To me it looks like the diodes in the bridge are connected in parallel and provide only half wave rectification. It will work but with higher than normal ripple and more stress on the filter capacitors. The DC output voltage probably is a bit lower than full wave rectification would provide.
Your power supply is not correct. You are running a half wave rectifier to the +30v supply and AC to the -30v supply. I am surprised that the 10,000uf capacitor on the -30v supply has not exploded. You need a transformer with a center tapped secondary or dual secondaries. See power supply schematic examples at either chipamp.com or audiosector.com
That's correct. That's one problem with using a single secondary. I would rather use two such transformers, or a center-tapped transformer, and two full-wave bridges.
I just simulated (with LT-Spice) the power supply used, with a 4 Ohm resistor from each rail to ground, and a current source in series with each 4 Ohm resistor to force it to draw 100 Watts peak power. The current waveform I used was pulse-like, with the correct polarity for each rail, and the rise and fall times fairly slow. And the two rail currents were out of phase with each other, so that only one rail went to 100W at a time. The repetition frequency was 500 Hz. I used a typical ESR (equivalent series resistance) for the 10000 uF electrolytic capacitors of 0.03 Ohm. For the 0.1 uF caps, I used an ESR of 0.001 Ohm.
For that test, the voltage ripple was 5.5V peak-to-peak, for each rail, dropping the average DC voltage magnitude to about 23 V per rail. The ripple currents through the electrolytics were 32.2 Amps peak at 50 Hz and 5 Amps peak at 500 Hz, with about one half of a 50 Hz cycle at 75A, at startup. The average ripple current through each electrolytic, not including startup, was about 8.7 Amps RMS, and their average power dissipation was 1.4 Watts each, while the transformer was supplying about 151 Watts average and each rail was supplying about 69 Watts average.
OK, that was with silicon diodes that weren't rated for that much current (MUR460). Using big 25A Schottky diodes, the peak diode currents were about 17.4 Amps, with 1.52A average and 4.6A RMS, and average power dissipation of about 0.8 Watt per diode. The electrolytics' current went to about 9.1 Amps RMS (35 Amp peaks at 50 Hz and 5 Amp peaks at 500 Hz) and each rail was supplying about 71.1 Watts while the transformer was supplying about 153 Watts average.
- Tom
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Actually, he gets half-wave rectified DC for each rail.
But I definitely agree that it would be better to have two secondaries, either by using two single-secondary transformers, a dual-secondary transformer, or a transformer with one center-tapped secondary. Then he could full-wave rectify each rail.
You could use one center-tapped transformer, like 19-0-19. Or you could use two like the one you already have, like 19-0 0-19, and tie them together to make a "center tap"..
But, if you really want +/-30V rails (and I think that you DO want +/-30V rails), then you will want higher-voltage secondaries, like 22-0-22 to 24-0-24, with a big-enough VA rating (maybe 250 VA?). [Note that if you wanted to build a _regulated_ supply, you would need even-higher secondary voltages, to allow for the regulator dropout voltage plus a margin for variation, like 28-0-28 to 30-0-30.]
The basics of linear power supply design are all covered at:
Unregulated Power Supply Design
And here is a great page with some of Carlosfm's power supply designs, both un-regulated and regulated:
Building a Gainclone chip amp with snubberized PSU.
which were talked about on this thread, here at diyaudio:
http://www.diyaudio.com/forums/chip-amps/56106-lm338-regulated-snubberized-psu-audio-amplifiers.html
- Tom
But, if you really want +/-30V rails (and I think that you DO want +/-30V rails), then you will want higher-voltage secondaries, like 22-0-22 to 24-0-24, with a big-enough VA rating (maybe 250 VA?). [Note that if you wanted to build a _regulated_ supply, you would need even-higher secondary voltages, to allow for the regulator dropout voltage plus a margin for variation, like 28-0-28 to 30-0-30.]
The basics of linear power supply design are all covered at:
Unregulated Power Supply Design
And here is a great page with some of Carlosfm's power supply designs, both un-regulated and regulated:
Building a Gainclone chip amp with snubberized PSU.
which were talked about on this thread, here at diyaudio:
http://www.diyaudio.com/forums/chip-amps/56106-lm338-regulated-snubberized-psu-audio-amplifiers.html
- Tom
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OOOOOOOOO YYYYYYYEEEEEEAAAAHHHHH
i've just resolved the problem!!!! that's the heatsink!!! i changed it with another one and now it works perfectly! so, i've used a No-alluminium heatsink and i've got a thermic transfer problem, than i buy a new heatsink and one fan for each LM3886!!! goood.... thank you very much for all!!!!!!!!!!!!!
i've just resolved the problem!!!! that's the heatsink!!! i changed it with another one and now it works perfectly! so, i've used a No-alluminium heatsink and i've got a thermic transfer problem, than i buy a new heatsink and one fan for each LM3886!!! goood.... thank you very much for all!!!!!!!!!!!!!
That half wave doubler has 2 unnecessary diodes. but it should be fine as long as you do not exceed the current of one diode. (diodes in parallel do not double their rating)
P.S. I am glad you got it working!
I'm curious. Why do you call it a "half wave doubler"?
If you were referring to the diodes' current ratings, two diodes in parallel will indeed be able to carry about twice the current of one diode, effectively doubling the current rating compared to using only one diode. Or am I missing something?
Manufacturing tolerances lead to unequal current sharing between two diodes. That is, why parallel diodes should not be used up to their full current rating. Rule of thumb is to calculate the total permissible current as 0,85 times the nominal rated current times the number of parallel diodes. For two diodes that is 1,7 times their individual rating.
Re: half wave doubler.
Both he positive and negative rails only get a half wave rectified part of the AC, but you get 2x the transformers secondary value (2 rails)
You can roughly compensate by using 2x the size capacitors you normally would on the power supply. (the capacitors have 2x as long to discharge between getting power from the diodes)
I dont mind using half wave with scrounged up transformers for lower power things although I havent seen it in an amp for quite some time. but, transformers are expensive, and scroungers cant be choosers
Both he positive and negative rails only get a half wave rectified part of the AC, but you get 2x the transformers secondary value (2 rails)
You can roughly compensate by using 2x the size capacitors you normally would on the power supply. (the capacitors have 2x as long to discharge between getting power from the diodes)
I dont mind using half wave with scrounged up transformers for lower power things although I havent seen it in an amp for quite some time. but, transformers are expensive, and scroungers cant be choosers
Re: half wave doubler.
Both he positive and negative rails only get a half wave rectified part of the AC, but you get 2x the transformers secondary value (2 rails)
You can roughly compensate by using 2x the size capacitors you normally would on the power supply. (the capacitors have 2x as long to discharge between getting power from the diodes)
I dont mind using half wave with scrounged up transformers for lower power things although I havent seen it in an amp for quite some time. but, transformers are expensive, and scroungers cant be choosers
Now I understand! Thank you.
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