Franz,
Not sure which circuit config you are using...
Probably one of two things is happening, maybe three.
3) the high input Z through the attenuator (?) has added capacitance causing the leading edge to be slowed - check the signal (and post?) that is found at the input of the amp. Or maybe there is a cap to ground at the input for RFI?
2) insufficient current through the jfets - can't drive the input capacitance of the Mosfets properly, OR there is added capacitance going to the gates of the Mosfets (like are you using shielded cable there, a long run?)
1) somehow there is extra/undexpected parallel C in the feedback leg
Check the input signal, the output of the jfet signal (with and without Mosfets) and at the gate of the Mosfets, and at the output - preferably with the feedback eliminated or reduced considerably...
Not sure which circuit config you are using...
Probably one of two things is happening, maybe three.
3) the high input Z through the attenuator (?) has added capacitance causing the leading edge to be slowed - check the signal (and post?) that is found at the input of the amp. Or maybe there is a cap to ground at the input for RFI?
2) insufficient current through the jfets - can't drive the input capacitance of the Mosfets properly, OR there is added capacitance going to the gates of the Mosfets (like are you using shielded cable there, a long run?)
1) somehow there is extra/undexpected parallel C in the feedback leg
Check the input signal, the output of the jfet signal (with and without Mosfets) and at the gate of the Mosfets, and at the output - preferably with the feedback eliminated or reduced considerably...
Hi Bear
Maybe you missed it: it is a trial, to get a 4 channel "Mini F5" e.g. reduced voltage, reduced dissipation and reduced power around 5W per channel.
I will use it to drive my tweeters and midrange horns.
And the treble rolloff I measured, has nothing to do with input impedances, attenuators and so on.
It was a low impedance square wave generator and an scope showing what I am hearing.
I am sure: the low voltage for the MOSFET's does result in undesired gate capacitances.
Thats why I don't investigate in this treble loss, but I wait for delivery of other MOSFETs for the Mini F5.
I will also build soon another "full" F5, the parts are ready:
(image of pirated merchandise removed by moderators)
I had very good luck today and could buy this Talema TRT5002218 500VA trannie for only 108sFr (about 95US$), 50sFr cheaper than I expected.
Sometimes, friday 13th is not as bad as some people are thinking...
Franz
Maybe you missed it: it is a trial, to get a 4 channel "Mini F5" e.g. reduced voltage, reduced dissipation and reduced power around 5W per channel.
I will use it to drive my tweeters and midrange horns.
And the treble rolloff I measured, has nothing to do with input impedances, attenuators and so on.
It was a low impedance square wave generator and an scope showing what I am hearing.
I am sure: the low voltage for the MOSFET's does result in undesired gate capacitances.
Thats why I don't investigate in this treble loss, but I wait for delivery of other MOSFETs for the Mini F5.
I will also build soon another "full" F5, the parts are ready:
(image of pirated merchandise removed by moderators)
I had very good luck today and could buy this Talema TRT5002218 500VA trannie for only 108sFr (about 95US$), 50sFr cheaper than I expected.
Sometimes, friday 13th is not as bad as some people are thinking...
Franz
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BTW:
the dammned thing (missing treble but driving the tweeters) is burning in and sounding better, day per day!
No, the square wave does still look the same, but it is sounding better for my brain every hour I use it
I am 54 years old and I my listening capabilities are restricted over 12 to 13 kHz.
But: my brain does compare the reproduced sound with the reality.
And the brain is correcting many missing things, over time.
Happy to have a burn in experience!
(Smile)
Franz
the dammned thing (missing treble but driving the tweeters) is burning in and sounding better, day per day!
No, the square wave does still look the same, but it is sounding better for my brain every hour I use it
I am 54 years old and I my listening capabilities are restricted over 12 to 13 kHz.
But: my brain does compare the reproduced sound with the reality.
And the brain is correcting many missing things, over time.
Happy to have a burn in experience!
(Smile)
Franz
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Just be very careful there Franz, You might be missing something.
You see a few years ago I had Electric Shock Therapy,
all thought that burned my brain in,
I still miss little things,
and the little thing I miss the most is my mind.
So be careful how you handle that big 500VA trannie.
Hello Franz,
Please he/she can tell me where he/she bought these PCBs? So that I can order.
