Carver Crimson 275 Review (Tube Amp)

[DamianW]

This was addressed in the first thread. Yes, both Amir and I have done the measurements with the negative speaker terminal floating.

Thank you.

 

[paulbottlehead]

If a high voltage wire were to touch the inside of the chassis the B+ fuse will blow.

If the mains hot touches the chassis, what happens?

 

[solderdude]

Yes, it is safe. Note most audio product use ungrounded cords. We have done this for several decades and over untold thousands of products with nary an issue.

In that case one should use a 2 prong socket and indicate on the back that it is double insulated.
Are these devices (or at least a representative production unit) tested for safety in an independent lab ?

Like this one:

When using 3 prong IEC inlets it is the logical thing to tie the safety ground pin to the chassis.

 

[LTig]

In that case one should use a 2 prong socket and indicate on the back that it is double insulated.

Wouldn't that be a lie?

 

[solderdude]

Not necessarily when there is no way that mains can make contact with the chassis, so shrink tubing, mains wires fixed so they cannot move when they break etc. and enough clearance is present from the chassis.

 

[SIY]

Not necessarily when there is no way that mains can make contact with the chassis, so shrink tubing, mains wires fixed so they cannot move when they break etc. and enough clearance is present from the chassis.

Also transformers insulated from the chassis and unable to be touched.

So the 15W transformers are deliberate, and we can conclude that the advertised performance is a lie. That's really pitiful.

 

[Descartes]

This is a review and detailed measurements of the Carver Crimson 275 tube stereo power amplifier. It was purchased new by member @paulbottlehead and given to me for testing. It costs US $2750.
View attachment 179227
I really like the way the amplifier looks. The burgundy color is attractive as is the handle. On the latter, the unit is very light though so the handle while handy, is not necessary to lift the thing. Back panel shows high quality connectors:
View attachment 179230

The tubes, four Tun-sol KT120, pair of 12AT7W and 12AX7 can in their original boxes for the owner installation. Went to open one of the small tube boxes but found nothing in it! Worried, I looked around and it had come out of its box and was just floating in the larger box that they all came in.

Prior to installation of tubes I had something to investigate: there was clearly something loose in there, rattling around. So I took the back panel off to find a metal screw rolling around in there:

View attachment 179235

Not sure where it was supposed to go. There is a hole for something above the second fuse from the bottom but I think that would for a nut.

I did not like lack of safety (earth) ground from the IEC terminal:
View attachment 179238

Instead, there is some kind of local, star grounding referenced to neutral using a resistor. That naturally won't work for safety purposes. With that power supply board mounted vertically with voltages as high as 300+ volts, I sure as heck would want this metal case grounded. I don't care what audio/electrical problem they were trying to solve there. I want a safe product first and foremost. Naturally there is no safety/regulatory certification which I expect a company with the name "Carver" to be able to afford.

I got a kick out of the beefy speaker terminals but ultra-thin wires leading to it! Yes, the lengths are short and at this wattage is probably fine but from "optics" point of view, you would want to use something better than hair thin wiring (see gray and red wires).

I was sad to see the VU meter glued to the case:

View attachment 179239

I realize welding a couple of threaded stand-offs to the case costs money but at this price, I expect such. The meter is not backlit which was another disappointment. But was useful for checking bias which was right at the spec at 100 milliamps.

So nice looks but under the skin, a number of concerns.

Carver Crimson 275 Measurements
I usually let amplifiers warm up some and watch their behavior and also let things stabilize before measurements. Manual states that bias can be checked after 20 minutes so I let it run for that long and a bit more:
View attachment 179241

Note that the vertical scale is only 3 dB so don't be alarmed by the variations. Generally speaking, unit is table after a couple of minutes of warm up. But it is fascinating to see performance gradually get worse as it kept warming up (again, at micro level).

So next comes our usual dashboard. My Audio Precision analyzer by default has floating (non-earth connected) RCA terminals. But I had to override that by grounding it as I observed oscillations (frequent occurrence with some amplifiers). No other attempt at grounding made a difference in power supply/mains hum:


View attachment 179242

The power supply noise really dirties up the FFT spectrum but looking past that, we see that the low SINAD (sum of noise and distortion) is dominated by distortion. Unlike the common reputation for tubes, distortion is third harmonic for the most part, not second. Naturally the high level of distortion places the 275 very low in our scale, second only to one other amp ever tested:

View attachment 179243

Company spec is quite good for noise level relative to full power. I could not get that without a-weighting:

View attachment 179244

But applying the a-weighting filter and with it, getting rid of power supply noise, we do essentially get there:

View attachment 179245

Crosstalk was poor:
View attachment 179246

Frequency response has an odd shape and good bit of loss at high frequencies with 4 ohm load:
View attachment 179248

Output impedance is high enough that is combining with the load to change the high frequency roll off. Things get better as such with an 8 ohm load:

View attachment 179247

There is an RC filter on the speaker terminals. Wonder if that is what is providing the roll off.

Using 32 tones to simulate "music" we see a high level of "grass" which would obscure any low level detail:

View attachment 179249

Notice how the worse performance is in low frequencies.

