F5 power amplifier

[tinitus]

Careful, it may be a bit tricky to assemble, and do work on
Takes practice

Anyway, a very tall box design with F5 would result in the upper half of the box being empty, which seems like waste to me

[AndrewT]

Originally Posted by generg

I like the sound of the F5 without current limiter more, may be because my Thiel SCS 4 has only 4 Ohm.
But my current is going up and up, slowly but sure. Will be there a stop? Or is it impossible to get a balance?

Oh I forgot I put away the thermistors too!

the current limit is set too low for 8ohm speakers played loud.
It is far too low for 4ohm speakers played loud.

If your amp blows up, or takes out your speakers, because you deleted the thermistors, then you deserve all you get.

[tinitus]

Originally Posted by AndrewT

If your amp blows up, or takes out your speakers, because you deleted the thermistors, then you deserve all you get.

A bit harsh I would say

Anyway, with multiple output devices I suppose theres no need to worry

[Russellc]

Anyone know if the Large gold heat sinks over on the Apex thread in vendors forum would work for F-5?

Russellc

[jacco vermeulen]

Russell,

if you mean the $20 each RF heatsink, the best you can expect is 0.50C/W

Or 2 times 0.60C/W, the equivalent of 0.30C/W, if you saw the goldy locks in half.
The densely spaced ribs make it a low efficiency heatsink for heights above 6"

[vdi_nenna]

Anyone know if the Large gold heat sinks over on the Apex thread in vendors forum would work for F-5?

Yes they will. Use 2 per channel.

[sekess]

I am using some Hammond 159ZL chokes for the CLC power supply. With air core inductors I have read that the inductors should be mounted as far away from each other as possible (and/or at 90deg angles to each other) to minimize magnetic coupling.
When using the iron core Hammond chokes, is mounting proximity still an issue? Or, is it not that significant since more of the magnetic field will be concentrated atthe iron core?

Thanks,
Steve

[tinitus]

Originally Posted by vdi_nenna

Yes they will. Use 2 per channel.

They are 170x250mm
Yes, 2 pr channel ought to work
I would prefer more like 4 pr channel
But will it still be a bargain?

[generg]

Originally Posted by AndrewT

the current limit is set too low for 8ohm speakers played loud.
It is far too low for 4ohm speakers played loud.

If your amp blows up, or takes out your speakers, because you deleted the thermistors, then you deserve all you get.

I trust in God and Nelson Pass:
The circuit of Figure 5 illustrates the basics and does in fact work, but has a tendency toward instability ...and the bias drifts with temperature, requiring a lengthy adjustment period.
.... This allows adjustment of the output stage bias current and also the output DC offset.
We can stop here, and the amplifier will be fully functional. The remaining additions will enhance temperature tracking and provide for output current limiting.

[AndrewT]

Originally Posted by generg

has a tendency toward instability ...and the bias drifts with temperature,

if the heatsinking is marginal or the ambient temperature rises then the thermistors are no longer optional.

If the heatsinking is designed for worst case condition as Pass would do, then the stability with temperature brought about by adopting the full thermistor compensated circuit is neither a problem nor a necessity , just a time saving exercise.