Take a 7812 regulator (bolted to heatsink with insulator) and use good 1uF bypass caps on input and 10uF electrolytic and 1uF film on output to steal 12v from 24v rail. I sometimes use 100ohm 5W resistor to slow fan down to inaudible if you don’t have a large diameter quiet fan. Be careful not to stall fan. If doing fan cooled as primary means of cooling, use mechanical bimetallic overheat (75C) power cutoff safety switch connected to heatsink.
2 x 167F 75 Celsius Temperature Controlled Switch Thermostat KSD302 N.O
2 x 167F 75 Celsius Temperature Controlled Switch Thermostat KSD302 N.O
Thanks X! One final question for now, in series of Juntuin's stupid questions;
For BB, I have those 2x30va 545va trafos, two of them. So 42,4v rail voltages without load. If I add one CapMX per monoblock 42,4v - 4v = 38,4v. Still on high side, but too high? Have anyone tried to take some rounds of secondary wirings off and reduced output voltage this way? I asked this earlier but can't remember to get answered 🙂
For BB, I have those 2x30va 545va trafos, two of them. So 42,4v rail voltages without load. If I add one CapMX per monoblock 42,4v - 4v = 38,4v. Still on high side, but too high? Have anyone tried to take some rounds of secondary wirings off and reduced output voltage this way? I asked this earlier but can't remember to get answered 🙂
What's a good number of KSA992FBU devices to get for matching hFE? Not sure what to expect from the distribution.
BK
Hi
The 2x30AC transformer will give you 2x36VDC at Class A operation.
I think that is still OK with the 3 pair power mosfet
Calculated with CRC or CLC power supply, I think the regulated PS will give you the same V. I have similar transformers 2x30V 1KVA (for both channel) or I have 2X28V 800VA option. Both are great quality Plitron transformer. I do not plan to purchase more transformers. 😀
Hi
The 2x30AC transformer will give you 2x36VDC at Class A operation.
I think that is still OK with the 3 pair power mosfet
I have similar transformers 2x30V 1KVA (for both channel) or I have 2X28V 800VA option. Both are great quality Plitron transformer. I do not plan to purchase more transformers. 😀
Hi!
I hope that's correct, it would be nice to have suitable trafos ready and waiting 🙂 I don't know where I have this trafo output x1.4 = rail voltage in my head?
Wow, those transformers are monsters 😱
Hi Juntuin,
I’ve got a 10uF Silmic II without any bypass cap and am pleasantly surprised with them. When I have my final chassis completed I will replace them with “Fancy” caps. But will the sound improve?? That’s a whole topic all on its own 😀
38v under load of 3amps will probably sag to about 35-36v so I think you are fine. The issue is now you may need 50v rated caps to be safe and not 35v. But you could be ok within tolerance of limit but not advised. Caps go up in pride quite a bit $6 to $10 from 35v to 50v for 33mF.
Two dozen should do it. They are so cheap. 100 was $7. Compare that to cost of genuine 2SK170BL for input stage on some other Class A amps.
I'm relived 🙂 50v caps ain't problem, since you don't need so many of those with capmx, what I'm planning to use with BB's also.
Hi X,
what do you think if I will use my aluminium cabinet ( for midbass horn ) like heatsink for Alpha amplifier? ( 60cm height, 30cm wide, 20cm depth, 25 kgs about, all sides soldered )
what do you think if I will use my aluminium cabinet ( for midbass horn ) like heatsink for Alpha amplifier? ( 60cm height, 30cm wide, 20cm depth, 25 kgs about, all sides soldered )
Monotube2,
Wow, you are quite the over-achiever! Those cabinets are the most over-the top I have seen this side of Magico. I think 25kg of 20mm thick welded aluminum plates would be more than enough for a 60w ALPHA 20 to sink heat into. Very nice cabinets!
Wow, you are quite the over-achiever! Those cabinets are the most over-the top I have seen this side of Magico. I think 25kg of 20mm thick welded aluminum plates would be more than enough for a 60w ALPHA 20 to sink heat into. Very nice cabinets!
X,
Take care with 25VW caps on 24V rails; you should not go over 80% rating for long life. I would strongly suggest 35VW.
Cheers,
Hugh
Take care with 25VW caps on 24V rails; you should not go over 80% rating for long life. I would strongly suggest 35VW.
Cheers,
Hugh
Thanks, Hugh. Will keep that in mind. Interesting how caps on many Pass Class A project PSUs specify 25v caps for all the +/-24v rail projects.
I wasn't aware of that, but it's sailing close to the wind and I never do it with commercial product.
HD
My BB CPU coolers arrived. These are really nice. (note that just order them directly from Amazon rather than the eBay link I posted as that is a drop shipper store that just resells Amazon). Anyhow, these are triple heat pipes with direct contact to the MOSFET being cooled. I hope the included brackets line up with JPS64's holes cutout on the PCB. I just got word from Hugh that we will only go with single large outputs rather than allow for three smaller IRFP's as they need to be matched over both Vgs and Gm, a real difficult problem requiring a sample size of at least 100. So let's just buy the $8 big MOSFET and be done with it. So PCB will not have triple output option. I will order a small order of 5 boards to test the amp and make sure it works before offering the PCB as a GB for the Forum and then committing to a big order.
These are PWM fans with 4-pin connectors that I assume will fit the pins that JPS has spec'd for the fan controller board. That board has an NTC temp sensor on 2-pin connector and that goes to the cooling block and the fan speed will be adjusted accordingly to keep noise levels low. The 120 mm fans are supposed to be really quiet. This is a pretty high tech Class A amp and it will resemble a computer more than audio. Actually a PC cabinet may not be a bad thing.
I still need to order the pair of 400VA 25V Antek donuts.
These are PWM fans with 4-pin connectors that I assume will fit the pins that JPS has spec'd for the fan controller board. That board has an NTC temp sensor on 2-pin connector and that goes to the cooling block and the fan speed will be adjusted accordingly to keep noise levels low. The 120 mm fans are supposed to be really quiet. This is a pretty high tech Class A amp and it will resemble a computer more than audio. Actually a PC cabinet may not be a bad thing.
I still need to order the pair of 400VA 25V Antek donuts.
Attachments
Last edited:
That su...s at least to me😱. Here it goes the BB project. My only hope the 20W Alpha will satisfy my needs.
It would be an incredible waste of fund, energy etc, to give up the already existing 15" tall about 25-30Lb heatsink enclosure (ready-made for an Aleph 4) and start from scratch with fan cooling what I hate so much. My second amp was a Technics fan cooled cr...... always shut off the power.
I said never again. But the main reason these over to me because I have everything ready, transformer, heatsink, PS caps etc
. I do not have the tools to do it by myself with the 3 par transistor. I wish you good luck to all for your build.🙂