F5 power amplifier

[kpsthakur]

ZTX450, 550


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[AndrewT]

Are they inserted the correct way around?

 

[kpsthakur]

Yes they are...exactly same as working 1st channel


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[kpsthakur]

Infact this channel is working well while using the current limiter jig, and bias set's too around 0.56V with 0 DC offset, but as soon as I remove the current limiter, it never stabilise


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[fgroen]

maybe you should check for oscillations.

 

[juma]

Infact this channel is working well while using the current limiter jig, and bias set's too around 0.56V with 0 DC offset, but as soon as I remove the current limiter, it never stabilise

You can not set the bias of F5 properly with current limiting contraption like "bulb tester" (it's useful for class B amps but not in case of F5).
First take some time to read this (especially pages 6-18) and understand how this amp works and how to set it up correctly :
http://www.firstwatt.com/pdf/prod_f5_man.pdf

 

[kpsthakur]

Sure Juma, I understand, but F5 was drawing too much current and would blow the resistors, transistors and fuses, the limiter had to be included...well on a sample basis it solved some part of it and I could hear Music...so its more a confidence building thing...will go through the link and retry...thank you for the support


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[Steve Duffy]

My F5 drew too much current when I had the MOSFETS reversed, it's easy to do, I suggest you check

 

[kpsthakur]

Nope, all good at that end


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[strawa]

home made f5

Sounds fantastic on test psu 2x20V, mosfets from ebay. Worked like a charm from the first powerup, no nasty surprises. With 2x100r resistors gain is too low for my sound card, so I guess I'm going to experiment with some higher values there.

 

[wdecho]

I like seeing builds like yours. Nice work.

 

[nkdk]

f5 home made

Looks very nice, hardwired f5, only thing ,you properly need a bigger heat sink.
vel done

 

[strawa]

Thx guys, I'm learning a lot on this forum and implementing that as I go. I'm listening Armin Van Buuren right now on F5 and testing it. Heat sinks will be adequate in the final version, depending on the casing of course.

 

[peafarmer]

For R21 and R22 is there a consensus as to whether 10K or 22K1 resistors work better? I just soldered the 10K resistors in, and then found the extra set of 22K1 resistors from the kit unused. So, am kicking myself a bit for not knowing this before soldering, but is it really worth replacing the 10K resistors? I have only started one channel, so I am also thinking about building the second channel with the 22K1 to see if there really is a difference (to me). Thoughts? Thanks, Andy

 

[Dennis Hui]

Hi Andy,

I'm not sure, but are you referring to the Vfet2 amp? I'm wondering it you might
have posted this in the wrong thread.

Cheers,
Dennis

 

[jackinnj]

I found that I have some F5 kits.....

 

[cviller]

22k is preferred. It was a very early schematics where the value was 10k. You're not in trouble though, you're just letting your current limitor kick in a little earlier. If you change it to 22k , the limitor will have less of an impact on the sound.

 

[2 picoDumbs]

I found that I have some F5 kits.....

Which PCB?

 

[peafarmer]

Dennis, this is the F5. Pico, I'm using the Peter Daniels boards. I might be sqeamish, but the boards are so small that I'm not really looking forward to de-soldering. I might just splice in a 12K like 6L6 did for his bias resistors, though. Thanks, guys! Andy

 

[jackinnj]

Which PCB?

just transistors and passive components. the design is NP's IP