F5 Turbo is posted

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lhquam

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Joined 2010
Melon Head said:
.MODEL MUR3020wt D(IS=2.09832e-06 RS=0.0102995 N=2 EG=1.27539 XTI=0.5 BV=200 IBV=1e-05 CJO=1.14907e-09 VJ=0.4 M=0.888092 FC=0.5 TT=7.76886e-08 KF=0 AF=1)
Click to expand...

Thanks for the Spice model. I now get THD plots very similar to yours. The main difference is that my 2nd harmonic is higher than yours in both cases. Could be due to differences in Spice models for the IRFP240/IRFP9240 MOSFETs, or slight differences in biasing. My biasing looks good: it required careful adjustment to get 15 V peak without leaving class-A.
 

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L

lhquam

Member
Joined 2010
Melon Head said:
Something just occurred to me about the circuit.
I think it is capable of even better performance, just need to wait till tomorrow to confirm it.
Click to expand...

Before I saw your non-Turbo/Turbo THD plots and did some simulations, I was not convinced about the Turbo. EUVL has proposed an alternative based on reducing the source resistors to near zero, which helps, but increases the problem of bias current vs. temperature.

I am now a believer in the Turbo.
 
EUVL

EUVL

Member
Joined 2003
xen-audio.com
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
 
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A

AndrewT

R.I.P.
Joined 2004
Simply adding in a parallel diode to the source resistor is not advised.

I have asked a few times what is the set up procedure to give the diode version of the F5 a real chance to perform well. To date I seem to be the only one answering myself.

I still have to write up partIII.
 
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