Solid State Power Amp Reviews

Classé Delta Mono monoblock power amplifier A Class-A Icy Tunnel

Sidebar 1: A Class-A Icy Tunnel

Up to their continuous-current limit, a class-A amplifier's output transistors are fully turned on all the time. As well as the devices thus being in thermal equilibrium and therefore relatively immune from having their transfer function thermally modulated by the signal current, the nonlinearities that result from switching the devices on and off during every cycle of the signal—generally referred to as crossover distortion—are sidestepped. Electronically, this is an elegant solution; practically, it is the opposite, in that two-thirds of the power drawn by the amplifier from the wall is wasted in the form of heat.

Classé has take a different approach to ensure that the output transistors operate in a thermally stable environment. Instead of conventional, massive external heatsinks, the Delta Mono's devices are attached to an aluminum tunnel that runs the entire depth of the chassis. The inside surface of the tunnel is stuffed with multiple aluminum fins of relatively low mass to dissipate heat—and a fan draws in air from a concealed slot in the front panel and exhausts it from a rear-panel vent. The key to what Classé calls the Intelligent Cooling Tunnel, or ICTunnel ("icy tunnel"), is to take advantage of the low thermal mass of the heatsink array inside the tunnel by allowing a microcontroller, fed by pressure and temperature sensors, to actively control the operating temperature. The Delta Mono's fan mechanism is 35mm thicker than that used in earlier amplifiers and can spin at the lowest speed necessary. The output devices therefore continually run at their optimal temperature regardless of the signal's voltage and current conditions.—John Atkinson

COMPANY INFO
Classé, a division of Sound United, LLC
380, rue McArthur Saint-Laurent
Québec H4T 1X8
Canada
classeaudio.com
ARTICLE CONTENTS

COMMENTS
Bogolu Haranath's picture
Submitted by Bogolu Haranath on June 24, 2020 - 11:29am

Are you ready for a brand new beat? ...... Summer's here and the time is right ...... For dancing in the 'seat' (street) :-) ......

supamark's picture
Submitted by supamark on June 24, 2020 - 1:10pm

"Fortunately, Sound United, whose brands include Denon, Marantz, Polk, Definitive Technology, and Boston Acoustics, then acquired Classé."

Sound United has shuttered Boston Acoustics, the brand effectively no longer exists. Per Wiki, "Currently they maintain the brand name, but no engineering is budgeted and there is no future production planned for Boston Acoustics." Y'all should probably stop mentioning Boston Acoustics when talking about Sound United, except to note that they liquidate some of the brands they aquire. Maybe they'll sell the brand name to someone who wants to make (sealed box) speakers... but doubtful.

Ortofan's picture
Submitted by Ortofan on June 25, 2020 - 11:34am

... active cooling solution, then try the Rotel Michi S5 or M8.

https://www.hifinews.com/content/rotel-michi-p5s5-prepower-amplifier-lab-report

https://www.rotel-inzahlungnahme.de/fileadmin/daten_rotel/Rotel_MICHI_Stereo_01_20_-_Der_Weg_der_Vollendung.pdf

John Atkinson's picture
Submitted by John Atkinson on June 25, 2020 - 5:21am
Ortofan wrote:
If want a power amp with an active cooling solution, then try the Rotel Michi S5 or M8.

Stereophile will be reviewing the Rotel Michi S5 in a fall issue.

John Atkinson
Technical Editor, Stereophile

Bogolu Haranath's picture
Submitted by Bogolu Haranath on June 25, 2020 - 8:45am

It would be interesting to see MF review the Rotel Michi M8 (1080W/8 Ohms and 1800W/4 Ohms) with his Wilson Alexx speakers :-) ........

rom661's picture
Submitted by rom661 on September 8, 2020 - 9:05pm

Right. I'm auditioning the Classe stereo amp right now. You're right of course. The fact that the Rotel and the Classe have cooling fans makes them equivalent. Also, please note, a Hyundai and a Ferrari both run on petrol so, of course, they are the same. It's nice that you apparently like Rotel. I sold them for years. Your comment is nonsensical.

Ortofan's picture
Submitted by Ortofan on September 9, 2020 - 1:43am

... chi-chi Mundorf capacitors.

With Rotel, you have to settle for British patented slit-foil, high-efficiency, low-ESR bulk storage capacitors.

Mikk's picture
Submitted by Mikk on June 24, 2020 - 7:00pm

I always enjoy gear reviews, but can't help feeling that using a few other speakers with this amp would provide greater insight into how it performs, overall.
Given the amps price, and the apparent engineering that's gone into it, i imagine Classe would have hoped it got a more thorough workout too?
Sorry to nitpick an otherwise detailed review!
(Edit- apologies if recent events within Stereophile made further tests not do-able).

