Carver M-1.5t Review (Vintage Amp)

[phoenixdogfan]

I was a live and well in the '80s, (maybe more so than today). In the day I never gave any serious though to a Caver amp; I was always suspicious of them you might say.

OTOH, through the '80s and '90s I was running a Phase Linear 400 amp, a very well-measuring amp for the day. At the time I was very confident that I had a amp that was as good as any. It took me 20 year to understand that the PL 400 was a truly hideous sounding amp. I'd had the PS capacitors replace at one point but that help. It was amps like the 'Phase' that gave solid state a bad rep for many audiophiles. Not only were the highs shrill & glassy but detail and transparency were totally lacking; "opaque" would be an appropriate adjective.

I owned one of those in the mid '70's, fortunately it got burglarized. Used the proceeds of the insurance settlement to buy Roger's LS 3/5 a's and an Audionics CC2.

I'd have to say I came out ahead on the deal.

 

[phoenixdogfan]

The m1.0 was used in the challenge, not the m1.5t, and the competitor was a Conrad Johnson, not a Mark Levinson, but you have raised a good point. Were the "t" series amps intentionally designed to have distortion levels that matched the Conrad Johnson? If so, that sheds a new light on this amp's performance, although not the lower than specified power. The CJs I heard were not good sounding amps, in my opinion.

No, he made one amp with the transfer function of the Levinson ML2 as well.

 

[perdido34]

I appreciate Amir reviewing this! I have a pair of Caver M400a cubes which are ~200w into 8ohms and 400w into 8ohms when bridged for mono, which is how I am using them. They also do not have a power switch, and now I know why as they are also magnetic field power amp designs- though they get switched on when the preamp comes on by a separate relay circuit due to the power they can pull. As far as I know they are original, and sound good and allow me to crank it up when I desire

The m1.0t has a power switch on the back.

 

[Willem]

For 1976 measurements of the then new 2x100 watt Quad 405 current dumping amplifier, see: http://www.meridian-audio.info/public/quad_405_test_reports[2314].pdf The later 405-2 and even more so the 1986 2x140 watt 606-2 improve on this even more. This goes to show that already at that time sonically perfect amplifiers were possible.

 

[amirm]

It actually states that the owner replaced them "The owner has replaced the capacitors in this unit." Were they professionally done and was it an 'upgrade' or a 'replacement'? Those seem like different things that could affect the performance; especially since in the audiophile world upgrades often take things out of original spec.

This is all I know from the owner: "It had some caps replaced a couple of years ago, and is in good working condition." Once I get a hold of him, maybe he will explain more.

 

[Blumlein 88]

I'd love to see the test results from the Adcom GFA555 to compare. I have a soft spot for Nelson Pass due to his generosity towards the DIY community and am curious how the GFA holds up in a battle of 40-year old designs. I spent hours in my youth drooling over both Carver (TFMs) and Adcom amps. They, and to a lesser extent, H/K and Bryston, were the high-end lines sold by the big electronics stores when I was in high school.

Adcom GFA-555 power amplifier Specifications

Sidebar: Specifications Description: Output Power: 200W into 8 ohms (23dBW); 325W into 4 ohms (22.1dBW), all continuous power, 20Hz-20kHz, with 0.09% THD. Input impedance: 22k ohms. Sensitivity: 130mV.Dimensions: 17" W by 7" H by 11.5" D. Weight: 34 lbs.Price: No longer available; $599.95...

www.stereophile.com

Adcom specs weren't much better than the Carver is doing here. It exceeded them slightly in testing. Spec at full power was .09% or -40.9 db. (EDIT:I missed a decimal point that should have been -60.9 as others have pointed out down thread by @HammerSandwich) Some of the very top amps from those years only claimed THD at power specs of -60-65 db. As an example look at the Threshold Stereophile measured. Those were also Nelson Pass designs.

Threshold T-200 power amplifier Measurements

Sidebar 2: Measurements A full set of measurements of the Threshold T-200 was made in the amplifier's unbalanced mode, with selected measurements made in the balanced mode. Unless otherwise noted, the results presented are for the unbalanced configuration. The sample tested (SN 10926) was...

www.stereophile.com

Threshold Stasis SA/12e power amplifier Measurements

Sidebar 3: Measurements

www.stereophile.com

 

[AudioTodd]

The problem is IMHO, should such devices be "panthered" in absolute terms, or relative to their age - this one is 42? years old. In its "market" time, ist was probably on par with most of the competition?

