So what do you think of Class D amp for subwoofers

Kijanki - switching noise is typically defined as clock noise in this digital world we live in. Although it is technically correct to say "switching noise" when a diode turns on and off, that noise is insignificant to clock noise on the output of a Class D amp. It is incorrect to say a Class AB linear output stage produce switching noise when moving from positive to negative or back. If it produced switching noise, it wouldn't be linear by definition.

I will have to check to see what Class D noise curves I have left over from when I worked at Maxim. I know I have some white papers showing some noise at 15 KHz.

It really is amazing how much noise there is in the output of a Class D amp. Unless you have a filter on the output, you will have noise, there is no question of it. The only question is at what frequency ranges the noise will peak.

The filters in question here are hardly zorbel networks, although they would help a bit. The filters i have seen in use are usually 3 or 4 poles and are rather aggressive, high Q passive networks.

Depending on the amp, you may or may not have audible noise at 15K Hz. As I mentioned above, comparing the inexpensive Maxim chip to an audiophile piece of gear such as your Rowland is just not comparing apples to apples. Frankly, if your Rowland produced audible switching noise at 15KHz, I would send it in for repair. Just understand that noise at 60 db down will impact the sound, you just won't hear it as noise. My personal belief, based on designing a lot of audio amplifiers, is anything above 140 dBV inside a linear amplifier with some loop feedback will impact the sound in a negative way to some degree.

You don't need a quarter wave antenna to jam the airwaves so that FM broadcast won't get through. I suspect the noise problem I have is more harmonically related than fundamental related. A 1/4 wave antenna at FM frequencies is on the order of a few feet, depending on the propagation velocity of the wire.

Also, my Class D amp is only 10 feet from the tuner and maybe 3 feet from the antenna. The FM broadcast antenna is miles from here. Granted, the broadcast antenna is in kilowatts and the amp is not, but the energy from both decreases as a square of the distance. The amp may not produce as much energy as the broadcast antenna, but here in my living room I wouldn't bet any money on which produced more signal in the antenna.

I don't know if you live near me but a few seconds of having this Class D amp powered on with FM will convince you there is a serious radiated or perhaps conducted noise problem here. As I write this, I have the FM radio on, but the subs are not powered on!

What I do find really encouraging about all of this are the number of folks who are really happy with their Class D amps. If everyone here was telling me I have a problem simply because I was dumb enough to buy a Class D amp, I wouldn't bother to try and fix this problem.

Just a thought but -- have you tried a different tuner? I used the Sangean HD-Radio tuner with three class D amps in very close proximity and had no problems picking up even very weak stations. In fact, if you want to try it, I'll sell you mine super cheap -- space considerations and a system relocation forced me to switch to a Pro-Ject tuner box (whichb also works fine in reasonbly close proximity to a different set of Class D amps.

Spatialking - yes your FM antenna is miles away but the output LC filter of class D amp is set to about 60kHz and at, for instance, 60MHz has very very high rejection.
(and 60MHz harmonic of 60kHz is a very small fraction to start with).

Also FM transmitter, as you mentioned, has kilowatts and not watts.

Carrier frequency, or rather 1% of it that gets out, is not audible (unless one can hear 500kHz) and cannot even create intermodulation on nonlinearities on the tweeter since its membrane won't move at 500kHz at all.

Jeff Rowland made many preamps using batteries in power supply. One of his newest creations (with extremely fast op-amps) Capri - praised for great sweet airy sound has switching power supply. High frequency noise is easy to filter out. The noise I was talking about was not the output noise in class AB amp but power supply current spikes it creates (not so easy to filter out).

It is possible that your class D amp is simply faulty or poorly designed.

It is amazing to me that many people (not you) wouldn't consider class D even for subwoofer but never heard one.

If class D is not good enough even for subwoofer please read fragment of the review of the Cabasse La Sphere 5200W (fifty two hundred watts) Icepower class D system by John Atkinson (Stereophile):

"In terms of organizational skills, timing and phase coherence, and timbral and textural accuracy, Cabasse's La Sphère system sets new sonic standards. Its reproduction of the piano and the human voice is light-years ahead of anything else in my experience. Its ability to produce solid, three-dimensional images on a stable, remarkably well-organized soundstage also beats anything I have ever experienced anywhere, and by a considerable margin. And in terms of textural solidity, harmonic structure, overall control, and low-end extension, its bass performance is similarly unprecedented."

Its been said many times before...its not the class of the amp, its the implementation. We shouldn't compare cheap SS designs with the best SS, nor cheap tube designs with the best, nor cheap early renditions of Class D with the best. Class D was known for its radio interference in its early days. New designs like my Bel Canto are light-years ahead in design. As time marches on, amps designs will continue to improve. Tube has the longest history, SS next, and now Class D. No doubt there will be superb designs of Class D, and new classes of amps in the future, as long as people will buy them. As ong as the amps are working for you, be content. If you upgrade to newer and costlier designs you will hear the difference.

Thank you Grisham, you beat me to the punch! In answer to Bob_reynolds, there are some problems in citing the D-100 review to prove that switching amps are inherently problematic.

1. The review is of a moderately priced amplifier deliberately engineered to meet an affordable price point. D-100 was not intended to redefine the absolute state of the art in monoblock amplification such as Spectron monoblocks, JRDG 312 and 301, Mark levinson No. 54 (hope I got this model correctly).

2. The article is obsolete. It was published in August 2005, probably written about 6 months earlier. . . essentially it is 4 years old, which is a lifetime ago when it comes to the significant strides that the rapidly evolving class D designs are making.

3. From a symbolic logic point of view, the induction step according to which 1 tested amp of a given class having been found to have a flaw, all amps of the same class bear of necessity the same flaw is, . . well. . . flawed itself.

G.