First watt F2j with SJDP120R085

[Zen Mod]

I meant 5mm on both surfaces .... however , do as you wish - that's your playground

 

[kinku]

Thanks Zen , but I want to play it safe. It is not easy to draw 5mm traces , that is why.i know 10mm is better but what is a good compromise. I seen the pictures of board from first watt. Does not look like 5mm but may be he used 5 Oz traces?

 

[Zen Mod]

with Nelson ........ it really depends of his mood at specific day (of drawing pcbs)

 

[Nelson Pass]

I spec heavy copper, which means different things to different vendors,
and the trace width is usually whatever fits the space I'm working with.

The main thing is, I don't get too excited about it, as the resistance values
are always lower than the other stuff in the circuit.

 

[Zen Mod]

.....
The main thing is, I don't get too excited about it,......

 

[kinku]

Thanks Papa.which are the high current tracks ? And how much current is flowing through them?

 

[kinku]

The SJEP could be thought of as an enhancement mode JFET, hence the "E" in SJEP. Since there aren't a lot of affordable power JFETs in production, you'll be probably looking for a SiC mosfet. Have a look at the part you're replacing and try to find something with similar (or lower) capacitance, Vgs, and transconductance. The F2 isn't a super fussy circuit. Try some stuff.

Will this Fet SCT10N120 a better option than SJEP ?
https://www.digikey.com/product-detail/en/stmicroelectronics/SCT10N120/497-16597-5-ND/6137190
Half the Ciss of SJEP120R

 

[Michael Rothacher]

I'd use the parts I sent you.

 

[kinku]

Of course Mike. Just paranoia sets in when you know they are the only two. What if I damage them etc.

 

[Michael Rothacher]

Fortune favors the bold.

 

[kinku]

��. True.

 

[maxlorenz]

of course that you can ....... but in this case SJDP is taking role of invisible part , while mosfet is still governing one .......... and entire circuit would remain (almost) same in sound character

practically -

Dear ZM,

Do you speak theoretically of from practical experience?
I ask because I will start cascoding all my amps, when time allows..

The Sony TA-N7 sounds like a VFET amp and the small BJTs seam to be transparent...

Thanks,
M.

 

[Zen Mod]

Dear ZM,

Do you speak theoretically of from practical experience?........

both

 

[maxlorenz]

OK. Thanks.

I'll do it anyway.

Cheers,
M.

 

[Zen Mod]

read this : http://www.firstwatt.com/pdf/art_cas_amp.pdf

 

[maxlorenz]

Thanks.

 

[e_fortier]

Hi

Couldn't find the R100 so just bought some Wolfspeed C2M0280120D.

For the power supply would a quiet 24Vdc, 5A (120W) per channel SMPS sufficient ?

My load is a 8 ohm full range. I have read on this forum that the amp draws at idle 35W per channel and somewhere else 75W. Which one is right so I can size my heatsinks properly?

Thanks for your help.
Eric

 

[Zen Mod]

regular F2 is drawing around 75W per channel

if SMPS is of decent quality , you're good

 

[e_fortier]

Thanks ZM,

So 75W dissipation for 5W output, correct ?

Is there a way to reduce bias from 2.7A if I'm only using 8 ohm speakers. Is the bias rated for 8 and 4 ohm load ?

F2 is rated 5W @ 8ohm and 10W @ 4 ohm, of course the 4 ohm load needs more current.

I'd really like to try the F2 but not if it requires 75W dissipation/ch.

Thanks,
Eric

 

[Zen Mod]

F1 100W diss/ch 10W/8E/ch

F2 75W diss/ch 5W/8E/ch (10W/4E/ch)

F3 100W diss/ch 15W/8E/ch

F4 80W diss/ch 25W/8E/ch (buffer)

F5 60W diss/ch 25W/8E/ch