I noticed that ceratin solid state amps have "toroidal"" transformers in their power supplies ,which look like a donut of wire. For example, my ABN Evo II 500 has them and I think certain of the Mark Bass amps have them too. In their literature , Mark Bass credits the availability of high quality torroidal transformers as one of the items that has enabled these compact amps to handle the low frequencies better . They add some weight to the amp, but I was wondering if amps that have these types of transformers are superior in producing the lower frequencies and transient responses , etc. These transformers are used in different classes of amps , including for example Class AB ( Evo II) and Class D (MB F500) , but other Class D designs do not use them.