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F5-style pre
F5-style pre
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Old 19th December 2017, 09:20 AM   #1
Abrandt is offline Abrandt  Sweden
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Default F5-style pre

Hello guys!
Some pictures from my latest project.
I needed a preamp with some gain to drive my ZV9. The B1 I used had not the juice to drive the amp to full output with some programmaterial.
I wanted a solid state amp and I had already made the powersupplie so the +-15V was in place. I tryed some other preampideas from the internet but I was not fully satisfied. Then I got the idea to do something F5-like. And it worked out rather well I think. Please give me some feedback. More pictures if you want.
Merry christmas from Sweden, Abrandt
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Old 19th December 2017, 10:18 AM   #2
Zen Mod is offline Zen Mod  Serbia
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F5-style pre
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Old 19th December 2017, 11:11 AM   #3
EUVL is offline EUVL  Europe
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Balanced version :
The F5X Preamp


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Old 19th December 2017, 01:27 PM   #4
indra1 is offline indra1  Indonesia
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Hi Abrandt, could you kindly share your reason(s) for your choice to cascode the input jfets and your choice to reference the bases of cascode transistors to supply voltage instead of ground?
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Old 19th December 2017, 01:35 PM   #5
xrk971 is offline xrk971  United States
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F5-style pre
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Beautiful work! Love the bare wire 3D sculptures to the RCA’s.
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Old 19th December 2017, 05:59 PM   #6
Abrandt is offline Abrandt  Sweden
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Indra1
The cascod is mostly because I would try to do it and maybe to get a little less distortion. You could absoluteley make a version without them. Your question about the reference voltage, I don't understand. I have to get fixed voltage at about 5 Volt's at the bases. I could done that without the zeners maybe but ??
/Abrandt
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Old 19th December 2017, 06:06 PM   #7
EUVL is offline EUVL  Europe
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He was asking whether you connected the Zeners to Gnd and the resistors to the rails, as it should be.
The other way round was shown in your hand sketch schematics.


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Old 19th December 2017, 06:21 PM   #8
indra1 is offline indra1  Indonesia
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Hi Abrandt, in case you have not done listening comparison, you may want to try 9.1V at the bases of the cascoding transistors by switching the zeners and the 4k7 resistors. I think the jfets will perform a bit better with ~8.5V at the drains.
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Old 19th December 2017, 06:35 PM   #9
Abrandt is offline Abrandt  Sweden
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OK I se now what you mean. Du you think that would make any differens? Are not the voltage fixed at the bases in both cases? And Indra1 do you say that the FET's do a better job with 8V at the drain? / Abrandt
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Old 20th December 2017, 12:59 AM   #10
indra1 is offline indra1  Indonesia
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Yes, I think so due to lower Crss and Ciss while IGSX is still quite low.
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