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Old 16th November 2009, 07:26 PM   #5911
Ryssen is offline Ryssen  Sweden
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Quote:
Sommething not so funny happend,I heard it sounded distorded
and I opened the F5 ,and at the bottom was R11 from one channel and R12 from the other laying...lose...
I fitted new resistors,and it seems to work.
However I was going to check the bias and offset,but it seems I lost the instruktions,anyone got a link,don´t wanna read the whole tread again..
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Old 16th November 2009, 07:31 PM   #5912
cviller is offline cviller  Denmark
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Quote:
Originally Posted by Ryssen View Post
I fitted new resistors,and it seems to work.
However I was going to check the bias and offset,but it seems I lost the instruktions,anyone got a link,don´t wanna read the whole tread again..
Sounds extreme... maybe you should check if your solder joints overheat while playing.

The adjustment instructions can be found here:
http://www.firstwatt.com/downloads/F5-om_sm-080527.pdf
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Old 16th November 2009, 07:38 PM   #5913
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Set pots to zero.
Measure dc offset across output, measure bias across 0.47R source resistor.
Do not connect speakers while adjusting.
Bias = V/0.47
eg. 0.94V/0.47 = 2A bias
0.6V/0.47 = 1.28A bias

This applies to single output pair
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Old 16th November 2009, 07:40 PM   #5914
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by thanh1973 View Post

The improved simulated performance was from using the higher voltage rails (eg +/-40V) and not from cascoding.

Best Wishes, Don't give up just yet


That I suppose is not the only thing that happens with cascode
Not from whats written about it
But why on earth you think its rude to ask questions is beyond me
But I like your chin up remark


Just a side remark
You know fore a fact that NelsonPass wants us to experiment and learn
Its not just about copying his designs
Nelson supported multiple outputs
He also suggested cascode
And gave other small hints
Like a good teacher does

But sure, things have gone a bit out of control
But I sure know the question "how do I design the perfect speaker"
There is no answer
But if its about learning, almost anything goes
Its a crime putting limits to the possibility of learning
Theres plenty of that around the world

Last edited by tinitus; 16th November 2009 at 07:46 PM.
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Old 16th November 2009, 07:44 PM   #5915
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I never said it was rude to ask questions.
I said it was rude to ignore or disregard advice after asking for help

As a scientist I am all for experimentation. If you have read my posts hopefully that message would have come across.
I don't think I have ever tried to discourage anyone here from trying new ideas.

Last edited by Melon Head; 16th November 2009 at 07:47 PM.
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Old 16th November 2009, 08:22 PM   #5916
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by thanh1973 View Post
I don't think I have ever tried to discourage anyone here from trying new ideas.
No, you have not
Always been helpful
And maybe learned something as well

Just a memory
Do someone else but me remember a long time ago when Nelson supported a couple of young lads trying to use a gainclone thing as a driver stage fore ZEN amp
Or something like that
It was quite impressive to follow
It was going on intensively quite a while
Young lads who were eager to learn
But also seemed to learn fast
I believe one was chinese or korean
That was my first time reading this forum
I knew right away it was something special

A long time ago now, and many other things have happened
I do wonder tho
The connex guys design amps with a gainclone thing as driver
Im not sure that a common thing, is it
Just a crazy thought
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Old 16th November 2009, 08:29 PM   #5917
Ryssen is offline Ryssen  Sweden
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Quote:
Sounds extreme... maybe you should check if your solder joints overheat while playing.
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.
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Old 16th November 2009, 09:09 PM   #5918
smyslow is offline smyslow  Europe
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Quote:
Originally Posted by EUVL View Post
In my published circuit, which is identical to what I built, I did use different resistor values for the top (2SK170 / 2SJ201) and the bottom (2SJ74 / 2SK1530) halves. This is because while the MOSFETs are perfect complementary devices, the JFETs are not. Using different resistor values would allow gain balancing between the two halves, such as they contribute equally to driving the load, and also allow better harmonic cancellation.

Patrick

Hi Patrick,

I'm sure, your choice for the resistor values improve the thinks here. But during the building of my F5 I decided to use in a first step the original values and to switch to your values (or maybe new values) at a later time. This, because I wasn't sure where I would end up: your X proposal, a simple (not grounded) connection between the JFET source resistors or four single F5s. Now, some month later I must say I was quite lazy. I spent all my free time listening to this wunderful amp and a lot of money for buying new CDs.

Cheers, Uwe


Quote:
Originally Posted by EUVL View Post
Balanced, all JFET, no global feedback, 2MHz bandwidth, battery powered, drives 200 ohm load with ease, .....
BTW, have you published your preamp design somewhere here on diyAudio? Or maybe elsewhere?
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Old 16th November 2009, 09:56 PM   #5919
smyslow is offline smyslow  Europe
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Quote:
Originally Posted by EUVL View Post
Since smyslow has apparently built the X-version with floating X, maybe he can also share his experiences.
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.

For a first rough bias and offset adjustment I have shorted the X and connected this node to GND. After setting the bias for every board I removed the short and all the following fine adjustments were done in the final X configuration without any problems. Of course the bias and DC offset adjustment for the Xed F5 is more time-consuming then for the original one.

Regards, Uwe
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Old 16th November 2009, 10:04 PM   #5920
smyslow is offline smyslow  Europe
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Quote:
Originally Posted by P. Lambda View Post
Would I be able to use SE input by grounding the minus input ?
Yes, I used the amp in this configuration three month or so without any issues. But keep in mind that the Xed F5 isn't a perfect single to balanced converter, i.e. the amplitude at the inverting output is lower then at the noninverting output. You get the best even distortion cancellation results only with a balanced input signal.

Regards, Uwe

Last edited by smyslow; 16th November 2009 at 10:07 PM.
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