Carver PT-2400 Dual Mono Vintage Amplifier Review

[Bruce Morgen]

I never worked on a PT-2400 but the early M400's certainly were a PIA to service. Carver modified the later versions so you could actually access the under side of the driver PCB's.

The entire M400 lineage is intrinsically problematic due to electrolytic capacitors with inadequate WVDC ratings. Even the notoriously underspecified 50WVDC caps across the 48VDC rails of the early Aiyima A07s were a more conservative component choice than what Carver used in those amps given the context of the actual in-circuit voltages involved.

 

[Imakeller]

the question i have is that is there a stereo class D power amp for sale that has 750w x 2 and is less than 50lb and less than $2,4k?

tbf 750w is insane... like realistically for people here what are you doing with 750w that cant be done with 250w given every has reasonably efficient spks

You could get two Purifi 1ET9040BA monoblocks from Buckeye:

Buckeye Amps

Buckeye Amps utilizes the most advanced audio amplifier technologies available. Authorized seller for Hypex and Purifi Class D amplifiers. Based in the US. Free shipping and worldwide service!

www.buckeyeamp.com

 

[amirm]

To be clear, the $2,400 price was for when it was new. I think I saw a used for $300 and change on ebay. You would then have to have it refurbished so probably close to $1000 total.

 

[Xyrium]

I gave it a "meh"....average for its of class C for crap.

 

[ROOSKIE]

Is anyone here going to argue that the distortion of the relic isn't sufficient to produce an audible difference versus current ultra-low distortion amplifiers? I hope not.

Its distortion, particularly its high level of high-order harmonics will render it a pretty nasty listen.

Yes I will. I would argue that.

This would therefore be a perfect amp to ABX blind test with. Nothing short of an actual test like that will convince me that the levels of distortion presented here are a 'nasty listen'.

I'd rather have the high power vs a low powered cleaner amp.

Yes, of course I'd buy the Hypex if the money was similar or not a factor and I'm not looking to do refurbishment on an old Carver. If this was available and tested like this one I'd feel no shame in using it. ( It would also be an obviously great subwoofer amp.)

I have not seen the evidence that folks hear things like -50db distortion levels (0.3%), let alone -70db levels (0.03%) or -80db (0.01% nope!) no matter what frequency or situation.

Very good early 90s performance.

And again a great amp to keep and AB/ABX with the new ultra clean Hypex, Purifi & other chip units - along comparing with a Benchmark in mono. It would be really interesting.

 

[amirm]

And again a great amp to keep and AB/ABX with the new ultra clean Hypex, Purifi & other chip units - along comparing with a Benchmark in mono. It would be really interesting.

I don't think it would be hard to detect its noise floor vs state of the art amps. It is just a matter of how sensitive the speaker is.

vs

We are talking 70 uvolt idle noise vs 400 microvolt.

 

[Endibol]

Oh, and the fan, which is not counted as part of S/N ratio but probably should be.

Not when you play at 700 Watts, I reckon.

 

[Nopiano]

I’m an old fart, so I think it’s Great for its purpose as designed 35+ years ago. Lots of power, long service, low enough noise and distortion, and ok to run 24/7 if necessary.

 

[Gorgonzola]

1% is no worse than what's typically produced by loudspeakers and the rooms they are placed in. Also, the louder you go, the speaker distortion tends to increase dramatically.

Vis-à-vis loudspeaker distortion, typically it is predominantly 2nd plus 3rd order harmonic distortion whereas the Carver distortion, (and that of many S/S amps of the era), is strongly higher order distortion generally considered more disagreeable.

 

[Mart68]

Vis-à-vis loudspeaker distortion, typically it is predominantly 2nd plus 3rd order harmonic distortion whereas the Carver distortion, (and that of many S/S amps of the era), is strongly higher order distortion generally considered more disagreeable.

Inclined to agree, doesn't high order harmonic distortion cause intermodulation distortion? Which sounds bad at lower than 1 percent? Had a listen to one of these the other day: https://www.stereophile.com/content...ister-phono-integrated-amplifier-measurements

Rough as a badger's arse. Similar spray of high order distortion.

 

[Gorgonzola]

I’m an old fart, so I think it’s Great for its purpose as designed 35+ years ago. Lots of power, long service, low enough noise and distortion, and ok to run 24/7 if necessary.

Ha!! I'm at least as old a fart, and my recollection (a bit vague) is that Carver amps had unique design aspects that permitted higher power and lower weight than typical of amps of the era. E.g. "Magnetic Field Power Supply". I also recalled that their reception by hard-care audiophiles at the time was, at best, mixed.

