Newbie here. I'm upgrading a rack-o-parasound gear from 1999 to a new Integra 9.8 (yes - actually have one!) and need to pair up am amp. I read the other posts from HTBloggingGuy (and others) re his noise issues with the 7700, and his option to stick with a B&K. I like the B & K too, but Edward almost has me convinced to get a 7700 (cheaper, even considering shipping to AK).

My internet research on amps, however, leaves me with a bunch of questions about amp classes. I've read the Wickapedia explaination of different amplifier classes (A, A/B, D, G, H). My basic understanding is that A and A/B "traditional" amps are not very efficient and run hot, but most forums (AVS, HTSpot, Polk, etc.) conclude they are pretty much the best preformers overall if you can handle the heat and the weight. Not sure I agree, but all I've every used is a Parasound HCA 806 class A/B six channel.

The "hybrid" designs, like the 7700, use different kinds of technology that I don't understand (something to do with rail switching and a bunch of microfarads), and I don't think I need to. I know there are some very bright electrical engineers on these posts who may be able to distill this into 5th grade english for us idiots.

Anyway, seems like most people are happy with the 7700, so I assume the hybrid amps perform well, but I'd still like to know if anyone has switched from a class A-A/B amp to a hybrid, and if they notice a difference.

Thanks for any info!

The model 7700 is a traditional class A/B liner design. This type will yield better sound quality than any of the other classes except for class "A" types which are very rare and expensive (and extremely inefficient).

Class "G" is a rail switching type which uses a lower power supply rail up to a pre-determined output, then switches to a higher voltage set of rails. This switching is never perfect, but the point of switching is usually placed at a high enough level that is is inaudible over the signal.

Class "D" amplifiers are digital - technically they use pulse width modulation. They are very efficient, but there are several problems with this type of amplifier, not the least of which is a high amount of ultrasonic clocking signal which cannot be filtered from the output.

The Outlaw amps are extremely well made - Buying the 7700 is a real no-brainer of a choice.

Class D amps are just a different type of switching amp and are not digital amps...this is a misnomer.

http://en.wikipedia.org/wiki/Electronic_amplifier#Class_D

The 7700 is not a hybrid design at all but is a full differential A/B amp.

For the most part, I agree that it is well made, unfortunately I think they made some compromises to the power supply section of the amp that result in unwanted issues in some instances as has been noted in my review.

Personally, if you like the B&K, I'd stick with that unless the difference in price is large (>$500). You should be able to find them for at least $2250 if not lower.

Uh....pulse width modulation IS a form of digital processing. "Digital" encompasses more than just PCM, Sigma-Delta modulation or other variants. "Switching" by it's very nature is one of several digital processes.

I'd love to hear more about these "unwanted issues" about the power supply. I'm pretty familiar with the circuitry of that amp.

BloggingITGuy had an unfortunate problem with the 7700 that he couldn't resolve. There are lots of us who have them (with no issues) and love them.

Here's a great article on class d http://sound.westhost.com/articles/pwm.htm

Unwanted issues being things like transformer noise loud enough that you can hear the transformers humming from 7-8 feet away from the amp.

The B&K 200.7 does not suffer from this problem at least not in my experience. They chose to compromise on amount of heat sinks instead. Both amps sounded about the same to my ears.

The Outlaw probably has more actual power, although I only say this since I had to adjust each channel down about 7db, which might just be a factor of sensitivity of the inputs on the 7700.

Home theater amplifiers today are designed to have as close to 28dB of voltage gain as possible (this is also the THX target gain). I know for a fact that the Outlaw amps hit this target pretty closely. What you experienced is more of a case of the B&K amp being around 7dB more sensitive than is standard. An amplifier having more or less gain is neither good nor bad, but the target is 28dB for compatibility's sake.

Toroid transformers in general will hum when fed 120 volts AC that has high amounts of harmonic distortion on the line. The 2nd harmonic distortion is especially bad in this respect because it is non-symmetrical, and as a result causes a DC shift on the AC waveform which, if bad enough, can saturate the core. At the very least, DC on the core eats up the capacity of the transformer to supply the required current.

Fed clean AC, a transformer will not buzz or hum.

Unfortunately, commonly available power conditioners and filters will do nothing to eliminate distortion on the AC line. To do that, you need to use a power regenerator, which is expensive and in any case, not recommended to use with a heavy load such as a power amplifier.

Perhaps you should read my blog post on the subject to get up to speed on what I went through: http://itmanager.blogs.com/notes/2007/12/200-watt-home-t.html

Please note that my experiences are based on direct, repeatable observations of two separate Outlaw 7700 amps, 2 separate B&K amps and my old Kenwood amp. Out of those, only the Outlaw had the problem of the humming transformers that could be heard from my listening position.

I'd also be willing to bet $5500 that the Integra Research RDA-7.1, a very similarly designed amp to the 7700 would not have the same issue in my home.

As it stands, I can only recommend the 7700 to two kinds of people...those who can't get a similar or better amp for around the same price, or those who need an amp they can put into an enclosed rack.

All others would be better off, in my opinion, going with a different product.

For what it is worth, I've watched the 7700/7500 forum since it was set up in 2005 or so (before I even got my 7500) and have not seen transformer hum as a common malady. Like several others, I have placed my ear against my 7500 and not heard anything. I can't explain why both amps' transformers reacted adversely to your installation, but I hardly consider it endemic to the design.

I don't doubt your experiences. Some transformers are more prone to being influenced by high AC line distortion than others. I _do_ know however that the transformers in the 7700/7500 are not built to any lower of a standard than those from any other manufacturer - there were no "compromises" involved in it's manufacture for cost reasons.

I'm also quite sure that if you placed distortion analysis equipment on your AC line, you'd see that you have abnormally high amounts of harmonic distortion in your location. This mainly comes from the pole step-down transformers, and is aggravated by heavy loads from people who share that transformer or ones upstream.

If it was such a universal problem, everybody would have the exact same experience, even those with clean AC service. The fact that the problem is as scarce as it is and that there are many who don't have this problem, points to the quality of your AC line.

The B&K amp you have is simply more tolerant of line distortion, nothing more.