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F5 Turbo Builders Thread
F5 Turbo Builders Thread
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Old 2nd January 2020, 08:05 PM   #5921
Hikari1 is offline Hikari1  United States
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Also, I lot of us here subscribe/watch both threads. So you will be covered in the regular F5 thread as well.
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Old 2nd January 2020, 08:47 PM   #5922
djn is offline djn  United States
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Thanks guys for all your help so far. I just found out our contract with the DOI was not renewed so I have to put all projects aside until I land another gig.
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Old 14th January 2020, 10:55 PM   #5923
Maciej is offline Maciej  Poland
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Default Jfets Id again

I'm powering up my F5T v2 with cascode. Jfets were purchased as matched BL grade from diyaudiostore.
On one channel I had to increase R5/R6 to 2k2 to be able to bias properly.

The second channel required even higher resistance - 4k7, but finally worked.

What worries me is unequal measurement of Id on that board. I'm measuring 35mV on R3 and 40mV on R4. The P3 was precisely set to have <5-10 mOhms difference on R3/R4.

I was able to bias it to 0.9A per output pair with DC about 5mV.

Should I worry then about Id difference?
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Old 15th January 2020, 12:02 AM   #5924
Zen Mod is offline Zen Mod  Serbia
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F5 Turbo Builders Thread
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Old 15th January 2020, 12:21 AM   #5925
Maciej is offline Maciej  Poland
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Thanks ZM!
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Old 21st January 2020, 01:38 PM   #5926
CentralCoast is offline CentralCoast  United States
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Hi, I am building F5-turbo monoblocks. I would like to test them out one at a time using +25V and -25V rails from two meanwell 24V supplies ‎GST120A24-P1M‎. I have the supplies from my ACA amps. Is the F5-turbo biased specifically for +-36v rails? Will running them at 25v lead to anything suboptimal except lower power? Do I need to change the circuit if I run it from +-50V rails someday?
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Old 21st January 2020, 01:52 PM   #5927
Sangram is online now Sangram  India
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F5 Turbo Builders Thread
Quote:
Originally Posted by CentralCoast View Post
Hi, I am building F5-turbo monoblocks. I would like to test them out one at a time using +25V and -25V rails from two meanwell 24V supplies ‎GST120A24-P1M‎. I have the supplies from my ACA amps. Is the F5-turbo biased specifically for +-36v rails?
No. You are the person that will bias the amp and can bias it anywhere you like.

Quote:
Will running them at 25v lead to anything suboptimal except lower power?
No.

Quote:
Do I need to change the circuit if I run it from +-50V rails someday?
Yes. You will need to re-evaluate the cascode setup and add more output device pairs to handle the additional dissipation.
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Old 21st January 2020, 01:56 PM   #5928
CentralCoast is offline CentralCoast  United States
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Thanks for the quick reply.
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Old 21st January 2020, 01:59 PM   #5929
Sangram is online now Sangram  India
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F5 Turbo Builders Thread


I normally use a very low current supply, with 1A fuses just in case. My first bias point will be 100mA, and I play for an hour or so with test speakers to ensure the amp is working.

The F5T is a powerful beast and mistakes can be expensive.

The reason I know this is because I made many mistakes myself while building, destroyed lots of expensive components so I now build with some safety margin.
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Old 21st January 2020, 02:30 PM   #5930
airborne11b is offline airborne11b  United States
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Quote:
Originally Posted by CentralCoast View Post
Hi, I am building F5-turbo monoblocks. I would like to test them out one at a time using +25V and -25V rails from two meanwell 24V supplies ‎GST120A24-P1M‎. I have the supplies from my ACA amps. Is the F5-turbo biased specifically for +-36v rails? Will running them at 25v lead to anything suboptimal except lower power? Do I need to change the circuit if I run it from +-50V rails someday?
Bias is really just based on the constant current your output devices see. It doesn’t care what the rail voltage is. What is your power supply rated for? I wouldn’t be surprised if your existing PS is not up for the task in general if it came from an ACA. I believe you can cascode your jfets even if you use a lower voltage PS. If this is the case, and you plan on going higher voltage later, you should cascode. 25V rails seems very low for F5TV3 monos. It is a very expensive build. My opinion, spend the extra money and put a beefier PS in.
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