Well, if you aren't carrying too many F4's then you can take our rapid transit system, BART, directly from the airport now. Then switch to a bus to go over the hill to the site. Otherwise, a van from the airport shared with other passengers isn't too bad.. The driver can take you to the closest hotel to the event. Then take a taxi.
I'm sure we can get youto the event if you decide you really are coming. Places to stay at member's houses seem to be rare unless someone posts here that they can take someone..
Thanks guys for your very kind comments. I hope my wife feels similarly 
I think she suspects though- it is being built on the kitchen table!
I have to leave the Bizarre Heatsink for a surprise at the Burning Amp show. It is more big than bizarre anyway..
Choky, I like to keep my picture off of the web so I won't be hunted down by angry ex-members, but you found it!! Now I'm ruined 😉
Variac
I think she suspects though- it is being built on the kitchen table!
I have to leave the Bizarre Heatsink for a surprise at the Burning Amp show. It is more big than bizarre anyway..
Choky, I like to keep my picture off of the web so I won't be hunted down by angry ex-members, but you found it!! Now I'm ruined 😉
Variac
Variac said:
😉
I'm always here to serve ..............
hehe - sort of half Mod .............
'cause you are here to serve & protect
Member
Joined 2002
jleaman said:
hm.... maybe I'm just overlooking something here but - what is exactly BOM and why you need it
that nomenclature always slips near me...... is it plain sheet of elements or with included info " where to purchase,code for purchase etc "
?
mpmarino said:
than I'm lucky......... I always know where to buy my drek ........
at Harvey Keitel's Tobaco Store .......
This is an up to date one I believe.
http://www.diyaudio.com/forums/attachment.php?s=&postid=1263192&stamp=1185337158
Remember that Nelson changed the values for the resistors afterthe initial post
So any prudent builder would first go to Nelson's site as mentioned in the first post and find the file about the F4 , then download the entire NEW owner's manual
Then compare the BOM in question with the
schematic (Version 0 dated 6/4/07 I believe, but check for yourself.. )
the older BOM's are good resources for alternate parts- if they are changed to the correct value if required.
I was very brave and ordered different resistors , 3w resistors (got 5w) trimmer pots (bourns- mentioned in a different BOM, bridge, power caps, It was fun to mix and match and feel like I actually had an opinion of what is best!!
Digikey worked for me, except for the resistors, 'cause of my weird resistor desires!! and they sent me a new catalog twice as thick as my 5 year old one!!
http://www.diyaudio.com/forums/attachment.php?s=&postid=1263192&stamp=1185337158
Remember that Nelson changed the values for the resistors afterthe initial post
So any prudent builder would first go to Nelson's site as mentioned in the first post and find the file about the F4 , then download the entire NEW owner's manual
Then compare the BOM in question with the
schematic (Version 0 dated 6/4/07 I believe, but check for yourself.. )
the older BOM's are good resources for alternate parts- if they are changed to the correct value if required.
I was very brave and ordered different resistors , 3w resistors (got 5w) trimmer pots (bourns- mentioned in a different BOM, bridge, power caps, It was fun to mix and match and feel like I actually had an opinion of what is best!!
Digikey worked for me, except for the resistors, 'cause of my weird resistor desires!! and they sent me a new catalog twice as thick as my 5 year old one!!
Last edited:
Heatsink calc
A friend is helping me build my F4s (archetypal British understatement). He has done some calculations to determine how serious the heatsinks need to be but suggested I post the calcs on this thread to see if others think they stack up:
Each device is passing 0.43A so at 23v
(minus 0.2v
dropped across the resistor) the total power dissapated at
idle is 6 *
0.43 * 23 - 0.2 ) = 59W.
So, for a running temp of 50Deg, and room at 25deg, the
heatsink will be
at 25deg above ambiant. So the total thermal resistance
needs to be
25/59 or 0.424 C/W
The chip to case thermal resistance of the mosfet is 0.24
C/W, so for 6
devices thats 0.04 C/W, assuming efficient coupling from
the device to
the heatsink,
Assuming 1 C/W insulation for the device to heatsink,
again, thats in
parallel, so thats .16 C/W, so a total Chip to sink of 0.2
C/W, so that
leavs us needing
0.424 - 0.2 = 0.224 C/W
Any comments?
A friend is helping me build my F4s (archetypal British understatement). He has done some calculations to determine how serious the heatsinks need to be but suggested I post the calcs on this thread to see if others think they stack up:
Each device is passing 0.43A so at 23v
(minus 0.2v
dropped across the resistor) the total power dissapated at
idle is 6 *
0.43 * 23 - 0.2 ) = 59W.
