whadda ya tube guys think/know about digital amps?

[avman]

sony has released preliminary info on a new receiver that features 200 w.p.c. 's-master pro' digital amplifiers built in. any thoughts based on actual knowledge of these or digital amps in general?

avman.

[NOSValves]

Not sure about that but I'm currently listening to Leo's PM6 8 watter and its pretty amazing for the little unassuming box its in !! I think this is digital of some sort. I'm lost in SS land LOL !!

Craig

[avman]

thanks for the reply, anyone else??

av.

[leok]

Scaleability is a concept that is important when applying digital (pulse width modulation with error correction) amplification technologies.

Instead of power, think signal-to-noise. Digital amps have a 70 to 90 dB signal to noise capability. If you make the max output no bigger than you need, then you have the most dynamic range before you hit the noise floor. Digital amps can be scaled .. so, an amp with 6 Watts max output will have a much lower noise floor than a 100 Watt amp.

Transistor amps do not scale well. Their transfer characteristics are based on fixed semiconductor junction voltage characteristics that don't change much from large to small. That's why it's hard to make a good, low power transistor amp. Also, transistor voltage to current relationships tend to be exponential, not linear. The noise floor for a 10 Watt transistor amp isn't necessarily much lower than that for a 100 Watt amp.

Back to PWM amps: The best PWM amp is the smallest possible. Unfortunately, the smallest PWM amp I know of, outside of my own 8 Watt P6D, is the 150 Watt PS Audio HCA-2. By my math, that amp is 15 times bigger than I could ever use which means the distortion and noist is 15 times as big as it should be for my application. Since I can build my own, I did.

Tubes also scale. So, until you can get a good 10 Watt, or 15 Watt PWM amp, get a good 10 Watt or 15 Watt tube amp instead.

leok

[jt1stcav]

I'm totally clueless concerning all this technological hoopla! Didn't Pass Labs and/or Bel Canto design/engineer the Tripath amp? Just curious...

[leok]

I think Bel Canto used Tripath.

leok

[Mike82]

I've heard the TACT, BelCanto, and Spectron digital amps. They are pretty good. Kinda like solid state without the grain. But not good enough for me to leave tubes, especially with my Khorns! But if I had inefficient sepakers and needed lots of power, they'd be on my list.

Other attractions to digital amps are they run cool, so shelf placement is not an issue and they won't heat your house up during the summer. They also use comparatively very little electricity which is a big plus if your live in CA.

[jt1stcav]

Last year a friend of mine in Singapore experimented with the tripath design. He had two exhausted Meridian chassis that he gutted their innards and transformed them into two tripath monoblocks for his Magnepans. The jpg shows the old Meridians in their final testing stage...the old empty Phase Linear cabinet was another tripath transformation for a friend. As far as I know, his tripath installs are still up and running!

[avman]

thanks again-these amps (7 of'em) are in a new sonyES piece

strda5000ES. they are rated @ 200 w.p.c.

if i can see/hear one when it comes out, i will follow-up.

BTW- i was reading 'the life-the legend' the other night, and was dreaming about how sweet a pair of k-horns w/belle center would sound powered by some sweet tubes!

i have yet to hear tubes hooked up to my klf-30's,i like it LOUD, and classic rock/movies are my primary material. can tubes cut it for what i like??

thanks, avman.

[jdm56]

Sharp (yes, the "sharp minds" people) came out with a $10,000. 2-channel power amp a couple of years ago, that was favorably reviewed in Stereophile. You could probably find the review in the S-phile archives. The Sony and Panasonic digital amps I've seen so far are based on the same 1-bit technology. The same as SACD, in fact.

I have been real tempted by Sony's AVD-S50ES, but have held off due to it's lack of flexibility. Harmon-Kardon has also brought out a couple of digital amp receivers. If I was betting, I'd wajer digital amps will soon be the mainstream.

I don't really follow the assertion that performance of digital amps tends to go down at higher power levels. I can't really argue the point on a technical level, but I don't recall ever "getting" that from anything I've read of digital amplifiers.

[leok]

James,

It's not that the performance of a digital amp goes down at higher power, but that noise and distortion, as a percent of a signal at a fixed output power (say 1 Watt) is greater for the larger amp.

Consider two hypothetical amps, both with distortion and noise that is 0.001% of rated output. One amp is 100 Watts, the other is 10 Watts. When each amp is delivering 1 Watt, the 100 Watt amp is delivering 1/100 of its capability so the distortion, which doesn't drop with output power is now 0.1% of that 1 Watt output. The 10 Watt amp is delivering 1/10 of its capability so its distortion, is 0.01% of its 1 Watt output.

The above example is a simplification, but maybe it will help you understand how excess power increases the noise and distortion of a fixed level output. If you look at the distortion vs power curves published in Stereophile amp reviews, you will see that distortion, as a % of actual output (not of rated output) often increases dramatically below a Watt. This is true even of the digital amps they have reviewed.

I would be very careful to audition a digital amp before buying it for use with a speaker as efficient as most Klipsch models.

leok

[jdm56]

OK, I think I got that. But, like you said, an oversimplification, because amp. distortion will vary with frequency and load, too. One thing that I think would tend to render the point moot, though: Wouldn't the rising percentage of distortion at low power levels tend to be buried in the noise? I'm not trying to be difficult; just trying to understand.

I agree that a care should be taken before jumping at these new digital amplifier designs for powering klipsch speakers; particularly at the lower price levels I'd be looking at. I am very anxious to audition them, though.

[leok]

It would depend on the amp. and how noisy it is. But both distortion and noise should be something like 70dB down at normal listenng levels. For me, normal listening is under 1/4 Watt. Very many amps don't have that capability, and higher powered ones almost never do. My Tripath based P6D does have distortion and noise 70dB below 1/5 Watt. That's why the high frequencies are so smooth.

Specs I've seen, Tripath included, for any digital amp that produces over 50 Watts, show higher distortion and noise at sub-Watt output powers.

Besides creating harsh sound, the noise will hide detail, and music will sound flat, without ambience. Recordings will not sound lifelike.

Still, all of the above is relative, and most pwm amps will probably sound better than a ss amp of similar cost and power. Do you know of a pwm amp that has output rating under 100 Watts?

leok