F5 power amplifier

[Zen Mod]

you can't measure effective DC offset at full blast ;

if clipping is approx. symmetric , bring your speakers and enjoy .

[bobodioulasso]

Originally posted by pro
I would not have ever believed.

Without caps

Unbilievable but true!

How is the sound?

[pro]

MONO



but sounds
no hum, very clear. I have measured about 1hom of output impedence. Bias is 350mA, enough for the FIRST WATT in class A.
maybe I'll leave it with this bias, so I can listen in summertime also, withot sweating. I have already the Zen V4 for this

[Nelson Pass]

Originally posted by pro
About 19V clips the positive, the negative something more.
Is it normal 200-300 mV of offset at this voltage?

Perhaps your limiters are kicking in. Are you using 22K for R21 and R22?

[bobodioulasso]

I have measured about 1ohm of output impedence.

How did you measure that?

From PDF:
"...
Measured Performance
The gain of the circuit is 15.15 dB. The input impedance is 101 Kohm, and the output impedance is 0.1 ohms, for a damping factor of 80."
..."

[pro]

R21-R22 10K.
Maybe the mains was a little bit low because was 23.3 VDC or the couple not matched of IRFP 140N/9140.
Bobo I measured 21.2 V without load, and then 19V with 8 hom load. So 19V/8hom=2.375A. 2.375A/2.1V(the difference beetwen Unloaded and loaded) =1.13 hom. DF=8/1.13=7.
Or not

Mr Pass, this morning I have read the review of your XP-15 phono stage. One of the best in the world at that price. Ccongratulations.

[bobodioulasso]

I measured 21.2 V without load, and then 19V with 8 hom load. So 19V/8hom=2.375A. 2.375A/2.1V(the difference beetwen Unloaded and loaded) =1.13 hom. DF=8/1.13=7.

Do you mean Peak to Peak output voltages ?
The voltage difference is mostly due to output devices residual voltage and emittor resistors drop out.
So, you dit not evaluate the dynamic output Z ( Z speaker / Damping factor) which takes NFB in account.
Though i cannot tell how to measure it...

[AndrewT]

reduce your signal so that the output voltage is well below clipping.
Now measure the effect of connecting and disconnecting the load.

If it is as bad as 2V then you have built something wrong.
A ClassA amplifier should hardly drop at all, due to the continuous loading on the PSU.

[pro]

Bobo, the measure is made on a resistor.
This is the dark side of the moon.



Andrew, actually the bias is only 350mV so no class A at clipping, but I will do some measure at lower level, as you say, and i'll report results.

[bobodioulasso]

Sorry for my wrong last post.