Front end board biased up to .780 Vdc now or so, slowly crept up from .750 once I put the lid on and let it cook a bit. The last BA-3 board I biased up stopped around low .780s. Once this happens I will power down, wire the out put boards to it and go at it again biasing them up and setting offset. Let the whole mess cook an hour, reset everything and assuming all is well, put it in the system for a trial run!🙂
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" To start, set 0.25V measured across the 1.0ohm source resistors.
Use it few days at 90% of desired bias , then check and set to 100%"
What is full (100%) bias?
Thanks, Russellc
Use it few days at 90% of desired bias , then check and set to 100%"
What is full (100%) bias?
Thanks, Russellc
I have a question about the value of R13.
R13 is 332 3W (3.3k ohm?)in BA3 cirucit, but it is 330 ohm 3W in the picutre.
What is rihgt value?
I'm preaparing part's to build BA3 as a preamplifier.
R13 is 332 3W (3.3k ohm?)in BA3 cirucit, but it is 330 ohm 3W in the picutre.
What is rihgt value?
I'm preaparing part's to build BA3 as a preamplifier.
I might be posting this in the wrong thread, but I am having trouble finding info on the BA-3SE. Lucky me just got 6 pairs of matched IRFP240s in the mail, so what would be more natural than building a dual mono BA-3SE with fat PSUs...? 😀
The question in mind is what rail voltage I should use; am I stuck with 24V, or would 32V work just as well (or maybe even better)?
Thank You for listening!
Jorgen
The question in mind is what rail voltage I should use; am I stuck with 24V, or would 32V work just as well (or maybe even better)?
Thank You for listening!
Jorgen
if you're going to higher rails (thinking of higher power) ...... 3 pairs per channel isn't exactly enough
So I'm scratching my head around heatsing dissipation calculations.
I'm planning on a 32v, 3 pairs per channel build.
I will try to bias around 0.5A per device, so around 3A total per side. At 32v this gives me 96W dissipation per channel.
The 5U store case has 4 sinks with 0.28W/C each, so each heatsink will have to dissipate 48W (3 devices per sink) which gives me this result:
Ta + (P * (Rjc + Rcs + Rsa))= Tj
30º + (48W* (0.83+0.24+0.28))=94.8º
This is way above the 65º recomended when reading the temperature in the mosfets.
I know I'm making a mistake somewhere as I'm not considering the dissipation being done by 3 devices.
So I thought about making the calculation with just one mosfet but dividing the heatsink Rsa by 3 since it shared by 3 mosfets, like this:
30º + (16W* (0.83+0.24+0.84))=60.56º
This is a much better result, it somewhat makes sence in my head but it's always good to double check.
Is my reasoning correct?
I'm planning on a 32v, 3 pairs per channel build.
I will try to bias around 0.5A per device, so around 3A total per side. At 32v this gives me 96W dissipation per channel.
The 5U store case has 4 sinks with 0.28W/C each, so each heatsink will have to dissipate 48W (3 devices per sink) which gives me this result:
Ta + (P * (Rjc + Rcs + Rsa))= Tj
30º + (48W* (0.83+0.24+0.28))=94.8º
This is way above the 65º recomended when reading the temperature in the mosfets.
I know I'm making a mistake somewhere as I'm not considering the dissipation being done by 3 devices.
So I thought about making the calculation with just one mosfet but dividing the heatsink Rsa by 3 since it shared by 3 mosfets, like this:
30º + (16W* (0.83+0.24+0.84))=60.56º
This is a much better result, it somewhat makes sence in my head but it's always good to double check.
Is my reasoning correct?
I thought you did a PM with me way back.
In that there was a very full explanation with example calculations.
Did you get that?
In that there was a very full explanation with example calculations.
Did you get that?
No !
3pair @ 0.5A each is 1.5A for the total
1.5A times 32Vdc = 48W dissipation for the upper half. Another 48W dissipation for the lower half. That then gives 96W total dissipation for the 3pair output stage biased at 1.5A using ±32Vdc. Right answer wrong calculation.
No.
You have omitted the temperature de-rating. This is usually given in the manufacturer's datasheet, but I'll bet you did not get that from the retailer.
For a cool heatsink the de-rating factor (DF) can be as high as 1.5
do the calculation in separate easy to follow stages.
Ta?
Ts?
apply DF
new Ts estimate
Tc?
apply device derating for Tc
Pmax? at this estimated Tc.
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Do we know this derating factor for the hifi2000 heatsinks?
I still don't understand how to factor in multiple devices into the calculation.
I still don't understand how to factor in multiple devices into the calculation.
do the calculation/modeling one stage at a time.
Ts to Ta is the whole heatsink - the dissipation of 3 devices
Tc to Ts is one device - the dissipation of 1 device
Ts to Ta is the whole heatsink - the dissipation of 3 devices
Tc to Ts is one device - the dissipation of 1 device
Building a 32v BA3, should I go with 33000uf (cornell dubelier) at 85C temp rating or 27000uf (panasonic) at 105C?
The ripple current rating is about the same using the temperature multipliers to 60C which is probably the temperature inside the case when finished and fully biased.
The ripple current rating is about the same using the temperature multipliers to 60C which is probably the temperature inside the case when finished and fully biased.
I would use the 105°C capacitors for the inside of a ClassA amplifier.
It gets hot in there.
I would also place them on the floor of the Chassis with adequate ventilation holes under them, so that the heat inside pulls cooling air in via the capacitor bodies.
It gets hot in there.
I would also place them on the floor of the Chassis with adequate ventilation holes under them, so that the heat inside pulls cooling air in via the capacitor bodies.
They will be mounted in a PCB and around and beneath it i will drill several holes to allow for maximum ventilation. I might also add a small low noise fan extrating heat from the case.
Comparing to the official push-pull output stage schematic from Nelson's BA-3 article there are a couple of resistors (R129 and R130) and capacitors (C102 and C103) missing. Not sure what's the function of these parts - some additional filtering?
Assuming we are thinking the same thing, that is a good question.
These are rated at 0.18C/W Dissipatore 300 X 40 H 210 mm
But at what temperature above ambient? Heatsinks are more efficient the hotter they get.
Conrad suggest a derating figure for their heatsinks Conrad Heatsinks - Technical Details (bottom of page), but modushop offers no advice.
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I can tell from experience the 5U 400mm case will easily dissipate 100W per side of the case or in other word easily dissipates 50W per heatsink (4 heatsinks on the case).
I don't trust the numbers modushop quotes
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You have quoted it wrong, it should be 0.28C/W not 0.28W/C. Makes a huge difference in the calculation.
Assuming modushops specification is accurate then 48 x 0.28 = 13.4 degrees above ambient (in reality it maybe closer to 20 degrees above ambient)
Either way you are not going to have any issue with that case for BA3.
most heatsinks are rated for a deltaT of 70C to 80C degrees.
most heatsink manufacturers issue de-rating data/tables for their heatsinks when DeltaT is less.
For a deltaT of around 13C degrees expect the de-rating factor to exceed 1.5
i.e. 60W into 0.2C/W and using a DF of 1.6 gives DeltaT = 60 *0.2 *1.6 = 19.2Cdegrees
If Ta = 28°C, then Ts = 47°C
most heatsink manufacturers issue de-rating data/tables for their heatsinks when DeltaT is less.
For a deltaT of around 13C degrees expect the de-rating factor to exceed 1.5
i.e. 60W into 0.2C/W and using a DF of 1.6 gives DeltaT = 60 *0.2 *1.6 = 19.2Cdegrees
If Ta = 28°C, then Ts = 47°C