More text from the expert
"The amplifier is not designed for a load of 4 ohms.
A possible revision of the DH-120 and the test results are shown in the following figures.
It is important to reduce the resistance of the volume control potentiometer.
The output inductance is reduced to 0.2 µH.
Turn on after revision through a 60 W incandescent bulb, and only after making sure of stable operation, you can start testing.
If you measure THD with Audoprecision, you are unlikely to find changes.
Changes, I hope, you will hear on the musical signals."
"The most obvious difference in the operation of the two variants of amplifiers is visible when measuring distortion on the same scale.
Changes are circled in red circles."
small explanations.
“Slew” distortion is nothing more than the loss of micro-level HF information in an audio signal.
The main reason for this process is the signal propagation delay (time Propagation Delay) through the amplifying path. Amplifiers with negative feedback are in the worst position, since the delayed signal returns to the input at the summation point and introduces additional distortion.
As an analogy with this type of distortion, we can imagine the following process:
- we take mineral water rich in minerals and having a characteristic smell and taste;
- we divide the water in half and subject one half to the distillation process;
- then we compare distilled water and mineral water in taste and smell.
Approximately the same thing happens in amplifiers, when, as a result of the loss of microinformation, the sound becomes sterile, but “dead”
Initially, the distortion spectrum was measured on the 4th period (I note that we listen to music starting from the first period, whether it is a drum hit, a piano key or a cymbal).
The latest versions of the program do not allow you to measure distortion at earlier periods where distortion is maximum, as it was before the 9th version of the Micro Cap program inclusive.
And here is the result of testing in steady state. As you can see in the steady state, both circuit options have the same parameters (this is what Aduoprecision will show).
