new amp vs old amp

i bought a acurus a150,i also have a dynaco st120,very different amps!one circa 1970 the other 1990'ish.ive done brief a/b testing,swapping them back and problem,i hear very little difference.why?do i need to listen longer?ive always though i had a good ear,i can here light notes and quiet backround instruments in music that most people cant!!!whats wrong
Sometimes if you using cheap interconnects such as a lamp cord you will have a problem telling a diffrence. Maybe you need to get a better amp to hear a diffrence (no offense) Maybe they are equal in quality and also share the same characteristics as one another?
Not to belittle your purchase, but i can believe that there might not be a drastic difference between your old "Dyna" and the Acurus. Many of the old Dynaco products were "overachievers" in terms of price and age. If the Dyna was a current product, it is quite possible that it would cost at least as much or more than the Acurus that you've mentioned.

With that in mind, i've noticed that a piece that is WAY better than the old piece can be "held down" or limited in performance by the other components in the system if they are not up to snuff. In other words, the old adage "only as strong as the weakest link" still applies. As such, buying new gear to replace old gear might not seem like a step forward for a few reasons. Any / all of these MIGHT apply to your system.

(1) Synergy. The "old" combination may have actually worked quite well together. Just because it might not be "the latest & greatest" does not mean that it isn't capable of quite respectable performance.

(2) The new component does not compliment what you already have. In effect, it MIGHT be a better component but just isn't "right" for that specific system. As hard as it might be for some to swallow, the new component seems like a step backward.

(3) You are used to hearing things a certain way. If the new component sounds "different" this can be percieved as "better" or "worse" depending on one's mood or personal tastes.

(4) It is possible that there are little to no differences between specific components. As such, this sometimes takes time to become familiar with them or notice their strengths and weaknesses.

(5) The component that you replaced was NOT the "bottleneck" in the system. As such, ANY component that you put into the system may run into a "brick wall", i.e. the component that IS limiting the sonic potential of the entire system. Until that weak link is removed, everything is limited to a "sound" or level of detail. This can result in all components sounding the same or changes making a minimal difference. You've heard of systems "not having enough resolution to tell the differences between components" ??? That's why some changes seem more like a step sideways rather than a step forward.

These are but a few things that i've encountered along the way. I'm sure that others can add to this list with a few other experiences of their own. Sean
What are your other components? I recently played around with two different amps that I owned (Aragon 8008BB & Pass Labs X150) It was a quick audtion in my own room with my gear. The differences were subtle in some recordings obvious in others. On these recordings even my girlfriend who really just humors my obsession in audio was able to pick out the Aragon and the Pass. She did it over and over again! So I think as the post above say it really depends on many things such as your system, the quality of the recording, etc.
Hi Ampzilla; Sean has a good list of possibilities above. One I would add is becoming very, very familiar with a particulat recording with one of the amps. I mean get so familiar that you are almost sick of it-- then put in the other amp and see what you think. If the music still sounds the same, I would guess there is a weak link somewhere else in your system.

At some point you need to become totally confident in your hearing and hearing perception(s), ie maybe they really do sound the same. Although I would guess that there should at least be a difference in bass character/quality. Good Luck. Craig.
I'd like to share my expierences in changing audio pieces or cables. This may seem strange but I've run across this many times. On occasion when auditioning a different piece of gear or cable I would hear either subtle or no difference. But when I would put the original piece or cable back in my system is when I would realize the different characteristics of the piece or cable that I had taken out of the system. This may not seem to make any sense but for me it has become part of my auditioning pratice. Perhaps I don't have the golden ears others have, or I wish I had. ----->Ray
Ampzilla: your "brief A/B testing" makes it seem as though neither piece was warmed up thoroughly. By "thoroughly warming up" I mean powered on for at least 30 hours.
In solid state equipment it takes that long a time for the power supply regulators to attain thermal stabilization; any comparisons prior to that may be preliminary at best.
for the record the rest of my system,aside from the new and old amp!are amc cd8b,p.s audio 4.5 vandersteen model 1,and also some tannoy proto j' about to replace the p.s audio in favor of an older preamp,believe it or going to buy a thalia,well see what happens,thanks for all your helpfull advice!!!amp.
All of the suggestions above are good ones. I would like to comment on the Dynaco ST-120. It was a great amp with performance way beyond its price and time. I owned one in a second system of mine in the 70's and recommended it to my cost conscious and tube averse friends throughout the 70's.
However, sound wise you should be able to hear it showing its age. If you could borrow someones tube amp and if you still don't hear a difference I would say that you have some rather serious limitation in the rest of your system. On the otherhand, while I don't know the Acurus, maybe its not that great an amp.
Ampzilla747, Isn't the thalia preamp you are looking to get made by GAS?

I have a little experience with the brands you are comparing. I own a Dynaco 400 and have had a Aragon 8008BB in my system for a short while. The 400's front end has been modifyed by me but even with that taken into account I believe that the 8008BB was more refined. I believe the differences should be clearly audable in your system. (I use the 400 as a sub amp most of the time)

On the other hand there are several factors that could make your observations different than mine. 1) The most likely reason is that I have not heard the exact amps you have. 2) In agreement with the others, the Dynaco was a very good amp in its day, and if the capacitors were replaced (they really do age and dry out) has the potential to be very close to the Aragon. To my knowledge, transistors do not deteriorate with age and the Borbely designed Dynaco 400 is not really much different than the topology used in the Aragon 8008BB. The biggest difference is in the power supplies where a toroid is used in the 8008BB. This difference should be most audable in the bass. 3) I will chime in with everyone else and agree that there could be a bottleneck else where in the system. I have a non working PS Audio 5.0 that I could repair and give you some feedback on it in the future. I have heard PS Audio equipment at trade shows and I feel that it is reasonable stuff and well suited for the rest of your gear.

I share your desire to use older equipment. I upgrade the parts as required and I get a kick out of someone saying "That old stuff sounds that good?". I woulg really like to get an Ampzilla (and many others) after I get rich.
Feel free to email for help on repair if you want. Chris