DIY F2 clone

[giulio]

Hi,

what is the gain of the F2? There is no way I can figure it out myself.
I am clueless about discrete designs.

I am asking since I use a (3 way) passive preamp and a gain of >20 is what I need if I do not want to introduce an active stage.

TIA
Giulio

 

[jacco vermeulen]

The gain is around 6, some 15 1/2 dBV

 

[giulio]

Jacco,
many thanks! That's not good...

Giulio

 

[hugz]

I've got a build log going on over at headfi because I post there lots and I also dont want to clog up the pass labs forum here with it

It's my little journey as a noob building the f2.

For any other newbies wanting to build the F2, you may find my thread helpful because I post up my layouts etc

http://www.head-fi.org/forums/showthread.php?t=221290

Many thanks to Nelson for providing us all with the opportunity to build our own amplifiers of your fantastic designs. As a young college student, you've certainly helped to bring good music into my life

 

[giulio]

hugz,

many thanks! You read my mind. After seeing the image you posted on the previous page, I was just about to ask... Very good job.

And, of course, many thanks to NP, genius and philanthropist for making it possible!

Cheers
Giulio

 

[vitalstates]

The heaviest tranny I can find here in the uk is 225VA. Is this too weedy for what I want??.

I've looked at the 400VA on ebay that Kofi posted but that has US primaries and would give me too much secondary with a UK primary of 240v. Would this be a problem?

Regards

Ed

 

[veteran]

This picture should be a little better

 

[len_scanlan]

The heaviest tranny I can find here in the uk is 225VA. Is this too weedy for what I want??.

Rapid Electronics do a 300VA 18-0-18 toroidal and they have pretty good prices too. I bought a bunch of non-RoHs toroids off them a while back for next to nothing!

www.rapidonline.com/

 

[Ipanema]

Guys,

I try to build F2 with whatever I have in my parts bin. Here's the results of some modification in the current source by using two T0220 MTP12P10 instead of one IRFP9240. For the source resistor, I'm using two 1R2 3W resistors instead of six 1R 3W resistors. Do you think that this modified F2 will work at all?

 

[Ipanema]

Board layout

 

[Babowana]

I try to build F2 with whatever I have in my parts bin. Here's the results of some modification in the current source by using two T0220 MTP12P10 instead of one IRFP9240. For the source resistor, I'm using two 1R2 3W resistors instead of six 1R 3W resistors. Do you think that this modified F2 will work at all?

I would try as shown below.

 

[Ipanema]

Hi Babowana,

Thanks for your comment. I've made the modification. Is everthing OK now?

 

[Ipanema]

new board layout

 

[vitalstates]

Rapid Electronics do a 300VA 18-0-18 toroidal and they have pretty good prices too. I bought a bunch of non-RoHs toroids off them a while back for next to nothing!

www.rapidonline.com/

Thanks Len, believe it or not I discovered the 18v on rapid about 5 mins after I posted...they seem good value.

You don't happen to know of any heat sink suppliers in uk as well. I have sent emails to conrad in Oz but so far no replies.

Regards

Ed

 

[Dennis Hui]

Thanks Len, believe it or not I discovered the 18v on rapid about 5 mins after I posted...they seem good value.

You don't happen to know of any heat sink suppliers in uk as well. I have sent emails to conrad in Oz but so far no replies.

Regards

Ed

Hi Ed,

Rapid sure has some good prices on their transformers.
Too bad shipping from the UK to Canada will probably
kill me.

Unless you find something local, Conrad is probably
your best bet. Apparently, their prices and shipping
are both reasonable.

Cheers,
Dennis

 

[Babowana]

I've made the modification. Is everthing OK now?

I believe that every thing is arranged to work.
And, you could have fun further with minor variations after the first finish.
Enjoy

 

[apassgear]

Guys,

I try to build F2 with whatever I have in my parts bin. Here's the results of some modification in the current source by using two T0220 MTP12P10 instead of one IRFP9240. For the source resistor, I'm using two 1R2 3W resistors instead of six 1R 3W resistors. Do you think that this modified F2 will work at all?

Hi Impanema,

Guess R5/6 will not have enough disipation if you bias the amp at 2 amps, you will need to burn around 8 Watts so a 12 W resistor or combination will be preffered.

 

[Babowana]

Hi Impanema,

Guess R5/6 will not have enough disipation if you bias the amp at 2 amps, you will need to burn around 8 Watts so a 12 W resistor or combination will be preffered.

I agree with you, Tony.
I also like to recomment 5W rating
because the current per source R (R5 and 6) is 0.66/.47=1.4A
and dissipation per source R is 1.4x1.4x1.2=2.4W
Considered the 3W rating having only mere margin.

 

[Ipanema]

Hi Babowana and Apassgear,

Thanks for the warning on R5 and R6. In this case I need to increase it to four 2R4 3W resistors in parallel then, which will be 12W. Two will be solder on the bottom of the PCB. Hope this work without changing the layout.

Since I'm using BC550C instead of ZTX550, will it have any effect on the performance?

Thanks.

 

[Babowana]

Since I'm using BC550C instead of ZTX550, will it have any effect on the performance?

That PNP TR is used to set up the constant bias current of the gain MOSFET, using its B-E on voltage. The design allows any PNP TR having the B-E-on voltage of about -0.66V. In this respect, BC550C is useful because its typical B-E-on voltage is about -0.62.

Another thing we should consider is the C-E voltage rating with respect to the actual C-E voltage. As far as I understand, BC550C satisfies this requirement too.

Probably, the TR having higher current gain might be better in regulating the constant bias . . .


Arr . . .
ARE YOU SURE BC550C is PNP type?
YOU SHOULD USE PNP TR!!!