 

[beagleman]

Yes I will. I would argue that.

This would therefore be a perfect amp to ABX blind test with. Nothing short of an actual test like that will convince me that the levels of distortion presented here are a 'nasty listen'.

I'd rather have the high power vs a low powered cleaner amp.

Yes, of course I'd buy the Hypex if the money was similar or not a factor and I'm not looking to do refurbishment on an old Carver. If this was available and tested like this one I'd feel no shame in using it. ( It would also be an obviously great subwoofer amp.)

I have not seen the evidence that folks hear things like -50db distortion levels (0.3%), let alone -70db levels (0.03%) or -80db (0.01% nope!) no matter what frequency or situation.

Very good early 90s performance.

And again a great amp to keep and AB/ABX with the new ultra clean Hypex, Purifi & other chip units - along comparing with a Benchmark in mono. It would be really interesting.

I think where my comment came from, is based on having owned about a dozen amps and set ups over the years that had even higher distortion, AND were still very listenable and not "Nasty" seeming.

Maybe not the last word on "Clean and perfect" sound, but hardly hard to listen to nor a bad experience. I have owned Tube stuff, console stereos, All in one systems, and boom boxes etc etc, and while yes there is a point where listening DOES become iffy, its not where this Carver is.

 

[Cogito]

Vis-à-vis loudspeaker distortion, typically it is predominantly 2nd plus 3rd order harmonic distortion whereas the Carver distortion, (and that of many S/S amps of the era), is strongly higher order distortion generally considered more disagreeable.

It's only disagreeable if it's audible. I still contend that the distortion level of this Carver unit is inconsequential with normal use, especially considering it's intended application.

 

[Gorgonzola]

I think where my comment came from, is based on having owned about a dozen amps and set ups over the years that had even higher distortion, AND were still very listenable and not "Nasty" seeming.

Maybe not the last word on "Clean and perfect" sound, but hardly hard to listen to nor a bad experience. I have owned Tube stuff, console stereos, All in one systems, and boom boxes etc etc, and while yes there is a point where listening DOES become iffy, its not where this Carver is.

It scarcely needs mentioning that tube amps are high in 2nd and/or 3rd order distortion, but NOT, (at least relatively), the higher order harmonics that are shown by the Carver and other solid state amps. That is, the distortion profiles of tube vs. S/S amps is quite different and comparing their respective "total" distortion isn't meaningful.

My "theory" is that rise or return to popularity of tube amps in the '80s and '90s was due the audible difference, (however subtle), between the character of the distortions produced. Lower, 2nd/3rd order distortion is benign and even pleasant to some folks whereas higher order distortion is "nasty". Also some believe the 2nd/3rd order masks the unpleasantness of the the higher orders. Thus a tube amp may have much higher total distortion than a S/S amp but sound better to the ears of many.

 

[shuppatsu]

It scarcely needs mentioning that tube amps are high in 2nd and/or 3rd order distortion, but NOT, (at least relatively), the higher order harmonics that are shown by the Carver and other solid state amps. That is, the distortion profiles of tube vs. S/S amps is quite different and comparing their respective "total" distortion isn't meaningful.

My "theory" is that rise or return to popularity of tube amps in the '80s and '90s was due the audible difference, (however subtle), between the character of the distortions produced. Lower, 2nd/3rd order distortion is benign and even pleasant to some folks whereas higher order distortion is "nasty". Also some believe the 2nd/3rd order masks the unpleasantness of the the higher orders. Thus a tube amp may have much higher total distortion than a S/S amp but sound better to the ears of many.

I don't think anyone doubts your theory in theory; most if not all of us know that higher-order distortion is both more audible and more unpleasant than low-order distortion. We're just arguing over where it starts to sound audible. And admittedly none of us is bringing any empirical data to the fight, so no one is going to convince any one either way. Just planting a flag that these issues about the audibility of "poor performing" amplifiers such as this are still in contention.

A lot of my intuition about these things comes from the Audible Dynamic Range Sound Test, which might have some methodological quibbles but still gives a pretty solid sense for how quiet -70dB from a comfortable FS is. And that is with no masking! Once you have masking, I find it difficult to imagine someone being able to pick out the distortion from the signal. But my imagination fails me all the time! It's entirely plausible that some people can do it, but it takes a another leap of imagination beyond that to suppose that anyone who could pick out the distortion would perceive it as anything but extremely subtle. Even then my intuition could fail me. But I'd have to be convinced otherwise.

