Hi guys, I am here with one question: which transformer voltage to buy?
I am building two PA03 modules for bridge operation to 8 Ω. Building manual says ±35 V DC for 120 W do 8 Ω. But there is a lot of informations from the internet that ±35 V DC is too much for bridge configuration to 8 Ω and LM4780's will get too hot to run. According to the datasheet I should use only ±25 V DC for standard non-bridge configuration to 4 Ω.
So, am I supposed to buy 2x24 V AC (cca ±34 V DC) or 2x18 V AC (cca ±25 V DC) transformers for bridge to 8 Ω?
I am probably the last man in the world who builds this amp :-D
I am building two PA03 modules for bridge operation to 8 Ω. Building manual says ±35 V DC for 120 W do 8 Ω. But there is a lot of informations from the internet that ±35 V DC is too much for bridge configuration to 8 Ω and LM4780's will get too hot to run. According to the datasheet I should use only ±25 V DC for standard non-bridge configuration to 4 Ω.
So, am I supposed to buy 2x24 V AC (cca ±34 V DC) or 2x18 V AC (cca ±25 V DC) transformers for bridge to 8 Ω?
I am probably the last man in the world who builds this amp :-D
I discussed it with Upupa Epops on our local forum and he didn't directly said 2x24 V AC is right or not, but said that everything in his building manual is correct and nobody ever complained. And in his manual is written this:
Basic parameters (valid for supply voltage ±35 V DC)
Output power:
2x 60 W into 4 Ω
2x 45 W into 8 Ω
120 W into 8 Ω – bridge circuit
120 W into 2 Ω – parallel operation
...so I believe him. In his manual he also highly recommends to have properly matched resistors to avoid too much offset and unnecessary heat for bridge solutions. So maybe this is the key how to not get LM overheating?
Unfortunately I do not have any extra boards. But if that will happen, that two bridged PA03 with proper heatsinks and matching will get some overheating with 2x24 V AC, I will sell them completed (and undamaged!) and full of Vishay, Wima and Panasonic components
Basic parameters (valid for supply voltage ±35 V DC)
Output power:
2x 60 W into 4 Ω
2x 45 W into 8 Ω
120 W into 8 Ω – bridge circuit
120 W into 2 Ω – parallel operation
...so I believe him. In his manual he also highly recommends to have properly matched resistors to avoid too much offset and unnecessary heat for bridge solutions. So maybe this is the key how to not get LM overheating?
Unfortunately I do not have any extra boards. But if that will happen, that two bridged PA03 with proper heatsinks and matching will get some overheating with 2x24 V AC, I will sell them completed (and undamaged!) and full of Vishay, Wima and Panasonic components
My recommendations are based on the Texas Instruments Lm4780 data sheet ,
If each half will see 4 ohms impedance then you need ±25V DC
If each half will see 6 ohms impedance then you need ±30V DC
If each half will see 8 ohms impedance then you need ±35 V DC
For ±35 V DC :
Output power:
2x 60 W into 4 Ω : each half of the chip will see 4 ohm impedance , NOT GOOD
2x 45 W into 8 Ω : each half of the chip will see 8 ohm impedance , GREAT
120 W into 8 Ω – bridge circuit
In this case each half of the chip will see 4 ohm impedance , NOT GOOD
120 W into 2 Ω – parallel operation
In this case each half of the chip will see 4 ohm impedance , NOT GOOD
If each half will see 4 ohms impedance then you need ±25V DC
If each half will see 6 ohms impedance then you need ±30V DC
If each half will see 8 ohms impedance then you need ±35 V DC
For ±35 V DC :
Output power:
2x 60 W into 4 Ω : each half of the chip will see 4 ohm impedance , NOT GOOD
2x 45 W into 8 Ω : each half of the chip will see 8 ohm impedance , GREAT
120 W into 8 Ω – bridge circuit
In this case each half of the chip will see 4 ohm impedance , NOT GOOD
120 W into 2 Ω – parallel operation
In this case each half of the chip will see 4 ohm impedance , NOT GOOD
Hi there! So my two PA03s are built, connected to two toroids with final ±35 V DC. In bridge mode into 8 Ω and with smaller temporary heatsinks it is not overheating even after 20 minutes of loudly played music. Talking about heatsinks and chips too. Looks like Upupa's design and knowledge are unbeatable
Now I am designing enclosure with bigger heatsinks and then I will test more.
Now I am designing enclosure with bigger heatsinks and then I will test more.
Some posts have been moved. R.I.P Upupa Epops.
https://www.diyaudio.com/community/threads/r-i-p-pavel-dudek-aka-upupa-epops.400369/
https://www.diyaudio.com/community/threads/r-i-p-pavel-dudek-aka-upupa-epops.400369/