Amplifier for B&W

[Art Vandelay]

Originally Posted by Wised

Class Ds are perfectly fine for "subs". Virtually all self powered subs have gone that route. First time that Ive heard of some biamping with one. Seems like a good idea! How do you match the amps?

Voltage gain matching is an issue when bi-amping with different amps, yes.

I first measured the voltage gain and then built a couple of in-line attenuators to pad the class D amplifiers by the required 4.5dB.

A secondary issue can be the reactive load that results at the crossover frequency from uncoupling the bass from the mid-treble section of the crossover. To avoid my class AB amplifier seeing a very capacitive load I went to the trouble of designing and installing a conjugate matching network which connects in parallel with the load, so it has zero effect on the signal other than creating a more resistive load for the amplifier. Adding this network had a far greater effect (subjectively) than I was expecting. Obviously for the better.

See results below. The matching network keeps the phase angle within +/- 30 degrees.

[meltemi]

Originally Posted by Wised

Ample current reserves is kind way to say expensive. 200 watts RMS per channel is a useless specification for example. On the other hand power reserves dynamic headroom etc are the true measures of "current reserves". Quality amps are in general not only heavy but expensive too since all that reserve current takes large capacitors and transformers. Amps can have particular sigantures which may or not be appreciated by anyone in particular. However the best signature is none at all. The so called openess amp heads so much talk about is the capacity to provide ten times a nominal output of 100watts, for example, to 1000 while still staying within much less less than 1% distortion. Few to none maintream "hifi gear" can provide that type of power aka current". Of course it depends on the speakers but thereare few very good quality speakers with efficiencies of significantly more than 90db or so. If you want to listen at realistic live performance levels of over 90dbs plus you need a ton of power. My 200 watt mac 6700 could not drive my 803D3s without cranking it to clipping levels to do it, so I had to jump to the MC462. An amp that can provide 3 times the peak power than the receiver can provide 1800 vs 600 watts. That type of headroom is why big high current amp seem to breath regardless of brand, the capacity to accurately portray live music in all its splendor.

IMHO the problem with the McIntoshs is their use of output transformers. Depending on the taps used, the output power remains "constant" for the given load impedance. However a speaker's load impedance is almost never constant at all.
So if one uses the 8Ω output taps, how much current can the amp then deliver at say 3Ω (a B&W's minimum impedance) ? McIntosh does not specify.
In addition, using output transformers leads to a relatively low damping factor; hence the amp can not truly control the speakers.

There are amps which can deliver the current required by the speakers regardless of the actual load impedance.
Example: Accuphase A-250 nominal Class A 100W@8Ω / 200W@4Ω / 400W@2Ω / 800W@1Ω
And their damping factor is >1000 @8Ω (i.e. their output impedance < 8mΩ !)

[Art Vandelay]

Originally Posted by meltemi

IMHO the problem with the McIntoshs is their use of output transformers. Depending on the taps used, the output power remains "constant" for the given load impedance. However a speaker's load impedance is almost never constant at all.
So if one uses the 8Ω output taps, how much current can the amp then deliver at say 3Ω (a B&W's minimum impedance) ? McIntosh does not specify.
In addition, using output transformers leads to a relatively low damping factor; hence the amp can not truly control the speakers.

Mac's use autoformers, so when used on the 8 Ohm tap there's probably next to no winding in series with the speaker terminals. Point taken though that damping factor isn't impressive as many other amplifiers when driving low impedance speakers from the 4 or 2 ohm taps.

Fwiw, Stereophile's review of the new 462 reveals very impressive performance overall.

https://www.stereophile.com/content/...r-measurements

[Wised]

Originally Posted by meltemi

IMHO the problem with the McIntoshs is their use of output transformers. Depending on the taps used, the output power remains "constant" for the given load impedance. However a speaker's load impedance is almost never constant at all.
So if one uses the 8Ω output taps, how much current can the amp then deliver at say 3Ω (a B&W's minimum impedance) ? McIntosh does not specify.
In addition, using output transformers leads to a relatively low damping factor; hence the amp can not truly control the speakers.

There are amps which can deliver the current required by the speakers regardless of the actual load impedance.
Example: Accuphase A-250 nominal Class A 100W@8Ω / 200W@4Ω / 400W@2Ω / 800W@1Ω
And their damping factor is >1000 @8Ω (i.e. their output impedance < 8mΩ !)

Quite the contrary the auto formers are the sauce! Other manufacturers quote you an 8 ohms figure for their THD at RMS and 8 ohms not at any other impedance. MC guarantees its nominal rms power and distortion regardless of impedance. No other company rates its THD that way, because the power ratings at those lower levels are close if not over 1%! The different taps on autoformers dont mean it cant drive at a lower one it simply tailors the amp to the speaker, so the amp can drive them without ever straining it s power transistors thats why MCs never get hot!

[crwilli]

Originally Posted by Wised

...The different taps on autoformers dont mean it cant drive at a lower one it simply tailors the amp to the speaker, so the amp can drive them without ever straining it s power transistors thats why MCs never get hot!

Unless they have 16 KT88s.

[Wised]

Originally Posted by crwilli

Unless they have 16 KT88s.

Dang I had to look than one up
Im not an engineer!!!
Plus, Ive never used tubes except when my stepdad plays with his antique radios of which he has literally hundreds. His particularly proud of his Awater Kents.

[meltemi]

Originally Posted by Wised

Quite the contrary the auto formers are the sauce! Other manufacturers quote you an 8 ohms figure for their THD at RMS and 8 ohms not at any other impedance. MC guarantees its nominal rms power and distortion regardless of impedance. No other company rates its THD that way, because the power ratings at those lower levels are close if not over 1%! The different taps on autoformers dont mean it cant drive at a lower one it simply tailors the amp to the speaker, so the amp can drive them without ever straining it s power transistors thats why MCs never get hot!

Accuphase A-250 has a guaranteed THD of 0.05% @2Ω @400W and 0.03% @8Ω @100W.
I must admit that a pair of Accuphase A-250 Class A monoblocks cost substatially more than an MC462.
However I do consider them as one of the very best matches for my B&W 800 D3.

Stereophile (see link from Art Vandelay) measured the heatsink temperature of the MC462 after one-third power for 30 minutes into 8 ohms at 158.6°F (70.3°C). So MCs never get hot?

[Wised]

Originally Posted by meltemi

Accuphase A-250 has a guaranteed THD of 0.05% @2Ω @400W and 0.03% @8Ω @100W.
I must admit that a pair of Accuphase A-250 Class A monoblocks cost substatially more than an MC462.
However I do consider them as one of the very best matches for my B&W 800 D3.

Stereophile (see link from ArtVandalay) measured the heatsink temperature of the MC462 after one-third power for 30 minutes into 8 ohms at 158.6°F (70.3°C). So MCs never get hot?

Absolutely! There are good amps from a variety of manufacturers that will do the job just fine. BTW , that is a test to do exactly that, make the amp get real hot. It applies an artifical, constant 8hm load at full tilt till it gets hot. That never happens in realit its an artificial "conditioning regimen*. Ive run the 462 for hours at essentially full tilt, it gets warm at most.
Im glad accuphase is one of the few manufacturers that state distortion at different impedances the majority dont..

[hartmann-nbg]

For me that is the best choise.

[mike175gr]

Awesome set up! Any issues blending in the DB1D?