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PostPosted: 30 Dec 2012, 21:26 
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Joined: 06 Jun 2008, 18:23
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Location: Australia
It's been a while since I have built one of these but a work friend asked me to build one for cash. How can I say no? He is buying some better phones and wanted a driver\amp for them. Not much new in this build except I used the Russian PIO caps on the input. The caps are 0.47uf and rated 160V. I bought them specifically for low voltage projects where I felt quality caps would be needed.

The amp is on a proto board. Silver solder was used and switching jacks. Both input and output jacks have to have plugs in and the amp turned on (switch at back) for power to flow. Mil spec chip socket and solid core copper wire for the audio path where required. The bigger caps allowed direct connection from jacks to cct. brd. No hook wire required on the brd. it is all compoent-2-component wiring. Sticky Al foil lines the base and lid for a bit of RF protection and case dampening. The chip is the OPA2134.

How does it sound? Early days but fat and natural at this point from my Cowon on FM radio.
Attachment:
ChipHPamp.jpg
Attachment:
ChipHPampInsideII.jpg
Attachment:
ChipHPampInside.jpg


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PostPosted: 01 Jan 2013, 00:26 
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I was checking some voltage around the chip expecting about +/- 9V. But I found 6V and 12V. After a lot of stuffing around I realised I had one of the 200uf low ESR caps in backwards. It was rated 16V so 9V was not going to destroy it short term. What I didn't know is that it can effect the voltage across the cap and therefore the imbalance across the chip. The cap looked fine so, this time, I put it in the right way and hey presto I now get a correct voltages readings.

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PostPosted: 03 Jan 2013, 16:47 
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Joined: 25 Sep 2009, 15:44
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Location: ENGLAND, BABY- YEAH
MW,

The Cmoy circuit is a great little DIY project, (I have made a few), they can drive almost any headphone you can throw at them!! It was a good idea to install the socket rather than hard solder the BB IC to the board, try some "chip rolling", NE5532 work surprisingly well here as well as some of the AD8xxx chips.


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PostPosted: 03 Jan 2013, 17:08 
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It has been sold. It was a commission job. I am going to make another for my self. Never thought of chip rolling. I may have to try.

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PostPosted: 03 Jan 2013, 23:17 
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Location: Winnipeg, CANADA
Hi Mark. Can we talk you into adding an extra opamp to your next build as an output buffer? :lildevil:
Let us know and we will give you some schematic ideas. Another idea you can try is to bias the chips into class-A operation. We you going to go battery power or from a supply?

Cheers

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PostPosted: 03 Jan 2013, 23:59 
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Gio:I want to make it portable so batteries for the PS. Class A operation interests me not sure about an extra chip for a buffer. Got a schematic?

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PostPosted: 07 Jan 2013, 20:54 
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For portability and battery power, proabbly best you stick with the single op amp. A buffer and class-A will kill battery life and increase size. One thing you can try is to use a rail splitter for the virtual ground.
http://tangentsoft.net/elec/vgrounds.html
I sent you some TLE2426 chips a few years back that you can use.

Cheers

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PostPosted: 07 Jan 2013, 21:49 
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The first of the HP amps I made was a commission job and is gone. So I made another. This time I got the cct. brd. even neater and added snubbing across the storage caps (0.01 polyesters). Also I thought I would go wild and add an "on" LED (with snubbing of course). And I changed the switch to a push button. The switch is a lot bigger but I think better. I used wire-wrap wire for signal hookup. Here are some shots of the cct. brd. # 2:
Attachment:
CctBrdV.jpg
Attachment:
HPIII.jpg
Attachment:
HPIII_I.jpg


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PostPosted: 07 Jan 2013, 22:39 
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Gio wrote:
For portability and battery power, proabbly best you stick with the single op amp. A buffer and class-A will kill battery life and increase size. One thing you can try is to use a rail splitter for the virtual ground.
http://tangentsoft.net/elec/vgrounds.html
I sent you some TLE2426 chips a few years back that you can use.

I used the standard rail splitter resistive network. This is dead simple and works fine.

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PostPosted: 16 Jan 2013, 16:36 
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As posted on another thread, I sold my HP amp at an audio club buy, swap and sell. I have a prototype K272B to complete so maybe not all bad ( or good depends on how you look at it).

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