• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Carver Crimson 275 Review (Tube Amp)

Rate this amplifier

  • 1. Poor (headless panther)

    Votes: 379 95.0%
  • 2. Not terrible (postman panther)

    Votes: 5 1.3%
  • 3. Fine (happy panther)

    Votes: 6 1.5%
  • 4. Great (golfing panther)

    Votes: 9 2.3%

  • Total voters
    399

Xulonn

Major Contributor
Forum Donor
Joined
Jun 27, 2018
Messages
1,828
Likes
6,311
Location
Boquete, Chiriqui, Panama
Rumored quote from Frank Malitz:

"Damn, I knew we should have potted those transformers!"

==========================================
For those who don't now what "potting" is:

Potted Transformer.jpg

Potting.jpg
 

whazzup

Addicted to Fun and Learning
Joined
Feb 19, 2020
Messages
575
Likes
486

atmasphere

Addicted to Fun and Learning
Technical Expert
Audio Company
Joined
May 26, 2021
Messages
501
Likes
779
I've read Bruno's article.
Stereophile will often use a 50 hz test for seeing how the low end of tube amps hold up . They do 1 khz also and 1 khz for any amp I've seen them review. Not once do I remember a 100 hz tone test. Maybe there have been some, if so you could point one out. It darn sure isn't common or the norm for them.
I stand corrected and thank-you for that!

However we still see the problem of rising distortion with frequency and the other issues of concern (insufficient feedback causing bifurcation of the signal, resulting in higher ordered harmonics) is still an issue. For example its well-known since the 1930s at least (see Radiotron Designer's Handbook, 3rd edition) that the ear is very sensitive to the 7th harmonic, which in the case of 1KHz is 7KHz, right in the area of the loudness curve.
 

paulbottlehead

Active Member
Audio Company
Joined
Dec 22, 2021
Messages
209
Likes
843

atmasphere

Addicted to Fun and Learning
Technical Expert
Audio Company
Joined
May 26, 2021
Messages
501
Likes
779
The more a forum censors content they don't like, the more that will drive their users to other places.
I don't think the moderators care about it one way or the other- as far as I know they are not audiophiles. It may have been deleted by accident too- although given the tone of things that seems unlikely to be coincidence.
 

SIY

Grand Contributor
Technical Expert
Joined
Apr 6, 2018
Messages
10,383
Likes
24,749
Location
Alfred, NY
The main reason audiophiles support tube amplifiers and tube production is the brightness they perceive in solid state amps. This should not in any way be controversial.
Then why did Gordon Holt continually describe "tube sound" as "bright and forward"?

Most of that is anecdotal on my part- the problem here is that certain amps get a reputation for being bright- and you have to ask yourself why that is when the amp tests perfectly flat on the bench and has a damping factor of over 100. Its clearly not coming from a frequency response error!

Its origin is the same as most other nonsense in the audio world- evaluation without even a shred of basic controls.

With modern software, it's easy to test things like your hypothesis about 7th harmonic (funny, Curl always rants about 9th harmonic!). Putting aside that I can't find an example of a solid state amp where 7th or 9th is significant or even within 20dB of 2nd or 3rd, you could take this past anecdote and show that you can distinguish music unaltered vs added (say) 0.01% 7th. Are you willing to try that?

Also, since I don't have one to put on the bench, could you show the distortion spectra of an Atma-Sphere amp at bass, midband, and treble, perhaps at 1W and near the power limit?
 

jjptkd

Member
Joined
Jan 13, 2022
Messages
14
Likes
15
Also, since I don't have one to put on the bench, could you show the distortion spectra of an Atma-Sphere amp at bass, midband, and treble, perhaps at 1W and near the power limit?
Damn gloves are off! Seriously it would be interesting to see how they compare to the 275
 

SIY

Grand Contributor
Technical Expert
Joined
Apr 6, 2018
Messages
10,383
Likes
24,749
Location
Alfred, NY
Damn gloves are off! Seriously it would be interesting to see how they compare to the 275
My guess: much better bandwidth, meets power specs, much higher output impedance, distortion not great but good enough. Just a guess.

