LM3886 amp with NE5532 volume control board - diyAudio
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Old 22nd November 2012, 10:36 PM   #1
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Default LM3886 amp with NE5532 volume control board

Ok guys here is my problem. I built a LM3886 based amplifier. I used a 24-0-24 ac center tap transformer and a smoothing DC power supply board that I built from a schematic that I found online. The volume was just a mute switch substituted with a pot. I wanted a better volume control so I purchased and built the NE5532 based volume control board. It needs 15-0-15 VAC power. My transformer is 3 amps and I can not find a current draw spec on the volume control. Can I just use a couple resistors and run the two boards in parallel off of the same transformer? Does anyone know a better schematic I can use for the amp power supply? I am just not getting full potential out of what I have. If so I need help with knowing the sizing of the resistors and how to set it up. Here are links to what I have. The transformer is a 120 VAC primary 24-0-24 VAC secondary 3 AMP
Volume Control Kit - NE5532 Volume Control Board Components 10 Times Pre-amp

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Old 22nd November 2012, 11:03 PM   #2
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it looks like the kit includes regulators. if the smoothing caps are rated high enough you may get away with 24AC. NE5532's draw a lot of current compared to some op amps, but that still isn't very much at all. maybe you could put a small heatsink on the regulators if you find them getting hot. what voltage is written on the big caps? and what is the voltage regulator?
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Old 22nd November 2012, 11:43 PM   #3
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The big caps are 25V 220uf. I have left the regulators off just for that purpose. I do have the heat-sinks already and they are 7815 and 7815 regulators. After looking at what I have I am wondering if I shouldn't just scrap the power supply board that I have built and start from scratch. That would put me at an AMP board, volume control board, and a 24-0-24VAC transformer.
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Old 22nd November 2012, 11:44 PM   #4
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Quote:
Originally Posted by Bradford336 View Post
The big caps are 25V 220uf. I have left the regulators off just for that purpose. I do have the heat-sinks already and they are 7815 and 7815 regulators. After looking at what I have I am wondering if I shouldn't just scrap the power supply board that I have built and start from scratch. That would put me at an AMP board, volume control board, and a 24-0-24VAC transformer.
Those caps will not survive. If you replace with 50V caps you may be ok.
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Old 23rd November 2012, 12:51 AM   #5
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Quote:
Originally Posted by Bradford336 View Post
I have left the regulators off just for that purpose.
It's common to mount regulators on the enclosure with an insulator kit (teflon pad + plastic grommet) and run wires to them. You'll find TO220 insulator kits on ebay.

Other than that the circuit will probably work fine if you sub in higher voltage caps.

You could use a PSU PCB like this one:- Bridge rectification PSU PCB using 4 ultrafast diodes ! | eBay

...which will eliminate any doubts you may have about your PSU. I don't necessarily recommend that particular board. There are numerous boards on ebay, or I see they do a part kit, you just need to buy the caps.

Bridge rectification PSU PCB using 4 ultrafast diodes partial kit! | eBay.

Output voltage with a 24-0-24 tx will be of the order of 33V, 35V caps are marginal in this application, 50V are really required.

You may have a bit too much gain with the 10x in that NE5532 board, depending on how the 3886's are set up, particularly if running off a CD player or DAP, they're often pretty loud in their own right.

The current for the 5532 board is not much of a concern, but a 3A transformer will be a bit stretched if you are running stereo 3886's at much volume, particularly into 4 ohms. Typical output limiting (one channel) operates @ 7A IIRC. Music power is considerably less than peak power, but still...
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