Not even close. Look at Hafler products and tons of Japanese units.

 

[Blumlein 88]

Not even close. Look at Hafler products and tons of Japanese units.

Again memory with rose colored glasses. Hafler big SS units in those days claimed rated power at .05% or the same thing most Marantz AVR's claim and achieve. THD of -66 db. Also they weren't all that powerful.

Some of the Yamaha and Pioneer (and maybe Denon) big amps were claiming THD of -90 db or so back then.

 

[Zutroye]

It actually states that the owner replaced them "The owner has replaced the capacitors in this unit." Were they professionally done and was it an 'upgrade' or a 'replacement'? Those seem like different things that could affect the performance; especially since in the audiophile world upgrades often take things out of original spec.

Not knowing the quality and full extent of the work makes it a bit hard to judge. It is a bit like driving a 35 year old car and judging the company that built it rather than the people that maintained it.

The 50/80 V Caps were replaced

 

[PeteL]

This is all I know from the owner: "It had some caps replaced a couple of years ago, and is in good working condition." Once I get a hold of him, maybe he will explain more.

I do feel those results seems a little off. I see at least two adjustment potentiometers in this box, quite possibly a couple more. Sometime Bias, balance or some key voltages.. The very least of maintenance on a 40 Year old units is to be able to measure a few test points with a Scope and adjust to specs. Just swapping all caps and putting the lid back on without any measurments, honestly the chances of having it back to specs are slim. It would be interresting to know what he really did.

 

[JayGilb]

The 50/80 V Caps were replaced

The m1.5t and several other Carver models came with the 50v and 80v rail caps in the same capacitor. The 2 in 1 caps soon became impossible to acquire and Carver put out a service bulletin and a custom pcb that allowed separate 50v and 80v caps to be used in a drop in solution.

 

[capslock]

Just for reference, here's distortion measurements of a Pioneer A-441 from 1987 that had a list price of DM 500 including VAT ($ 250 before tax at the time). Service manual is available online without registration from electrotanya or with registration from hifiengine. Solid circuit design, but not spectacular:

- bjt long tailed input pair, no emitter degeneration
- current mirror load
- Darlington VAS loaded by current source
- some sort of non-switching BIAS IC
- triple EF output, using a single pair of Toshiba A1516/C3907 25 MHz output transistors (one notch down from their RET)

The only remarkable thing is that there's a bit of lead-lag compensation and caps at some transistor bases to suppress local oscillation but I can't see the usual Miller cap for dominant pole compensation. The 100 pF caps at the bases of the predrivers look pretty large and might set the dominant pole but it might have been better to choose them to be smaller and use a Miller cap on the VAS as this linearizes the VAS through local feedback and also damps the Early effect in the VAS transistor.

Verstärker und das Klirrspektrum.

- about - 96 dB HD2 at 1 kHz, 6 W into 8R
- -102 dB HD3, stays that low as frequency increases
- -100 dB sum of HD5, 7, 9 and 11

Pioneer A-441 | Hifi-Wiki

www.hifi-wiki.de

 

[Mnyb]

Is it not time to realise that mr carver always been more of a "personality" than anything else, products always a bit gimmicky . Always chosen new and novel before tried and true .
From marketing perspective one can see that , why build another textbook design SS amp, like everyone else ? why not dable into class-H and market the heck out of the accomplishment even if the side effects may be a bit much .

I,m convinced that mr carver now the truth about flat frequency response low noise and low thd and low damping factor . How then to differentiate ?

Likewise with the sunfire subwoofers he was very early with the very small enclosure long xmax drivers witk kW sised amps type of sub. Now it's commonplace .

He should probably had a companion refining the designs a bit before release

Wonder if the side effects where audible on 1980's speakers , maybe on Quad electrostats ?

The bad performance aside , it's a lot of power and power is needed . This would probably drive speakers better than some 20wpc class A amp of the era ?

 

[mhardy6647]

Take the assertions with a large grain of salt. Rosenberg’s connections to truth and honesty were at best tenuous.

Part of his charm, though.

