F5 power amplifier

[AndrewT]

no.

Don't use silver. The drain of the FET is electrically connected to the heatsink interface.
That is why you are installing an electrical insulator.

If this shorts to the heatsink you could blow up the amplifier.

[sangram]

Just use regular white compound. Arctic Silver will get you a slightly lower FET temperature but is highly capacitive even if it is not conductive. If you feel like spending money, get either Ceramique or MX-3 (Arctic Cooling). These are high-performance compounds but only really useful for high heat loads (100 watts/device). In the case of this amp, you may not see more than 0.5-1 degree difference, if at all.

Also rub down the heatsink with a bit of 100 grit paper on a wood block so the mounting surface is uniform. You should see about 10 degrees difference between the FET tab and the heatsink.

[prooptiki]

Originally Posted by sangram

Just use regular white compound. Arctic Silver will get you a slightly lower FET temperature but is highly capacitive even if it not conductive. If you feel like spending money, get either Ceramique or MX-3 (Arctic Cooling). These are high-performance compunds but only really useful for high heat loads (100 watts/device). In the case of this amp, you may see more than 0.5-1 degree difference, if at all.

Also rub down the heatsink with a bit of 100 grit paper on a wood block so the mounting surface is uniform. You should see about 10 degrees difference between the FET tab and the heatsink.

Thanks I am going to try it!
I own some MX-2 (Arctic Cooling)!

[kasey197]

I saw a couple of posts up a balanced f5 - unless I'm mistaken, i believe the one posted by Patrick (EUVL) which the OP ref with the tosh fets is this one ... haven't really seen much written up on this (well not in one place), so perhaps someone who knows much more abt the amp can give some comments re supplies, power o/p, grounding and what degradation (?) occurs if you use same resistors in both top and bottom halves... best that I can recall from reading the archives, they're unequal due to diff transconductance between the P n C channel devices, but wonder how much of this is, well, academic...

[sekess]

what's the difference between a bridged F5 and a balanced F5 with respect to output power? Do you get double the voltage in the balanced version as you do with the bridged version?

Thanks,
Steve

[AndrewT]

as one speaker terminal voltage goes up the other goes down.
The voltage between the two speaker terminals is double what would appear between one speaker terminal and ground.

If the load impedance is the same the current will try to double.

Double the power into double the impedance.

NOT
quadruple the power into the same impedance.

[sekess]

So basically the total voltage potentially seen by the speakers is the same going bridged or balanced.

So, what is the advantaged of going balanced over going bridged?

Thanks,
Steve

[sekess]

Oh sorry -- just got the end of your post -- got it now.

Thanks,
Steve

[prooptiki]

Does MUR860 8A Diode have enough current for the bridge or I should choose something with higher current (which is optimal)?

In addition I saw alot of diodes with three legs (bigger current), for a bridge we use also 4 of them and we ignore the one leg?

Thanks

[labjr]

Originally Posted by AndrewT

as one speaker terminal voltage goes up the other goes down.
The voltage between the two speaker terminals is double what would appear between one speaker terminal and ground.

If the load impedance is the same the current will try to double.

Double the power into double the impedance.

NOT
quadruple the power into the same impedance.

Is there a disadvantage of balanced or bridged?