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Old 15th December 2011, 04:25 AM   #11
ZLyzen is offline ZLyzen  United States
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Originally Posted by ! View Post
Using a different transformer with more secondary windings is what I'd prefer.
Honestly I really have looked. This is also what I originally intended to do.
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Old 15th December 2011, 04:57 AM   #12
ZLyzen is offline ZLyzen  United States
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this would be ideal, but I think it's custom made for these RPK monitors

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Old 15th December 2011, 05:47 AM   #13
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another question, these regulators provide a constant current and a specified voltage
A voltage regulator regulates voltage. That means if the load resistance goes down, it outputs more current; if the load resistance goes up, it outputs less current. If the voltage into the regulator goes up or down, the regulator adjusts to maintain its set output voltage.
You're building these active monitors "from the ground up." Design and build them to use separate transformers for the op amps and power amps.
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Old 15th December 2011, 12:02 PM   #14
Elvee is offline Elvee  Belgium
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It is always possible to find "creative" solutions to such problems.
Depends of course on the level of complexity you are prepared to tolerate:
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Old 15th December 2011, 03:49 PM   #15
AndrewT is offline AndrewT  Scotland
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Zy,
copy exactly an existing proven to be correct build & assembly instruction set.

You are not ready for electronic design.
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Old 15th December 2011, 03:58 PM   #16
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Zy,
copy exactly an existing proven to be correct build & assembly instruction set.

You are not ready for electronic design.
I concur.
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Old 15th December 2011, 04:12 PM   #17
cbdb is offline cbdb  Canada
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Ditto. That first schematic is all wrong, transformer puts out too much voltage, no centre tap, caps are the wrong size, resistors are too large. There are lots of good proven designs you can easily find.
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Old 15th December 2011, 07:12 PM   #18
Elvee is offline Elvee  Belgium
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It is always possible to find "creative" solutions to such problems.
I just noticed a small error there.

I'll rectify tomorrow, the principle are not in cause anyway.


Simple curiosity: has someone noticed what this error is?
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Old 15th December 2011, 07:40 PM   #19
! is offline !  United States
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Originally Posted by ZLyzen View Post
Yes the transformer is rated as 2 x 24VAC windings. I guess to clear some things up:

Would it be fine to use the current -/+ 24V rails for the larger LF opamp?

and as for the HF IC and the op amps for the filter I should regulate the voltage down using something like a LM317?

These are AB class amp chips and they will both be heatsinked
24VAC on a (corrected) implementation your schematic shows would be about 32VDC. That is too high for (easy, reasonable) linear regulation or a resistor voltage divider to reach 17VDC, let alone 12VDC, whether it be an LM317 or some other linear regulator. There are ways you could make it work, but it's far from ideal and would waste a lot of power, create a lot of heat.

I'm not sure what you mean by "for the larger LF opamp". If you mean "-/+ 24V for 1 LM3886TF chip", yes LM3886TF can run from 32VDC, though this voltage is a bit higher than ideal if your (speaker) driver is less than 8 ohms. If your heatsink is on the back of the speaker cabinet (highly recommended if not in a separate amp enclosure) then cooling will be easier than if it's entirely enclosed in the cabinet. Same goes for linear regulator heatsinking or power resistor heatsinking but IMO power resistor voltage divider isn't reasonable at all except in some stranded-on-a-desert-island-and-that's-all-the-parts-I-have, type scenario.

The above is under the assumption that the transformer current rating is appropriate for the load. I'm not implying it's not, rather I don't recall seeing any spec for that mentioned.

As a couple people mentioned already, there are enough issues with the project/parts that it now seems a matter of what your primary interests are, whether they be learning to design & build, or copying an existing design to get done faster and with least issues to resolve.

Last edited by !; 15th December 2011 at 07:48 PM.
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Old 15th December 2011, 07:55 PM   #20
ZLyzen is offline ZLyzen  United States
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So lets say I go with Sofa Spud's advice and use two separate transformers with center taps for two separate supplies, one for the power amps and on for the filter board.

I could, instead of using a hf and lf power chip, use a LM4780. One half of the chip for HF one half for LF. This would solve the problem of the two separate amplifier chips needing separate voltages.

Now when the power is rectified and smoothed with caps the voltage is higher than the transformer (forgot about that), which isn't necessarily bad, not what I was planning on, but isn't this more headroom? (The speaker can handle "35RMS/70 max" watts and is 8ohm) and the amp chip can accept quite a bit of rail voltage.

So I guess the separate transformers would be my best option, which isn't necessarily bad since each one will need to supply less current than one supplying everything.

I plan on just working out a design for a few months before I go into implementing so I'm just learning as much as I can. Thank you all for the advice so far and anything else would be greatly appreciated, I will post another (better) schematic in a few days once I'm done with finals and things are less crazy.
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