• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). There are daily 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: 373 94.9%
  • 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
    393

pseudoid

Major Contributor
Forum Donor
Joined
Mar 23, 2021
Messages
2,787
Likes
1,666
Location
33.6, -117.9
Well, I was thinking maybe things were better in Carverland -- but, maybe, not so much.
I will confess to Schadenfreude. Sorry, Carver fans.
I am assuming that the Carverland (you refer to) was originally USA.
Do you possibly think that those habitants really know the difference between Schadenfreude and :eek:shut the front door:eek:???
 

mhardy6647

Master Contributor
Joined
Dec 12, 2019
Messages
7,202
Likes
14,973
I am assuming that the Carverland (you refer to) was originally USA.
Do you possibly think that those habitants really know the difference between Schadenfreude and :eek:shut the front door:eek:???
Oh, I dunno... but I am honest enough to admit to deriving somewhat perverse enjoyment from watching certain train wrecks occur. ;)
 

fpitas

Major Contributor
Forum Donor
Joined
Jul 7, 2022
Messages
3,025
Likes
3,604
Location
Northern Virginia, USA
Well, I was thinking maybe things were better in Carverland -- but, maybe, not so much.
I will confess to Schadenfreude. Sorry, Carver fans.
I expected better, too. I almost hope they goofed it up on purpose to get a warm, fuzzy sound. Better that than incompetence.
 

solderdude

Grand Contributor
Joined
Jul 21, 2018
Messages
13,033
Likes
29,358
Location
The Neitherlands
Looks like they have the specs for the 350 and 25 duplicated/mixed up...

350 (mono amp)
Dimensions (H x W x D) 7.2” (183mm) X 12” (305mm) x 14” (355,6mm) x 2
Weight: 44lbs (19.95 kg) per chassis x 2
https://www.bobcarvercorp.com/crimson-raven-features-specs

25 (stereo amp)
Dimensions (H x W x D) 7.2” (183mm) X 12” (305mm) x 14” (355,6mm) x 2
Weight: 44 lbs (19.95 kg) per chassis x 2
https://www.bobcarvercorp.com/black-magic-features-specs

Why 2 for the 25?

Ohms

specs for the BM25:

SPECS (my emphasis)

Gain: 29 dB
Power: More than 24 Watts Per Channel, both channels driven at eight ohms with no more than 1% Total Harmonic Distortion. Distortion decreases at lower levels
4Ω Power 25 watts
8Ω Power 25 watts
16Ω Power 25 watts
Noise: Better than 100 dB below 25 watts, A-weighted
Frequency Response: +0, –2 dB from 20 Hz to 20 kHz
Distortion Less than 1%
Source Impedance 1.7 ohms
Input Impedance 100 kΩ
Vacuum Tubes: EL-34 (optional 6550, KT88, KT120) 12AX7, 12AT7
AC Power:
120 Volts, 60 Hz (US)
240 Volts, 50 Hz (EU
Weight 19 lbs / 8.61 kg
Color: Satin Textured Black, Chrome, Natural Aluminum
Country of Origin: USA
 

fpitas

Major Contributor
Forum Donor
Joined
Jul 7, 2022
Messages
3,025
Likes
3,604
Location
Northern Virginia, USA
specs for the BM25:

SPECS (my emphasis)

Gain: 29 dB
Power: More than 24 Watts Per Channel, both channels driven at eight ohms with no more than 1% Total Harmonic Distortion. Distortion decreases at lower levels
4Ω Power 25 watts
8Ω Power 25 watts
16Ω Power 25 watts
Noise: Better than 100 dB below 25 watts, A-weighted
Frequency Response: +0, –2 dB from 20 Hz to 20 kHz
Distortion Less than 1%
Source Impedance 1.7 ohms
Input Impedance 100 kΩ
Vacuum Tubes: EL-34 (optional 6550, KT88, KT120) 12AX7, 12AT7
AC Power:
120 Volts, 60 Hz (US)
240 Volts, 50 Hz (EU
Weight 19 lbs / 8.61 kg
Color: Satin Textured Black, Chrome, Natural Aluminum
Country of Origin: USA
I wonder, is that 1.7 ohms Source Impedance the output impedance to the speaker?
 

