Hi d,
K170 and J74 does not seem to be designed for mounting on heatsinks. GR and BL versions look exactly the same.
But anyway, please use BL if you have them on F6.
Thanks,
Doug
Doug,
The heatsinks in question are little fin caps that sit on the jfets. Digikey has them as Part Number HS251-ND I believe
Sinc,
d
The heatsinks in question are little fin caps that sit on the jfets. Digikey has them as Part Number HS251-ND I believe
Sinc,
d
F6 and F5 are very different scenarios.
Idss of 10mA is completely fine on F5. No heatsinks are required at this Idss on F5.
Idss of 10mA is completely fine on F5. No heatsinks are required at this Idss on F5.
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More than 2 hours of warm up produced no problem. Bias and output dc offset are both stable.
So I connected source and speaker and played music.
DANG!
I found the problem (Q1 on the OT)!
That is the speaker protection circuit of one channel that is overly sensitive. While output offset reading from DMM is ~0, the protector turns on and off depending on the source level. That was what caused one channel on and off!
I don't know what happened to this protector, but I basically wasted my time building a new set of F5, made mistake soldering, used wrong jfets (too low Idss), and back to zero!
Well, I had fun figuring out the problem and talking to other members, but now I have to figure out what's wrong with this speaker protector.
By the way, what type of slow blow fuse is good for speaker protection purpose?
So I connected source and speaker and played music.
DANG!
I found the problem (Q1 on the OT)!
That is the speaker protection circuit of one channel that is overly sensitive. While output offset reading from DMM is ~0, the protector turns on and off depending on the source level. That was what caused one channel on and off!
I don't know what happened to this protector, but I basically wasted my time building a new set of F5, made mistake soldering, used wrong jfets (too low Idss), and back to zero!
Well, I had fun figuring out the problem and talking to other members, but now I have to figure out what's wrong with this speaker protector.
By the way, what type of slow blow fuse is good for speaker protection purpose?
24v rails - 4.2v bias - 0.8v across source R is 19v across the jfet. Assuming 8mA Id for a 10mA jfet, that's 152mW. A TO92 device has 200c/w thermal resistance j/a, which would result in die temperature of 30.4 above ambient temperature. Roughly 70 to 80 degrees if it's inside a nice toasty case.
Whether or not you would like a heatsink is personal choice, but definitely can't hurt.
Nothing wrong with heatsinks if you want, you just don't need them.
I've been running an F5 with 10mA jets about 5 years now.
My first F5 also had run (now it lost jfets due to my wrong diagnosis) for 4-5 years without heat sink on jfet.
Anyway, from the recent couple of days experience of building another F5, I confirm that F5 is a great gift PAPA gave us. It's easy to build, and it produces nice music!!
Now I have another set of F5 boards only I have add jfets, only thing I (my wife too) don't like is that I need heavy heatsinks. I might try forced air or water-cooling this time. There are nice water cooling system available for computers.
Anyway, from the recent couple of days experience of building another F5, I confirm that F5 is a great gift PAPA gave us. It's easy to build, and it produces nice music!!
Now I have another set of F5 boards only I have add jfets, only thing I (my wife too) don't like is that I need heavy heatsinks. I might try forced air or water-cooling this time. There are nice water cooling system available for computers.
Hi Goug,
There's plenty of medium air flow, 'silent' fans around these days - you could even use a slow running 8" tangential across the pair of side-by-side heatsinks without any problems as you only need a couple of cubic feet/ minute - getting the hot air thru a long 'waste tube' out the window in summer was a problem
I tried a heat tube solution awhile back with a much lower heat distribution 'gain clone' amp and it wasn't totally successful and went back to basic 'metal with fins' - maybe better these days.
There's plenty of medium air flow, 'silent' fans around these days - you could even use a slow running 8" tangential across the pair of side-by-side heatsinks without any problems as you only need a couple of cubic feet/ minute - getting the hot air thru a long 'waste tube' out the window in summer was a problem
I tried a heat tube solution awhile back with a much lower heat distribution 'gain clone' amp and it wasn't totally successful and went back to basic 'metal with fins' - maybe better these days.
Hi jh,
I am an old school, I still dream about owning big monoblock amps with big fins, like Pass Alephs and Mark Levinson MLs.
But my wife is different. First, she says "why do we need another amp?" and second, she says "why don't we just buy Bang & Olufsen which just looks WoW?".
So, If I build another F5 with big fins, I will be grounded and will not be able to enjoy my other hobby (motorcycle). I would like to make (if I do) the second F5 as small as possible.
Or, I will just use small heatsinks and bias it very low.
I am an old school, I still dream about owning big monoblock amps with big fins, like Pass Alephs and Mark Levinson MLs.
But my wife is different. First, she says "why do we need another amp?" and second, she says "why don't we just buy Bang & Olufsen which just looks WoW?".
So, If I build another F5 with big fins, I will be grounded and will not be able to enjoy my other hobby (motorcycle). I would like to make (if I do) the second F5 as small as possible.
Or, I will just use small heatsinks and bias it very low.
Nah, with the big fins comes the big cases that leads to crazy big power supplies, back breaking weight, and maybe better sound - on the other hand, a small case, silent computer fan, biased to the max (about 1.7A), smart power supply, much lighter wallet, and for the Mrs, a coat of pink paint! (well, THAT is a line never to be crossed - maybe white for domestic harmony!)
I've been trying to complete a small classA amp like I described for years - never seems to get finished - I did do a tangential fan version with small heatsinks but then went a bit crazy on power supplies and it ended up the usual black behemoth anyway!
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