Thank you very much,
José Pedro
those boards are pirate stuff 
look up the spec sheets, and study transistor orientation carefully, and ofcourse F5 manual
in a week or two you will be able to build it on some of those point whole proto boards
not very difficult, and maybe even much better
btw, I think all kinds of power supply boards sucks
as a minimum one should learn how to build and wire a simple power supply
then it might make sense to use boards
well, thats just my personal opinion
look up the spec sheets, and study transistor orientation carefully, and ofcourse F5 manual
in a week or two you will be able to build it on some of those point whole proto boards
not very difficult, and maybe even much better
btw, I think all kinds of power supply boards sucks
as a minimum one should learn how to build and wire a simple power supply
then it might make sense to use boards
well, thats just my personal opinion
those boards are pirate stuff
Hey you don't miss much
sadly in some parts of the world its all at the time, we new was available,
But the world wide publicity they give to Pass Labs / First Watt, I would think Mr Pass makes up for that way, and the stamp "PASS F5" on them dose just that.
What you lose on the swings you pick up on the roundabout.
Excuse me but "People in Glass Houses shouldnt throw stones."
meaning: LucasAdamson's Avatar
But you do make a point about fault.
To Franz:
On my version of your board my "Q1" is in the complete opposite direction to yours, and mine sounds brilliant, even tube lovers with McIntosh valve gear love it.
Franz see page 779 for more details and juma's comment on that page. I'm to scared to try it the way on your board in case i mess up the detailed sound.
I
problem - they have difficulty selling these without my name on
them.
Sorry, Your right It is your name, they are selling on,
And although people like me have got involved the wrong way round at the time, I didn't know of any other options, But with out these forums there market would dry up as its the forum that irons out "there" faults and gives support.
From forum readers who know very little about these things its a million dollar support channel they are not paying for, and if there was anything I could do for someone in your position to show my appreciation I wouldn't hesitate, Because of my learning difficulty which have always stopped me going forward, You cant imagine how much this whole forum (which wouldn't work with out your support and input) means to me and those like me.
So A big thank you Mr Pass , and my words stand corrected sorry.
AWC,
Just to clear up another apparent misunderstanding, the forum is NOT here to help iron out the faults of the pirated boards and provide support to people who buy them.
What the forum does do is enable access to APPROVED Group Buys for boards and, through the diyAudio community, provide support to those who choose this legitimate path.
So there are other, better options!
Currently approved F5 boards are available from cviller and Peter Daniel on diyAudio. In both cases they provide excellent support. Here's the two links:
http://www.diyaudio.com/forums/blogs/cviller/191-gb-f5-guide-pcb-version-2.html
http://www.diyaudio.com/forums/group-buys/140306-f5-pcb-group-buy.html
Just to clear up another apparent misunderstanding, the forum is NOT here to help iron out the faults of the pirated boards and provide support to people who buy them.
What the forum does do is enable access to APPROVED Group Buys for boards and, through the diyAudio community, provide support to those who choose this legitimate path.
So there are other, better options!
Currently approved F5 boards are available from cviller and Peter Daniel on diyAudio. In both cases they provide excellent support. Here's the two links:
http://www.diyaudio.com/forums/blogs/cviller/191-gb-f5-guide-pcb-version-2.html
http://www.diyaudio.com/forums/group-buys/140306-f5-pcb-group-buy.html
Ok so some good has came out of this unintentional thread hijacking,
With Mr Pass and jimbo51 along with tinitus comments.
Everyone will now know beyond a shadow of a doubt under no circumstances buy Chinese made boards or come to this forum seeking advice if you have,
whether your aware of the other options mentioned by jimbo51 or not.
I apologize for taking up your time and have already apologized to Mr Pass but just be beyond a shadow of a doubt, I'm sorry again Mr Pass for using Chinese made boards and taking up your time, and thanks again for making it possible to hear the quality sound im hearing,
no other manufacture would have bothered let alone constantly go that extra mile.
I will now remove myself from DIY forums cause I have a Chinese made board.
awc.
With Mr Pass and jimbo51 along with tinitus comments.
Everyone will now know beyond a shadow of a doubt under no circumstances buy Chinese made boards or come to this forum seeking advice if you have,
whether your aware of the other options mentioned by jimbo51 or not.
I apologize for taking up your time and have already apologized to Mr Pass but just be beyond a shadow of a doubt, I'm sorry again Mr Pass for using Chinese made boards and taking up your time, and thanks again for making it possible to hear the quality sound im hearing,
no other manufacture would have bothered let alone constantly go that extra mile.
I will now remove myself from DIY forums cause I have a Chinese made board.
awc.
