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Old 1st December 2013, 09:31 AM   #501
Zen Mod is online now Zen Mod  Serbia
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F3 Builders Thread
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Old 1st December 2013, 04:38 PM   #502
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Thanks ZM! The babysitter is an option.
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Old 30th May 2014, 09:13 PM   #503
audioquestM-40 is offline audioquestM-40  Canada
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Default Heat sink temp

I just picked up a built DIY F3 and curious what the typical heat sink temp should be in a 70 degree room with the amp sitting totally in the open

Thanks
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Old 30th May 2014, 09:15 PM   #504
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Not more than 55C
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Old 31st May 2014, 04:27 AM   #505
audioquestM-40 is offline audioquestM-40  Canada
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Not more than 55C
Thanks, much appreciated. I put a small fan near it and the heat sinks measure 45, it was 65 without it
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Old 31st May 2014, 05:22 AM   #506
jameshillj is offline jameshillj  Australia
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If it's of interest, the factory version (First Watt F3) gets to about 45*C at about room temp 28*C - my 'clone got 'upped' a bit and runs a bit higher current and I found it sounded slightly better at about 55*C on the sinks - used those Thermo isolation pads so the transistors were only a couple of degrees hotter t(han using mica & goop) until mid summer and they got to about 65*C plus -
I imagined they sounded better but I did same thing with small fan and cooled it down a bit 'just in case'

There's just something 'right' about the sound of this amp,IMO ....
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Old 31st May 2014, 11:31 AM   #507
AndrewT is offline AndrewT  Scotland
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Is James' "better" due to extra output bias current, or due to hotter devices?

Do hotter devices with less power capability, perform better than cooler devices that might last ten times longer?

I suspect the "better" is due to extra output bias current and the more effective cooling gives the ten times longer life while the devices have the same power capability due to running at the cooler Tc.
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Old 31st May 2014, 12:45 PM   #508
jameshillj is offline jameshillj  Australia
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I'm not sure Andrew - I've held the opinion over the years that keeping power fets hot will give you a better sound, but this obviously depends on all sorts of other things too, and this is a very simplistic (and limited) view of fet operating reality

I vaguely remember some discussion about this also in the F5 development and I think the highest safe operating temp (for the Fet junctions) was below 100*C so we were encouraged to use the best thermo transfer insulator material available.

Now, the sound difference with the extra temp is a bit of a puzzling thing - when I ran it at about 1.5A and low 40's temp, it certainly lacked some life and when I boxed up the sinks and raised the temp to mid 50's, it certainly came more alive (sorry about vague terms)

However, with higher 1.7A current, the sound quite definitely became more dynamic, etc as you would expect, and the heatsink temp got to about the mid 50's with open fins so it appears to be a combination of higher current and higher junction temp - I'm hesitating to say an opinion here as I again pushed the current up past the 1.8A and again achieved an improvement in the amp's sonics and the heatsink get to over 60*c.

In the summer here on hot days, amp h/sink can get well over the 70's but didn't notice any change in the sound, but when I tried fan cooling to low 50's, sound deteriorated a little, became 'thicker' or perhaps slower and lost some detail which is one of this amp's better qualities and I set it at about the high 50*C point and that's where it now stays.

Curiously, I built a slightly different circuit of Patrick's (EUVL) with the same/similar components (the DAO headamp) and it runs about 350mA but have the heatsinks sizzling about 70*C all the time (estimate junction temp over 110*C) and this does make quite a difference in the sound via the AKG k701 heaphones (this is added just to confuse!!)- I do think I'm pushing things a bit here, but ....

Sorry this meandering chatter is so imprecise and lacking in measurable details, test results, etc - [it's Sat night here and my mind is on holiday!]


I built this second F3 with Peter D's boards and they're more compact than the factory amp and have different resistors, the original design electro signal caps (for active current source) are now big Propylene caps and some other component differences have made it a much "faster" amp (sorry about the vague description)
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Old 31st May 2014, 12:54 PM   #509
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More heat, better conductor, higher Yfs?
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Old 31st May 2014, 12:59 PM   #510
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more current means modulated current is lesser percentage of steady one

more heat means heat modulation is lesser percentage of steady one

go figure

left leg usually goes combined with right one

especially if you have two pairs of them

legs



term combined is where one needs to point peripheral vision

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