There has been controversy regarding ability of the 275 to produce its rated power of 75 watts so let's start with 4 ohm load as I usually do:
View attachment 179250

The amplifier produced 29 watts after which it blew its 3 amp mains fuse. Fortunately two spares were provided, allowing me to continue testing. Company specs distortion at "less than 1%" so let's see power at that rating:
View attachment 179251

Very dramatic difference between 1 or 2 second power (used for left side) vs short bursts. There is clearly a capacity problem to produce sustained power. Note that this is at 1 kHz as is industry convention. Note that allowing just 1% THD reduces the power even more than what I allowed in my power sweep.

I was surprised to not see selectable output impedance for 8 ohm load so proceed with the test as is:

View attachment 179252

We blew the second fuse but now power is much more healthy at 60 watts.

Hoping to not blow the last fuse, I kept the max power level lower as I changed frequencies:

View attachment 179254

Performance was "reasonable" (for at tube) but once we got down to 20 Hz, it became super erratic and blew the third fuse. It produced only 14 wats which is well short of 30 watts it produced at higher frequencies. I would have wanted to test at more frequencies but it was past midnight and I did not feel like hunting around to find my own replacement fuses.

Conclusions
As a Carver owner of 40 years (solid state), I have a soft spot for the designer. Alas, while I like some things about this amp like the nice looking paint, I am very disappointed in the QC and construction of the unit with respect to safety. Loose screws and glued meters should not be part of a nears $3,000 amplifier. Measured performance is awful of course and one would expect that for many audiophile tube amps. But having third harmonic be dominant blows away the story of why that is audibly a good thing. Clearly the specifications of the amplifier is incorrect for 4 ohm load (company even allows usage for 2 ohm loads!). And low frequency behavior is very poor.

Unless you are going to buy the Carver Crimson 275 to just look at it, I can't recommend it for many reasons stated above. I expect more from the man, the legend....

P.S. It was nice to take a break from drying up our flooded home and get back to some "normalcy" with testing this amp. It cheered me up to be "working" again and doing what I enjoy.

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Thank you for an other great review! Did you ever review PrimaLuna ProLogue Premium integrated amplifier or any other from that brand?

 

[restorer-john]

In that case one should use a 2 prong socket and indicate on the back that it is double insulated.
Are these devices (or at least a representative production unit) tested for safety in an independent lab ?

Like this one:

When using 3 prong IEC inlets it is the logical thing to tie the safety ground pin to the chassis.

That's those Carver monoblock models with the mysteriously shorted (jumpered) 4R and 8R speaker terminals for 'tappings' I pointed out way back in this thread...

Love to see the explanation for that.

 

[amirm]

Thank you for an other great review! Did you ever review PrimaLuna ProLogue Premium integrated amplifier or any other from that brand?

No. But my company did have an evaluation unit and I found them to subjectively sound distorted (this is 10 to 12 years ago).

 

[restorer-john]

In that case one should use a 2 prong socket and indicate on the back that it is double insulated.

Do you remember this? :

March Audio or Audiophonics?

Right that's why I was curious because I thought you are only supposed to solder those on the back of the PCB. This is based off my extensive soldering training which consists of several You Tube Videos and a practice kit. Yes you only solder from one side but you would expect the solder to...

www.audiosciencereview.com

 

[traderitch]

If the mains hot touches the chassis, what happens?

I would love to know, based how the amp was designed , what you believe happens.

 

[paulbottlehead]

I would love to know, based how the amp was designed , what you believe happens.

The loose screw on the amp I bought moves over and wedges itself between the chassis and the power switch.

*or*

A wire pops off the switch and touches the chassis plate.

 

[dougi]

No. But my company did have an evaluation unit and I found them to subjectively sound distorted (this is 10 to 12 years a

No. But my company did have an evaluation unit and I found them to subjectively sound distorted (this is 10 to 12 years ago).

Stereophile did in 2012. High output impedance, fairly low power (~35W with matched taps), pretty noisy.

 

[traderitch]

The loose screw on the amp I bought moves over and wedges itself between the chassis and the power switch.

*or*

A wire pops off the switch and touches the chassis plate.

Fantastic.

You have now put forth two scenarios.

I would appreciate knowing what the measured voltage would be - present on
on the chassis in those scenarios.

 

[warnerwh]

Didn’t the “doctor” admit that David Hafler had more of a hand in their design?

I thought I read an interview with Carver stating that Hafler had a hand in the design. It seems he said David did most of the design. After this many years I won't say anything for sure though.

 

[paulbottlehead]

Fantastic.

You have now put forth two scenarios.

I would appreciate knowing what the measured voltage would be - present on
on the chassis in those scenarios.

120V AC.

 

[traderitch]

120V AC.

You are absolutely certain that their is nothing in the circuit design that would prevent this from happening?

 

[paulbottlehead]

You are absolutely certain that their is nothing in the circuit design that would prevent this from happening?

Well, if you have your interconnects hooked up and they are earthed at the preamp end, then whatever current is required to blow the circuit breaker in your home's panel will flow through your interconnects and preamp to make that happen. Being that this is external to the amplifier itself, the answer would be no.

 

[BrianD]

Also transformers insulated from the chassis and unable to be touched.

And probably certain construction details in the mains transformer itself to ensure adequate separation of the primary and secondary windings for certified double insulation.

 

[amirm]

You are absolutely certain that their is nothing in the circuit design that would prevent this from happening?

If that screw wedges itself between the mains hot lead and chassis there is no circuit in the amp that can do anything. Not that there is anything in there to mitigate such a problem.