Owen,
in the beginning you proposed a transformer-"We could ask for custom transformer that was say 60-50-0-50-60 @ 0.1A-7A-0-7A-0.1A with both 120 and 240V primary windings and that would work for everyone that wanted about 300W into 8 ohms". I assume this is for one mono block, if I wanted to make a stereo would you recommend doubling that size? As far as power supply most of mine have been CRC for class A amps, is there any significant change in power supply design for class AB amp? I have used the BrianGT power supply boards at chipamp.com for my class A amps would they be suitable for this project? It is built with 4 mur1560 diodes 2caps resisters and 4 more caps.
Bill
in the beginning you proposed a transformer-"We could ask for custom transformer that was say 60-50-0-50-60 @ 0.1A-7A-0-7A-0.1A with both 120 and 240V primary windings and that would work for everyone that wanted about 300W into 8 ohms". I assume this is for one mono block, if I wanted to make a stereo would you recommend doubling that size? As far as power supply most of mine have been CRC for class A amps, is there any significant change in power supply design for class AB amp? I have used the BrianGT power supply boards at chipamp.com for my class A amps would they be suitable for this project? It is built with 4 mur1560 diodes 2caps resisters and 4 more caps.
Bill
I will be using the additional small transformer approach as well. This works well as long as the regulation is relative to main PS ground.
Here is a question for the group: What would happen if the LME PS regulation were relative to "quiet ground" instead of main PS ground?
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A better way, if you're buying a toroid and it's not potted, is to simply add some windings of your own.
Eg, if it's 2 turns per volt and you want ± 12V extra. Then do two windings of about 6 turns. You'll have to measure it.
That's how all of ours have been made. 0.56mm diameter enamelled copper wire was used.
I'd suggest to pay attention to amount of extra volts though to allow not just to clear the output stage and the regulators minimum overhead but also for the mains to swing, or if you one day might want to sell the amps to someone with a much higher or lower mains voltage than yours typically is.
On one Hafler DH200 I modified, I added an early stage, done with this method of a replacement toroid with extra windings joined to the main windings and to their own bridge and following main res caps then regs, the early stage earth was about +5V DC from the main earth star and centre tap. I ran a thin wire between the early stage regs earth and the main earth to equalise the voltage.
Eg, if it's 2 turns per volt and you want ± 12V extra. Then do two windings of about 6 turns. You'll have to measure it.
That's how all of ours have been made. 0.56mm diameter enamelled copper wire was used.
I'd suggest to pay attention to amount of extra volts though to allow not just to clear the output stage and the regulators minimum overhead but also for the mains to swing, or if you one day might want to sell the amps to someone with a much higher or lower mains voltage than yours typically is.
On one Hafler DH200 I modified, I added an early stage, done with this method of a replacement toroid with extra windings joined to the main windings and to their own bridge and following main res caps then regs, the early stage earth was about +5V DC from the main earth star and centre tap. I ran a thin wire between the early stage regs earth and the main earth to equalise the voltage.
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Thanks for the correction. I do now recall seeing what looked like about 20 to 30 turns on them. Of course it will vary with the size of the transformer.
That is very ingenious. So you connect wires in series with the secondaries, give it a few turns and the original center tap is also the center tap for the new secondaries?
Yes. If connected this way, just like having taps for, eg, 92 - 80 - 0 - 80 - 92.
The 80's go to a big bridge, the 92's to a small one. Then the two earth's formed from the low and the high voltage capacitors are wired together.
....edit: I just read AP2's post which says the same.
The 80's go to a big bridge, the 92's to a small one. Then the two earth's formed from the low and the high voltage capacitors are wired together.
....edit: I just read AP2's post which says the same.
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I used to use 7815 and 7915. Fitted two, eg, 33V (ish), Zeners in series from the ground pin to the ground to 'pedestal' the regulator. The Zeners shift when warm, so after an initial build and power up and let the settle, I measure the voltage drop across them all then usually taken them off and swap them to make matching ± voltages. Laborious. I think I'd do it with the 317 and 337 next time. Or maybe try out the SuperTeddy Power Reg or a simple discrete transistors design.