Casouza - yes, transformer should be oversized since mentioned current spikes, while driving recifier/capacitors, heat up the windings (RMS much higher than Average) and their high frequency content heats up the core but 10x is perhaps overkill. Imagine 40% efficient class AB 200W amp with 5kW transformer. Large amount of capacitors is beneficial providing better filtering but when you think of it - linear power supply is really a bad case of SMPS working at 120Hz. SMPS working at 100kHz will do the same with 10x smaller toroidal transformer, is line and load regulated and is quiet since higher frequency is easier to filter out, non-audible and switching is done (in modern SMPS) in zero voltage/zero current. For that reason Jeff Rowland uses SMPS in Capri preamp (where efficiency is not important). SMPS got such bad rap from cheap ones used in computers that people don't want them even for class D amps (that are SMPS) and designers do what sells.
Preamps need some oversizing perhaps 2x-3x to cover losses related to operation with rectifier and losses in voltage regulators that have to work in 90-132V mains range. Filtering here is done mostly by the regulators and current is pretty much constant (class A) with transitional current supplied from local caps.
Benchmark DAC1 supply is not an overkill - it takes from mains "16W peak" of average power but because of mentioned much higher RMS value of current spikes it needs to be about 32W and it looks like 30W toroidal transformer to me. It is toroidal because outside field of evenly woven toroidal transformer is zero and Benchmark achieves measured 140dB S/N.
You are right about power supply caps being in series with the speaker. People don't realize how important supply caps are. Cheap caps not only have high ESR "eating out" dynamics that amp could provide but also have high inductance filtering out fast transitions. Placing film caps in parallel is a band-aid and often a bad one since pure capacitance in parallel to main caps inductance creates parallel resonant circuit that rings (cap is in series with the speaker). There are low inductance caps (like slit foil caps) but very expensive. I would rather go with fast responding SMPS and that's what Jeff Rowland did (AFAIK) in latest high power class AB amps.
Preamps need some oversizing perhaps 2x-3x to cover losses related to operation with rectifier and losses in voltage regulators that have to work in 90-132V mains range. Filtering here is done mostly by the regulators and current is pretty much constant (class A) with transitional current supplied from local caps.
Benchmark DAC1 supply is not an overkill - it takes from mains "16W peak" of average power but because of mentioned much higher RMS value of current spikes it needs to be about 32W and it looks like 30W toroidal transformer to me. It is toroidal because outside field of evenly woven toroidal transformer is zero and Benchmark achieves measured 140dB S/N.
You are right about power supply caps being in series with the speaker. People don't realize how important supply caps are. Cheap caps not only have high ESR "eating out" dynamics that amp could provide but also have high inductance filtering out fast transitions. Placing film caps in parallel is a band-aid and often a bad one since pure capacitance in parallel to main caps inductance creates parallel resonant circuit that rings (cap is in series with the speaker). There are low inductance caps (like slit foil caps) but very expensive. I would rather go with fast responding SMPS and that's what Jeff Rowland did (AFAIK) in latest high power class AB amps.