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Old 2nd May 2012, 10:55 AM   #1361
AndrewT is offline AndrewT  Scotland
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Even if it were a bass only speaker.

I keep referring to our average listening levels of 10 to 30dB below our maximum power levels, when listening loud.

It appears Members are not appreciating average levels and always assuming that peak levels are continuous. Peak levels cannot be continuous except with DC and we don't listen to DC !
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Old 2nd May 2012, 11:22 AM   #1362
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I agree 100%. Psu diodes may present slightly different issue, but as far as source diodes go, I think it is only necessary to couple them to each other vs major heatsinking. In V3, with just 1A through each diode, you can pass, 8A to the load. With 32Vthe rails, that is a lot of power. Considering also that your diodes will only be dissipating 1W each and 8wthe total, and that is figuring safely.
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Old 2nd May 2012, 11:33 AM   #1363
AndrewT is offline AndrewT  Scotland
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Have we seen advice on what the Vr (=Vf) should be across the diode bypasses/source resistors for normal operation?

The previous Vr of >=500mV does not seem appropriate. That forces the diode to pass an unknown current that is completely unrelated to the stabilising effect of the source resistor.
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Old 2nd May 2012, 12:55 PM   #1364
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I note that the F5 Turbo V3 uses unobtainable FQA19N20 MOS-FETs.

Now I can get FQAxxNxx devices that have a higher Ciss, Cgs and Cout --

OR FQP19N20 devices that are electrically identical but have almost double Th(js) due to their TO220 packaging.

Does anyone have any views as to which would be the better way to go?

I would guess that the FQP19N20 would be better but more attention would have to be taken to cooling.
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Old 2nd May 2012, 01:00 PM   #1365
Tea-Bag is offline Tea-Bag  United States
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Quote:
Originally Posted by KatieandDad View Post
I note that the F5 Turbo V3 uses unobtainable FQA19N20 MOS-FETs.

Now I can get FQAxxNxx devices that have a higher Ciss, Cgs and Cout --

OR FQP19N20 devices that are electrically identical but have almost double Th(js) due to their TO220 packaging.

Does anyone have any views as to which would be the better way to go?

I would guess that the FQP19N20 would be better but more attention would have to be taken to cooling.
My solution to that - build a board that will do both...
TO-220 front, backTO-3P/247 packages.

Also using Vishay U30DCT diodes in smaller package as an option.
I think bias levels may have to suffer, but with adequate sinking and attachment to sink, its possible. The actual part inside the packages are very small, so it's about spreading drain heat afiak. Otherwise the FQP's make equal spec part (except dissipation) and are still available, not obsolete etc.
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Last edited by Tea-Bag; 2nd May 2012 at 01:03 PM.
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Old 2nd May 2012, 01:10 PM   #1366
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I guess that I might have to go to 6 devices per side just to get Junction to Heatsink transfer somewhere near manageable ???
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Old 2nd May 2012, 02:53 PM   #1367
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Quote:
Originally Posted by AndrewT View Post
Have we seen advice on what the Vr (=Vf) should be across the diode bypasses/source resistors for normal operation?

The previous Vr of >=500mV does not seem appropriate. That forces the diode to pass an unknown current that is completely unrelated to the stabilising effect of the source resistor.
Actually, If the diodes are kept away from the heat of the mosfets, they shold conducting in perfect unison with the Vdrop across the parallel 1R source resistors. If you attach them to the heatsink and and they see the heat generated by the mosfets, they will begin to conduct earlier andit would seem that you lose some of the degeneration and stablilization effect of the source resistors.
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Old 2nd May 2012, 02:54 PM   #1368
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Quote:
Originally Posted by KatieandDad View Post
I note that the F5 Turbo V3 uses unobtainable FQA19N20 MOS-FETs.

Now I can get FQAxxNxx devices that have a higher Ciss, Cgs and Cout --

OR FQP19N20 devices that are electrically identical but have almost double Th(js) due to their TO220 packaging.

Does anyone have any views as to which would be the better way to go?

I would guess that the FQP19N20 would be better but more attention would have to be taken to cooling.
Look at my signature If the susbstitute doesnt suit you, TeaBag is selling the FQP counterparts i believe.
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Last edited by buzzforb; 2nd May 2012 at 03:19 PM.
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Old 4th May 2012, 02:23 AM   #1369
a.wayne is offline a.wayne  United States
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Is there a preference for the V3 and why .....?
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Old 4th May 2012, 10:00 AM   #1370
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Default few pairs of final transistors

definitely I will buy a few pairs of final transistors ,somebody has to sell?
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