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Old 28th September 2006, 09:03 PM   #1
Nordic is offline Nordic  South Africa
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Default Mini Ipod headphone amp DIY project

Today it is my honour to add my first developed and tested project implementation of my own, based on the popular CMOY circuit.

I spend the last few weeks trying to get the best quality yet smallest portable amplifier I could possible build.

Now, I'm no engineer so even though it is a simple project I am proud of havenig done it myself and it took many hours of testing and many unsatisfying prototypes before I got to this one

It is build into the Hammond 1551kbk case 3.19" x 1.57" x 0.79" (8 x 4 x 2cm) yep its tiny, in fact its shorter than my first generation Ipod shuffle.

My finished copy is a beaut, which inspired me to share the eagle file and main concept for anyone who wants to try their hand at doing something for themself.

Zero hiss, Zero humm, Zero distortion (well unless the battery is flat), It is so far the best I have heard the opa2132 sound... no input caps is the best input caps as they say (well unless you are going to put a DC source to it.. so please stick to ipods and mp3 players.

Also because there is no background hiss, one tends to keep upping the volume in between songs thinking the player stopped... the silince is a bit less severe with the stock earphones but is on the verge of imperceptablity to my hearing.

Bass is unrelenting and tops very clear due to the absence of highpass filter on the input -please add no dc here-
WARNING CAN PUT OUT SERIOUS VOLUME WICH CAN LEAD TO HEARING LOSS.
This is countered to some extent by the single cell power supply wich will start to clip the output when you start getting silly with the volume level.

OK now for the diagramme, I'm a bit tired and glowy now from a job well done and a very satisfying result I am proud to add my name as an audio amateur to.

Tommorrow, God willing, I will add a bit of descriptions and more instructions, like how to add the LED etc.

Click the image to open in full size.
Attached Files
File Type: zip mini5.zip (5.3 KB, 298 views)
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Old 28th September 2006, 11:25 PM   #2
maxw is offline maxw  United Kingdom
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Looks like a nice tidy design. You should show the people on head-fi, they are into this stuff big time
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Old 29th September 2006, 08:52 AM   #3
Nordic is offline Nordic  South Africa
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OK got a few minutes to add a few lines.....

First here is a picture of the case I used.
Click the image to open in full size.

Its the Hammond 1551KBK this case is also available with a flanged lip for permanent instalations like on a motorbike etc....
http://www.hammondmfg.com/dwg9.htm

It costs R20 about $2 your side....

Not sure what you call that type of 3.5mm socket but it has a very convenient pin layout.... it was all I could find on short notice... it was a millimeter or so too long so I snipped of some of its cover to leave space for the decoupling cap.

For decoupling caps I settled on 10nF (=.01uF) encapsulated Wima Poly film. Click the image to open in full size.
NP0 or COG type ceramics should work just fine... just stay away from normal ceramics.

The resistors as seen from top to bottom in the diagram are
51R
0R (wire)
10k
1k
100k

Use as large caps as you can fit in the space next to the battery... I think its about 9mm... (2/5 inch)

12V and anything from about 220uF should do just fine

For the led, solder one end of a 5k1 resistor to th exposed leg of the 3k3 resistor right at the bottom of the circuit use a pice of thin insulated wire to cover the distance to the LED position...
the positive leg of the LED gets connected to the exposed pins on the back of the switch above where it goes into the pcb... it goes on the pin farthest away from the battery again with some insulated wire to avoid shorts....

To get a better look at the picture download eagle and the attached board file.... I did the first prototype with a black marker and ferric chloride.... its that easy.... I'll attach a picture later that you can print, attach with selotape to a board and drill your holes before drawing the traces.
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Old 29th September 2006, 10:46 AM   #4
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Very nice.

I just etched a PCB for the first time yesterday and this looks like a nice simple project to help hone my copper dissolving skills.

Will this work with a TL072 opamp? I have a bunch of them but will order a few OPA2132 if I have too.
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Old 29th September 2006, 02:40 PM   #5
Nordic is offline Nordic  South Africa
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Sure it should be able to use any dual opamp even if its just for testing... obviously you gets what you pays for... just make sure it uses the standartd pin layout - the chip you mentioned, does...

Congrats on the etching, I'm still an amatuer too, have progressed from black marker and pool acid to feric chloride, and now experimenting with photo etching... just came back from the shop with some UV leds going to make an exposure light now...

Then I'll come add some more details on the headphone amp...

P.S. gave it some thought, you may be able to get quite a few uF more in on the PSU caps if you use 6.3V ones, they tend to be nice and small...
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Old 29th September 2006, 03:48 PM   #6
gmikol is offline gmikol  United States
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Quote:
Originally posted by Nordic
OK got a few minutes to add a few lines.....

Not sure what you call that type of 3.5mm socket but it has a very convenient pin layout.... it was all I could find on short notice... it was a millimeter or so too long so I snipped of some of its cover to leave space for the decoupling cap.

Great work Nordic--

Can you give us a reference on that 3.5mm jack? Like a part number or a distributor?

Thanks--

Greg
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Old 29th September 2006, 04:02 PM   #7
Nordic is offline Nordic  South Africa
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I will have to phone the company I got it from in the morning...


I think its totaly feasable to cut that bit of PCB or even fit a regular case mount socket in the space above the pcb, connected to the appropriate holes with little leads...

You will need a small handfile too anyway to trim the PCB into the case...
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Old 29th September 2006, 05:07 PM   #8
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Quote:
Originally posted by Nordic
Sure it should be able to use any dual opamp even if its just for testing... obviously you gets what you pays for... just make sure it uses the standartd pin layout - the chip you mentioned, does...

Congrats on the etching, I'm still an amatuer too, have progressed from black marker and pool acid to feric chloride, and now experimenting with photo etching... just came back from the shop with some UV leds going to make an exposure light now...

Then I'll come add some more details on the headphone amp...

P.S. gave it some thought, you may be able to get quite a few uF more in on the PSU caps if you use 6.3V ones, they tend to be nice and small...
I used the "toner transfer" method to make my boards and I am extremely happy with the results. I figure inkjet photo paper and standard PCB is easier and cheaper to get than the supplies to do photo etching so thats why I went that route.

Is there anyway you could post a printable file of just the board traces in black and white? I just installed Eagle last night and I can't figure out for the life of me how to get it done.

Thanks
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Old 29th September 2006, 05:30 PM   #9
Nordic is offline Nordic  South Africa
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The only chemical supplies you need above what you currently use is some lye, also known as casutic soda.. you can get it from the hardware shop, dirt cheap...

I would much rather help you with the printing....

eagle prints whatever you have in the view screen on the board... go to view> show hide layers and hide most of the stuff except the layers an vias and the few funy ones at the bottom of the list, it won't show, until you click ok... then go to printing... for the bottom layer, you should tick mirror, solid and black...
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Old 29th September 2006, 07:09 PM   #10
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Quote:
Originally posted by Nordic
... for the bottom layer, you should tick mirror, solid and black...
...are you sure about that If I am not mistaken it is the top layer that should be printed in mirror format. The bottom layer shold be left as is. Picture it like you are looking through the board and you will get the idea. If you are using the toner transfer method you can also "silkscreen" your board by printing the "TPLACE", "TNAME" and "TVALUE" layers mirrored. Just iron it onto your board after you are done etching and presto...a nice component placement silkscreen.

Also take a look at the LM4562 for a dual opamp...it's a nice one!

Good luck with the project!

G.
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