Here is a pic of my Fan Voltage Board. 
As I'm not quite sure what DC rail voltages I am going to end up with (when the AN boards are all connected up), I used a 120 ohm resistor in the Phoenix connectors on the fan voltage board. Then, using a benchtop power supply that I have, I fed 20v & then 22v to the board.
Interestingly, the fans were seeing (ie. after the resistor):
* 11v with a 20v supply, and
* 12.25v with a 22v supply.
The resistors measure smack on 120 ohms - so the current draw of each fan would appear to be 75-80ma (using the supplied NA-RC7 Low Noise adapter cable) - not the 110ma mentioned in the specs.
Andy
As I'm not quite sure what DC rail voltages I am going to end up with (when the AN boards are all connected up), I used a 120 ohm resistor in the Phoenix connectors on the fan voltage board. Then, using a benchtop power supply that I have, I fed 20v & then 22v to the board.
Interestingly, the fans were seeing (ie. after the resistor):
* 11v with a 20v supply, and
* 12.25v with a 22v supply.
The resistors measure smack on 120 ohms - so the current draw of each fan would appear to be 75-80ma (using the supplied NA-RC7 Low Noise adapter cable) - not the 110ma mentioned in the specs.
Andy
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Hi X,
Looks good (and a bit familiar!). Are you planning to use them fanless or are you going to cool them somehow?
Cheers,
Jacques
They are oversized and hoping to get away with fanless. Will have to monitor temps to see how hot it gets. Might add resistors to slow down the turbo fan. Or use a Noctua with low speed. I am having a problem with it cold-starting up a 3A load on Alpha BB. I might try adding NTC as soft start to see if that helps it get over the startup auto shutdown. I have plenty of volts to throw away here as 50v maybe a bit much. The NTCs drop about 1.5v or so once warmed up.
-- Hi X , Small short detour -- Great News on the TPA3255 Group Buy - Glad they are here - So looking forward to hearing the Amplifier in action!!
- I had a question regarding the Alpha Nirvana Amplifier -- I live in Texas and the heat be a hundred degrees from June thru September and still hot 85 - 95 degrees most of the rest of the year too. Our air conditioning bills can be almost unbearable on our fixed income - Can the Bias be scaled back to help alleviate some of the heat from the Class-A build? - Thank you
- I had a question regarding the Alpha Nirvana Amplifier -- I live in Texas and the heat be a hundred degrees from June thru September and still hot 85 - 95 degrees most of the rest of the year too. Our air conditioning bills can be almost unbearable on our fixed income - Can the Bias be scaled back to help alleviate some of the heat from the Class-A build? - Thank you
Could that startup issue have to do with whatever amount of power supply filter capacitance that needs to be charged during start up? They used to spec the load capacitance that a SMPS would charge at startup, but I don’t see that spec much these days.
That's because SMPSes can't charge any bigger caps...
I tried several different SMPSes, and if I'm lucky they can charge 2 x 2200uF,
In most cases they just refuse to start.
I found out that my issue was that the main output MOSFETs were blown at some point and measure 2 ohms from drain to source - so it was a dead short. I hadn’t run this amp for a long time and not sure when they got damaged. I hope it wasn’t the SMPS that fried them.
Not really, as I see it.
Surely, a Class A amplifier is simply a Class AB amplifier that has a very high bias current setting ... which keeps it in Class A all the time. IOW heat is intrinsic to Class A operation.It would seem you need a Class AB amplifier for Texas.
Or even Class D (even less heat than Class AB).Andy
No, Hallcon. I'm sorry. You have to have a healthy current through the output if you are driving an 8R load, even more if a 4R.
Each channel of the AN will consume 100W continuously. You WILL see the electricity usage increase over your existing situation, particularly if the AC is not turned on! This is the price all Class A guys pay. In the northern states, it's bagatelle, particularly NY, Pennsylvania, Michigan, Wisconsin - but not in Texas, Louisiana, Alabama, Oklahoma, CA.
