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Old 10th November 2010, 02:04 PM   #631
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Owen

Wich are the proper heatsinks for power resistors?

Cheers

Felipe
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Old 10th November 2010, 03:15 PM   #632
qusp is offline qusp  Australia
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Look up the datasheet and see what they need. They won't need quite as much as the zfoils, but will still need a decent sink and must really be under the board. Use the floor it's easiest and cheapest.
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Old 10th November 2010, 03:22 PM   #633
qusp is offline qusp  Australia
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Oh and I meant to post this last night, but the iPhone was giving me the ***** on the forum. But someone was asking whether I was using salas with the buff. For one, I'm nit using the buff, I'm using ackodac and 2 the ackodac already has high end linear low noise ad797brz based regs For all main supplies for the sabre. I'll prob give the salas a go with the ackodac and I'll probably release the buff from it's cramped portable home for a head to head, but it's home is in a portable a123 LiFePo4 powered balanced headpphone amp for my iems
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Old 10th November 2010, 03:25 PM   #634
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Thank you
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Old 10th November 2010, 08:12 PM   #635
NicMac is offline NicMac  Italy
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Hi Owen,
Thank you for the concise information and for the very well "mastered" circuit and group buy. Top notch.
Nic

Quote:
Originally Posted by opc View Post
Hi Guys,
NicMac:

My plan is to use +/-45VDC, and that's more or less what the board is designed for. You can use up to +/-50VDC, or down to whatever voltage you want. I saw a steady decrease in distortion as voltage was increased, but distortion started to increase again above +/-45VDC. Performance was slightly worse at +/-50VDC, and when you factor in the added dissipation, I see no reason to use anything other than +/-45V unless power dissipation is a problem and you're willing to give up performance in exchange for running lower rails. I posted some THD+N curves at different voltage levels to show this somewhere earlier in the thread. +/-45VDC is what Nelson would call "The sweet spot" for this particular circuit.

You'll see between 110 and 120mA of current draw from each leg with +/-45VDC. That means each channel will draw about 230mA total from the regs.

Regards,
Owen
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Old 10th November 2010, 10:47 PM   #636
pidesd is offline pidesd  Canada
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ok thanks for the explanation opc. i just cant argue with you. you already gave so much that in the end i can only be grateful.

in fact, i would not use the smds on any pro pcb, just a regular pad per hole board. the reason i wanted the kit was because it would save me some space and make the design more compact. also, because i would only use a couple of the smd parts for the build (like caps) and use the rest for other things, it wouldnt make the whole thing too akward. and lets just say that, taking everything elase out of the equation,for the price , you get a pretty nice little bunch of parts.
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Old 11th November 2010, 12:12 AM   #637
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Default protection diodes

They say a little knowledge is a dangerous thing. In researching parts, v regs in particular I was struck by the recommendation that with >25 volt output and > 10UF capacitance an output protection diode be included from the adjustment pin to the output pin. Was this an oversight or is there a good reason that this isn't needed in this circuit? The input protection diodes are there so I am guessing that I am missing something, and that makes me dangerous.

On a different matter Newark in the US (97K5040) or Farnel have a (MHP35201F) 200 ohm thin film R rated for 35 watts and a 50 ppm tempco. Similar price to a Caddock thick film. Ought to go well with those other $$$ Rs.

Another place to upgrade is the digital isolation transformer. Scientific Conversion part number SC947-02LF looks like the best out there. It is a 1:1 so it can work with SPDIF or AESEBU. It is surface mount and $17 but if we can get interest for 50 pieces it drops to $12. I would even be willing to set up a group buy if there is sufficient interest. I know I want 4 right away.
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Old 11th November 2010, 02:16 AM   #638
opc is offline opc  Canada
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Hi Guys,

pidesd:

I'll keep an eye on what parts I have left, and I'll get in touch with you when the dust settles. If I have enough parts to make an SMD only kit for you, then I'll do my best to get one together.

Hang tight for now, and we'll see where we are in a week when everything is shipped out.

stephen1212:

You are indeed correct that two diodes are often used, one for the bypass and one for the output to input. Because the bypass capacitor is small (10uF) there isn't really a need for any protection on that node. Some people do like to put massive values there, and that diode is more intended for that sort of application (IMHO). I have never used one with 10uF bypass caps, and I've never seen a reg fail as a result (or ever really for that matter, they're pretty bomb proof).

Just the same, a small SOD23 can be soldered across the 240R resistors if you are concerned. I don't see a need for it though.

Cheers,
Owen
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Old 11th November 2010, 02:38 AM   #639
Horio is offline Horio  United States
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Quote:
Originally Posted by opc View Post
Hang tight for now, and we'll see where we are in a week when everything is shipped out.

I'm crossing my fingers that when the dust settles next week, there will be an extra board/SMD for me...
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Old 11th November 2010, 03:07 PM   #640
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How about FQA34N20? It's almost the same as FQA32N20 with higher current and less Crss...
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