I don’t see that as a problem, just double check and make sure your legs are in the correct holes.
Thank you Vunce,
then i am not going to use the snubber boards.
Should i alter anything other item?
then i am not going to use the snubber boards.
Should i alter anything other item?
The flying leads to quick connect Molex MiniFit Jr connectors are the best thing since sliced bread for DIY amps. If you ever need to pull the main PCB to rework something. It takes 5 minutes to remove and reinstall vs half an hour or more. If you are a serial amp builder it lets you keep the same heatsink and MOSFETs and change amps (assuming they are Minifit Jr connector compatible amps).
PCB mounted is always an option with some ingenuity.
PCB mounted is always an option with some ingenuity.
COOLING THE NIRVANA
Oracle1 (in Delphi?)
Your heatsink is likely too small.
One channel of the Nirvana will be 25Vx2x1.8A=90W of dissipation, and this means 45W from each output device. You need a large heatsink which in still air will give you a thermal capacity of 0.2C/W, and that would be around 12" long and 6" tall with 2" fins. This would then run at 90x0.2=18C above ambient. In summer in Greece I would expect temperatures up to 38C (correct me if I'm wrong) so this would take the heatsink up to 56C, which is about as high as I like to take it for good life for the mosfets.
OTOH, if you use force cooling you can use a heatsink with around 2.5 times higher impedance, that is, 0.5C/W because this is the improvement factor of running a fan.
Heat is the enemy for Class A, and while you are unlikely to have your amp sitting in a room in your home at 38C (you may use AC, or live at a much higher altitude) but you need to design for the worst case. Too often the worse case seems to happen, and if you are selling amp to the public, it ALWAYS happens!
Hugh
Oracle1 (in Delphi?)
Your heatsink is likely too small.
One channel of the Nirvana will be 25Vx2x1.8A=90W of dissipation, and this means 45W from each output device. You need a large heatsink which in still air will give you a thermal capacity of 0.2C/W, and that would be around 12" long and 6" tall with 2" fins. This would then run at 90x0.2=18C above ambient. In summer in Greece I would expect temperatures up to 38C (correct me if I'm wrong) so this would take the heatsink up to 56C, which is about as high as I like to take it for good life for the mosfets.
OTOH, if you use force cooling you can use a heatsink with around 2.5 times higher impedance, that is, 0.5C/W because this is the improvement factor of running a fan.
Heat is the enemy for Class A, and while you are unlikely to have your amp sitting in a room in your home at 38C (you may use AC, or live at a much higher altitude) but you need to design for the worst case. Too often the worse case seems to happen, and if you are selling amp to the public, it ALWAYS happens!
Hugh
Hi pinkfloyd4ever,
The 4U 300mm will not have enough heatsink with a bias at 1.8A, it will become too hot in summer.
See the calculations of Hugh.
I have the 4U/400mm for my Alpha and that works fine.
Also there's always not enough place inside a case 🙂
especially with dual mono
The 4U 300mm will not have enough heatsink with a bias at 1.8A, it will become too hot in summer.
See the calculations of Hugh.
I have the 4U/400mm for my Alpha and that works fine.
Also there's always not enough place inside a case 🙂
especially with dual mono
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I have done extensive measurements: in my 'case', a 4U 300mm dissipante, the AN temp raises up to 25°C above ambient and stays there.
Not recommended in the hot summer indeed.
Alpha Nirvana 39w 8ohm Class A Amp
x, or anyone else who's used Anteks in a similar fashion (single chassis Dual-mono PS used for swapping out multiple amps, including Pass/FW designs) have thoughts on PS voltage? Can I successfully power the Alpha Nirvana and an Aleph J or other Pass/FW designs with the same PS voltage and VA (and thus the same transformers?) Or will I need a regulator or some other way to drop some voltage for the Pass/FW designs?
Yeah I've looked at them a bit. But when you look closely, the shipping costs are usually as much as the chassis itself, making them nearly the same price as a comparable Modushop/Hifi2000 case. If there's that little difference in price, I'd just assume stick with the tried and true quality option that has most (or all) of the difficult holes and machining already done than spend the same money on something from Ali/Ebay that still needs to have heatsinks drilled/tapped and some holes drilled or otherwise punched/nibbled in the back panel.
BUT if you (or anyone else) have had good experience with any ebay/Ali chassis, that are indeed still a more economical option once shipping to the US is accounted for, send me a link to the seller please because I'm not opposed to exploring that option more.
