JD: People can believe whatever and whomever they want to believe. All we can do here is share opinions and ideas while trying to learn from one another.
Having said that, most of the Bryston amps are not real strong performers into lower impedances. We have discussed this in the forums here before on more than one occassion.
As most know, these are SS amps with low output impedances and relatively robust output stages. As such, the only reason that this could be so would be due to the limited current capacity of the power supply. Since the power supply starts at the transformer, one should be able to draw logical conclusions as to what is going on here.
Clio09: The higher the capacitance of a power transformer, the more coupling there is between the primary side of the transformer and that of the secondary. As such, the greater the capacitance, the less isolation the transformer can offer. In such a case, a higher percentage of line noise is allowed to enter into the circuitry with a higher capacitance transformer as compared to a lower capacitance transformer.
As a general rule, toroids are typically much higher in capacitance than a well designed EI. This makes them less suitable for isolation purposes, as i previously stated. On the other hand, EI transformers are typically more lossy as frequency climbs, making them less suitable for wide bandwidth circuits. As such, a well designed tubed amp might make use of an EI in the power supply and toroidals as output transformers. This should achieve the best of both worlds i.e. lower noise floor with wider bandwidth / better transient response. Sean
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