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Old 13th January 2013, 01:19 AM   #81
m145mcc is offline m145mcc  United States
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what If I used another RC filter after the bridge?
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Old 13th January 2013, 01:52 AM   #82
JMFahey is offline JMFahey  Argentina
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Well, you don't really need it.
The basic idea is this:
1) the bridge + a 1000 to 4700uF provides unregulated 16 or 17V DC, with, say, something in the order of 1V ripple.
2) the regulator provides *exact* 12.6V or whatever it's set to, and in the bargain ripple goes down to, say, 1 millivolt.

So prefiltering its input is not really necessary.
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Old 13th January 2013, 01:55 AM   #83
m145mcc is offline m145mcc  United States
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OH! I got ya, I will do that then. I think I have a 2200uF in a box somewhere.
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Old 13th January 2013, 01:57 AM   #84
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Quote:
Originally Posted by JMFahey View Post
Well, you don't really need it.
The basic idea is this:
1) the bridge + a 1000 to 4700uF provides unregulated 16 or 17V DC, with, say, something in the order of 1V ripple.
2) the regulator provides *exact* 12.6V or whatever it's set to, and in the bargain ripple goes down to, say, 1 millivolt.

So prefiltering its input is not really necessary.
To add to this, a cap between adj and ground will knock another 20dB off the ripple and get it to, say, 100uV. It's all in the datasheet.
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Old 13th January 2013, 02:10 AM   #85
m145mcc is offline m145mcc  United States
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your right, but the mic29150 is a fixed supply of 12vdc. should I use an adjustable to get exactly 12.6 or can I get by with 12?
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Old 13th January 2013, 02:29 AM   #86
JMFahey is offline JMFahey  Argentina
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Never heard of mic29150 , but if it were a 7812 , an old_as_the_mountains trick is to add a 1N4002 or similar between the "ground" leg and actual ground.
Instantly rises 1 diode drop (around 0.65V) .
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Old 13th January 2013, 02:40 AM   #87
m145mcc is offline m145mcc  United States
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No way, that's genius. I have some slight changes to make, thanks.
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Old 13th January 2013, 10:46 AM   #88
m145mcc is offline m145mcc  United States
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Digikey has a very limited number of heat-sinks, would this be over kill or just the right amount? Newegg.com - Logisys Computer CC8 Copper Heatsinks only I should probably mention its for the LM3876 on a more serious note I was considering this on Ultra U12-40658 Carbon X1 Low Profile CPU Cooler - Intel LGA 775, ITX, MATX, HTPC at TigerDirect.com It's a low profile fan cooled unit for a computer cpu, I assume the fan runs off of 12vdc so I could tap into my heater supply.

Last edited by m145mcc; 13th January 2013 at 11:14 AM.
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Old 13th January 2013, 01:43 PM   #89
JMFahey is offline JMFahey  Argentina
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Why go with such weird heatsinks?
The first of which, by the way, is a *very* poor design.
I couldn't care less that it's made out of copper if the heat transmission to the fins is through long thin bars.
Yes, it does *look* as if it were the CPU cooler in R2D2's brain , of Star Wars fame.
Go for a good solid classic heatsink, like the one Robert Kesh used successfully.
Agree that Digikey is not very clear as to where to find their heatsinks, I also got steered into the CPU area.
The proper ones are at:
Fans, Thermal Management | Thermal - Heat Sinks | DigiKey
Don't remember what Chip Amp you settled on, but for a 20W class one (TDA2050/LM1875) this one or larger should do:
VHS-95 CUI Inc | 102-1489-ND | DigiKey
For an LM3886 this one or larger:
1963856-1 TE Connectivity | A100339-ND | DigiKey

As a seat_of_the_pants rule, based on experience, 2"x3" or equivalent is enough for 15 to 20W and a 4"x6" for up to 100W.
*Always* with many fins, mounted vertical, and allowing for free air flow, either mounted outside the cabinet or inside but with generous cooling slots.
Unless absolutely necessary, try to avoid fans, one extra complication and what many forget to mention; a source of NOISE.
I mean electromagnetic noise.

FWIW, I use *these* for my 100W Guitar or Bass amps:
Click the image to open in full size.
5" wide by 2" high, mounted with vertical fins, bolted to the aluminum back panel, so the amp is inside, but the actual fins are outside.
A common solution for MI amps.
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Old 14th January 2013, 05:24 AM   #90
m145mcc is offline m145mcc  United States
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I got every thing finally drawn up and scanned in. If anybody finds any discrepancies let me know, but as far as I know its build-able. I tried to include the parts list on the schematic for everyone. (Edit) I just noticed something on the tube psu C3 & C4 should be rated at a min of 150v not 15v and C2 doesn't need to be 200v more like 20v.
Attached Images
File Type: jpg 12AX7 Pre.jpg (673.3 KB, 35 views)
File Type: jpg LM2876 Power Amp.jpg (718.4 KB, 34 views)
File Type: jpg Power PSU.jpg (726.5 KB, 32 views)
File Type: jpg Tube PSU.jpg (747.3 KB, 29 views)

Last edited by m145mcc; 14th January 2013 at 05:34 AM.
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