External SMPS supply

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I know this has probably been argued before but I'm wondering where everyone sits on the internal vs external power supply issue.

I have a number of mini-amps that use external SMPS bricks, like laptop chargers but at 24v 4+ amps. I gotta say they sound pretty good...

I recently came across one with an internal analog supply and it sounded pretty good too... But it had a bit of AC hum that I've never heard from a Class D amp before.

Considering a new project, so I'm wondering what others may recommend...
Internal vs External .... SMPS vs Analog
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Internal is the most handy as you only have to worry about one mechanical unit. Internal can leave some coupling of noise from the power supply to the amplifier if you are not careful. Internal means that the power supply is dedicated to that amplifier and cannot easily be used with another amplifiers.

External has little risk of radiated noise from the external power supply to the amplifier. It is sometimes unhandy with two separate units in handling. Due to the longer physical distance between power supply and amplifier the buffer capacitors (power line decoupling) have to be correctly distributed between the power supply and the amplifier. An important convenience with "external" is that you can quickly use a power supply with another amplifier if needed. As long as you can use a kind of standard power adapter, external is often the cheapest.

SMPS vs analog is a long discussion that actually involves four types: regulated SMPS (very common), unregulated SMPS (rare), unregulated "analog" (with a net-transformer - very common) and regulated "analog" (typically based on a net-transformer but may be downstream of an SMPS - more expensive and therefore less common).
For continental Europe, the time has passed midnight so I will not elaborate on the advantages and disadvantages for each option right now. There are strong defenders of each type of solution so you can look forward to a good and slightly heated discussion.
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To my surprise nobody has given their opinion on "SMPS vs analog". I will then state my personal opinion.

SMPS - regulated: Main benefit is low power-loss (heating). As SMPS are often produced in large numbers for general purpose use, they are often very cheap for the power capacity and actual design complexity. Most include regulation features inherent in the design such that they are delivered "complete". On the more problematic side, the regulation features may not be well suited for audio power amplifiers due to SMPS design for general purpose use. For some, modification can help significantly. SMPS are quite complex of nature and if poorly designed, they may be quite unreliable or poor performing. If they are designed well, they are fully reliable. SMPS may radiate noise and they have inherent output ripple to take into account, if not equipped with post analog regulators. They are difficult to modify for very different performance due to the complexity and individual components in the design, such as the power transformer. Fault finding can be difficult.

SMPS - unregulated: Offer some particular power conversion advantages such as very low power losses (resonant converters) or high power conversion density (such as for push-pull converters). Not all SMPS configurations offer the possibility of regulation and if not equipped with post regulation, the output impedance is somewhat high compared to regulated designs.

Analog - unregulated: Typically based on a net-transformer, they are simple in design and if few design rules are complied with they are very reliable and rather easy to design for individual needs. Without regulation facilities, they have a higher output impedance and no overload protection features in case of trouble. They can deliver good current bursts but eventually with some voltage sagging in return. Due to the transformer and well sized energy storage capacitors, they are quite heavy and bulky. Fault finding is easy.

Analog - regulated. The regulation system does not include separation from primary power or rough voltage adaptation of the power from the net. Therefore, analog regulation systems are "add-on"s to rough power converters providing isolation to the net. Analog power regulation offers, in my view, the best dynamic load response and lowest output noise. They are easy to design for individual purposes, with or without protection features included. The power loss (heating), which can be considerable, is the main drawback. They are increasingly rare for power amplifier use because the power supply rejection ratio (PSRR) of the power amplifiers normally is sufficient to handle unregulated power supplies. They allow for use of amplifier circuits with a strict supply voltage limit (such as the TPA3116/18) to be used close below that supply voltage limit as the output voltage is pretty constant. With present regulator ICs, they can be cheap to include and they are very frequently used for low power delicate circuits like DACs and pre-amplifiers where the current demands are moderate.
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One more beneifit of using external SMPS ... in a power amplifier it lets you put the output stage on a regulated DC source, which I think greatly improves the sound quality.

Simple experiment... take an old school audio amp, hook one channel to a dummy load and the other to a speaker. Now feed the channel with the dummy load a fairly strong music signal... what do you hear from the speaker?

Not to say that I'm 100% sold on external SMPS... still trying to figure that out...
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