Not really off topic - MOSFET VAS variant simulation
Have fun, Toni 😉
- during lab cleanup I found a couple of IRF9610 lying around from an old papa Pass project
- found an IRF9610 spice file
- simulated SA2013 v3.4 using IRF9610 for VAS
Have fun, Toni 😉
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After Reading through This thread i have a few comments.
It is true that In some cases a single output pair would perform better than Multiple output pairs. But In most cases designers adds extra pairs without changing the driverstage. This is a major fault!! Redesign the AMP to drive the extra pairs well and it will not be a problem .
Secondly doing a 150watt into 8r with only one pair of 250watt devices is a risky business .
I would say use several pairs at that point to keep peak power Below 30 to 50% of max power available through devices, thermal interface and heatsink .
If you run devices close to max current they get unlinear.
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It is true that In some cases a single output pair would perform better than Multiple output pairs. But In most cases designers adds extra pairs without changing the driverstage. This is a major fault!! Redesign the AMP to drive the extra pairs well and it will not be a problem .
Secondly doing a 150watt into 8r with only one pair of 250watt devices is a risky business .
I would say use several pairs at that point to keep peak power Below 30 to 50% of max power available through devices, thermal interface and heatsink .
If you run devices close to max current they get unlinear.
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1pr of 250W devices gives a 500W output stage.
30% of that is 150W, 50% of that is 250W
What did you mean to say when you gave us that guidance?
With an +/-60VDC supply and 150W into 8R you will have around 4.3Arms => 260W. That is an pure resistive load.
260W into an 0.4K/W heatsink is 103K. An 250W device have an Junction to case of 0.5K/W. => So this will generate 125Watt/device x 0.5K/W => 62.5K.
Max temperature is 150 degrees celcius. We are now at 165.5K + room temperature.
3 pairs of 250Watt devices will mean 43.3Watt per device -> 21.6K per device meaning 125K + room temperature....
Do you get the picture?
So an amp producing 150Watt into 8R needs an good heatsink of below 0.4W and more than 3 pairs of 250W output devices as possible. If anyone
Then there is the crest factor which is normally set to ~20%. So an amp delivering 300Watt into 4R with 3 pairs , 0.4Watt heatsink and +/-60Vdc supply will produce something like 105W with music signal.
42K (heatsink) + 9K (Per transistor) + 9K (Thermal interface) = 60K + room temperature 25 - 50degrees (Depending where you live and how crowded there is around the amplifier)
So with an room temperature of 25 degrees there will be a margin of 65 degrees.
With one pair it will leave 3 degrees to the room temperature. That is going to fail!
260W into an 0.4K/W heatsink is 103K. An 250W device have an Junction to case of 0.5K/W. => So this will generate 125Watt/device x 0.5K/W => 62.5K.
Max temperature is 150 degrees celcius. We are now at 165.5K + room temperature.
3 pairs of 250Watt devices will mean 43.3Watt per device -> 21.6K per device meaning 125K + room temperature....
Do you get the picture?
So an amp producing 150Watt into 8R needs an good heatsink of below 0.4W and more than 3 pairs of 250W output devices as possible. If anyone
Then there is the crest factor which is normally set to ~20%. So an amp delivering 300Watt into 4R with 3 pairs , 0.4Watt heatsink and +/-60Vdc supply will produce something like 105W with music signal.
42K (heatsink) + 9K (Per transistor) + 9K (Thermal interface) = 60K + room temperature 25 - 50degrees (Depending where you live and how crowded there is around the amplifier)
So with an room temperature of 25 degrees there will be a margin of 65 degrees.
With one pair it will leave 3 degrees to the room temperature. That is going to fail!
I recognise what you want to say. I agree with you in principle, but your initial explanation was incomprehensible to me. The long explanation is still incomprehensible to me. Maybe that is my fault.
I propose that this is far simpler:
The maximum output of a BJT ClassAB amplifier is around 1/5th to 1/6th of the total Pmax of the devices in the output stage.
i.e. one pair of 250W devices amounts to a total Pmax of 500W.
That gives a range of maximum output power of approximately 80W (500/6) to 100W (500/5).
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Fine Way to cook it Down ... But you have to look on the thermal resistance to air from output devices.
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Here we are.
Note: there is no protection for your soundcard. A better solution is to build the measure box as can be found on ARTA homepage.
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Heatsink ...
... this one will be used for SA2013 - 2 channels mounted per heatsink as SA2013 v3.4 will be a 4 channel amplifier driven by active crossover.
Heatsink dimensions: 400x210x86 mm, < 0.15RthK(K/W)😉
Datasheet: ct-540 from cooltec
... this one will be used for SA2013 - 2 channels mounted per heatsink as SA2013 v3.4 will be a 4 channel amplifier driven by active crossover.
Heatsink dimensions: 400x210x86 mm, < 0.15RthK(K/W)😉
Datasheet: ct-540 from cooltec
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CCIF IMD is only DFD2 (see ARTA manual page 45/46)
- 0.00021% @ 100W @ 8R
- 0.00028% @ 200W @ 8R
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Literally the excerpt does read that way.
But I suspect it is not true that the actual specification is only DFD2.
Instead, that some CCIF type instruments only measure DFD2.
Anyone have a copy of the standard to check?
DFD3 will be well masked by the particular CCIF frequencies, but not by real music.
So I think the DFD3 is like 20 kHz 2nd harmonic distortion test. Still a reasonable test of linearity even if the specific measured frequency is inaudible.
You need not care because in your amp they are all inaudible😉
Best wishes
David
I notice that CCIF specifically recommends 19 + 20 kHz for amplifiers but you have chosen lower.
I expect you have a reason that is not just to improve the numbers?
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The reason is the 48kHz sampling rate where generated 13/14k sinus has more as only 2 sampling points. 😉
You mentioned you had an ASUS Xonar. I don't know all the different models but I think they do at least 92 kHz sample rate?
Best wishes
David
In Stereophile Magazine , John Atkinson talks in a first time about f2-f1 product , 1khz in 19+20 khz case, because it is in audio band and it is far away from test frequencys. Obviously the best is to have all the products small. Astx made a very good amplifier, almost perfect.
I repeat the measurement at SARA, my amplifier, at half of power, 50W in 8 ohm and DFD2 is 0.00005 %....Of course DFD3 is much bigger, but nobody is perfect 😀😀😀
Good job, well done Astx, go on. 😉
I repeat the measurement at SARA, my amplifier, at half of power, 50W in 8 ohm and DFD2 is 0.00005 %....Of course DFD3 is much bigger, but nobody is perfect 😀😀😀
Good job, well done Astx, go on. 😉
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Thanks!
DFD2 of SARA looks really excellent - but why is DFD3 so much higher? Try to repeat your measurements with linear frequency scale and an averaging of about 8 to 16 times...
Same again as loopback reference to be sure, DFD3 does not come from soundcard.
Yes my Xonar can do 96k/192k. But noise level is higher choosing 96k and even higher using 192k.
Need a better soundcard ...