F5 power amplifier

[bobodioulasso]

Smyslow,
How far did you match the two sides of the X?

[cviller]

Originally Posted by Ryssen

The sink does get sligtly warmer now than before,The offset and Bias(1,3A)is spot on.How can it then get hotter?
It sounds fine,no distortion.

I was referring to the resistors that fell out of the board - this may have been due to the resistors cooking more than what good was. I'm not sure how plausible it is, but if the resistors R11 and R12 were off (too high) resistance it could have caused them to heat up more while playing music and at the same time having less dissipation on the heat sink.

Another thing and probably more plausible could be incorrect adjustment.

[smyslow]

Originally Posted by bobodioulasso

How far did you match the two sides of the X?

Only the JFETs regarding Idss, if I recall correctly something around Delta_Idss = 100uA (Idss ~ 10mA). And the MOSFET source resistors and feedback resistors. All other resistors are of 0.1%.

Uwe

[gaborbela]

Hello
Guys when I understand the advise clearly of course I take it , I would be crazy not to do that .
Especially from JUMA who was always so helpful . I have BL , and GR grade JET , now days hard to find these JETs .Especially in V grade (and enough parts to match them for 4 board) . I have to stick with the BL grade .
Juma I take your advise and I use 4k7 resistor to feed the BJT and 2k7 frome base to the ground .
Next time if I'm tired ( I didn't slept more than 24 hours) I do not ask for help .It will be no more misunderstanding .
I hope you can forgive me !
Thanh we always used the word JET (probably wrong to do that) not jFET --- that is why I got confused !
Now I slept I see different way all and clear to me .
generg thank you !
Thank you one more time guys , no more question "just hands on" !!
Greets

[EUVL]

> I hadn't any problems with increased DC offset drift (neither absolute nor differential) beside the well known absolute offset drift after power on (during heating). Right now the absolute offset is something around 10mV and the differential offset is around 1mV for both channels.

I was referring to drift during power-up. Once at steady state, it was very stable.

The Xed-F5 does have some DC feedback, so it is not anywhere as bad as the AX during warm up. The drift will be worse with Fairchild devices (as they are in the SE version). But I still recommend loading each of the outputs to ground with say 33R 50W.

Perhaps you could also commend on the sonic difference between grounded and floating X. For me, the difference was not significant. But I have not been listening for long, and also it was a long time ago.


Patrick

[tinitus]

Now you are at it, regarding cascode connection
We have had two variations
One with base resistor/cap connected directly to Jfet
Other variation connected directly to ground
Nelson clearly stated that probably somewhere in between
Or that it would be best to try it out, what to choose

And what really makes the difference
Certainly not the present 10R ground resistor, at least I guess not
So, it must be the direct connection to Jfet that might be critical
Is it the 2K7 or maybe the cap

I have decided to replace the original 10R ground resistor with 3x 5R resistors
They are ofcourse individually adjustable
Maybe a trim pot might work too, maybe just in paralel with resistor to fine adjust
Just my thoughts about it
Please read #NOTE#, pinout is changed to use lateral Renesas

[gaborbela]

I will try something like these .
The 10R s are will be not grounded after I set up the bias and the offset !
Of course just for the X version.
Greets

[alazira]

Originally Posted by AndrewT

---
I have never seen a Mega Farad but I would not enjoy crashing into it with my car (automobile).

I think a Mega Farad is the thing that lives in the Loch Ness.

[EUVL]

If you really have to cascode, why not just use a simple JFET as cascode, a la Borbely?
You can use J111 / J174 for that purpose. Will give you 5V Vds across the Toshibas at about 6mA Id.


Patrick

[gaborbela]

Thank EUVL
Good idea , I have to take a look if I found something at Mr Borbely site .
Thanks one more time .
I'd like advise like yours , you do not write to me just give it up !
Always helpful.
Greets