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Old 13th March 2015, 11:19 PM   #1
Einric is offline Einric  United States
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Default Headphone Buffer With Power Supply

I had this great idea to use some unity gain OpAmp buffers to provide a headphone output for any gain stage you have.
I figure that this will supply about 350mA of current to drive most headphones.
This would allow people who have hard to drive headphones to be able to drive them from their iPod or other portable music device.
I will be attaching this to the tail end of an Aikido 12VAC.
I think it will make a pretty nice setup.

I would really appreciate it if any of the circuit design guru's out there would take some time to help me tweak this circuit.
I have only been using Eagle for about a week so I'm still learning.


P.S. Moderators, can you please merge my previous thread or just delete it?

Thanks,
Rich
Attached Files
File Type: pdf Headphone Buffer Combined BRD.pdf (36.9 KB, 38 views)
File Type: pdf Headphone Buffer Combined SCH.pdf (23.1 KB, 62 views)
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Old 13th March 2015, 11:24 PM   #2
Einric is offline Einric  United States
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Here is a screenshot for people who don't have a pdf reader.
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File Type: jpg HP Buffer with PSU BRD & SCH.jpg (277.1 KB, 223 views)
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Old 13th March 2015, 11:28 PM   #3
Einric is offline Einric  United States
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This board is VERY small, about 2"x4"
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Old 14th March 2015, 12:08 AM   #4
6L6 is offline 6L6  United States
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That looks like a very versatile circuit -- Parallel NJM 4556 should drive anything, even the most power hungry, high impedance planars.

So the idea is to use this after the gain stage of choice? You mention the Aikido, but you could use anything, right?

That's a great idea!!

Are you going to make a group buy of the PCB? If so, count me in for at least one.
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Old 14th March 2015, 12:24 AM   #5
Einric is offline Einric  United States
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I estimate the input impedance of this circuit is somewhere between 500kΩ and 1MΩ so just about anything that is under the rail voltage you choose to run the buffer on will work.
The datasheet notes that the maximum input voltage is 30V P2P with the maximum input voltage limited to the +-Rail Voltage if below +-15VDC.
The maximum input rail voltage is 18V Bipolar but this circuit could be used as low as +-2VDC, it would just limit the input signal voltage.
A 12V 10VA transformer would be more than sufficient for this design and give you maximum flexibility for input level.
I imagine if you had some ridiculous headphones on either end of the spectrum (current or voltage) and you HAD to listen to a song on an iPod or something that this buffer would allow you to drive them to the max output of the iPod.
Where otherwise the iPod wouldn't cut the mustard.

I would like to do a group buy if there is enough interest and the layout/design is well received.
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Old 14th March 2015, 02:42 PM   #6
Einric is offline Einric  United States
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Default Prototype

I have prototyped the Power Supply and buffer circuit separately.
I will try to attach it to my Aikido 9-Pin All In One that is driving my F4 to see how it sounds.
Attached Images
File Type: jpg HPB PSU.jpg (658.2 KB, 177 views)
File Type: jpg HPB PerfBd.jpg (787.2 KB, 159 views)
File Type: jpg HPB Trans.jpg (963.4 KB, 148 views)
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Old 15th March 2015, 09:33 PM   #7
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Nice.

Those are stock Radio Shack DIP boards.

I really like your compact, board mount toroidal transformer. I was looking at those.

You could build a nested feedback version on a bigger Radio Shack DIP board. You can get nicer "prototype" DIP boards from Digikey.
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Old 15th March 2015, 10:06 PM   #8
Einric is offline Einric  United States
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I just used what I had on hand.
There are 4 jumpers under the board.
I may add a couple extra jumpers for the V+ & - just to simplify wiring.
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Old 16th March 2015, 03:09 AM   #9
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I think it's great. I breadboarded some parallel 5532s and I thought it worked pretty good as a headphone amp. I did end up building something different, but I have most of the parts to whip up a 5532 parallel headphone buffer. I could use it.

Where did you get your transformer? I was looking at some of those for a headphone amp. I did look at Digikey and Mouser. I was wondering if there were ano other good (cheap) vendors for this type of product.
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Old 16th March 2015, 04:36 AM   #10
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Just in case if any of you is looking for a PCB to prototype this... I have something around 9 pcs of this PCB left - "The Crocodile" I'll be happy to get rid of them.
The output stage of this amp is essentially 4 opamps configured as a buffer and connected in parallel. You can fit pretty much any unity gain stable dual opamps in SOIC8. Or even some CFAs - the PCB has a placeholders for feedback resistors. Just don't fit anything on place of the front end stage.
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