After ages of dithering, I finally pulled the trigger on Aleph J boards and two Universal PS boards from the DiyAudio store. I am now putting together the BOM for the project. With respect to the power supply, I have a couple of questions before I can order the parts. (If this post should be in the Aleph J build thread, please let me know.)
First, I know that for a stereo build 8 caps of 15,000 uF each are recommended (for a total of 60K per rail or 120K total). I also know that since each psu will only power one channel, I can reduce the capacitance somewhat. I cannot, however, find anything that says precisely how much. Is half appropriate? Is there any advantage to having greater capacitance? I could use 120K in each channel if that would be advantageous. I recall reading somewhere that too much capacitance in a ps capacitor bank can be counter productive. Can someone help me out on this? I tried Duncan, but that appears to be a little over my head at the moment.
Second, I have discussed in other threads that I have 4 ohm speakers and thus would be creating extra heat to no good effect if I run the amp at +/-24 volts (unless I increase the bias beyond the capacity of my heat sink). (Incidentally, I will be using two DiyStore 4U 300 mm heatsinks, one on each monoblock.) I would like to aim for +/-19-20 volts. Would a 15-0-15 volt transformer work for that? Would I be better off using the typically recommended 18-0-18 transformer and then adding some resistors to reduce the voltage a bit?
Thanks for any help anyone has to offer.
Jazzzman
First, I know that for a stereo build 8 caps of 15,000 uF each are recommended (for a total of 60K per rail or 120K total). I also know that since each psu will only power one channel, I can reduce the capacitance somewhat. I cannot, however, find anything that says precisely how much. Is half appropriate? Is there any advantage to having greater capacitance? I could use 120K in each channel if that would be advantageous. I recall reading somewhere that too much capacitance in a ps capacitor bank can be counter productive. Can someone help me out on this? I tried Duncan, but that appears to be a little over my head at the moment.
Second, I have discussed in other threads that I have 4 ohm speakers and thus would be creating extra heat to no good effect if I run the amp at +/-24 volts (unless I increase the bias beyond the capacity of my heat sink). (Incidentally, I will be using two DiyStore 4U 300 mm heatsinks, one on each monoblock.) I would like to aim for +/-19-20 volts. Would a 15-0-15 volt transformer work for that? Would I be better off using the typically recommended 18-0-18 transformer and then adding some resistors to reduce the voltage a bit?
Thanks for any help anyone has to offer.
Jazzzman
If you want less voltage ripple feeding your amp then use more capacitance, if you want more voltage ripple feeding your amp (and noisier output) use less capacitance.
A 4U 300mm heatsink may not be adequate. Please don't take risks like this.
You have 4 Ohm speakers, I would want to bias this amp to around 2.5A, in which case 4U x 300mm will not cut it.
You would be better off getting the 4U x 500mm case and doing dual mono.
A 4U 300mm heatsink may not be adequate. Please don't take risks like this.
You have 4 Ohm speakers, I would want to bias this amp to around 2.5A, in which case 4U x 300mm will not cut it.
You would be better off getting the 4U x 500mm case and doing dual mono.
Thank you, 2 PicoDumbs. I appreciate your assistance. I guess I should rethink a few things. I understood that with the standard build I could expect about 13 watts output into 4 ohms. That should be more than enough for my 91db speakers in my moderately small listening room (19' by 16') (the speakers are along the long wall, so I end up being about 10 to 11' from the speakers at my seated position) at moderate volume (I rarely hit above 80 db while listening, with loud peaks around 90 db). I also understood the standard build to contemplate a bias setting at .85 amps (approximately 18 watts per device). Am I wrong about this?
Your suggested 2.5 amps would undoubtedly be quite a bit warmer. For me, a 5U case would be too big (I assume you meant 5U at 400mm chassis). I could go with a 4U 400mm case, but it seems the DiyAudio store has the pre-tapped heatsinks only in 4U 300mm or 5U 400mm. There is a 3U 200mm heatsink, that I suppose I could double up to make 400mm, but again that heatsink does not come pre-tapped.
I do not want to do anything risky. Could I compromise somewhere on the bias and perhaps go with the double 3U 200mm sinks and have them drilled?
Thanks again for your help.
Your suggested 2.5 amps would undoubtedly be quite a bit warmer. For me, a 5U case would be too big (I assume you meant 5U at 400mm chassis). I could go with a 4U 400mm case, but it seems the DiyAudio store has the pre-tapped heatsinks only in 4U 300mm or 5U 400mm. There is a 3U 200mm heatsink, that I suppose I could double up to make 400mm, but again that heatsink does not come pre-tapped.
I do not want to do anything risky. Could I compromise somewhere on the bias and perhaps go with the double 3U 200mm sinks and have them drilled?
Thanks again for your help.
You could easily bias as high as 1.3A per device or 2.6A total with the right heatsink.
It really makes sense biasing the amp for your load, with an Aleph circuit.
I would bias 2A bare minimum, but as high as your heatsinks will allow.
It really makes sense biasing the amp for your load, with an Aleph circuit.
I would bias 2A bare minimum, but as high as your heatsinks will allow.
I think you would be better off building an M2 if you're trying to keep your heatsinks small.
Or F5.
Or F5.
Thank you again. I will explore the other projects you mentioned. However, I hate to give up too quickly on the Aleph. If I were to put two fans under the heatsink blowing up, would that remedy the situation? I built a computer using Noctua fans and they are dead silent.
Thanks! Back to my original question though, is there a point of diminishing returns with respect to PSU capacitance?
Yeah but it's much higher than what you're proposing.
Once you get to 1,000,000 uF you're at the point of diminishing returns. You're not near that so, well it's your decision.
Once you get to 1,000,000 uF you're at the point of diminishing returns. You're not near that so, well it's your decision.