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Old 18th March 2012, 03:40 PM   #3311
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Originally Posted by neoinc View Post
How exactly is it to build a crippled F4 with a BA3?

I thought of building them in modules and interconnect like a BA3 pre to a F4 power. The BA3 gain should be more than enough to drive a F4 properly from what i understand.

If someone could suggest a better way, I would be happy to learn it.
Crippled F4 is basically BA PP output stage. You make FE capable of driving it,like BA2 or 3, or even what FLG is suggesting. I thought an LU SRPP or mu Follower biased at about 300ma might do the job nicely.
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Old 18th March 2012, 03:44 PM   #3312
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Originally Posted by jacco vermeulen View Post
Euh, any reference ?
I have been playin garound with the LU in sims for quite a while. After i get th eFairchild thing sorted, i plan to actually build it. From what i ahve read, th SRPP lperforms very well as voltage amplification stage into high impedance loads. Perhaps in this case, the F4 might be better suited than BA output. I hope to see.
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Old 18th March 2012, 03:47 PM   #3313
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no biasing network for the output stage....?
I think tje 200R resistor should provide bias, but perhaps This is why FLG says it needs some work
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Old 18th March 2012, 04:23 PM   #3314
generg is offline generg  Germany
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indeed the current through the 200 Ohm seems to be sufficient to produce the necessary bias voltage....
I have not seen it in this way before....

elegant flg.....
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Old 18th March 2012, 04:26 PM   #3315
generg is offline generg  Germany
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the only point i just remember that the two 220uF also served as antiplopp when turning on...
but there are other possibilities......
and maybe the input stage without feedback has a higher drift and there can be more offset drift...

but there are more compentent people around here...
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Old 18th March 2012, 05:25 PM   #3316
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Originally Posted by flg View Post
I was thinking of trying something like you see below. This is only a start. I think maybe more thinking is in order around that 200 ohm resistor...
http://www.diyaudio.com/forums/attac...89d1332079795-Click the image to open in full size.
Guess the front end needs some power too...
The bias current resistor should be variable one way or another; R200 becomes P1. Or use a TL431 setting like in BA2 output.
And - - - have a DC point as this is floating now. Instead of DC feedback to the input sources, it is also possible to connect the speakers to a pair of capacitors of say 10.000 muF to both rails.
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Old 21st March 2012, 12:10 PM   #3317
Itsmee is offline Itsmee  England
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Default F4 variation

I haven't built this yet, so I don't know if it works. I am curious to see how much the 220uF coupling caps affect the sound, probably not much and easier to find out the 'cap sound' by fitting one to the input of an F5 - but the cap wouldn't have a bias voltage as it does in the F4. Anyway, this is my brain fart, the 1M and 1uF at the input can be dispensed with, and some of the values may need tweaking. Can't help feeling I've over looked something, I'm sure someone will point it out.
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Old 21st March 2012, 12:17 PM   #3318
Zen Mod is offline Zen Mod  Serbia
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gate zeners , as $#@!! Hapenning Preventers ?

in fact -= everything is OK , as long you're staying cool with input sine
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Old 21st March 2012, 12:29 PM   #3319
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gate zeners , as $#@!! Hapenning Preventers ?
I don't have the correct symbol, It represents a TL431.

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everything is OK , as long you're staying cool with input sine
Thank you ZM.

I left out the input bootstrap for clarity.

I must be getting old, any more than 5V RMS output is too loud
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Old 21st March 2012, 01:31 PM   #3320
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I meant on output gate's protective zenners , preventing excessive Ugs

you need them .
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