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Old 26th March 2013, 04:13 PM   #1
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Default Simple DIY Rectifier?

Hello all,

I am currently building (cobbling together) a hybrid integrated amp.

The tube pre-amp board requires ~12v AC

The amp board (Tripath 2020) requires ~12v DC

I currently have:

- 110/120vac-to-12vac transformer rated at 3.33 amps

- 110/120vac-to-12vdc transformer rated at 2 amps

It all works quite well during testing (see photo), however I would like remove the DC supply and implement a simple rectifier between the 12vac supply and the amp board.

Click the image to open in full size.

I have read and understand the theory of a diode bridge and output smoothing. Diode bridge - Wikipedia, the free encyclopedia

I have a box full of spare parts with all kinds of the square metal bridge rectifiers and capacitors.

Is it as simple as hooking the 12vac leads to the AC terminals of the bridge rectifier and then connect the load to the DC terminals, with a large capacitor in parallel?

Click the image to open in full size.

Last edited by cogitech; 26th March 2013 at 05:16 PM.
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Old 26th March 2013, 04:17 PM   #2
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By the way, the pre-amp board only draws a max of .833 amps from the 12vac supply, which would leave 2.5 amps for the amp board, which is still more current than the dedicated 12vdc supply.

Another question; with that huge Mallory in the picture, is a paralelled "output smoothing" cap still necessary?

Last edited by cogitech; 26th March 2013 at 04:22 PM.
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Old 26th March 2013, 04:38 PM   #3
Mihkus is offline Mihkus  Estonia
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That longass wires to the cap is like 1000uf cap on pcb.
Try 10k uF on pcb it might sound a bit better.

And 12V supply, well thats way too low

Last edited by Mihkus; 26th March 2013 at 04:41 PM.
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Old 26th March 2013, 04:40 PM   #4
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Actually, stock configuration had 3300uF on PCB.

It sounds much better this way, and this is a test setup. Things will be optimized/relocated during final build.

But this is off-topic anyway. Do you have any comments about simple 12vac to 12vdc rectification?
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Old 26th March 2013, 04:52 PM   #5
DF96 is offline DF96  England
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If you rectify 12V AC RMS you get about 16V DC, not 12V DC.
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Old 26th March 2013, 04:54 PM   #6
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Quote:
Originally Posted by DF96 View Post
If you rectify 12V AC RMS you get about 16V DC, not 12V DC.
Interesting. This seems important!

So the next question is, how to I bring that back down to 12v? Resistance?

Looks like I found my answer... http://www.raltron.com/cust/tools/voltage_divider.asp

But if you have any other pointers, I'd be happy to hear them.

Last edited by cogitech; 26th March 2013 at 04:56 PM.
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Old 26th March 2013, 05:14 PM   #7
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According to the TA2020 white paper, it looks like I can safely run it at 13.5-14 volts without issue, so I will aim for that when designing my voltage divider circuit.
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Old 26th March 2013, 05:21 PM   #8
FoMoCo is offline FoMoCo  United States
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Quote:
Originally Posted by Mihkus View Post
That longass wires to the cap is like 1000uf cap on pcb.
No. More like a 10,000 uF cap in series with a small amount of inductance and resistance. If there's decoupling on the PCB, those wires aren't that big of a deal. It's not pretty, it's not good engineering practice, but it will work perfectly fine. In no case does the capacitance change!

Quote:
Originally Posted by DF96 View Post
If you rectify 12V AC RMS you get about 16V DC, not 12V DC.
+1
Since the OP doesn't seem to understand this, the formula would be 1.414 x 12, minus two diode drops.

Quote:
Originally Posted by cogitech View Post
So the next question is, how to I bring that back down to 12v? Resistance?
Voltage regulator. But, most cheap and dirty three terminal regulators won't do the job because of the 4 volt drop.

Quote:
Originally Posted by cogitech View Post
Looks like I found my answer... Voltage Divider Calculator
Not hardly. This isn't viable for more than milli-amps.
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Last edited by FoMoCo; 26th March 2013 at 05:22 PM. Reason: Can't spell. Darn Pulaski County Schools...
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Old 26th March 2013, 05:26 PM   #9
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Why don't you use a voltage regulator?
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Old 26th March 2013, 05:27 PM   #10
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Quote:
Originally Posted by FoMoCo View Post
No. More like a 10,000 uF cap in series with a small amount of inductance and resistance. If there's decoupling on the PCB, those wires aren't that big of a deal. It's not pretty, it's not good engineering practice, but it will work perfectly fine. In no case does the capacitance change!
This is what my gut was telling me, but I don't know much about electronics so I decided to keep my mouth shut.


Quote:
Voltage regulator. But, most cheap and dirty three terminal regulators won't do the job because of the 4 volt drop.

Not hardly. This isn't viable for more than milli-amps.
Hmmm. OK. Well, I really only need to drop down to 14 volts. Not sure how much that changes things.
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