2 Rectifier bridges : Why ?

[ThorstenL]

Hi,

Originally posted by Asen
Kuei

What does it mean? A bridge, made of pairs of diodes, or what?

Of course not. Full Wave Rectification means full wave rectification. See attached, this shows the configuration of a single of the at least two supplies.

Sayonara

[Bricolo]

why should we use dual diodes instead of single ones?


someone said in this topic, that discrete components are better, since you can match them

[2Bak]

Originally posted by Kuei Yang Wang

Two Bridges. If you use more than two life becomes interesting.
It's basically one Bridge (or better discrete diodes) per secondary.

My personal recommendation for gainclones BTW is to use two moderatly sized (80VA or so) Torroids per channel, each using full wave rectification with Dual Schottky Diodes to give one single Voltage.

So a 2-Channel "clone" has four transformers, 4pcs Dual Schottky Diodes (and 4pcs of Supply Capacitors).

I just like to use loads of Iron. It works for me.

Sayonara

Thanks at lot !! That explains why my fuses keeps blowing when I have more than one chanell hooked up. See pic, where I use six (!) bridges in parallel for three channels. I will try with two bridges only ;-)

/Jan

[chiily]

Does it fly?

[2Bak]

Originally posted by chiily
Does it fly?

It rocks !

Sound is good. I am gonna use this three-channel as amp for surround and center speakers.
Details: This circuit. MU metal around toroid, 300VA. LM3875T. No special components. Roedenstein film caps, normal metal films. Standard 1000uF caps. Caddock 0,2 in output.
Case is from an old tube pre-amp, Audio Innovations

[2Bak]

...another

[2Bak]

last one

[Fred Dieckmann]

At the risk of further confusion I thought I would jump off... um actually into; the great bridge debate. First off is the ground is used as a references to the other voltages on a schematic and the ground paths seldom show in detail on most schematics. the large charging currents from then transformer secondariness mean the even return wiring resistance of a few milliohms can result in significant voltages between the ground reference for input cable ground, speaker return grounds, filter capacitor grounds, and amplifier input and feedback ground points.

Referencing the top figure in the schematic included: the wiring resistances for the return path between the transformer secondary center tap and the filter caps ground terminals are given as Rw1 for filter C1 and Rw2 for filter C2. As the charging current to the filter caps is returned through the wiring resistance Rw1 and Rw2 a voltage is developed between the capacitor ground terminals that is given by Vcapgnd1 - Vcapgnd2. This voltage appears the across resistances for the ground returns described above as given by Rw3 though Rw8 as the ration for return resistances Rw3/ Rw3 to Rw7/Rw8 can easily differ from unity and the various ground reference voltages given by Vgnd3 to Vgnd6 will be at different voltages due to the Vcapgnd1 - Vcapgnd2 drop across the unequal resistances Rw3 to Rw8.

A thick plate of a low resistance material is often used to tie these ground returns together and minimize the ground return resistances. I worked on a BandK amp where ground return wires contained ring terminals that were connected to the chassis with a large screw and nut. The order in which these terminals were placed on this screw made a difference in the measured 120Hz noise at the outputs.

Referencring to the bottom figure on the schematic of the two bridge circuit, it is seen that the return currents through rw1 and Rw2 are galvanically isolated by the seperate secondary windings. Thecapacitor charging currents do return not return through the the series combination of Rw1 and Rw2 so that the Vcapgnd1 - Vcapgnd2 drop due the charging current is zero. Either method will work but the single brige requires much greater attention to the ground return path. Hopefully this shred some light into why getting the hum out of an amp requires close attention to the grounding scheme. Hopefully it will also help to explain single point grounding and the use of transformers to isolate ground loops. More likely that it will get me thrown back into the sin bin.

[fdegrove]

Hi,

More likely that it will get me thrown back into the sin bin.

Why would that be?

This same topology I use in OTL amps, it does make a lot of sense to me.

Nice work,

[grataku]

Fred,
that was a lucid, concise and to the point explanation that was overdue in this thread. Looking forward for more of the same from you on other, equally important issues. No reason to evoke sinbin memories here, just keep the 'Hmmmm's to a minimum.