Why aren't there preamplifiers that use digital?

Bemopti123 · « **on:** 3 Dec 2005, 07:41 pm »

I am wondering about digital amplification technology, from Tripath based chips to B&O ICE modules, to Sharp's Sigma Bit and hybrid technologies. The Digital amplification drive has begun in earnest for what it seems to me about 5-6 years ago and it keeps getting better than better, in terms of features, and the least, in terms of watts per $.

The question I have is this, if digital amplified watts are more than suitable in higher quantities as well as low quantities, wouldn't they be suitable in under 1 watt applications such as preamplifier output driving?

I have yet to read about a preamp that uses digital amplification state. Is there such a beast and if they do not exist, what prevents it from becoming reality?

Watson · « **Reply #1 on:** 3 Dec 2005, 07:48 pm »

It doesn't make sense. Preamps deal with so little power that they can be easily biased into class A with no heat issues. Why would you want to run in class D when you can run in class A?

Bemopti123 · « **Reply #2 on:** 3 Dec 2005, 07:57 pm »

So, that is my answer. It is no feasible to use digital at low wattage, it is only useful at high wattage, right? But, then, what about the pristinness of the digital sound quality, wouldn't that be worth the effort?

If biasing in Class A at such a low wattage makes digital amplification unnecessary, what about preamplifiers that use tubes? They do spend more energy than SS, and yet, they seem to be the standard setters. I am wondering what manufacturers into doing one and skipping another method of design.

Watson · « **Reply #3 on:** 3 Dec 2005, 08:06 pm »

Good tube preamps run in class A by default. (There aren't too many push-pull tube preamps, and the ones that exist (e.g. white cathode followers meant as preamp/headphone amps) run in class A for small signals.)

Digital power amps sound different than traditional class AB power amps largely because of their distortion behavior. With a preamp you're never pushing it into clipping, so that's not really an issue. For small signals, it's not clear to me that a switching (digital) amp would have competitive distortion numbers anyway. The other reason digital amps are popular is because, pound for pound, they're much cheaper than traditional class A amps. 50 watts class A requires huge heatsinks and costs $1500+ commercially.

Another big other issue is that most digital amps alter their frequency response as the load impedance changes. That's not a big problem when the load only varies between 4-8 ohms, but when you could be driving a load between 5k and 100k, it's an issue.

bubba966 · « **Reply #4 on:** 3 Dec 2005, 08:19 pm »

Quote from: Watson

With a preamp you're never pushing it into clipping, so that's not really an issue.

You can certainly push a pre into clipping. Sure, it's not common, but I've seen it done on more than one occasion.

Watson · « **Reply #5 on:** 3 Dec 2005, 08:24 pm »

Doing what? With most power amps, you only need between 1-2Vrms for maximum output. Are you saying you've seen preamps that can't deliver 2Vrms without clipping? That would be a pretty awful preamp.

If you were trying to drive speakers or headphones with a preamp, that's a different story, of course.

ghersh · « **Reply #6 on:** 3 Dec 2005, 09:37 pm »

Quote from: Bemopti123

So, that is my answer. It is no feasible to use digital at low wattage, it is only useful at high wattage, right? But, then, what about the pristinness of the digital sound quality, wouldn't that be worth the effort?

If biasing in Class A at such a low wattage makes digital amplification unnecessary, what about preamplifiers that use tubes? They do spend more energy than SS, and yet, they seem to be the standard setters. I am wondering what manufacturers into doing one and skipping another method of design.

Pristiness of the digital sound quality? I don't think we are there yet. Class D has its own share of distortions, though the nature of distortions is different from either solid state or tube based amplification. (either A or A/B).

DVV · « **Reply #7 on:** 3 Dec 2005, 11:48 pm »

Quote from: Bemopti123

So, that is my answer. It is no feasible to use digital at low wattage, it is only useful at high wattage, right? But, then, what about the pristinness of the digital sound quality, wouldn't that be worth the effort?

Why would you want to run preamps in digital mode in the first place? What is there to be gained by running them in digital mode? After all, class D amps are run in digital mode for the sake of cheap power only thus far, although there are some which are very good, and despite the fact that they are the future. But a future is something that has yet to come.

Quote

If biasing in Class A at such a low wattage makes digital amplification unnecessary, what about preamplifiers that use tubes? They do spend more energy than SS, and yet, they seem to be the standard setters. I am wondering what manufacturers into doing one and skipping another method of design.

"Seem to be" is right. Just because something uses tubes or SS or whatever, does not automatically turn it into a standard. Most of any technology is mediocre, only a few truly shine - much like with most other industrial products. Some tube preamps are really great, but so are some SS preamps.

Spending of energy as such is not a measure of anything, really. I could show you very expensive preamps with tubes, wasting a lot of energy, but delivering only so-so sound - just as I could show you a few SS preamps sounding very good indeed with far less energy wasted.

Point is, you can't use any one single criteria to pass judgment on even a single type of product, much less an entire technology. And the other point is, money is what it's all about in the industry; if they discovered tomorrow that yoghurt makes a great basis for a power amp, you'd have your first samples of yughurt power amp the after tomorrow.

Cheers,
DVV

Dan Driscoll · « **Reply #8 on:** 4 Dec 2005, 05:15 pm »

Quote from: Bemopti123

So, that is my answer. It is no feasible to use digital at low wattage, it is only useful at high wattage, right? But, then, what about the pristinness of the digital sound quality, wouldn't that be worth the effort?

Not everyone accepts the premise that class D digital sound quality, particularly with low level signals, is better than analog class A. In fact, I think most audio enthusists and audiophiles would reject the idea.

Quote from: Bemopti123

If biasing in Class A at such a low wattage makes digital amplification unnecessary, what about preamplifiers that use tubes? They do spend more energy than SS, and yet, they seem to be the standard setters. I am wondering what manufacturers into doing one and skipping another method of design.

It isn't so much the low power usage that makes digital amps attractive, as the lack of waste heat. Class A power amplifiers give off tremendous amounts of waste heat, requiring large heatsinks, losts of ventilation and serious consideration WRT placement. To a lesser extent, class A/B power amps have the same issues. Resolving thses problems cost money. Class D digital amps don't have any of those problems and consequently, cost a lot less on a per watt basis. But in a preamplifier the amount of energy required and waste heat generated is so much less than what is necessary for a power amp that the issue of energy usage and heat generation really isn't a significant factor.

BTW, a good quality class A or class A/B power amp still sounds better than the best class D digital amps, IMO.