F5 Turbo is posted

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#502
EUVL said:
You are misquoting me I am afraid.

My proposed alternative (in post #42) is not based on reducing the source resistor (only).
The key to my proposal is using MOSFETs with much higher Yfs (e.g. 2SK3497).
That, combined with a reduction in Rsource will give the same current gain as a 2SK1530 plus a diode.

See :
http://www.diyaudio.com/forums/pass-labs/206240-f5-turbo-posted.html#post2896992

And I do not consider 0R33 for Rsource to be low. The F5X uses 0R22 since day one.
Nor have I ever experienced any bias stability at steady state.
Yes, the bias is a bit lower when cold. But once it has warmed up, it stays there.
Assuming of course your heat sinks are properly sized.

And I am still not a believer of the diode.


Patrick
Click to expand...

I was indeed "under-quoting" you.

My enthusiasm for the Turbo has declined to agnostic after more LTspice simulations. I do not trust the device models. Until I actually perform live tests I will defer judgement on the Turbo.

I do agree with you (EUVL) about the balanced F5 at 16V with low source resistors. I am built one as reported in: http://www.diyaudio.com/forums/pass-labs/213152-balanced-f5-small-footprint.html#post3033426. It uses .25 ohm source resistors and achieves very low THD up to 50 watts at bias currents as low as 1 amp.
 
#505
Amazing what you find when you have a look.
 

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#506
lhquam said:
I was indeed "under-quoting" you.

My enthusiasm for the Turbo has declined to agnostic after more LTspice simulations. I do not trust the device models. Until I actually perform live tests I will defer judgement on the Turbo.

I do agree with you (EUVL) about the balanced F5 at 16V with low source resistors. I am built one as reported in: http://www.diyaudio.com/forums/pass-labs/213152-balanced-f5-small-footprint.html#post3033426. It uses .25 ohm source resistors and achieves very low THD up to 50 watts at bias currents as low as 1 amp.
Click to expand...

Funny thing is, you don thave to hav eon eor the other. Melon head has shown the improvement it makes. If you like Rs that is low, like .22R, then run the bias @ 2A an dstill use the diodes. You get the distortion improvement from higher bias, you are using a lower Rs, and the diode is still there for a little extra grunt.
 
#507
Yeah no worries.
You can have any source resistance you want (with or without the diodes).
The higher the source resistance the greater the bias will jump when the diode completely turns on.
The lower the source resistor the lower the bias will jump when the diode completely turns on.
 
#512
Turbo current plots

Here is an LTSpice simulation of the F5 Turbo V1.2.

32 volt rails
1 amp total bias (.5 A per MOSFET)
4 ohm load
100 watts output

As you can see, the current thru the diodes "kicks in" smoothly.
 

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#514
Ih,
I can't see a value for Rs (R7etc) for the output mosFETs.
Can you state Rs & the quiescent Vrs for your Ib=500mA/device?
Can you also add a cursor @ Vin=+0.5V (instantaneous value, not AC & not DC)?
Then read off the values of the various plots at that cursor?
 
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