John Atkinson's picture
Submitted by John Atkinson on June 25, 2020 - 5:19am
Mikk wrote:
I always enjoy gear reviews, but can't help feeling that using a few other speakers with this amp would provide greater insight into how it performs, overall.

That's a valid point, but it wasn't possible during the time I had the Classe amplifiers in my system.

John Atkinson
Technical Editor, Stereophile

Bogolu Haranath's picture
Submitted by Bogolu Haranath on June 25, 2020 - 8:56am

MF or JA2 could do a follow-up review of the Classe amps with the full-range speakers they have :-) ......

georgehifi's picture
Submitted by georgehifi on June 25, 2020 - 3:51am

Classic con yet again, manufacturers understating the 8ohm wattage by 27% to make the 4ohm look as though it doubles. and the 2ohm becomes even more of a joke. When will this industry con stop?
Would have had a chance if top and bottom were both N channel fets.

Cheers George

Jim Austin's picture
Submitted by Jim Austin on June 25, 2020 - 7:42am

I would call this "conservatively rated." You call it a con?

There is a common misunderstanding that doubling into half the impedance is a crucial metric. It only matters if you'll be operating the amp at or near its maximum power. What matters is having enough power to drive the load. For power-hungry 4 ohm speakers, it's much better to have a 380W amplifier that outputs 610W into 4 ohms than to have a 200W amplifier that doubles its output into 4 ohms and so provides 400W. For a low-sensitivity 8 ohm speaker, 380 ohms is better than 300.

If I were a manufacturer, and I knew about this widespread misconception--that doubling is important regardless of the output power--then I'd be tempted to under-specify the 8 ohm impedance, too. In any case, underspecifying the power is not a con.

Jim Austin, Editor
Stereophile

Ortofan's picture
Submitted by Ortofan on June 25, 2020 - 12:09pm

... power measurements, is there any plan to include in the reviews some form of transient peak power (aka dynamic headroom) testing, perhaps using a 200 ms burst signal, as was discussed in the following article?

https://www.stereophile.com/asweseeit/489/index.html

The article also suggests that equipment would be measured prior to sending it out for listening tests, in part to cull under-performing (let alone defective) samples. Was this procedure ever implemented?

michelesurdi's picture
Submitted by michelesurdi on June 25, 2020 - 8:12am

could you tell us exactly how to go about level matching?

Bogolu Haranath's picture
Submitted by Bogolu Haranath on June 25, 2020 - 10:46am

They place both components side by side and place a 'spirit level' on top of them and then level match ..... Just kidding :-) .......

John Atkinson's picture
Submitted by John Atkinson on June 25, 2020 - 12:13pm
michelesurdi wrote:
could you tell us exactly how to go about level matching?

I use the 1kHz, -20dBFS warble tone on Stereophile's Editor's Choice CD and equalize the RMS output voltages at the loudspeaker terminals to within 0.1dB.

John Atkinson
Technical Editor, Stereophile

michelesurdi's picture
Submitted by michelesurdi on June 25, 2020 - 10:54am

hooboy,what a scream

georgehifi's picture
Submitted by georgehifi on June 25, 2020 - 6:51pm

"I would call this "conservatively rated." You call it a con?"

Ok Jim, then why wasn't the 4ohm figure conservatively rated as well by the manufacturer?? It's almost spot on, out by just 2% on what JA measured?? Not 27%!!!! like their 8ohm figure

A blind man can see what the manufacturers are doing, and it just keeps getting done in their specs, "it's a con", and it's about time you guys called them out on it being reviewers, at least JA puts up the measurements, but his silence is a little muted about it.

You guys used to get yourselves and us sooo excited with those big Krell like amps, because when you tested them they did almost double down to 1ohm!!! let alone 2ohms, with words like you can weld off these speaker outputs!!!! And now with speakers like the Alexia ect ect, this spec is even more important.

I'm seeing even more exaggerated examples of "this con" with Class-D, when/if the 2ohm wattage specs are mentioned

Cheers George

Jim Austin's picture
Submitted by Jim Austin on June 26, 2020 - 8:42am

It is possible that some companies understate their 8 ohm power output in order to make it appear that the output doubles into half the load. But if they do so, it is a marketing decision aimed at people who do not understand what matters and what doesn't. As I wrote above, what matters (among much else) is not doubling but the maximum power an amplifier can deliver to a particular load. If a company understates its power output into 8 ohms in order to appear to double into 4 ohms, then, to people who understand, they are making the product look worse, not better. If it is an attempt at a con, then it is a failed attempt. To those with a correct understanding, they would be making themselves look worse, not better.

