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Old 5th April 2014, 08:49 PM   #1
pjanda1 is offline pjanda1  United States
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Default "Mini" F5

There are some rumblings in the big thread about folks trying a lower voltage, lower dissipation F5. There is a dedicated thread using 16V rails for F5X designs. But, I haven't seen much about folks actually trying a Mini F5.

I've got a Halfer chassis I'd like to use. But, I think the mini makes sense for quite a few folks in general. 10ish watts will do fine for many of us. You can save space, money on heatsinks, and quite a bit of carbon footprint (for those of us that care about such things).

12V transformers abound, so it seems like 16V rails should be the standard. It sounds like 2SK1530/2SJ201 (or 2SK1529/2SJ200 at a higher cost) might be the way to go. But, thoughts about bias? Resistor changes?

And more importantly, have folks actually built them?

Paul
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Old 5th April 2014, 09:23 PM   #2
tinitus is offline tinitus  Europe
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from what i understand about it, with the standard F5 mosfets you will probably have more distortion with lower voltage

but maybe it would work better if driving smaller TO-220 mosfets hard
I have been looking at a lot of them, and thought of using them in multiples
in the end I realised it would not make sense

but i never thought of using them for a 'mini-F5'
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Old 5th April 2014, 11:08 PM   #3
pjanda1 is offline pjanda1  United States
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Folks recommended the 2SK1530/2SJ201 for low voltage in the big thread. It does sound like the normal candidates don't do so well. In a perfect world, I'd find a TO-3 pair that would work well at 16V, as that is what my sinks are drilled for.

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Old 5th April 2014, 11:22 PM   #4
flg is offline flg  United States
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maybe F5 with 2SK2013/2SJ313 ?
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Old 6th April 2014, 09:33 AM   #5
juma is offline juma  Germany
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If we are looking at 16V rails and about 1A total bias per channel, 3 pairs of 2sk2013/2sj313 are better solution than 1 pair of 2SK1530/2SJ201 from standpoint of transconductance vs. parasitic capacitances. Also, IME it sounds better.

It's more probable that you'll get 16V DC from 12V AC with 2A constant load (1A per channel) if you use schottky rectifiers (much lower voltage drop across them) like MBR745 or similar. Good filter caps (low ESR) help too.
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Old 6th April 2014, 03:24 PM   #6
pjanda1 is offline pjanda1  United States
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Juma,

Thanks! I had seen that recommendation, but like other 'mini' talk, it is sort of scattered through threads and it isn't clear to me whether someone has actually tried it.

Silly question, but any worries about lead length or the way you hook the pairs up?

I know 16V may be a bit high, and I'm not terribly concerned about hitting that number. 1V doesn't seem like a big deal to those of us coming from the tube world, but I suppose it affects these operating points.

My goal here is in part to make an inexpensive F5. Schottkys are not that!

Paul
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Old 6th April 2014, 03:48 PM   #7
Bigun is offline Bigun  Canada
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You might be better off with Bipolar outputs at such low rail voltages ???
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Old 6th April 2014, 05:20 PM   #8
juma is offline juma  Germany
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Quote:
Originally Posted by pjanda1 View Post
... any worries about lead length or the way you hook the pairs up?
Not at all - I used 20cm (8") wire lengths without problem (just solder gate resistors directly to the pin of the MOSFET). Look at the actual build pictures in the link provided by flg in post #4:
Novi amp sa 2SK2013/2SJ313 - Stranica 2 - Solid State - diyAudio.rs
F5 with 2SK2013/2SJ313
Click the image to open in full size.

Quote:
Originally Posted by pjanda1 View Post
I know 16V may be a bit high, and I'm not terribly concerned about hitting that number. 1V doesn't seem like a big deal to those of us coming from the tube world, but I suppose it affects these operating points.
Not really. 15 or 16V rails don't make a difference - I just thought that it's important to you.

Quote:
Originally Posted by pjanda1 View Post
...My goal here is in part to make an inexpensive F5. Schottkys are not that!
33 cents a piece makes them dirt cheap in anybody's book:
MBR745G - ON SEMICONDUCTOR MBR745G - SCHOTTKY RECTIFIER, 7.5A, 45V, TO-220AC | Newark element14 US
Besides, they'll run cooler (because of lower voltage drop).

EDIT:
MBR1040 are even better choice. Cheaper too:
MBR1040 - MULTICOMP MBR1040 - SCHOTTKY DIODE, 10A, 40V, TO-220A | Newark element14 US

Last edited by juma; 6th April 2014 at 05:30 PM.
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Old 6th April 2014, 05:29 PM   #9
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by pjanda1 View Post
My goal here is in part to make an inexpensive F5. Schottkys are not that!

Paul
diodes are not expencive, but the 2013/313 might be

how about trying smaller 'automotive' output devices designed for lower voltage ?

Juma, nice photo with hardwired output
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Old 6th April 2014, 07:15 PM   #10
tinitus is offline tinitus  Europe
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how about this pair ?

http://docs-europe.electrocomponents...6b807912cb.pdf

http://docs-europe.electrocomponents...6b8079172c.pdf
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