So, for a running temp of 50Deg, and room at 25deg, the
heatsink will be
at 25deg above ambiant. So the total thermal resistance
needs to be
25/59 or 0.424 C/W
The chip to case thermal resistance of the mosfet is 0.24
C/W, so for 6
devices thats 0.04 C/W, assuming efficient coupling from
the device to
the heatsink,
Assuming 1 C/W insulation for the device to heatsink,
again, thats in
parallel, so thats .16 C/W, so a total Chip to sink of 0.2
C/W, so that
leavs us needing
0.424 - 0.2 = 0.224 C/W
Any comments?
Re: Heatsink calc
every day calculus :
U=23 x 2
I=,43 x 3 (3 verticals)
Ptot = 46 x 0,46 x 3 ~64W
Tmax ~ 50C
Tamb~ 25
Dt=25
Rth = (25 / 64) x 0,85 = 0,33
so-you'll have ~ 50C at heatsink
who cares for mosfets?
Studley said:
every day calculus :
U=23 x 2
I=,43 x 3 (3 verticals)
Ptot = 46 x 0,46 x 3 ~64W
Tmax ~ 50C
Tamb~ 25
Dt=25
Rth = (25 / 64) x 0,85 = 0,33
so-you'll have ~ 50C at heatsink
who cares for mosfets?
All aspects complete:
Rth____________________°K/W_____delta T
Heatsink_________________0,3_______20,7
Tmount-Heatsink___________0,1_______6,9
Isolator-Transistormounting__0,3_______3,5
Isolator-Transistor_________0,2________2,3
Transistor-Junction-case_____0,83______9,5__IRFP240 = 0,83
Dissipation W/transistor_____11,5____117watt total
amount of transistors________6
dissipation per channel______69W
dissipation stereo__________138W
rail voltage________________23V
total bias_________________1,5A
ambient T ________________25°C_____77°F
Junction T_______________67,9°C____154,21°F
Mounting temperature_____52,6°C____126,68°F
Heatsink temperature_____45,7°C_____114,26°F
Rth____________________°K/W_____delta T
Heatsink_________________0,3_______20,7
Tmount-Heatsink___________0,1_______6,9
Isolator-Transistormounting__0,3_______3,5
Isolator-Transistor_________0,2________2,3
Transistor-Junction-case_____0,83______9,5__IRFP240 = 0,83
Dissipation W/transistor_____11,5____117watt total
amount of transistors________6
dissipation per channel______69W
dissipation stereo__________138W
rail voltage________________23V
total bias_________________1,5A
ambient T ________________25°C_____77°F
Junction T_______________67,9°C____154,21°F
Mounting temperature_____52,6°C____126,68°F
Heatsink temperature_____45,7°C_____114,26°F
Variac said:
with np's amps you should always leave wide margins
-most of his amps run hot- use insulators bigger than
the devices thats what i reckon
cheers
😉
Hi, I am the person Studly has asked to do the build, can I just gheck something?
Should that not be
Ptot = 46 * 0.43 * 3 = 59.34
(ignoring the small amount of power that will be dissapated in the resistors)
But I am not sure where
Should that not be
Ptot = 46 * 0.43 * 3 = 59.34
(ignoring the small amount of power that will be dissapated in the resistors)
But I am not sure where
here's how i see it:
Rth(j-a) = (Tj max - Tamb) / Ptot
Ptot = 46 * 0.43 * 3 = 59.34
where:
T(j max) is the max of the junction temp we want to allow
Ptot is Vrails * Ibias
Rth(junction-ambient) = Rth(junction-case) + Rth(heatsink) = 0,83 (for IRFP240) + Rth
the matter is to know exactly which Tj you want... according to IRFP240 datasheet it seems that Tj max is 125°C but i guess that safe operating temp will be lower.
Let's say Tj max 100°C, so your heatsink should have Rth = 0,43°C/W
Is it correct? 😕
Rth(j-a) = (Tj max - Tamb) / Ptot
Ptot = 46 * 0.43 * 3 = 59.34
where:
T(j max) is the max of the junction temp we want to allow
Ptot is Vrails * Ibias
Rth(junction-ambient) = Rth(junction-case) + Rth(heatsink) = 0,83 (for IRFP240) + Rth
the matter is to know exactly which Tj you want... according to IRFP240 datasheet it seems that Tj max is 125°C but i guess that safe operating temp will be lower.
Let's say Tj max 100°C, so your heatsink should have Rth = 0,43°C/W
Is it correct? 😕
Hi~
I've got an idea about using a "small" F4 amp shematics as headphone amp. What I mean "small" F4 amp is substituting orignal 3 pairs of mosfets with a pair of BD139/140 and putting the voltage of PS to +-15.
Can it work? Or, any suggestion or comments will be welcome.
I've got an idea about using a "small" F4 amp shematics as headphone amp. What I mean "small" F4 amp is substituting orignal 3 pairs of mosfets with a pair of BD139/140 and putting the voltage of PS to +-15.
Can it work? Or, any suggestion or comments will be welcome.