fpitas

Major Contributor
Forum Donor
Joined
Jul 7, 2022
Messages
3,025
Likes
3,604
Location
Northern Virginia, USA

mhardy6647

Master Contributor
Joined
Dec 12, 2019
Messages
7,202
Likes
14,973
I wonder, is that 1.7 ohms Source Impedance the output impedance to the speaker?
I assume that's the amp's output impedance. If so, then, heck, that's lower (EDIT) higher than that of my zero NFB single-ended 2A3 amp (with output impedance of a hair less than an ohm)! :eek:
That would actually be a pretty remarkable engineering achievement* on the part of Dr. Carver! ;)

__________________
* engineering achievement, of course, being a vector quantity. I.e., the Gothic Cathedral at Beauvais (which collapsed several times during construction and ended up being more or less an outrageously glorified chapel, see Hartt's History of Art, vol. 1) and the "Galloping Gertie" bridge over the Tacoma Narrows were remarkable engineering achievements (just not in a good way). ;)

1280px-Beauvais_Cathedral_Exterior_1%2C_Picardy%2C_France_-_Diliff.jpg

Collapse-Tacoma-Narrows-Bridge-Washington-state-1940.jpg
 

fpitas

Major Contributor
Forum Donor
Joined
Jul 7, 2022
Messages
3,025
Likes
3,604
Location
Northern Virginia, USA
I assume that's the amp's output impedance. If so, then, heck, that's lower (EDIT) higher than that of my zero NFB single-ended 2A3 amp (with output impedance of a hair less than an ohm)! :eek:
That would actually be a pretty remarkable engineering achievement* on the part of Dr. Carver! ;)

__________________
* engineering achievement, of course, being a vector quantity. I.e., the Gothic Cathedral at Beauvais (which collapsed several times during construction and ended up being more or less an outrageously glorified chapel, see Hartt's History of Art, vol. 1) and the "Galloping Gertie" bridge over the Tacoma Narrows were remarkable engineering achievements (just not in a good way). ;)

1280px-Beauvais_Cathedral_Exterior_1%2C_Picardy%2C_France_-_Diliff.jpg

Collapse-Tacoma-Narrows-Bridge-Washington-state-1940.jpg
Your 2A3 anode resistance is probably pretty small compared to an EL34. Maybe if you opt for say, the KT88 output tubes the impedance is a bit lower. Maybe...
 

fpitas

Major Contributor
Forum Donor
Joined
Jul 7, 2022
Messages
3,025
Likes
3,604
Location
Northern Virginia, USA
Yeah, but I don't want no steenkin' tetrodes, kinkless or otherwise. (Power) triodes FTW!

;)
If I just had to use tubes, push-pull triodes would be it. Luckily though they made those scratchy old silicon carbide JFETs.
 

pseudoid

Major Contributor
Forum Donor
Joined
Mar 23, 2021
Messages
2,787
Likes
1,666
Location
33.6, -117.9
...zero NFB...
You mean like NO 'local' or 'global' feedback at all?
Are there many such beasts that do not rely on NFB?
They are probably all tube amps...
I always thought that (such stability w/o FB) was an audio fantasy.
 

fpitas

Major Contributor
Forum Donor
Joined
Jul 7, 2022
Messages
3,025
Likes
3,604
Location
Northern Virginia, USA

atmasphere

Active Member
Manufacturer
Joined
May 26, 2021
Messages
284
Likes
408
You mean like NO 'local' or 'global' feedback at all?
Are there many such beasts that do not rely on NFB?
They are probably all tube amps...
I always thought that (such stability w/o FB) was an audio fantasy.
FWIW negative feedback is a destabilizing design feature. If you want to see a stable circuit condition, apply positive feedback.
Amps without feedback can be quite stable; very resistant to oscillation, since negative feedback and phase margin issues don't play well together.
Class D amps can be built with zero feedback as well.
 

solderdude

Grand Contributor
Joined
Jul 21, 2018
Messages
13,033
Likes
29,358
Location
The Neitherlands
It is actually worse than 1.7ohm as it is load dependent due to the current feedback.... ahem... 'the back EMF and room sensing feedback circuit'.
 
Last edited:

tonycollinet

Major Contributor
Joined
Sep 4, 2021
Messages
3,609
Likes
5,592
Location
UK/Cheshire
FWIW negative feedback is a destabilizing design feature. If you want to see a stable circuit condition, apply positive feedback.
Amps without feedback can be quite stable; very resistant to oscillation, since negative feedback and phase margin issues don't play well together.
Class D amps can be built with zero feedback as well.
:facepalm:

You know what a nuclear detonation is? Positive feedback. As is any explosion - explosives not often described as being stable.