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i do share power supplies between various amps
always built it in separate box
but I use 2x18 AC secondaries, after rectifiers and filters, it gets to 2x27V DC, but when you plug it o the amps, it settles on 2x24V DC, which is what I like
no need to push it higher
always built it in separate box
but I use 2x18 AC secondaries, after rectifiers and filters, it gets to 2x27V DC, but when you plug it o the amps, it settles on 2x24V DC, which is what I like
no need to push it higher
That’s enough voltage for the AN? And is that with the DIYAudio CRC PS board? I’ll be using xrk’s SLB PS boards, which drops a little more voltage due to the active rectification.
Here is how I do the estimates for what trafo to use. Start with desired voltage DC under load.
For Alpha Nirvana, we want say 27v or 28v, now add 3v drop from SLB cap Mx, add 2v to 3v sag under Class A load (if Antek, less if a European or made in USA brand), we are at 27v + 3v + 3v = 33v. Now divide that by 1.41 we get 23.4v. Antek has them in 2v increments. You could get a 22v trafo but in general, always go "UP" one with Antek. So take the 24v. To get VA rating calculate the steady wattage dissipated. 27v x 2 rails x 1.7A = 91W or 91VA. For a stereo setup that is 180w disspation. I would get trafos at least 2x the VA rating or 400VA for stereo. For dual mono, 200VA could work, but I feel that little 200VA's sag too much and should get 300VA.
So dual mono is 300VA 24v, stereo is probably better off 500VA 24v.
For running different amps, you can put a variac between the wall and your PSU trafo.
Or get a surplus regulated bench linear power supply good for +/-30v and 3A for $75:
GW Instek GPC-3020, for example: https://www.ebay.com/p/1919387835
For Alpha Nirvana, we want say 27v or 28v, now add 3v drop from SLB cap Mx, add 2v to 3v sag under Class A load (if Antek, less if a European or made in USA brand), we are at 27v + 3v + 3v = 33v. Now divide that by 1.41 we get 23.4v. Antek has them in 2v increments. You could get a 22v trafo but in general, always go "UP" one with Antek. So take the 24v. To get VA rating calculate the steady wattage dissipated. 27v x 2 rails x 1.7A = 91W or 91VA. For a stereo setup that is 180w disspation. I would get trafos at least 2x the VA rating or 400VA for stereo. For dual mono, 200VA could work, but I feel that little 200VA's sag too much and should get 300VA.
So dual mono is 300VA 24v, stereo is probably better off 500VA 24v.
For running different amps, you can put a variac between the wall and your PSU trafo.
Or get a surplus regulated bench linear power supply good for +/-30v and 3A for $75:
GW Instek GPC-3020, for example: https://www.ebay.com/p/1919387835
Hello friends,
If i install the fqa directly to the pcb without the snubber boards schould i altered any part ?
Thank you.
If i install the fqa directly to the pcb without the snubber boards schould i altered any part ?
Thank you.
X please for your answer,
i want to install fqa directly to the pcb.
Shall i ohmite or alter anything?
i want to install fqa directly to the pcb.
Shall i ohmite or alter anything?
Oracle,
I would not suggest dropping the snubber.
These mosfets have very high transconductance, and they are running at high dissipation. Any oscillation would destroy the devices in an instant and likely take out your speakers as well.
Snubbers are suggested by Cordell and a very precautionary addition. Eliminating the long leads does not change the real tendency towards oscillation of these large mosfets.
Hugh
I would not suggest dropping the snubber.
These mosfets have very high transconductance, and they are running at high dissipation. Any oscillation would destroy the devices in an instant and likely take out your speakers as well.
Snubbers are suggested by Cordell and a very precautionary addition. Eliminating the long leads does not change the real tendency towards oscillation of these large mosfets.
Hugh
The PCB has provision for a snubber. Please populate it if not using the snubber helper boards.
Hi Oracle1,
Sorry my mistake. The Alpha Nirvana PCB does not have provision for main PCB mounted snubber as it doesn’t even have holes/pads for PCB mounted MOSFETs. If you mount them fo the PCB you will have to mount the snubber via dead bug style onto the legs.
That’s a lot of work - can I ask why you don’t use the external MOSFETs and snubber helper boards as designed? It really makes amp installation and removal for adjustments much faster and easier. Once you try it and see how it decouples the process of mosfet mounting to heatsink separate from PCB mounting, you will not go back.
Sorry my mistake. The Alpha Nirvana PCB does not have provision for main PCB mounted snubber as it doesn’t even have holes/pads for PCB mounted MOSFETs. If you mount them fo the PCB you will have to mount the snubber via dead bug style onto the legs.
That’s a lot of work - can I ask why you don’t use the external MOSFETs and snubber helper boards as designed? It really makes amp installation and removal for adjustments much faster and easier. Once you try it and see how it decouples the process of mosfet mounting to heatsink separate from PCB mounting, you will not go back.