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Old 4th January 2016, 09:30 PM   #1
Gyuri is offline Gyuri  Hungary
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Default F6 amp with SemiSouth SJEP120R100

F6 kit finally arrived.
I think I will build it based on Nelson Pass Talks at Burning Amp Festival 2012.
I would choose F6 with variable second harmonics.
Any thoughts?

Gyuri
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Old 4th January 2016, 09:38 PM   #2
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You could build it with just the pot on the mosfet powered from the negative rail if you don't need both positive and negative phase harmonic adjustment.
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Old 4th January 2016, 10:54 PM   #3
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Quote:
Originally Posted by 2 picoDumbs View Post
You could build it with just the pot on the mosfet powered from the negative rail if you don't need both positive and negative phase harmonic adjustment.
If you aren't matching or selecting devices, sometimes having the pot on the
top also is helpful.

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Old 5th January 2016, 12:13 AM   #4
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True
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Old 5th January 2016, 01:35 AM   #5
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Gyuri, while not a guarentee, if devices are nicely matched, I found I liked no resistance on top fet and from .05-.1 ohm of resistance on the lower fet. An LM329dz is a nice quiet alternative to a zener and gives you a little headroom over the LED.
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Old 5th January 2016, 07:09 AM   #6
Gyuri is offline Gyuri  Hungary
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Hi guys,

Thank you for the hints!
I'm not in hurry with it, so I welcome any other hints in the future.
Pots will be on positive and negative sides as well, it is for sure.
All the more so because they could only find couples among themselves.
These were from the last batches at Farnell.
I hope so these are genuine.
I have four of them yet, (two from Farnell, two from Generg).
These are working in my DIY J2.
I don't think that I disassemble it in hope of I would find close matched pairs.
And these four are from different batches for sure.
Thank you for the tips Buzz!
Thanks especially to you Papa!
You do not even think of that you teach at university?
Your presentations even I can understand more or less, despite my crappy english and my lack in knowledge in electronics.

Kind regards,

Gyuri
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Old 5th January 2016, 07:22 AM   #7
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I think Buzz's suggestion is a very good one.
It is also the simplest solution that should produce the predicted effect most people are probably hoping for.

If you can produce curves of Id vs Vgs for your parts that would be very informative/useful to give the correct advice.

Edit: To get the AC degeneration on the diyaudio pcb like Buzz is suggesting the cap lead needs to be routed to other side of resistor lead wire.

Sounds like you are interested in installing the pots for maximum adjustment though rather than choosing a fixed result.
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Last edited by 2 picoDumbs; 5th January 2016 at 07:30 AM.
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Old 5th January 2016, 07:24 AM   #8
Gyuri is offline Gyuri  Hungary
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I will do my best, I don't know how yét, but will do.
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Old 5th January 2016, 07:33 AM   #9
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If you are certain you want pots on both mosfets (which is certainly ok/desirable), you won't need to produce curves of Id vs Vgs. You can just adjust the pots by ear.
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Old 5th January 2016, 02:56 PM   #10
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I totally agree with Buzz and 2 pico.
I also settled on and enjoy that set-up
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