 

[davidc]

This is a review and detailed measurements of the Carver PT-2400 dual mono power amplifier. It is on kind loan from a member and cost US $2,400 when announced in 1991.
View attachment 543373
The amplifier came in both consumer (TFM-75) and professional versions. This pro version seems to have taken the consumer version and encased in thick sheet metal. I expected it to be light like my Carver amplifier but it is quite heavy. It has all the features of a pro amplifier include a fan that runs all the time:
View attachment 543374

As you see, it has dual 12-amp IEC inputs. I only have one circuit on my bench so resorted to testing just channel 1.

The amp was professionally restored by a Carver employee. It worked solidly in my testing, with case temps remaining at room temperature. The aforementioned fan makes a low frequency hum that is not too loud due to its large size.

Carver PT-2400 Amplifier Measurements
At max sensitivity, it delivers 33 dB of gain. To make things more of a level playing field, I dialed that down to about 22 dB:
View attachment 543375

I was disappointed by the spray of harmonics which delivers performance below the bottom quartile of all amplifiers tested:
View attachment 543376

Noise performance is not great at 5 watts but gets much better at full power (meaning noise is mostly static):
View attachment 543377

View attachment 543378

The rail switching architecture likely requires an output filter which may be responsible for some frequency roll off and small load dependency:
View attachment 543379

Distortion as expected, hurts multitone performance:
View attachment 543380
Although not too bad compared to today's Pro amps.

Name of the game here is power and the PT-2400 delivers a ton of it:
View attachment 543381
View attachment 543382
We can see the jump in distortion when the output transistor rail voltages are increased. Keeping the voltage low at lower power levels reduces idle power consumption and hence heat generated but has that price.

Good to see some headroom still:
View attachment 543383

Peak power at 40 Hz breaks records:
View attachment 543384

Sweeping at different frequencies we see that high frequencies get even more distorted, similar to class D amps:
View attachment 543387

The amp is essentially stable on power up:
View attachment 543385

Power on noise is the highest I have measured so expect some noise when turning it on:
View attachment 543386

Conclusions
The PT-2400 lacks linearity as evidenced by high distortion. It is however, quite powerful and keeps up with modern professional amplifiers. I don't know how much it costs to get it refurbished on top of purchase price -- likely much higher than today's pro amplifier. In that regard, it only makes sense if you value its nostalgic value. Performance wise it doesn't bring much to the table.
------------
As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

Hello Everyone, I am the owner of this amplifier.
I had it restored by Nelion Audio before sending it to Amir. I was curious how it would test compared with the Sunfire and Carver M1.5, which I don't believe had been completely restored.
I've been an audiophile since I was about 7 years old, and I'm now 65. My dad was an electronics engineer and was also an audiophile. He built his own solid-state transistor receiver back in the very early 60's when transistors were relatively new in home electronics. I still have much of his old equipment from the 50's-70's.
As I've gotten older, I've had a soft spot for equipment that I couldn't get when I was younger. Especially for Carver electronics and VMPS speakers. Neither Bob Carver nor Brian Cheney was afraid to buck the prevailing trend of the time. I remember going to Jafco Dept Store in Cherry Hill, NJ, and looking at the new Phase Linear Model 700. 350 watts RMS was astounding back then.
Anyway, I got this amp (and two more) from a guy who runs a business selling used concert equipment. He was in South Central LA and had about 20 PT-2400s and another 25 PT-1800s.
The PT-2400 was the most powerful amp Carver ever made. It was designed by him, but he had left Carver Corp just before it was released. There was also a consumer version of the amp (TFM-75), which is considered the "holy grail" by the Carver cult. There has always been speculation about the differences between the two. All that was put to rest in a double restoration project done by Nelion Audio. While the TFM-2400 was built a little tougher to take abuse, it was electrically the same as the TFM-75, with some minor differences that don't affect the signal path. You can read about this final confirmation of the amps from thecarversite.com here. https://thecarversite.com/topic/26802-carver-pt-2400-vs-carver-tfm-75/

While this amp was one of Carver's "Magnetic Field Amps, " it wasn't one of the lightweight versions. I believe it's about 65lbs. It is a dual-mono design that can be bridged in both series and parallel. Carver's other high-power amp at the time, the M1.5t, at 475 watts RMS into 8 ohms, was only about 29 pounds, I believe. And then the PT-1250, which came out a little later, had the same power output as the M1.5t but weighed only about 11-14 lbs.

The instruction manual, service manual, and a picture forum thread of the refurbishing of this unit are linked at the end of this post.

I decided to get the amp because I noticed that when watching movies, explosions could easily clip my approximately 600-watt RMS-per-channel M1.5t. So, this PT-2400 was about double the power, dual mono, and had a little more headroom. I sent it off to Amir for testing after it was restored, before I even hooked it up.

