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Old 6th October 2005, 03:17 PM   #11
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Location: Dallas, TX
Thanks for all the replys!

Quote:
Originally posted by wayne325
Newb,
Our man Nelson has
a rule of thumb to provide a VA rating that is 4x the idle power.
So if the idle power of your F1 is for example 100W, you should
use a 400 VA if they come like that, or a 500VA. Forgive me
Master if I've messed up. If it's a question of 250 VA or 300 VA
go with the 300. It's gonna hum less, and it'll give more oomph to the supply. When in doubt, go bigger on the supply as long as it will fit in your box.

I used Nichicon Super Through (type KG), 22,000 uF, 2 per rail in my Aleph 2s. I'm sure you could be happy with one of those per rail for a small amp like an F1. Do you need 2 per amp or one per amp ? They're rare and you may have trouble getting them.
Ok, let me see if I understand this. Each channel idles at 100W according to the service manual and its a stereo amplifier, so I need 400VA per channel or 400VA for the pair? I can't seem to find an 18V+18V with a rating that high. Does it make sense to use a toroid per channel? Avel makes a 160VA and 250VA with dual 18V secondaries. RE: PS Capacitors I plan on using the same panasonics Mr. Pass recommended in his first post.

Quote:
Originally posted by wayne325

Also, on the FET matching, you need 2 pairs, no ? If so you'll get a better result if you match out 16 transistors rather than 8. But 8 might be OK. What are they, like $1 each or less ???

W.
Thats the plan to get like 8 of each type so 24 total devices and match the best

Quote:
Originally posted by Alain Dupont
DIY_newbie,

>> I meant C4 and C5 on the channel schematic. The 220uf and 1000 uf
>> capacitors near the current sources.

35 volts good quality Panasonic M series or Nichicon VR, PW series
Heading over to Mouser/Digikey to start looking now

What do you think of using a single 250VA for each channel Alain?

Thanks again guys!

--Chris
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Old 6th October 2005, 03:49 PM   #12
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Location: Near to the Pacific Ocean
Quote:
Originally posted by DIY_newbie

. . . 400VA for the pair?

. . . match the best

Yes, you are right. I use 800VA, but it's overkill. I have chosen that big because I have often disappointed with maker's power rating.

Match the best. Even if difficult, don't be disappointed. If we read the original article carefully, there is an easy DC offset-killer. Who is Nelson . . . ? He is not bad at all. Actually, I have used unmatched MOSFETs. Having used the DC offset-killer, I have managed the offset less than 30mA. Don'y worry . . . clever DIYers will assist you.

Regards
jH

PS
F1 will not make you disappointed.
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Old 6th October 2005, 04:05 PM   #13
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Location: Paris - France
DIY_newbie,

>> What do you think of using a single 250VA for each channel Alain?

Good choice, 250 VA for each channel ! but 1 transfo 330/500VA is better!
A hassle to fix the 2 babies, and get a little pretty case.

PS: At this point draw the enclosure and try to place the transfo(s)
you'll get a better view of the final F1 you want.

Regards.

Alain.
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Old 6th October 2005, 05:53 PM   #14
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Quote:
Originally posted by Alain Dupont

PS: At this point draw the enclosure and try to place the transfo(s)
you'll get a better view of the final F1 you want.
Forgive the primitive nature, but I ran home at lunch and sketched 1/2 of it while driving

Toroids are 4.5" diameter 2" tall 250VA types I have the placed horizontally with the PS board above them, the other option is to place them vertically and the PS infront? The heatsinks are 10 3.35x5.25" eachh heatsink is 0.8C/W and I plan on mounting one power mosfet to each heatsink, how does this sound? Chassis is a 3RU rack mount 16guage steel black anodized.

Click the image to open in full size.

--Chris
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Old 6th October 2005, 06:10 PM   #15
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Location: Paris - France
DIY_newbie,

Check for the height over the 2" lost by the transfos, you need place for a support
and the cap's

Pana TS 50V / 12.000 microF height 35 mm or 1" 1/3
Nichicon VR 35/15,000 microF height 50 mm 2"
plus support ~ 10mm 1/2" mini...

You need about 1/2" for the transfo bolts...

Alain.
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Old 6th October 2005, 06:56 PM   #16
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Quote:
Originally posted by DIY_newbie
The Line capacitor in the PS: The schematic shows ".0033 LINE", I'm assuming its 0.0033 uF, so a BC Components 0.0033UF 275VAC X2 should work?
The line capacitor should be specifically rated for AC line - it
will say so in the catalog and it will bear the appropriate
safety markings.

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Old 6th October 2005, 07:19 PM   #17
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Join Date: May 2004
Location: Dallas, TX
Hmm

Torioid = 2"
Transformer bolt = 1/2"
Top + Bottom = 1/4".

Total space left = 2 1/2" that should be enough for the power supply board..

The other option is placing them vertically. But how do you mount a vertical toroid? do you strap it down through the center to the floor with a u-bracket? I can't mount it to the back since the input/outputs will be there..

Just got a quote on the heatsinks. $367 cut.. not too bad, gives me about 24-26 heatsinks enough for 2 F1s Each heatsink is rated at 0.8 degree C / Watt.

Another question, how do i mount the heat sinks? To the outside of the side/back panels? how do you guarantee good thermal transfer between the mosfet->sidewall->heatsink? Do I cut holes in the sides/back so that I can mount the mosfets directly to the heatsinks?

Thanks!

--Chris
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Old 6th October 2005, 08:03 PM   #18
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DIY_newbie,

>> Do I cut holes in the sides/back so that I can mount the mosfets
>> directly to the heatsinks?

Better remove about all the lateral sides to install the heatsinks ; and absolutly
bolt the MosFets to the heatsinks... {using mica and grease or good thermo pads}

For the heatSinks take a look at Conrad HeatSinks ; and check ThermaFlo

http://www.conradheatsinks.com/welcome.htm
http://www.thermaflo.com/index.shtml

Regards.

Alain.
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Old 6th October 2005, 08:54 PM   #19
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Location: Dallas, TX
Thanks for those links Alain,

The thermaflow E1387 looks promising : a 5.25"x9.97" section can disipate 100W of energy with a 34 degree C rise over ambient. It would be nice since I would only have to have heatsinks on the sides and not the back panel leaving more room for connectors. Is this sufficient power dissipation?

http://www.thermaflo.com/bin/exdatas...=Change+Length

--Chris
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Old 6th October 2005, 09:53 PM   #20
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Noob,

A delta of 34 is about as high as you want to go. That will
give you a temp of about 55C in the winter - approaching 60C
in the summer if you keep your apartment at 80F. Keep in mind
also those are free air figures and not stacked.

Just looking at those dimensions, that looks like a reasonable
size for the power you have to dissipate.

You can use a tiny bit of thermal grease or silicone thermal pads.
Check the transistors - if they are the same as the ones in the
Aleph, then they are electrically isolated so you don't have to
worry about electrical isolation. You must bolt the transistors
directly to the heatsink. Else much melty melty.





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