I've been tempted to build one using Ralph's basic circuit (I have a pile of 6528s that would do very well), but unfortunately don't have suitable speakers. But if I were to go OTL, that would be the way I'd go. The 275 is just a dull cut-and-paste of 1957-era designs with added cost-cutting so zero interest in duplicating it.
 

Blumlein 88

Grand Contributor
Forum Donor
Joined
Feb 23, 2016
Messages
20,521
Likes
37,050
I wish there were kits to build a David Berning type amp. Basically a switching amp using tubes and small transformers.

Or maybe you could make one at 2.4 ghz using microwave oven parts for cheap. ;)
 
Last edited:

atmasphere

Addicted to Fun and Learning
Technical Expert
Audio Company
Joined
May 26, 2021
Messages
501
Likes
779
Then why did Gordon Holt continually describe "tube sound" as "bright and forward"?



Its origin is the same as most other nonsense in the audio world- evaluation without even a shred of basic controls.

With modern software, it's easy to test things like your hypothesis about 7th harmonic (funny, Curl always rants about 9th harmonic!). Putting aside that I can't find an example of a solid state amp where 7th or 9th is significant or even within 20dB of 2nd or 3rd, you could take this past anecdote and show that you can distinguish music unaltered vs added (say) 0.01% 7th. Are you willing to try that?

Also, since I don't have one to put on the bench, could you show the distortion spectra of an Atma-Sphere amp at bass, midband, and treble, perhaps at 1W and near the power limit?
Regarding Gordon, I've no idea! He never said anything like that to me- he did comment to me that he liked the presentation of our amps (that was back in the early 90s when our amps had about 3x more distortion...). FWIW I learned that bit about the 7th harmonic being in the Radiotron Designer's Handbook from one of Curl's talks posted online. I had a copy of the book and looked it up- and sure enough it was there. However the 9th is certainly rant-worthy (I can rant about that one if you like ;)); for that matter any of the higher harmonics are simply not helpful! And yes, with modern software you can see this stuff pretty easily. I had an SET guy challenge me about some of my rhetoric regarding the harmonics of SETs and he showed me an ancient text from Olson. It was an old chart looking like it was from the 60s or some such and I had to break it to him that there was a lot more going on than that chart was showing!

I doubt I'd be able to hear much with just one harmonic- but I'm talking about a whole mess of them- the 5th all the way up to at least the 17th or so.

The last time we did a measurement it did not include spectra but its the same at all frequencies on the OTLs (they have power bandwidth well past 100KHz; only -3dB at 200KHz). The primary distortion product (if the test equipment isn't grounding one of the output terminals, which is a common measurement error) tends to be the 3rd harmonic. The 2nd is suppressed by the fact that the amps are fully differential from input to output. The distortion falls off a bit faster than in an SET on this account, since less distortion is compounded from stage to stage (owing to even orders being cancelled) and there's only one stage of gain. If you ground one of the speaker terminals the drive to the power tubes is essentially unbalanced at that point and the 2nd harmonic shows up- at that point the distortion spectra looks like a typical SET (and the amp won't make the specified power either).

We spec the amps at 120V at the IEC but to really do that right you have to pull the cover off and actually measure the voltage at the IEC at full power; the amps have considerable draw and there is often a voltage drop across the variac and AC cord. So you have to run the amp up to clipping, boost the AC power, run it up to clipping again and keep doing that until its actually 120V while the amp is at full power. That nuance has shot down some of the measurements made in the past.

Honestly I'm really happy to have our class D project finally bearing fruit. There can be so many variables with tube condition, tube matching, line voltage, speaker impedance and the like, all of which can be a real headache. With the class D amp you just turn it on and it works. And you don't have to worry about most of my rant material.
 

atmasphere

Addicted to Fun and Learning
Technical Expert
Audio Company
Joined
May 26, 2021
Messages
501
Likes
779
My guess: much better bandwidth, meets power specs, much higher output impedance, distortion not great but good enough. Just a guess.

