This is a review and detailed measurements of the Carver M-1.5t vintage stereo amplifier. It was kindly sent to me by a member.
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The M-1.5t came in an era where rack mounting meant serious business. As a Carver (receiver) owner myself, I remember all the advertising for the M-1.5t. Oddly, there is no power switch anywhere:
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I got a chuckle seeing that monster cable tag:
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And found the power specs ridiculously complicated but I am sure was appreciated by the aficionadas of the amp:
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The front LEDs don't light up until it is putting out a lot of power. I liked the top LED which was the limiting lights and nice protection circuit which kept the unit on no matter what.
This amp was part of Carver "Magnetic Field" amplification line which varied the power supply voltage to substantially reduce the size and weight of the transformer. As a result, the unit ran quite cool, maybe a bit warmer than modern class D but still, impressive for the time.
The owner has replaced the capacitors in this unit. Otherwise I think it is untouched.
Carver M-1.5t Measurements
I can see why there is no power switch as the amp did not stabilize for the 14 minutes I measured it:
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The level of instability is quite large, going beyond 10 db variation in SINAD! I am used to seeing 1 or 2 dB, but nothing at this level.
When I had the unit connected, and before I fed it signal, I could see constant switching noise:
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Not sure what that is about.
Here is our dashboard at 5 watts with 1 kHz tone:
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Third harmonic dominates distortion profile and with it, SINAD (relative sum of noise+distortion). Average SINAD of 55 dB for both channels is far, far below that median for all amplifiers I have tested to date (around 79 dB). On top of distortion, we have massive pulse train which oddly starts at 40 Hz. So definitely not very clean.
SNR though was better:
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Frequency response was nice, flat and extended:
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Crosstalk was "OK:"
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Multitone shows more than usual increase in distortion vs frequency:
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Front of the unit says it has low feedback which is likely responsible for this.
Claim to fame is lots of power so let's see how it does:
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We see a distinct jump in distortion at around 66 watts which must be when it switches to higher power supply voltage. Allowing for copious amount of distortion, there is good bit of power at 273 watts. Here is the same at 8 ohm:
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Now let's test peak performance:
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There definitely is a lot of headroom, allowing power to almost double! The 600 watt number and such must have been at higher distortion levels than what I allow.
Testing for frequency sensitivity we again see the higher distortion at higher frequencies:
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20 Hz performance also dropped with rising distortion at just 20 watts.
Finally, here is the ultrasonic spectrum:
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It is nice to test products that were iconic during my youth with state of the art measurements that didn't even exist then. Using that, we see that in noise and distortion the M-1.5t is outgunned by vast number of amplifiers today. However, it produces copious amount of power which would have been even more impressive then. The efficiency rivals class D amps today which was unheard of at the time.
Looking online, I see that non-upgraded but working units go for $500 or so. They seem to be a decent alternative to pro class D amp if you have a soft spot in your heart for vintage amplifiers.
As always, questions, comments, recommendations, etc. are welcome.
are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/