I want to thank Amir for his excellent review. Even though some of the distortion measurements were higher than I would have liked, I'm not worried about it. With most of my listening being home theater and loud rock and roll (and my hearing loss), I know I won't be bothered by distortion at all. (I should have listened to my mom when she told me not to listen to that rock 'n roll music so loud. It'll damage my hearing. But I didn't.

The correct rated power output is all rated at RMS watts per channel, both channels driven, from 20Hz-20kHz at a specific distortion level (as was required by the FTC back then. At home, I have each channel plugged into a separate circuit to my breaker box.


Power Output per channel:
Both channels driven (20Hz-20kHz)
8 ohm/ch. 750 watts
4 ohm/ch. 1200 watts
2 ohm/ch. 1500 watts

Power Output: Series mono operation
20Hz-20kHz)
8 ohm 2400 watts
4 ohm 3000 watts

Signal to Noise Ratio:
>100dB
(from rated power
@ 4Ω/A weighted)

Channel Seperation: >55db @ 1kHz
Slew Rate: 25V/µs
THD: 4Ω 20-20kHz (at
1200W) < 0.5%
IM Distortion: <0.1%
Damping Factor: >200 @ 1kHz
Sensitivity: 1.5 V rms
Gain: 34dB
Input Impedance: 15 Kilohms
Unbalanced
30 Kilohms
Balanced
CMRR: >70db @ 1kHz

Here is a link to the restoration of the PT-2400 vs the TFM-75

https://thecarversite.com/topic/26802-carver-pt-2400-vs-carver-tfm-75/

Here is a link to the owners manual and the service manual for the PT-2400. It actually an interesting read as it explains a lot.

https://thecarversite.com/manuals/mandir/Carver%20pt1250-pt1800-pt2400%20owner%20manual.pdf

https://thecarversite.com/manuals/mandir/Carver%20PT2400%20Service%20Manual.pdf

And here is a link to the thread that shows mine being restored.

Carver PT-2400 restore

This is for @davidc. A typical dirty and rusty specimen! Decent shape. No severe burning so that's a great start. Tear down. Lots of dirt. I will take care of that rusty fan grill, and install a new quiet fan and turn down the speed to make it QUIET. Chassis cleaned up and tested. Had to replace ...

thecarversite.com

 

[mrick39]

the question i have is that is there a stereo class D power amp for sale that has 750w x 2 and is less than 50lb and less than $2,4k?

tbf 750w is insane... like realistically for people here what are you doing with 750w that cant be done with 250w given every has reasonably efficient spks

Yes there is at least one...

https://www.crutchfield.com/p_845PX10/Yamaha-PX10.html

 

[RKV1]

Hello Everyone, I am the owner of this amplifier.
I had it restored by Nelion Audio before sending it to Amir. I was curious how it would test compared with the Sunfire and Carver M1.5, which I don't believe had been completely restored.
I've been an audiophile since I was about 7 years old, and I'm now 65. My dad was an electronics engineer and was also an audiophile. He built his own solid-state transistor receiver back in the very early 60's when transistors were relatively new in home electronics. I still have much of his old equipment from the 50's-70's.
As I've gotten older, I've had a soft spot for equipment that I couldn't get when I was younger. Especially for Carver electronics and VMPS speakers. Neither Bob Carver nor Brian Cheney was afraid to buck the prevailing trend of the time. I remember going to Jafco Dept Store in Cherry Hill, NJ, and looking at the new Phase Linear Model 700. 350 watts RMS was astounding back then.
Anyway, I got this amp (and two more) from a guy who runs a business selling used concert equipment. He was in South Central LA and had about 20 PT-2400s and another 25 PT-1800s.
The PT-2400 was the most powerful amp Carver ever made. It was designed by him, but he had left Carver Corp just before it was released. There was also a consumer version of the amp (TFM-75), which is considered the "holy grail" by the Carver cult. There has always been speculation about the differences between the two. All that was put to rest in a double restoration project done by Nelion Audio. While the TFM-2400 was built a little tougher to take abuse, it was electrically the same as the TFM-75, with some minor differences that don't affect the signal path. You can read about this final confirmation of the amps from thecarversite.com here. https://thecarversite.com/topic/26802-carver-pt-2400-vs-carver-tfm-75/

While this amp was one of Carver's "Magnetic Field Amps, " it wasn't one of the lightweight versions. I believe it's about 65lbs. It is a dual-mono design that can be bridged in both series and parallel. Carver's other high-power amp at the time, the M1.5t, at 475 watts RMS into 8 ohms, was only about 29 pounds, I believe. And then the PT-1250, which came out a little later, had the same power output as the M1.5t but weighed only about 11-14 lbs.

