Originally Posted by Porkloin DuBois
I've read a lot about how vintage receivers of the 70's - 80's were designed with sound quality in mind whereas modern amps concentrate on features at the cost of losing sound quality. Which leads to the question: What is better about older receivers? Is it simply a matter of beefier power amplifiers, which would allow me to use the existing Denon's pre-amp outputs with a vintage power amp to get the desired overall sound?
I can't imagine that as technology moves forward, manufacturers have forgotten what they've learned developing those old receivers. Could it be that inflation has made this a "bang for the buck" issue and if I were to cough up more money, I could have a modern amplifier that would rival a vintage one? How much would I have to spend on a power amp to rival the sound of a Pioneer SX-1250?
Discrete amplifier stages are still around, most of the midrange Onkyo stuff like the Onkyo 805 is still discrete and these can be had for less than $500
The Pioneer SX-1250 is a classic Japanese design from the Mid 70s
It shows the compromises and constraints of the semiconductor devices available at that time.
I assume you have basic familiarity with electronic schematics, notice that a triple darlington configuration is used in the final stage,
these circuits are not very linear and the designers have tried to compensate by increasing the gain and then applying lots of negative feedback, my estimate the feedback factor is about 20%
The downside is a reduction in the transient response performance and intermodulation distortion.
The 2SB600 output device is quite slow by today's standards (4MHz fTvs 30MHz in today's audio devices), the designers have had to apply additional compensation to keep the amp stable (C3,C7,C5,C9,C10 Miller Pole/Zero compensation), this worsens IMD
The amp basically has a lot of open loop gain and the design trades this gain off by applying large amounts of negative feedback, the open loop frequency response is also likely less than 20kHz and extending the closed loop bandwitdh to 20kHz by applying negative feedback.
The modern approach is to design design with a much wider open loop bandwidth and apply small amounts of negative feedback, on the Onkyo 805 the feedback factor is 3% vs 20% of the vintage Pioneer.
This is possible today because the output devices are much faster and designers do not have to resort to things like the triple darlington and its linearity problems
The 2SC5242 output transistor used in the Onkyo 805 has fT of 30MHz vs 4 MHz of the vintage Pioneer.
(fT, is the frequency where the current gain of the transistor is 1, to do useful work in a power amp this needs to be around 100 or more and the operating frequency falls with gain according to a specific formula, the gain bandwidth product)
You might want to take a close look at today's discrete designs from Onkyo and similar manufacturersEdited by Tong Chia - 1/2/14 at 4:28am