F5 power amplifier

[npapp]

I just got a meter with a temp probe. First using silica pads, the tab temp of the Fet were 80-83c. I switched to Mica and grease and I am now measuring in the 60-65C range on the tab. Is this acceptable?

What is a safe temp for the fet to be running if I am looking for longterm dependability?

Thanks, Nick

[npapp]

North Creek winds a nice inductor that uses high quality wire from 16-8g. I have purchase a few for crossovers they do not disappoint. Here is the price list but it's really only a guide. Email or call and they will give you the current pricing.

http://www.northcreekmusic.com/NorthCreekCoilPrices.pdf

[jackinnj]

Originally Posted by npapp

What is a safe temp for the fet to be running if I am looking for longterm dependability?

Thanks, Nick

You will see quoted that every 10 degree increase in device temperature HALVES mean time between failure. At room temperature a transistor is expected to live 50 years -- go figure.

[AndrewT]

Originally Posted by Magura

copper ....... is on the wrong side of 10$ /kg when an inductor that weighs in at 0.75kg,, is sold in retail for 25$ something is most likely not right.

1.44lb~0.65kg. @ $10/kg that is $6.50 for the copper leaving a mark up of 280% to cover the manufacturing and packaging costs.
$25 still seems expensive.
In the UK, scientific wire sell 1.6mm enameled copper for just over £10/kg ready wound on a reel. Why bother rewinding it?
This is an inductor to create a slope in the low pass filter of a PSU, 1% precision is not required. +100% -50% would get us in the ballpark

[jackinnj]

I simmed it with some better (0.05 ohm Panasonic ECG) transistors. Indeed the 2mH inductor reduces the ringing occasioned by the parallel banks of capacitors -- I would like to try it out in real life...

[AndrewT]

what about increasing the inductor value to between 4mH and 10mH?

[jackinnj]

Here's 10mH vs 2mH -- note again that this is a 1kHz signal which sees a load of 1A for 800uS and 3.3A for 200uS.

[cviller]

Originally Posted by jackinnj

I simmed it with some better (0.05 ohm Panasonic ECG) transistors. Indeed the 2mH inductor reduces the ringing occasioned by the parallel banks of capacitors -- I would like to try it out in real life...

Thanks for your sims! Yeah, the ringing appears because there is hardly any filtering with the 2uH choke.

How about showing a sim of the rail noise from charge current with a constant draw of 2.6A? - I think that would very relevant in the choke discussion.
For reference you could even show the CRC performance too.

[Magura]

In real life, there is little difference, between 2mH and 5mH. Above that, inductors tend to grow real big, or become very lossy, for this application.


Magura

[ichiban]

Originally Posted by tinitus

Does it sound better without current limiter ?

In Post# 2814 Peter Daniel says:

When I listened to F5 first time, I thought pretty good, but probably not good enough to replace GC, another wasted effort

Then I thought why not removing all the parts that are not really needed and off went current limiting circuitry: the amp opened up and instead of boring became much more interesting and involving, to a point that I spent whole evening listening to it.
===================================

Just remember, without the current limiter, if you accidentally short your speaker cable when connecting, then your outputs will probably go poof!