dual primary//dual secondary toroid

[larryg]

Hi AndrewT, the kit I purchased came with the two rectifier bridges. To use 1 and save the other, might be the way to go here.(gainclone) I welcome any advice.
Thanks, larryg

[AndrewT]

Hi,
are you building two channels?

Then use one diode bridge on each channel, each channel with it's own rectifier and smoothing bank.

If you adopt the dual, series connected diode bridges you will need two for each channel.
If you decide to use a dual bridge and share the +-supplies between channels, I think you will end up with poorer performance than using independant rectifier/smoothing bank per channel.

I have tested, using the equipment available to me, both types of rectifying scheme.
Type 1: The single rectifier using centre tapped transformer into series connected smoothing caps and taking the centre tap and the cap common (0Volt) to audio ground.
Type 2: dual rectifer using twin secondaries from transformer into independant smoothing caps and taking +ve from one cap and -ve from the other cap to the audio ground.

I have connected both types into two different amplifiers and all four combinations have immeasureable hum and buzz and noise on the output of the amplifier. Both types appear to have the same ripple on the supply rails. Type 1 produces about 1.6V extra DC.
I used a DMM with 200.0mVac scale rated from 20Hz to 500Hz with extended but inaccurate response out to about 100kHz (-8db) and a scope with 1mV/div vertical sensitivity. I plan to increase the sensitivity of these tests, so this is not my final report nor conclusion.

My recommendation is, go the simple, cheap, single route with the diode bridge. Add RC snubbers to each diode.
Take the 0volt common TO the audio ground.
DO NOT bring the audio ground to the rectifier common connections.

[richie00boy]

I agree with Andrew that if you only have two bridges then use one for each channel, in this small application.

[larryg]

ThankYou AndrewT&richie00boy. I will employ your advice. About the snubber caps; I have .022ufd caps for use here, are these okay? Thanks much for sharing your knowledge!
larryg

[richie00boy]

One of your 22nF caps across each bridge on the AC side will probably be all you need to do regarding snubbers.

[larryg]

Thanks richie00boy.
larryg

[Vidalgo]

Another advantage of the splitted secondaries & 2 bridges:
if you want voltage regulation (common way in low-power applications), you can get identical voltage regulators for both legs.

[AndrewT]

Hi Richie & Larry,
what resistor value do you suggest? for the RC snubber?

[AndrewT]

Hi,

you can get identical voltage regulators for both legs

thanks for the reminder.
A particular advantage when the -ve reg has poorer performance than the +ve side.

[richie00boy]

I'd use 10 ohms if you want to use a resistor.