using two transformers

[pyromaniac_]

I'm thinking of powering two LM1876 chips with two transformers (both at 24 V 60 VA). So, do I have to use two powersupplies then (one for each trafo and chip), or can I just wire the trafos in parallell and then connect them to the same powersupply? I'm also thinking of using a regulated powersupply btw.

[AndrewT]

two transformers may have slightly different turns on them. They cannot be paralleled without some form of power wasting balancing.
You need twin secondaries to produce a dual polarity supply for a dual polarity chipamp.
Use each 24Vac transformer to produce a 34Vdc supply. Connect these two supplies in series and you have a 120VA +-34Vdc supply for your 8ohm loaded chipamp.

[pyromaniac_]

Originally Posted by AndrewT

two transformers may have slightly different turns on them. They cannot be paralleled without some form of power wasting balancing.
You need twin secondaries to produce a dual polarity supply for a dual polarity chipamp.
Use each 24Vac transformer to produce a 34Vdc supply. Connect these two supplies in series and you have a 120VA +-34Vdc supply for your 8ohm loaded chipamp.

The transformers are centertapped, so I have to make two separate +-34vdc supplies then, right?

[tiltedhalo]

This will work as long as the transformers are the same.

[AndrewT]

Originally Posted by pyromaniac_

two transformers (both at 24 v 60 va).

Originally Posted by pyromaniac_

the transformers are centertapped,

tell us what you have.

[pyromaniac_]

Ok, I've got: two identical ring-transformers and both secondaries are at 2x24 V and 60 VA. Hope that's clear now.

Guess I can't do as tiltedhalo proposed, since there are two secondary windings at my transformers.

[AndrewT]

each 24Vac + 24Vac 60VA transformer (dual secondary) is capable of making a 60VA +-34Vdc dual polarity power supply.
Each 60VA power supply is capable of running a 30W to 60W power amplifier.

BTW,
a centre tapped is NOT the same as a dual secondary.
A centre tapped can make a dual polarity supply.
A dual secondary can make two single polarity supplies and can be converted to make a dual polarity supply.

[MJL21193]

Originally Posted by pyromaniac_

Guess I can't do as tiltedhalo proposed, since there are two secondary windings at my transformers.

His drawing has the transformers wired out of phase:

117.PNG

[AndrewT]

Originally Posted by MJL21193

His drawing has the transformers wired out of phase:

Attachment 152666

it works as drawn.
Each transformer generates it's own DC voltage and the outputs are connected in series.

Whether the primaries are wired as shown or one of them inverted makes no difference to the operation.

However when leakage current is taken into account you may find that the two transformers prefer the primary connected in either direction. One has to actually test for the reduced/increased leakage of the actual transformer and wire the primary accordingly.

[AndrewT]

Originally Posted by tiltedhalo

This will work as long as the transformers are the same.

this will work and the transformers do not have to be the same. It still works, you have two independant DC supplies that are isolated from each other and from the mains. Just connect them in series.