2. amps-preamps
  3. 1260904595

Can someone give me an explaination re: power amp.

So, I own a simaudio i-5 driving paradigm studio 60 v.3, and I am not happy with the sound at low volume. turn it up everything is great, but low volume has muffled sound. Everyone says the paradigms are efficient, but i go out looking for more efficient speakers, and happen to come home with a loaner power amp- a simaudio w-3 (125 wpc), and the sound at low volume sounds markedly better with the power amp. this is contrary to everything i have convinced myself to believe. i have convinced myself that a good integrated is all i need, but I cannot deny the sound. so instead of asking the age old separates vs. integrated question, i'm just going to ask- why does my system sound so much better at LOW volume with the power amp. Maybe the speakers aren't as efficient as I thought? Maybe the 70 wpc simaudio i-5 isn't as great a machine as i thought? maybe there's a technical explaination? Please enlighten me! and thanks, and merry christmas to all you audiophiles out there! (oh, and the reason I didn't come home with speakers is that i really love the full range of sound from the towers, and i couldn't find any highly efficient speaker that had the range I enjoy. not that it dosen't exist, but i just couldn't find it. I live in portland, oregon).
blazerfan
kijanki's avatar
kijanki
4,428 posts
 
Bob - It might be THD +S/N or some nonlinearities of output transistors in spite of feedback (there is no perfect regulator). I don't know if THD can be measured without noise. Traditional THD meter deliveres pure sinewave to the input and subtracts same sinewave from the (scaled) output measuring what left - harmonics + noise. THD + noise levels are really small - 1/100 of percent = 1/10000 (-60dB) of very small signal (0.1W). It is equivalent to about 1uV at the input. Tube amps, I looked at, had higher THD to start with, so this effect is probably hidden.
su27
1 posts
 
If you're after efficient speakers, try the Auditorium series speakers from Living Voice. These speakers are an easy load for amplifiers to drive; sound great at low volumes as well as at higher volumes.
atmasphere's avatar
atmasphere
11,784 posts
 
Kijanki, some tube amps will make higher distortion at very low power levels just like transistors. Others (SETs for example) the distortion becomes unmeasurable.

Feedback is appearing more and more to be a poor means of ridding audio circuits of distortion. An amplifier that might not have had much beyond the 5th or 6th harmonic will suddenly have harmonics beyond the 81st when feedback is applied.

Much depends on propagation delay and how effective the circuit was as an amplifier before the feedback was applied.
kijanki's avatar
kijanki
4,428 posts
 
Atmasphere

I agree - feedback is evil. It is less of a problem in class A amps since gains before feedback are as low as 200 but it might be big problem with class AB where gains before feedback are in order of 4000.

In class AB with most linear components available I would probably get 10% percent of THD without feedback. I would apply only enough feedbacks (avoiding global one)to bring THD down to about 0.5%. To eliminate TIM I would limit bandwidth at the input to one that amp had before feedback was applied. Low bandwidth, high THD amp might not interest too many people.
More to discover