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Old 25th October 2010, 05:35 PM   #281
neb001 is offline neb001  United States
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I'm surprised that you've become such a proponent of the Hifi2000 cases now, Patrick
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Old 25th October 2010, 05:51 PM   #282
EUVL is offline EUVL  Europe
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Only because of impatient people here who cannot wait until December, and already want to order things now.

Of course they may, but then I also don't want to be blamed that the case won't fit their GB components.

So a large case measuring so 500x500x200mm will fit anything.




Patrick
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Old 25th October 2010, 05:52 PM   #283
EUVL is offline EUVL  Europe
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I need one more volunteer to cross check my ACAD drawings vs those from bksabath.

Please send me a PM if you have a dwg and Gerber viewer.


Thx,
Patrick
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Old 25th October 2010, 06:50 PM   #284
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Patrick, you have a pm.
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Old 25th October 2010, 09:56 PM   #285
EUVL is offline EUVL  Europe
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You too.

Patrick
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Old 26th October 2010, 02:08 AM   #286
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Quote:
Originally Posted by thanh1973 View Post
Just an update on resistors.
I managed to find some Futaba MPC71 5W 0.22 Ohm resistors in my parts box (basically the same as mpc74).
I tested them at both 1A and 2A and the performance is as good as two cpf3 3W resistors in parrallel.
just for fun I tried to matched some .47 ohm resistors. It looks like measuring current or voltage is perhaps the better way to group the devices, even with a high precision ohmmeter.

Click the image to open in full size.

I think when it all comes down to it, either you don't bother as Patrick mentioned or you trim the resulting amp, as Zen Mod mentioned
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Old 26th October 2010, 02:10 AM   #287
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one more question with regard to the heat sink calculations. Are you leaving the option for attaching a regulated PSU to the heat sink, or are these calcs just for the amplifier boards?
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Old 26th October 2010, 02:21 AM   #288
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If you are intending on using a regulated supply, It will have to be in its own separate case with heatsinks.
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Old 26th October 2010, 04:30 AM   #289
EUVL is offline EUVL  Europe
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Correct.

Making a larger case with large heatsinks to accomdate more dissipation will make is too expensive to make and to ship.
Then it is better to buy commercial ones.

You may consider putting the regulator device on its own free standing heatsink within the case.
There is not a lot of spcae, but you might manage.
If you allow 4V drop & 4A bias, total dissipation is 16W, so the free-standing sink has to be 2W/°C.

Something like

V 5512G Profilkühlkörper - reichelt elektronik - Der Techniksortimenter - OnlineShop für Elektronik, Netbooks, PC-Komponenten, Kabel, Bauteile, Software & Bücher - ISO 9001:2000 Zertifiziert

(75x50x25mm, not small)


Patrick

Last edited by EUVL; 26th October 2010 at 04:37 AM.
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Old 26th October 2010, 04:35 AM   #290
EUVL is offline EUVL  Europe
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> It looks like measuring current or voltage is perhaps the better way to group the devices, even with a high precision ohmmeter.



> either you don't bother as Patrick mentioned

I do bother.

> you trim the resulting amp, as Zen Mod mentioned

That depends what you trim. You suggest trimming THD.
My approach is to trim second (and maybe third) harmonics without getting higher 4th, 5th, ....., before soldering.

If THD is the goal, then opamp and high feedback amp (like the Goldmund ?) rules.
No point going to Class A.


Patrick
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