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Gb: F5 Pcb

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#1,021
Hi botte,

Great questions. No I haven't tried the double output modification and my primary reason for making the boards larger is to spread out the devices more for the standard configuration - and then with more space I could just as well throw in some more footprints. 😉

You might be right about the added gain and thus more nfb - this could explain the better simulations we have seen on the F5 thread. Also I think the bandwidth is slightly lowered due to more gate capacitance. If it sounds better or worse I don't know, but for sure I would like to play around with it. 😉

Yeah, I have thought about cascoding, but I'm not sure it is needed. My argument is that if you want more swing, you can do balanced instead of increasing the supply voltages. But cascoding may be nice for linearity as well... if I can fit it on the board it may be worth while.
 
#1,022
cviller said:
Yeah, I have thought about cascoding, but I'm not sure it is needed. My argument is that if you want more swing, you can do balanced instead of increasing the supply voltages. But cascoding may be nice for linearity as well... if I can fit it on the board it may be worth while.
Click to expand...

I'm not positive 😕 but cascoding may also increase the input stage PSRR and thus shield it from output stage current/voltage perturbations (?) 🙂
 
#1,023
Hi Cviller,

The nice thing about your new board is that you can try the extra pair or not. That would also work for the casscode mod. Just jumper the devices and it’s just a regular F5.

By the way, thanks for making the boards you do a great Job.
 
#1,026
Go with Jumas, but allow the option to reference the cascode device to either ground or source.
I suggested referecing the cascode to source as noticed very unusual behaviour while biasing, that did not occur with the cascode referenced to source.
I would probably use toshiba 2sa970/2sc2240, but I think the original device suggested were BC550/560. I think these have a different pin out to each other.
I will have a look for the two schematics.
It is basically two resistors and a capacitor per cascode device.
 
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#1,028
cviller said:
I was thinking more in terms of something like this (just like borbeley does). Just need to simulate if it works in this application.
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Yes that would be the preferred approach, however I couldn't get it to work satisfactorily.

I got it working with 2sj103 and 2sk246, but you have to ensure they are bl (ie highest)graded parts and idss is greater than idss of 2sk170 and 2sj74.
You also need to increase source and feedback resistor values.
 
#1,036
cviller, How about turning the outside Fet 90deg to point off the boards at the short ends as Peter Daniels did on his small F5 board. This should provide better spread on the same size board.

I am interested in 2 sets based on price.

Thanks for your efforts
 
#1,037
npapp said:
cviller, How about turning the outside Fet 90deg to point off the boards at the short ends as Peter Daniels did on his small F5 board. This should provide better spread on the same size board.

I am interested in 2 sets based on price.

Thanks for your efforts
Click to expand...

Hi npapp, Thanks for your suggestion, but I prefer having the fets in line - it is kinda my thing. 😉

I already have signups for 38 boards, so it seems like this F5 is still pretty popular!! 😎
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Any objections against blue with gold rohs through-plating?
 
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