DIY MOSFET Headphone Amplifier

DIY MOSFET Headphone Amplifier

This project works really well and is based on two MOSFET per channel. A MPF102 in each input and a IRF510 in each output.

 

DIY Headphone Amplifier

The chassis is the main heatsink for the power MOSFET’s.  The aim of this project was to implement a simple headphone amp schematic from the many to choose all found on the internet. I have been using the 1590G enclosure by Hammond for other projects and have liked it very much. In this project the enclosure becomes the heat sink for the MOSFETs as the enclosure is aluminum and is large as heat sinks go. The finished device is easy to operate, handle and powers some larger headphones very well.

 

1590G projects pastHere are the last 1590G projects, the Headphone Amplifier, a Trotsky Overdrive guitar pedal, and a Aviation Headset interface for amateur radio.
The Headphone amp is well suited to this project box and is very solid and robust.

 

 

 

 

Headphone Amp with BatteryVarious power sources run this amp and in this image I am using a LiPo from the RC airplane community as it puts out a good 11.7 volts and is easy to charge. Included in this device are Stereo input volume control which allow you to  manage the sound for left and right, inside the headphones. The unit has RCA inputs and a 1/4 inch headphone jack output. I use a adapter to attach smaller 1/8th inch jacks found on ear buds. On the left side is power input and on the right side is the power switch, however pulling the plug does the same thing.

 

Circuit Plan and Bare CaseThe circuit is a class A amplifier and has a MPF102 as a gain stage ahead of A IRF510 Power MOSFET. The original called for IRF630’s but I had a set of IRF510’s that seem to be popular with other headphone amp projects I looked at.

The schematic is found at the DIY Audio Projects Forum.
It’s a common choice based on a design called Greg Szekeres that was used as a current buffer. This amp is preceded by a MPF102 gain stage FET to drive the IRF510.

Link for this here,
http://diyaudioprojects.com/Forum/viewtopic.php?f=10&t=3506

In my sketches, by hand I did much figuring to try to see how this circuit was going to install into this enclosure and how I was going to go about using the case as a heat sink for the 510’s.

IMG_20151101_131640In this shot, the whole enclosure is taped up with masking tape so I could mark up locations for input, power, controls, switch and output.

 

The hole is a doorknob hole. The workbench is a metal door. The workbench is really best suited to building large model aircraft with the use of Magnets. But that is a whole new conversation…

 

 

IMG_20151101_134829In this image, the RCA input jacks are installed, and the 100K pots are installed. The schematic called for 100K logarithmic pots but in my case they are inexpensive liner pots.

Using tape to make placements and draw on is easy and if I don’t like something I take the tape off, retape and then mark up again.

 

 

IMG_20151101_134906Here is an inside image of the progress so far, in the bottom installed, is the output stereo jack, the power switch and the Power plug socket. This left as much room as I could get for the board.

 

 

 

 

IMG_20151101_193459From the sketches done earlier, I was able to draw a preliminary wire diagram for the board and begin to finalize some details as to where things go. I started with the IRF510’s as they were critical in placement so that they could attach to the case to be used as heat sinks. From there the placements of the MPF102’s and this took a bit of re-drawing to get locations where the traces were logical.

 

I know that this is old school technique, I like pencil and paper a lot. One could work this all out in short order with a program like Fritzing and be done with it. However, I am not versed in this until recently. I hate learning software at the best of times.

IMG_20151101_193511

 

 

Another quick mash up of trace work to develop a circuit board.

 

 

 

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The quick and dirty etching of the initial board to get things going.

I actually drilled the board first from the traces made in Sharpie Pen then etched and got what I needed.

 

 

 

 

IMG_20151101_193529Board ready for components.

In the future, I will finalize boards in the next version and make more professional boards with the changes. I know already that I will have to add a power resistor and a filter capacitor but that will come later.

 

 

 

 

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Here is a completed board with components installed. But what is missing is the IRF510’s as they are added last.

 

 

 

 

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I test fit the board and components to see how it all goes and so far things fit fine.

 

 

 

 

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In this image one can see the IRF510′ on each side that are held in with insulators, mica spacers and some heat transfer paste. This securely bolts the board to the chassis. Other wires for input and output also add for some anchoring of the board. Tape is under the board to insulate from the chassis. The big capacitor is a 1000uF that really needs to be part of the board but in this application there was no room but to mount it off the board. It worked ok.

 

IMG_20151110_103338 Test run, and it worked first time with no trouble shooting. Until I found a broken trace later in it’s operation.

 
Sounds are nice with the right set of headphones and if the input is strong the gain is very good. Over time I will try some different headphones to see what is worthwhile.

 

 

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