Anything you apply positive feedback to goes to limits.


My room is getting hot - feed back that positively to the heating systme so that it puts out more heat. That is postive feedback.

Ever heard of thermal runaway - that is positive feedback also.
 
Last edited:

SIY

Master Contributor
Technical Expert
Joined
Apr 6, 2018
Messages
8,989
Likes
20,643
Location
Alfred, NY
FWIW negative feedback is a destabilizing design feature. If you want to see a stable circuit condition, apply positive feedback.
Amps without feedback can be quite stable; very resistant to oscillation, since negative feedback and phase margin issues don't play well together.
Class D amps can be built with zero feedback as well.
For any competent designer, stability is absolutely no issue- stability criteria have been well-understood for nearly a century. To quote Klaatu, "I find it works well enough to get me from one planet to another."
 

Gringoaudio1

Active Member
Forum Donor
Joined
Sep 11, 2019
Messages
263
Likes
310
Location
Calgary Alberta Canada
FWIW negative feedback is a destabilizing design feature. If you want to see a stable circuit condition, apply positive feedback.
Amps without feedback can be quite stable; very resistant to oscillation, since negative feedback and phase margin issues don't play well together.
Class D amps can be built with zero feedback as well.
You’ve got it backwards mate.
Turn in your EE degree.
 

atmasphere

Active Member
Manufacturer
Joined
May 26, 2021
Messages
284
Likes
408
:facepalm:

You know what a nuclear detonation is? Positive feedback. As is any explosion - explosives not often described as being stable.

Anything you apply positive feedback to goes to limits.


My room is getting hot - feed back that positively to the heating systme so that it puts out more heat. That is postive feedback.

Ever heard of thermal runaway - that is positive feedback also.
The statement was meant as humor; I was using the Chaos Theory definition of the term ;)

So, or 'but', depending on how you look at it:

A stable state is one that does not change. An amplifier in oscillation is in a stable state insofar as its output is concerned. FWIW positive feedback is the basis of self oscillating class D amps (like the Purifi) although at audio frequencies that feedback is negative. This BTW is why self-oscillating class D amps cannot be induced to oscillate when subjected to a strange load like one that is heavily capacitive. Its already oscillating... and therefor stable...

Of course there's more to it; apparently you missed this comment, perhaps when you did your facepalm:

Amps without feedback can be quite stable; very resistant to oscillation, since negative feedback and phase margin issues don't play well together.
(Emphasis added)

The reason negative feedback is destabilizing is due to phase shift. Phase shift is responsible for a design aspect all amplifier designers of amps with feedback must face, which is called 'phase margin'. If you exceed the phase margin of said amplifier, oscillation occurs. So it would appear that the amp is stable if that isn't done... except when the load on the amplifier's outputs messes with the feedback loop, which is a critical design in any amplifier with feedback (a simple resistor is rarely good enough...). Far too many amplifiers have been produced that can oscillate and fail when subjected to a slightly odd load, for example a Quad ESL57.
 

tonycollinet

Major Contributor
Joined
Sep 4, 2021
Messages
3,609
Likes
5,592
Location
UK/Cheshire
The statement was meant as humor; I was using the Chaos Theory definition of the term ;)

So, or 'but', depending on how you look at it:

A stable state is one that does not change. An amplifier in oscillation is in a stable state insofar as its output is concerned. FWIW positive feedback is the basis of self oscillating class D amps (like the Purifi) although at audio frequencies that feedback is negative. This BTW is why self-oscillating class D amps cannot be induced to oscillate when subjected to a strange load like one that is heavily capacitive. Its already oscillating... and therefor stable...

Of course there's more to it; apparently you missed this comment, perhaps when you did your facepalm:


(Emphasis added)

The reason negative feedback is destabilizing is due to phase shift. Phase shift is responsible for a design aspect all amplifier designers of amps with feedback must face, which is called 'phase margin'. If you exceed the phase margin of said amplifier, oscillation occurs. So it would appear that the amp is stable if that isn't done... except when the load on the amplifier's outputs messes with the feedback loop, which is a critical design in any amplifier with feedback (a simple resistor is rarely good enough...). Far too many amplifiers have been produced that can oscillate and fail when subjected to a slightly odd load, for example a Quad ESL57.
You know what phase shift does to negative feedback?


Turns it into positive feedback.
 
Top Bottom