F4 power amplifier

[carpenter]

Two questions about 74s and 170s :

1° - Do they need to be matched for the F4 ? (I've don't read it but I'm a newbie so... I'm asking the experts ! )
2° - How to match 74s and 170s ?
Many thanks to all.

Wish you stars for this new year.

Hi,

Mine don't match, but I noticed that the difference does show up as a small voltage mismatch which can be adjusted out with the pot that balances voltage between upper and lower groups of mosfets. IIRC, the voltage mishmatch seemed to match the difference in mismatch between the jfets.

 

[korben69]

Hi Carpenter, thanks.

Where do you place the pot to adjust voltage ?
I've missed the link... what are the specs of the pot ?

 

[carpenter]

Hi Carpenter, thanks.

Where do you place the pot to adjust voltage ?
I've missed the link... what are the specs of the pot ?

I'm rusty on which pot (P1 or P2). Just read the text and use the pot that adjusts the offset voltage.

Edit: According to Peter Daniel's checklist, it's P2 that adjusts the DC offset. BTW, he's ordering more F4 pcbs. Go to his thread and purchase some if you're able.

 

[korben69]

Ok thats clear for me now.
You're talking about trimmers P1 and P2.
Thanks

 

[anubisgrau]

Pardon my lazy question, is there an one-stop shop for all the parts for F4? Thanks!

 

[jacco vermeulen]

absolutely : here

 

[anubisgrau]

absolutely : here

not much DIY job left on that link

 

[Zen Mod]

not much DIY job left on that link

Jacco is Jaccovitty

he meant that there you certainly can find one - in one piece ....

are you really so desperate , regarding F4 ?

 

[anubisgrau]

Jacco is Jaccovitty

he meant that there you certainly can find one - in one piece ....

are you really so desperate , regarding F4 ?

i don't know what you mean by desperate, i've just thought that some shops would be clever enough to offer all the parts for sale - at least that's what i'd might do if selling parts. no hard feelings anyway

 

[Babowana]

Jacco's tongue is shrinking short.
Will lose entirely soon and start body language . . .

 

[jackinnj]

I put together a "sort of" kit -- for the matched IRF's, TL431, zeners, JFETs and the source resistors -- you supply the other discretes (res and caps) and led. You know where to find me.

 

[Zen Mod]

i don't know what you mean by desperate, i've just thought that some shops would be clever enough to offer all the parts for sale - at least that's what i'd might do if selling parts. no hard feelings anyway

there is no hard feelings , in any way ;
with "desperate " I meant - are you so curious to try F4 ......?

FR fever

 

[chrismercurio]

Minimum Impedance

How stable is the F4 when connected to speakers that drop below 4 ohms? 2 ohms? 1 ohm? Will I have a cool arc welding light show in my living room?

Thanks,

C

 

[carpenter]

Re: Minimum Impedance

Will I have a cool arc welding light show in my living room?

Thanks,

C

Oooooh, why not add a mirror disco ball and get back to us when it's all over...

 

[chrismercurio]

I tossed that in as a joke. I really DO want to know about connecting the F4 to low impedance loudspeakers.

Thanks,
C

 

[Nelson Pass]

Re: Minimum Impedance

How stable is the F4 when connected to speakers that drop below 4 ohms? 2 ohms? 1 ohm? Will I have a cool arc welding light show in my living room?

It's stable into anything I've tried. Depending on the values of
the Zener diodes, you will run out of current. Sotck, it poops out
around 10 amps peak, implying full swing into 2 ohms.

 

[chrismercurio]

Thank you Santa! I hope you avoided the CES "cold" and are well rested.

Peace,

C

 

[Skorpio]

High/low bias function?

I was wondering if it was possible to implement a low bias function for back ground listening?

I was thinking of af switch for changing the bias setting resistors?

 

[Zen Mod]

Re: High/low bias function?

I was wondering if it was possible to implement a low bias function for back ground listening?

I was thinking of af switch for changing the bias setting resistors?

why?

 

[Nelson Pass]

Re: High/low bias function?

I was wondering if it was possible to implement a low bias function for back ground listening?

I was thinking of a switch for changing the bias setting resistors?

No reason why not.