Hugh
Each channel of the AN will consume 100W continuously. You WILL see the electricity usage increase over your existing situation, particularly if the AC is not turned on! This is the price all Class A guys pay. In the northern states, it's bagatelle, particularly NY, Pennsylvania, Michigan, Wisconsin - but not in Texas, Louisiana, Alabama, Oklahoma, CA.
Hugh
Just completed AN build.
Tested, scoped, everything looks good.
Now time for thermal tests
Need to plug it in, and watch the temperature for a few hours, to see if these 2 heatsinks and fans are enough.
So far, after 10 min running, output transistors are running at 60 degrees C
(21V rails, will test 27V as a next step)..
PSU is external one - the box in the back, with VU meters. It's +/-80V (800W),
with speaker protection and VU meters.
I have auto-transforer in front of it, so I can adjust voltage as needed.
AN chassis is made from Alu slab, 8x8, 1 inch thick.
2 little boards behind the fans - voltage regulator to drop +rail to 12V, and fan controller.
PCBs are obviously different - smaller then originals, with power FETs soldered directly to the boards.
Thermistor sensor from the fan controller, is glued with thermal glue to one of the output transistors, but I guess
it doesn't matter - I expect these fans to run constantly...
More pics at http://www.slowbears.com/flickr/AlphaNirvana/
Tested, scoped, everything looks good.
Now time for thermal tests
Need to plug it in, and watch the temperature for a few hours, to see if these 2 heatsinks and fans are enough.
So far, after 10 min running, output transistors are running at 60 degrees C
(21V rails, will test 27V as a next step)..
PSU is external one - the box in the back, with VU meters. It's +/-80V (800W),
with speaker protection and VU meters.
I have auto-transforer in front of it, so I can adjust voltage as needed.
AN chassis is made from Alu slab, 8x8, 1 inch thick.
2 little boards behind the fans - voltage regulator to drop +rail to 12V, and fan controller.
PCBs are obviously different - smaller then originals, with power FETs soldered directly to the boards.
Thermistor sensor from the fan controller, is glued with thermal glue to one of the output transistors, but I guess
it doesn't matter - I expect these fans to run constantly...
More pics at http://www.slowbears.com/flickr/AlphaNirvana/
Attachments
Last edited:
Just completed AN build.
Tested, scoped, everything looks good.
Now time for thermal tests
Need to plug it in, and watch the temperature for a few hours, to see if these 2 heatsinks and fans are enough.
So far, after 10 min running, output transistors are running at 60 degrees C
(21V rails, will test 27V as a next step)..
PSU is external one - the box in the back, with VU meters. It's +/-80V (800W),
with speaker protection and VU meters.
I have auto-transforer in front of it, so I can adjust voltage as needed.
AN chassis is made from Alu slab, 8x8, 1 inch thick.
2 little boards behind the fans - voltage regulator to drop +rail to 12V, and fan controller.
PCBs are obviously different - smaller then originals, with power FETs soldered directly to the boards.
Thermistor sensor from the fan controller, is glued with thermal glue to one of the output transistors, but I guess
it doesn't matter - I expect these fans to run constantly...
More pics at http://www.slowbears.com/flickr/AlphaNirvana/
Love the look of that amp! 1” slabs of aluminum..... I love it!! At first the amp looked huge but when your measurement of 8x8” sinks in you start to realize that it is very compact. 60c after 10 minutes is pretty hot! It will likely go hotter before it stabilizes and you will need to monitor it if pushing past 21 volts. Can you adjust fan speed?
Yes, I can.
Also, 60C was observed BEFORE I glued thermistor to the output fet.
First, it was connected to the CPU heatsink.
Now, when it's directly sensing temperature of the fet, fans will kick in sooner, and at higher speed.
Fets are bolted VERY close to CPU heatsinks.
60C is not too bad, I'd be happy if it stays at 60C.
I built and tested this kind of cooling with other amps, but not A class, so we will see...