The instruction manual, service manual, and a picture forum thread of the refurbishing of this unit are linked at the end of this post.

I decided to get the amp because I noticed that when watching movies, explosions could easily clip my approximately 600-watt RMS-per-channel M1.5t. So, this PT-2400 was about double the power, dual mono, and had a little more headroom. I sent it off to Amir for testing after it was restored, before I even hooked it up.

I want to thank Amir for his excellent review. Even though some of the distortion measurements were higher than I would have liked, I'm not worried about it. With most of my listening being home theater and loud rock and roll (and my hearing loss), I know I won't be bothered by distortion at all. (I should have listened to my mom when she told me not to listen to that rock 'n roll music so loud. It'll damage my hearing. But I didn't.

The correct rated power output is all rated at RMS watts per channel, both channels driven, from 20Hz-20kHz at a specific distortion level (as was required by the FTC back then. At home, I have each channel plugged into a separate circuit to my breaker box.


Power Output per channel:
Both channels driven (20Hz-20kHz)
8 ohm/ch. 750 watts
4 ohm/ch. 1200 watts
2 ohm/ch. 1500 watts

Power Output: Series mono operation
20Hz-20kHz)
8 ohm 2400 watts
4 ohm 3000 watts

Signal to Noise Ratio:
>100dB
(from rated power
@ 4Ω/A weighted)

Channel Seperation: >55db @ 1kHz
Slew Rate: 25V/µs
THD: 4Ω 20-20kHz (at
1200W) < 0.5%
IM Distortion: <0.1%
Damping Factor: >200 @ 1kHz
Sensitivity: 1.5 V rms
Gain: 34dB
Input Impedance: 15 Kilohms
Unbalanced
30 Kilohms
Balanced
CMRR: >70db @ 1kHz

Here is a link to the restoration of the PT-2400 vs the TFM-75

https://thecarversite.com/topic/26802-carver-pt-2400-vs-carver-tfm-75/

Here is a link to the owners manual and the service manual for the PT-2400. It actually an interesting read as it explains a lot.

https://thecarversite.com/manuals/mandir/Carver%20pt1250-pt1800-pt2400%20owner%20manual.pdf

https://thecarversite.com/manuals/mandir/Carver%20PT2400%20Service%20Manual.pdf

And here is a link to the thread that shows mine being restored.

Carver PT-2400 restore

This is for @davidc. A typical dirty and rusty specimen! Decent shape. No severe burning so that's a great start. Tear down. Lots of dirt. I will take care of that rusty fan grill, and install a new quiet fan and turn down the speed to make it QUIET. Chassis cleaned up and tested. Had to replace ...

thecarversite.com

Excellent work by your repair guy, don't lose him.

 

[Gorgonzola]

...
A lot of my intuition about these things comes from the Audible Dynamic Range Sound Test, which might have some methodological quibbles but still gives a pretty solid sense for how quiet -70dB from a comfortable FS is. And that is with no masking! Once you have masking, I find it difficult to imagine someone being able to pick out the distortion from the signal. But my imagination fails me all the time! It's entirely plausible that some people can do it, but it takes a another leap of imagination beyond that to suppose that anyone who could pick out the distortion would perceive it as anything but extremely subtle. Even then my intuition could fail me. But I'd have to be convinced otherwise.

Perhaps it doesn't need saying, but I never heard an audiophile say, "Ah! I'm picking out the distortion from the clean signal". The usual complaints are "harshness", "brightness", "grain", "softness", "muddiness" and/or "opaqueness" i.e. lack of detail or transparency. Just as often we hear positives about distortion: "warm", "musical", "organic", "bloom", "decay", etc.

 

[EERecordist]

Just for curiosity I looked up the design. Each channel has 4 NPN and 4 PNP transistors in parallel. Each one is rated at 250V and 50A. There are modern replacements available. The Amp rails are reported to be +- 111V. Now I'm curious about the classic high power amplifiers of then and now, and the cycle of availability of high power FETs. I also wonder about the protection circuitry for high power amplifiers.

Just like there are some pretty wild antique high power vacuum tubes for radio transmitters, today the trend is higher power semiconductors in the electric power industry for AC-DC and DC-AC conversion and inverters/battery chargers. I think the largest AC-DC power line converters are in China at 12GWatts, the Zhundong-Wannan ±1100 kV transmission project. In the US they are running 2-3GWatts. Those converter stations take up a large building with semiconductor devices in series and parallel. Common utility scale inverters would be 2-3MW today.

Of course we discussed that audio doesn't need that much power in a previous thread!