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4. The sonic impact of the regulator device is less than if
the device was used as the actual amplifier. This is
probably due to the regulator device being one level
away from the amplifier action.
5. The source impedance of a regulator should be fairly
constant over the audio range. An example of problems
in this area is that the common three-terminal
regulators (7805, LM317, etc.) often have odd reactive
peaks in their source impedance just above the audio
range.
The sonic effect of regulators, as with other components in an audio system, is an area that needs more research and careful listening. When effects are repeatedly noticed, it is time to analyze the situation and pin-down the physical reason for the sonic impact of the circuit.
Economic and Practical Tradeoffs
in Regulator Design
If there were only economic tradeoffs in regulator design and everyone were rich, every amplifier would have dozens of near perfect regulators. However, even this ideal situation would have problems: reliability, size, heat, and complexity. So keeping a design simple for cost reasons has other tangible benefits if not overdone. Here are some of the guidelines for regulator design:
1. Choose between predictable and unpredictable
failure. At the voltages used in tube circuits,
semiconductors are especially prone to transient
damage and burn-out. Careful use of protective devices
helps, but sometimes using a tube (for example, as a
pass element) can be more rugged and reliable than a
transistor, despite the occasional and predicable need
for replacement.
2. Use devices appropriate for the voltages and currents
needed. Tubes work well when there is at least 25 volts
or more across them and can handle kilovolts or more.
Depending on the type, up to a fraction of an ampere
can be handled. Transistors and MOSFETs can handle
many amperes at low voltages (as low a volt or two)
and can handle up to 600-1000 volts at less current.
Their overload and over-voltage capabilities are poor,
though.
3. Use available devices. Due to the limited number of
tubes available and the somewhat lower impact of
regulator devices on the sound, it makes sense to use
commonly available types or some of the vast amount
of TV and odd-ball industrial tubes languishing in
warehouses.
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