Jim Austin, Editor
Stereophile

Bogolu Haranath's picture
Submitted by Bogolu Haranath on June 26, 2020 - 10:19am

Some companies like PS Audio specify their power amp output as minimum power outputs ....... For example, minimum power output into 8 Ohms .... Minimum power output into 4 Ohms etc . .....

Hi-Fi News measures dynamic power outputs in addition to continuous power outputs for the amplifiers ...... In many cases, lot of amplifiers put out more power during dynamic output than during continuous output :-) ......

georgehifi's picture
Submitted by georgehifi on June 26, 2020 - 1:10pm

Whatever you say to protect them Jim, doesn't get around the fact that their own specified 8ohm wattage is grossly underrated and in the same breath their own specified 4ohm wattage is correct. And to me it's done just to make it "look like" it can double down.
And the only way it's exposed is in JA's bench tests which 90% of your readers have no idea what their looking at, they just like to read the reviews.

THEY CAN'T HAVE IT BOTH WAYS

Cheers George

Jim Austin's picture
Submitted by Jim Austin on June 26, 2020 - 2:02pm

I'm protecting logic and good sense.

Is power in an amplifier bad or good? Because if power is good, then perpetrating a "con" by "grossly understating" it makes no sense. I'm not expecting you to change your mind, but I do want to make sure that other people reading these comments are not misled.

Jim Austin, Editor
Stereophile

Bogolu Haranath's picture
Submitted by Bogolu Haranath on June 26, 2020 - 2:45pm

George is making much ado about nothing :-) ..........

Lars Bo's picture
Submitted by Lars Bo on June 27, 2020 - 12:45pm

It seems to me, that EPDRs of 1-2 ohms are not at all uncommon for speakers typically matched with big, drive-it-all power amps (or vice versa).

Bogolu Haranath's picture
Submitted by Bogolu Haranath on June 27, 2020 - 12:57pm

Speakers with EPDRs of 1-2 Ohms sound better with amps like the Classe Delta monos :-) .......

georgehifi's picture
Submitted by georgehifi on June 26, 2020 - 8:46pm

"grossly understating" it makes no sense.

Yes understate by 27%!!! on the 8ohm figure. Then by only 2% on the 4ohm figure. (You never see them or others overstate the 8ohm as then will make the 4ohm will look real sad indeed)

I consider that a gross understatement, for a means to baffle/confuse/con/deceive call it what you wish.
It's not right that so many manufactures are doing this now, this is not an isolated indecent, it's only serves one purpose.
I've been calling on this now for a couple of years, it has crept into the manufacturers specs and it's not right.

Cheers George

RoryB's picture
Submitted by RoryB on September 2, 2020 - 7:55am

Whether chicken or egg, it is a marketing decision. That's why they are called "nominal" specifications. You're only making yourself look silly.

You got 27% more than you paid for? This is an OUTRAGE! (27% more is right around 2 dB, based on 20 log 1.27. Not enough extra to smoke a tweeter.)

Edit: So my math was wrong. Because power comes from the square of voltage, the actual formula is 20 log 1.127, which comes out to 1.03 dB. Cha-ching. Here, let me turn that down 1 dB for you.

a.wayne's picture
Submitted by a.wayne on June 29, 2020 - 7:26pm

Great measurements there Classe , fantastic except for the 2 ohm current limiting , these measurements puts this Classe into a similiar league to the big Boulder ...

Regards

Lee S.'s picture
Submitted by Lee S. on July 8, 2020 - 4:18pm

JA, A few years ago, you reviewed the Classe CA-M600 mono amps and gave them high marks. You said they were the best sounding amplifiers you had reviewed at the time. Your review immensely influenced my decision to purchase a pair. Best sounding amps I have ever owned. I know it’s been several years, but could you comment on the sound attributes between the CA-M600 and the new Delta monos to the best of your recollection. Thanks, Lee

georgehifi's picture
Submitted by georgehifi on September 2, 2020 - 12:49pm

Once again, and your silly if you can't see it.

"Yes understate by 27%!!! on the 8ohm figure. Then by only 2% on the 4ohm figure to make it look better."

Cheers George

Mike-48's picture
Submitted by Mike-48 on September 18, 2020 - 5:36pm

JA, I auditioned a previous Classe amp (CA-2300), and while I thought the sound was wonderful, I could occasionally hear the fan running during quiet passages. Are the fans in these monoblocks quieter?

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