I do believe that's the plaid of Clan Rosenberg.

Being a kid at the time, I never measured anything. What I can say is I never had to put my Technics SA-410 past half way on the volume, but when I put the Carver 900 into my system, I had to crank it to three quarters to max to achieve my normal listening volume.

You do understand that "volume control level" has nothing to do with amplifier output power per se and everything to do with: preamp gain, power amplifier sensitivity, and the maximum resistance and /or the "taper" of the volume control potentiometer, yes?

 

[mhardy6647]

Ok, I’ll run some 555 measurements next week. I still have the original power supply caps in there, so if time permits, I’ll do a before and after.

That should be intensely interesting! Thanks for volunteering to do that.

 

[HammerSandwich]

Adcom specs weren't much better than the Carver is doing here. It exceeded them slightly in testing. Spec at full power was .09% or -40.9 db.

-60.9dB there. Stereo Review (86/11) measured a bit lower distortion, though, which reveals a problem with a lot of specs. No text-only datasheet will provide what @amirm can show with a single graph:

 

[AudioTodd]

Again memory with rose colored glasses. Hafler big SS units in those days claimed rated power at .05% or the same thing most Marantz AVR's claim and achieve. THD of -66 db. Also they weren't all that powerful.

Some of the Yamaha and Pioneer (and maybe Denon) big amps were claiming THD of -90 db or so back then.

DH-220 claimed less than 0.02% THD which is better than this Carver by far from a measurement perspective. As you state, some of the Japanese units were at much better levels than that. All, though, are better than this Carver.

I currently use, among other amps, Benchmark AHB2s in both stereo and mono configurations. Nothing is close measurement wise, but I will not claim I can hear the difference between them and the other amps I have!!!

I love seeing these vintage pieces measured, though, and try for my amusement to see if they match in any way my memories of how I thought they sounded. I think this period was at the end of there being much legitimacy to impressions of amplifiers having a distinct "sound" and that was more from limitations of the technology and the resulting interactions with various speaker loads than any great magic of the designs themselves.

 

[SimpleTheater]

You do understand that "volume control level" has nothing to do with amplifier output power per se and everything to do with: preamp gain, power amplifier sensitivity, and the maximum resistance and /or the "taper" of the volume control potentiometer, yes?

I think we have to go back to the beginning. I was a kid (16 yrs old), and it was shocking to me (at that time) that a 45 watt Technics receiver, could play as loud as I wanted it to at 1/2 volume, but the Carver that took me a year to save for, had to be cranked to 3/4 to achieve the same level. And while I do understand that volume control level has nothing to do with amplifier output when I got older, I never got the bad taste out of my mouth as my friends would come over and be like "What is that, a 10 watt amp?".

 

[capslock]

Same guy, vintage Kenwood KA-990V, had a few mechanical problems like broken knobs and a relay but didn't require servicing of any electronic components.

Kenwood KA990V

List price DM1100 (about $560 pre tax) https://www.hifi-wiki.de/index.php/Kenwood_KA-990_V

Note the class H rail switching output stage that needs an extra set of output transistors. At low wattage like the FFT below, the single A1104/C2579 pair was the output pair. Those were decent Sanken 20 MHz transitors but nothing in bandwidth or gain linearity like the big LAPTs you can see on either side that take over beyond 20 W.

At 1 W into 8R: no harmonics down to noise level of -110 dB. I seem to remember those Kenwoods had their tone control implemented in the feedback network of the output stage, so it is probably high impedance even in tone defeat, explaining the highish noise. Apart from that, the performance would do a NCxxxMP proud:

https://i.postimg.cc/sXqYCQhJ/k2.jpg

Anybody still want to claim that mid-fi Japanese amps were as poor as the Carver in the 80s?

 

[beagleman]

I think we have to go back to the beginning. I was a kid (16 yrs old), and it was shocking to me (at that time) that a 45 watt Technics receiver, could play as loud as I wanted it to at 1/2 volume, but the Carver that took me a year to save for, had to be cranked to 3/4 to achieve the same level. And while I do understand that volume control level has nothing to do with amplifier output when I got older, I never got the bad taste out of my mouth as my friends would come over and be like "What is that, a 10 watt amp?".

You had me scared there for a moment....lol