Double diode bridge in class A Power Amps

[nar]

Hello all,

I was just wondering what are the advantages of using 2 diode bridge rectifiers in power amps.

Question is; I always apply this rule of thumb in pre-amps to get lowest noise floor.
I recently finished some Aleph_J mono blocs, using 2 diode bridge per channel in power supply. Other than the higher voltage drop, does it mean anything ggod ?
The first watt amps seem to have only one diode bidge per channel. Thus, ground is linked to common of 2 secondaries and maybe not as quiet as the 2xdiode bridge solution ( where ground is done by common point between the two bridges )

Thanks for your input,

Best

nAr

[AndrewT]

I, with my limited resources, have not been able to measure a difference in output noise of an amplifier whether fed from a dual bridge or single bridge dual polarity PSU.

The single bridge has the advantage of less wasted power.
The dual bridge has the dubious advantage of separate Main Audio Grounds for multi-channel amplifiers. If one builds monoblocks then that is no longer an advantage.

[triode_al]

As well as I understand it, and confirmed by implementations I did of double and single:
- if the transformer secondaries have the slightest impedance difference (two windings on top of each other) then there will be a residual hum with one bridge. The best way to avoid; use bifilar wound secondaries (e.g the Plitron series)
- the above is aggravated if there is just the (slightest??) difference in the capacitance in the cap bank between the rails. Therefore test the caps value. But ideally also the ESR need be tested if you go all the way.
- if the diodes have a difference in conduction point, then the same might happen in conduction/recovery, where there is a difference.

With two separate windings & two bridges the problems are circumvented. Now all residues of rectification should balance out . . . theoretically at least.

I used separate diodes that I tested for conduction (ohmmeter) and I selected within 0,2 mV. Maybe unnecessary, but it works.

If there is a slight misbalance in DC (say 50-100 mV) this is not important in many (pre)amplifiers. You can adjust the DC out.

albert