Hello!
For me the FET transistors are not good enough, because their characteristics are non-linear. Definitely the tubes are much better. But the tubes are expensive, not mobile and require dangerously high operating voltages. In addition the output transformer ruins the sound.
I would like a robust amplifier with no tendency to oscillate. I often work in rooms that are heavily "contaminated" with electromagnetic fields. Therefore, the use of global negative feedback loop is out of the question.
After much deliberation I designed the following simple amplifier. And its sound surprised me...
For me the FET transistors are not good enough, because their characteristics are non-linear. Definitely the tubes are much better. But the tubes are expensive, not mobile and require dangerously high operating voltages. In addition the output transformer ruins the sound.
I would like a robust amplifier with no tendency to oscillate. I often work in rooms that are heavily "contaminated" with electromagnetic fields. Therefore, the use of global negative feedback loop is out of the question.
After much deliberation I designed the following simple amplifier. And its sound surprised me...
You have no choice but to buy 50 different ones and listen. Of the 50, as always, 5 will remain that are suitable for audio.
And also: the smaller the types, the higher the sonic potential. It is the diameter, body, material, mass stiffness and more that influence the sound (all sort of "noise") more than THD, TMD...-)
And also: the smaller the types, the higher the sonic potential. It is the diameter, body, material, mass stiffness and more that influence the sound (all sort of "noise") more than THD, TMD...-)
Yes, they are good, but TO-220 is difficult to cool. So I suggest MJ15024 and MJ15025 in TO-3 for 19V.
I intentionally don't overload the power transistors. They operate in the relatively linear area. THD is just a few %. Above all, it is about 2nd harmonics. The rest only appears when the overdrive occurs.
BJTs are much much less linear than anything else, they have an exponential characteristic!! However they have supremely high transconductance which can be traded for linearity with local feedback effectively.
EMI is nothing to do with loop-stability. To address EMI you need to screen and filter out the interference, put everything in a Faraday cage and think about feedthrough capacitors and ferrite toroids. GNFB is not ruled out in the slightest.
BTW FETs are much better at evading EMI than bipolar transistors and sound like they might the correct choice for this environment.
Only if voltage driven. But BJT can be quite linear if current driven like in this amp.
With idle/quiescent temperature, power FET's actually have a 'negative temperature coefficient' regarding
bias current > thereby being effectively self regulating without the need for 'thermal sensing feedback'.
Also, if you compare the distortion characteristics of BIPOLAR vs FET amplifiers driven into overload-clipping,
the Bipolar = predominant odd-order harmonics (not musical), and the FET = predominant even-order harmonics
which are 'musical'.
It is my personal opinion that people use higher power amplifiers offering the user superior headroom and
the use of multiple output devices, thereby achieving much lower output impedance & higher current capacity.
The high output impedance shifted the speaker's crossover points. Every speaker will sound different.
Ed