choose. You will get better THD numbers with current-mode amp but not much better. What you do get here is a relative freedom from THD deterioration as bandwidth goes up. Those are the finer points in engineering but they will not change your audio life. In fact Bryston will deliver the same if not better numbers while utilizing a more conventional circuit topology.

Current mode topology is a neat design and it is certainly not a ‘me too’ approach to audio amplifiers. I would personally prefer it over the conventional voltage-feedback type topologies for the reason that it can offer better THD without too much design effort. The same THD can be had with in a conventional amp, but it is more difficult to achieve. When you look at Mark’s amp you would appreciate that cost of such amp is the same league as the cost of any conventional amp.

The CAST signal transmission is a fancy word for a simple and cheap circuit that connects the current output trans-conductance output stage to another stage that expects the current input. This is great as it is esoteric, but an engineer in me asks, - why do it? I tell you this; - it would surprise me to no end if a sensible reason for such techno-acrobatics is actually found.

In my opinion what we have here is an attempt by Krell to distinguish itself from all other companies by producing a truly different hardware. But in doing so Krell does not accomplish what it advertises, - Krell does not deliver an engineering excellence but it does ask you to pay for it.

It is, to put is mildly, a lot like a spoiler on your 07 Dodge Charger SRT, - looks good but does little.

regards,
Victor

[kurtholz]

Yup

you definently haven't heard Krell before, you might not understand the technical side,or like there presentation of why it is better, but you will be hard pressed to find anyone not putting Krell in the top echelon of audio

this sounds a little gruff, and isn't intended to, but you are bashing a product that is well respected by just about anyone with experience with there products.

Krell owner

:-)

[Victor]

kurtholz,

I heard many Krells and I was always impressed by the ability of Krell amps to drive anything with ease. Krell is one fine product, no doubt about that. I was not trying to bash Krell. I was trying to be as straight as possible. Let me tell you why, - it is because of the price that Krell commands.

Once you think about the money that one needs to pay to get the Krell product, you would agree that it is only fair to put Krell under the magnifying glass of the magnitude that I presented here. Is it fair? Under general circumstances, - no, - but it is fair to Krell and this is why what I wrote sounds a little gruff.

Look, - this current-mode technology has merit, but then say so and do not present this as the next best thing since sliced bread that nobody has. Doing proprietary current-type, or CAST in Krell’s language, transmition and then indicating that such transmission is somehow better then your typical XLR or RCA connection amounts to hot air.

There is nothing here that commands the price tag and in my opinion the reason given by Krell to an unsuspecting audiophile to induce him/her to purchase its product is inadequate on technical grounds.

I think you can’t have it both ways here, - you can say that your product sounds the best and I will never argue with that, but you cannot claim the best sound and use pseudo-engineering language to substantiate your claim of better sound. If you talk electronics then tell me in no uncertain terms why the CAST transmition and current-mode topology is best and show your test data to prove it as Mark Alexander did in the link I posted.

In the absence of that you’ll get gruff attitude…at least from me.

regards,
Victor

[ShadowZA]

This is more of a specialized area & I did not think that there would be any responses. So, I'm grateful for the info & opinions (whatever these may be).

Krell owner 2

[kurtholz]

Hi Victor

I am most certainly not in your league technically, i can only compare my thoughts based on owning many different components, Denon,Rotel,(demo McIntosh,Classe,Sim,and a few other), so my perspective is one from listening and not tech jargon

the best comparison i could make is, doubling the price from Rotel to krell to me was the best money spent, did it double the quality, of course not, but i am lucky to be one who can blow copious amounts for small improvements,

i always liken audio to wine, is a $1000 bottle of Petrus better than a $200 of Opus, is it that much better, i can enjoy both but the Petrus will always feel more special to me

my other hobby being cigars, is a new Cuban cohiba as good as a 20 year old Cuban Davidoff, 10 times the price, again, it's the small differences that bring me the pleasure, and being able to appreciate them

it's all relative, you most certainly have valid points, but you won't talk me or most any Krell owner out of there equipment, we love that extra bit of perfection, which of course can be attained thru many other brands

good luck

Kurt