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F5 Turbo Builders Thread
F5 Turbo Builders Thread
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Old 11th January 2018, 10:36 PM   #5011
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F5 Turbo Builders Thread
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Originally Posted by Rixsta View Post
... use of Toshiba 2SC2705Y outputs over the IRF-P pairs.
.......
typo , I resume .....
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Old 11th January 2018, 11:00 PM   #5012
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2SC2705Y is the cascode device.

2SK1530/2SJ201 are the mosfets in the above mentioned build.
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Old 12th January 2018, 08:02 AM   #5013
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F5 Turbo Builders Thread
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Old 14th January 2018, 10:34 PM   #5014
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Quote:
Originally Posted by Rixsta View Post
Its said that the F5 Turbo is more laid back than the original F5 but when I heard it my ears heard more power and authority (which really nocked my socks off!) , if the F5 Turbo was too laid back does anyone know for what reason or what part of the circuit would be responsible for that ? someone else said that the original F5 more neutral which I guess is a good thing!
Reduced feedback in turbo. Needed for stability with more mosfets and rail voltage. Also increases gain.

Regular F5 is more lively if kept within its power and current comfort zone.
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Old 16th January 2018, 03:01 PM   #5015
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Default MUR3020W VS MUR3020WT-N3

Hi all! First I want to thank everyone and especially Mr. Pass for your generosity of time, teaching and engineering skills. I'm still pretty green but have successfully built a B1 buffer and Pearl 2 to drive my beautiful Mcintosh MC-30's into my Klipsch Cornwall III's.

I'm happy as a clam and very grateful for everyone's contributions.

I'm building an F5T v2 and am stumped about the diodes. Is there an issue with using MUR3020WT-N3's in the amp stage instead of MUR3020W's?

Looking at the spec sheets the only difference appears to be that the WT-N3's have a 22ns recovery time vs the W's at 35ns. I'm not seeing any info regarding the impedance of these diodes.

Would I need to modify the value of the source resistors?

My gut is saying that faster is better, all other things remaining the same. Is there any reason NOT to use these? Aside from the price? Mouser is selling WT-N3's for double the price of the W's.
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Old 18th January 2018, 06:53 PM   #5016
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accidently doubled PSU voltage on F5 (42V per rail) for a short time. everything looked like normal, no smoke. then I fixed PSU and have got normal voltage about 22V and started to fire up.

got 0V on R7 R8 (jims audio F5kit) with 0 resistance on P1 P2. but increasing resistance on P1 and P2 didnt get any effect, still 0V on R7 R8, no heat from mosfet at all. then saw some little smoke from two amp boards separately. now I have 15-20V directly beetween 1 and 3 pin on mosfets, depending on P1 P2 resistance. 0 DC output, no heating.

what I have to check firstly?
thank you.
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Old 18th January 2018, 07:02 PM   #5017
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F5 Turbo Builders Thread
always first check outputs for shorts ; when you find group with short , take out one by one to find Dodo

after that check upstream for shorts ; if something look fishy , desolder and check with diode test (DMM) or matching jig (JFets)
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Old 18th January 2018, 07:15 PM   #5018
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Quote:
Originally Posted by 6767 View Post
accidently doubled PSU voltage on F5 (42V per rail) for a short time. everything looked like normal, no smoke. then I fixed PSU and have got normal voltage about 22V and started to fire up.

got 0V on R7 R8 (jims audio F5kit) with 0 resistance on P1 P2. but increasing resistance on P1 and P2 didnt get any effect, still 0V on R7 R8, no heat from mosfet at all. then saw some little smoke from two amp boards separately. now I have 15-20V directly beetween 1 and 3 pin on mosfets, depending on P1 P2 resistance. 0 DC output, no heating.

what I have to check firstly?
thank you.
Did you accidentally "double up the voltage" by not having a negative rail but instead having two positive rails?
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Old 19th January 2018, 08:41 AM   #5019
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Quote:
Originally Posted by Hikari1 View Post
Did you accidentally "double up the voltage" by not having a negative rail but instead having two positive rails?
yes
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Old 19th January 2018, 04:19 PM   #5020
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Quote:
Originally Posted by 6767 View Post
yes
Some food for thought:

I believe there is no cascode on the Jim's Audio board. Your jfets saw 44V...2sj74 is probably done. But this might be good news...since I doubt that the Jim's audio Jfets are genuine. I'd start by desoldering those and testing them. Apologies to Jim's Audio if they are genuine.

Then I'd move on to the Mosfets...the N side had reverse voltage on them. I'd remove them and test...I don't know if Jim's audio matches the mosfets. They need to be matched. So maybe a blessing in disguise again if you bought a kit with unmatched fets.

If you are using the diodes test them too.

Also test the trimpots by measuring the change in the resistor they parallel to see if they work.

And lastly...did you applied positive voltage to every cap on the negative rail? Was reverse voltage applied to the caps?

This would make me worried about the caps. I'd replace any caps on board and test the PSU caps....you might need a cap tester. But you might be OK...hard to know. It depends on how tough the caps are and how long they had reverse voltage.

And don't feel too bad about it. These things happen. Consider it payment for a better understanding of how this amp works.
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