F5 power amplifier

[Neutrality]

Current limiting, yay or nay?

[6L6]

I know there are people who remove the current limiting and say that the amp sounds wonderful, the gods speak, angels kiss you, etc...

I, personally, am going to build mine as designed, get it up and working properly, burnt in and happy. Then, and only then will I try it without the current limiting.

[AndrewT]

I'd say there are four different locations for a speaker protection circuit to be chosen.
In the output lead after the amplifier.
In the supply rails to the amplifier, but after the main energy store of the smoothing capacitors.
At the input to the amplifier.
Intrinsic to the circuit of the amplifier.
Any of these locations could be made to work for some of the fault scenarios that the speaker needs to be protected from. I don't think any one location satisfies the protection duty for all fault scenarios.

I think you need to mix and match to protect against the high risk scenarios.
I like input muting, cheap and easy and overcomes source faults. But it must latch for as long as the fault exists.
I like rail fuses, cheap and easy and does protect from long term almost DC output currents.
I like VI limiting, not so cheap and not so easy, but can prevent destruction of parts of the output stage.

But I am inclined to think that all these three together do not protect against all the high risks. Something else is needed, an output relay or output crowbar or? Preferably not an output fuse, neither outwith the global loop, nor within the Global loop.

[budwiser]

Any thoughts on techniques to mount mosfet's to the heat sinks. I used a pressure bar on my gainclones made from aluminum channel. I noticed that others use a washer, would the channel technique work on this amp ok.

[udailey]

Originally Posted by budwiser

Any thoughts on techniques to mount mosfet's to the heat sinks. I used a pressure bar on my gainclones made from aluminum channel. I noticed that others use a washer, would the channel technique work on this amp ok.

Both techniques are good. Look, again, here ESP - Heatsink design and transistor mounting
Notice that you should pay close attention that when you drill your hole in the heatsink you should also countersink a tiny bit to remove the upheaval of the aluminum.
Uriah

[max426]

Originally Posted by budwiser

Any thoughts on techniques to mount mosfet's to the heat sinks. I used a pressure bar on my gainclones made from aluminum channel. I noticed that others use a washer, would the channel technique work on this amp ok.

My F5 has been working just fine(about 1 1/2 yrs.) with alum channel securing the fets, as seen here DSCN3798 - My Photo Gallery

jim

[udailey]

I think that Andrew has a couple good suggestions. Of course he does and he knows much more than me. For protection I like his idea of input signal to ground and I like output of power supply interrupted. Could this pass over a transistor and then just turn transistor off in a short? This depends on the transistor's 'on resistance.' The transistor will run hot and we already have a lot of heat. Perhaps two relay positions. Relay after power caps to remove power to the amp, but dont remove power from protection circuit .... and relay to mute by sending signal to ground.
Uriah

[Neutrality]

I was thinking, if you have fast blow fuses after the filter caps in your supply, wouldnt that be enough to allow one to remove the current limiter from the F5 boards?

Or is a fuse not fast enough at disconnecting power?

[udailey]

How accurate is a fuse and what if one blows and the other one doesnt? Dunno if thats the answer. Maybe fast blow on AC but I dont see how you can purposely blow a fuse to protect a speaker against DC.. if thats the concern.

[udailey]

Happy post 10000!