Quote:
It’s not just about measuring RMS, Peak and transient power consumption of the DD motor. The electronics used to control the motor will have limited supply interference rejection that will vary with frequency, getting worse as frequency increases.
This means that the power supply should have good supply line interference rejection to reduce mains interference transfer to the load circuitry and it should have very low noise. The power supply should also maintain its output voltage as close to the required voltage as possible under dynamic load current swings, as any voltage error on the power supply output will be seen as noise/interference by the motor control circuitry.
“Off the shelf” mains transformers are built to a price in a very competitive market and corners are cut in material specifications and
construction, giving less than ideal performance.
One of the biggest problems with low cost transformers is rattling laminations, which vibrate in sympathy with the current flowing through the windings, giving rise to high levels of mechanical noise and unstable electrical power transfer. The smaller ones are not too bad in this respect, and the 60 VA Toroidal transformer I use in the lower cost SR3 is the best of the “off the shelf” variety I have found and it is pretty quiet.
Unfortunately the larger transformers in the range, like all the other ranges I have tried, get very noisy, which is unacceptable in an audio system. Another problem that is relevant to transformer electrical performance is that “off the shelf” transformers are built for highest
efficiency, which means they are designed to operate at high Flux densities.
This makes them very susceptible to any DC current flow in the windings, which can be caused by switch-on when the mains voltage
waveform is at a high potential and/or asymmetrical current draw from the transformer by the load, which can cause core saturation at
relatively low levels reducing the available VA rating dramatically.
The solution to this is to have a custom-made transformer that uses high quality materials and is carefully wound for low mechanical noise and for low flux density operation to avoid core saturation, which can cause a lot of interference on the supply line. This requires using a larger core than normal for a given VA rating. The custom transformer in the SR5 is rated at 160 VA and doesn’t suffer from appreciable VA loss due to core saturation. It is also very quiet.
The voltage regulator has the job of maintaining the DC supply rail at the specified DC voltage for any load current change. For this reason the voltage regulator is usually a DC coupled AC amplifier. Important parameters for this regulator in no particular order of merit are :-
1) The transient response and settling time should be fast enough to allow the regulator to track load current changes to maintain the
output voltage at the required level.
2) The output impedance should be as low as possible over the load operating bandwidth so any load current induced output voltage changes are minimised.
3) The regulator noise should be as low as possible so this does not interfere with the load circuitry because of the finite supply line
rejection abilities of the load circuits.
4) The regulator supply line rejection should be as high as possible across as wide a bandwidth as possible to reduce the effect of mains
line interference and rectification (conversion of AC current to pulsed DC current) interference.
The Technics motor requires a clean accurate drive signal to maintain accurate platter rotation. Essentially a clean stable supply will reduce signal corruption in the motor control circuitry leading to more stable platter drive and more accurate platter rotation.
A lot of that goes over the top of my head, but I understand the gist of it. You being a more technical chap than me, of course, should be able to make better sense of it :)