I've been tempted to build one using Ralph's basic circuit (I have a pile of 6528s that would do very well), but unfortunately don't have suitable speakers. But if I were to go OTL, that would be the way I'd go. The 275 is just a dull cut-and-paste of 1957-era designs with added cost-cutting so zero interest in duplicating it.
Pretty well correct (full power to 2Hz is no worries so squarewave tilt at 20Hz is unmeasurable). I feel like if we're hitting 1% we're doing fine- they can do 0.5% THD if things are set up right, but that's pretty rare. Either way not bad for a tube amp with zero feedback...

You have to be careful with the 6528s if you try that. They have a way of shorting internally (thus knocking out the bias voltage) and the resulting DC at the speaker terminals can fry a woofer in a heartbeat. We use the B+ transformer fuse in our amps as the speaker protection fuse (which is more likely to be needed if Chinese tubes are in the amp) and it works fine for that (or we'd not have made it over 45 years...). But with the 6528 I recommend an actual fuse or crowbar to protect the speaker.

BTW Tammy at audiogon thinks the thread deletion was a mistake, so its been restored.
 

SIY

Grand Contributor
Technical Expert
Joined
Apr 6, 2018
Messages
10,383
Likes
24,749
Location
Alfred, NY
I doubt I'd be able to hear much with just one harmonic- but I'm talking about a whole mess of them- the 5th all the way up to at least the 17th or so.
You can do that as well.

Looking at the last big AB amp I had here (a Parasound), the high harmonics you mention are all well below -105dB below fundamental at 100W+. I'm skeptical that this could be anywhere close to audible. The Class D amps here are significantly cleaner.

1643229564809.png


Appreciate the warning. I helped build a monster 64 tube OTL using 6528s back in the late '70s. The heat output was fierce, so we gave up that idea quickly! These are left over from that project. I've used them in several other designs since- the high gm means that idle current stabilization is extremely critical.

I'm always open to doing a review of any of your amps for AudioXpress, just sayin'.:D
 

solderdude

Grand Contributor
Joined
Jul 21, 2018
Messages
15,891
Likes
35,912
Location
The Neitherlands

egellings

Major Contributor
Joined
Feb 6, 2020
Messages
4,004
Likes
3,244
The big power amps are mono, and they are a circlotron design with the circlotron's big problem solved. Two pair of paralleled KT88 type tubes are connected in a bridge arrangement with two floating plate and two floating screen grid supplies. The small separate screen supplies solved the circlotron's problem of burning off the screen grid on a tube nearing saturation on loud passages. Audio distortion caused by the screen voltage varying with the plate voltage of the opposite side is removed. So basically, all 4 output tubes, operating in true pentode mode, are effectively paralleled across the transformer primary, AC-wise. That allows a low turns ratio on the OPT, which reduces leakage inductance, and in general, makes for a better OPT design. It works like a charm.
 

solderdude

Grand Contributor
Joined
Jul 21, 2018
Messages
15,891
Likes
35,912
Location
The Neitherlands
Maybe they got complaints or wanted to moderate stuff.. dunno.
The interwebs is a strange and magical place.
 

egellings

Major Contributor
Joined
Feb 6, 2020
Messages
4,004
Likes
3,244
OTLs can be scary if they fail, since large dangerous voltage can appear at the speaker terminals during a fault. I like the safety afforded by an OPT's isolation between the windings.
 

levimax

Major Contributor
Joined
Dec 28, 2018
Messages
2,348
Likes
3,462
Location
San Diego
OTLs can be scary if they fail, since large dangerous voltage can appear at the speaker terminals during a fault. I like the safety afforded by an OPT's isolation between the windings.
Yea but when your friends and neighbors come over an OTL blazing away makes more of an impression than any other amp .... being dangerous just adds to the effect.
 

JohnVF

Member
Joined
Dec 30, 2021
Messages
93
Likes
99
Yea but when your friends and neighbors come over an OTL blazing away makes more of an impression than any other amp .... being dangerous just adds to the effect.
I remember listening to a pair of Atma-Sphere MA-1s and while they sounded great, physically they were the most impressive amps I've ever seen. And, also, I was terrified of the idea of owning them. All those tubes, all that heat. But truly a visually imposing and impressive statement.
 

PatentLawyer

Senior Member
Forum Donor
Joined
Apr 13, 2021
Messages
398
Likes
690
Location
Deep in the Soundstage
Top Bottom