I have an Adcom amp./pre-amp set up driving Dali speakers. I am not enough of an Audiophile to know whether this is a good combination, however, a guy working in an electronics store suggested that Adcom put out 'negative harmonics' or something like this which makes it harder for your ear to listen. He suggested that I should geta Rotel amp which is 'positive harmonics', warmer sound and easier on the ear.
Can someone explain and perhaps recommend another amplifier that will also produce a warmer sound but that is less expensive?
Can I explain something you're not sure you correctly understood? Probably not.
If the salesperson truly said "negative" and "positive" harmonics, they are on to something. They are either smoking it or they should be marketing it. I suspect the discussion was about "harmonics" and therefore the structure of the harmonic distortion product each amplifier adds to the signal. The Adcom is a straight ahead bipolar transistor amplifier which typically means its disortion components are made up of high order, odd order harmonics. To understand harmonics without a long explanation here, just place "harmonic structure" in a search engine and you should find information that will clarify "odd order" and "high order".
What the Adcom produces is a distortion component not typically found in music and certainly not in "Western" music. Some listeners find this additional harmonic structure to be "non-musical" and fatiguing. Other people don't hear the disortion component as harmful and live happily with the Adcoms and other transistor amplifiers. You should decide whether what you are hearing is unpleasant to you. You don't indicate why you were in an electronics store. If it was because you are dissatisfied with the Adcom, then maybe you are hearing some of what the salesperson mentioned.
At any rate, this seems an odd way to sell a piece of audio gear. To focus on whether an amplifier produces a seventh order harmonic component is worthless IMO. If this is a way to sell you off your existing equipment, the salesperson is doing you no favors. People buy audio equipment for a variety of reasons but seventh order harmonic content is seldom high on the list.
An amplifier producing low order, even order harmonic components will often be described as more pleasing to the ear because the structure of that distortion component is more in line with what occurs in nature. I don't know that the Rotel has a distortion component drastically different from the Adcom's. The salesperson could have simply been spouting some promotional crap from the Rotel brochures. You can do some research on Rotel to find out what the amp does and does not do if you are truly curious about Rotel.
This "low order harmonic component" is not the same as saying an amplifier with a low T.H.D. spec is good. Paradoxically, all too often low T.H.D. specs lead to high order distortion components (less like nature) and low order components (more like nature) are found when an amplifier has a higher T.H.D. spec. And sometimes this isn't true at all. The point is generally to ignore specs and most tech talk and concentrate on the music that comes through the system.
Therefore, my advice at this point would be to simply ignore specs and most talk of technical benefits or disadvantages and listen to the music alone. There are too many competing technical advantages to any technology and gaining one advantage often means you give up another. The point of any good audio component should be its ability to engage you in the musical performance. To do so the component should have an equal balance of desireable and less desireable traits. This balance becomes all the more important as the budget grows tighter. These desireable traits are then combined through a synergistic mating of components to make a system that plays to each component's strengths and minimizes each component's weaknesses. One component can wreck the synergy of a system but one component alone cannot make a synergistic system. It is up to you to determine which qualities are most important to you and which you are willing to downplay to reach your budget and still have a well balanced, synergistic system.
If the equipment has to be explained in such a manner that you will constantly be wondering if the "positive harmonics" of the system are correct, then you really haven't allowed yourself to listen to the music.
Are there better components than your Adcom when it comes to getting out of the way of the music? I would say so. The Adcom was a budget oriented product. Expand the budget and you will typically get what you pay for, i.e. better quality. Are there better components than the Adcom for less money than the Rotel? Probably not if you want to buy new components and not pre owned. You are still looking at budget gear with the Rotel. Budget gear is considered exceptional value when it manages a good job of balancing its trade offs. One advantage here displaces another disadvantage there. The Adcom and the Rotel have their own peculiar and specific distribution of advantages and disadvantages but so will any other budget oriented product.
I would suggest you listen to a few components and not be in a rush to buy anything until you're covinced it is an audible improvement over your present system. If you haven't listened to live music lately, I would also suggest you go refresh your memory to what live sounds like because all too often it doesn't sound that much like reproduced music. Find those things that make live music interesting and listen for those things when comparing audio components. When shopping for new audio gear take your Adcom with you for comparison if need be. But my real suggestion would be to stay away from anyone selling you "positive harmonics". An audio salesperson should sell music and nothing else. If you ask about the why's and how's of a component, then the salesperson should explain in terms you can understand. If you don't understand, its your job to ask questions then, not on a forum where we don't know and what was said and what you actually heard. You wouldn't buy a car without knowing whether it had an automatic or manual transimission even if you don't know how either works. But I doubt you'd buy a car simply because it has a transmission.