Hi FM,
Correct we were able to increase the performance if bridging the 3B and the 4B while as you say the 7B, 28B and 14B are already series designs.
Correct the series mode gives more Voltage swing and less current whereas the Parallel mode gives more current and less voltage swing. Contrary to popular belief most speakers (4-8 ohms) perform better with high Voltage swing so we rarely sell a Parallel version.
james
Thank you James!
Correct me if I'm wrong, but besides the superior loudness capability of the Series mode due to a higher Voltage swing, wouldn't an amp in Parallel mode offer a better control of the speaker by having a lower output impedance and higher current delivery, thus a higher damping factor, which will make it more stable driving a complex load?
Out of curiosity, could you give the specifications of the 28B wired in Parallel (W/V/Amperes) to see how it compares to the Series model?
Hi,
While in theory it looks like a parallel amp would have half the output impedance of a single-ended amplifier and thus better control of the speaker cone, in practice a couple of things get in the way of that theory. One is that the speaker cable generally limits the total damping factor of the setup, so increasing it at the amp doesn't result in as much difference as you might expect. The second is that solid-state amplifiers cannot be paralleled without inserting a small ballast resistance between the modules' outputs to prevent excessive circulating current in the output stages. In the case of a 7B SST2, this resistance would be 0.1 Ohms, center-tapped to the output terminal. That results in a net increase of 0.025 Ohms in the output impedance, which is somewhat more than the net overall decrease in output impedance from the paralleling operation. Thus, the damping factor of a paralleled amplifier is 300, slightly lower than the 500 rating on either a single-ended or series-operated amplifier. (Note that the 7B SST2, 14B SST2 and 28B SST2, since they are permanently connected in series operation, can benefit from a reduction in the value of the output inductor for each module. This results in a damping factor the same as a single-ended amp like the 4B SST2).
The 7B SST2 and 14B SST2 already have massive output current capablity; pulses in excess of 60 Amperes per channel can be drawn. The 28B SST2 almost doubles this, to over 100 amperes per channel. Thus, there is little likelihood that any speaker would be capable of accepting more current than any of these amps would be capable of delivering. A paralleled 28B SST2 would have a theoretical output current limit of over 200 Amperes peak, but that could only ever be drawn if a speaker had an impedance that went below 1 Ohm and the amplifier was delivering peaks of over 40,000 Watts (not possible from a wall socket).
james
