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JBL4435 19th September 2011 09:37 AM

F5X from diyAudio Boards P-F5c-2V20e
 
2 Attachment(s)
Yes, I know there is a thread giong on F5X EUVL Approach but the diy Store boards are available and why not use them?

I'm currently building 2 mono F5X with the P-F5c-2V20efrom the diyAudio Store.
those are the boards with cacode option and 2nd output pair option.
I'll build the 2nd output option and "X" 2 boards for a mono block.

AFAIK Smyslow did this with the 1 output pair boards but it was not further commented.

To "X" the boards two pcb connections need to be cutted. Not nice but the boards have no "X-Option". See picture.

Here are my first 2 questions to the knowledgeable:

1. Input impedance
If I go with the 1k input resistir plus 100k reference to ground as in the original F5 I'll end up with only 500 ohms input impedance in a X design. This is fairly low. I built my AX amps with 10k input impedance and 10k reference to ground.
Here I would like to go with 22.1k input impedance and 221.1k reference to ground.
Would this be ok?

2. Relative DC offset resistors output to ground
Would it be helpful to implement the output to ground resistors from other X designs (33 to 68 ohms plus/minus output to ground) also in this design? Or is it unneccessary? If yes, why?

JBL4435 20th September 2011 05:46 AM

Input impedance F5X
 
Is there really nobody who can help me with input impedance of X-Amps and relative DC offset resistors?

Zen Mod 20th September 2011 08:31 AM

just use EUVL's schmtc

JBL4435 20th September 2011 09:07 AM

Quote:

Originally Posted by Zen Mod (Post 2717328)
just use EUVL's schmtc

Exactly this information was left out by EVUL

Zen Mod 20th September 2011 10:19 AM

you need to cross these two green/blue lines ;

in this moment my brain is sort in red , so check that twice :rofl:

gimme entire schematic which you want to use , so I can comment

heinz1 20th September 2011 10:43 AM

Quote:

Originally Posted by Zen Mod (Post 2717328)
just use EUVL's schmtc

EUVL's schematic can be found in post #1216 of the F5 thread.

Zen Mod 20th September 2011 11:20 AM

OK

use 1K in series with gates ( anti-oscillation measure ) , then anything between 22K-47K from gates to gnd .

that will be input impedance for each leg .

NB that's not same as XA amps , where is used inverting stage NFB for establishing SUSY function , which means that series gate resistor is dictating input impedance .

JBL4435 20th September 2011 12:59 PM

Quote:

Originally Posted by Zen Mod (Post 2717485)
OK

use 1K in series with gates ( anti-oscillation measure ) , then anything between 22K-47K from gates to gnd .

that will be input impedance for each leg .

NB that's not same as XA amps , where is used inverting stage NFB for establishing SUSY function , which means that series gate resistor is dictating input impedance .

Thank you!

THAT was helpful

Output resistors?

JBL4435 20th September 2011 01:00 PM

Quote:

Originally Posted by Zen Mod (Post 2717404)
you need to cross these two green/blue lines

Look at the inverted left part of the schematic.
They are already crossed

JBL4435 20th September 2011 01:02 PM

Quote:

Originally Posted by heinz1 (Post 2717437)
EUVL's schematic can be found in post #1216 of the F5 thread.

1 "Kiste" Beer if you show me the input resistors in that schematic


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