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PostPosted: 01 Dec 2016, 15:20 
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Joined: 06 Jun 2008, 20:12
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Location: Houston, TX
Power Supply
Your power supply must supply the amplifier board with dual polarity DC. You can use very low voltages if you need to but I suggest, for best sound quality, to stay between +/-12V and +/-15V. +/-17V is the max but I don’t recommend this extreme. When we say +/-12V, etc.. what we mean is you will need a supply that gives a positive 12VDC and a negative 12VDC. This must have a 0V point on the supply also. Maybe a more precise and detailed way to say it would be +12V/0V/-12V. You can power this from 12V batteries found here at EPO if you like. It will play quite some time and loudly from a pair of their 12V 7.2AH lead acid rechargeable batteries. If you go this route make sure to have a way to recharge them. Below is an example of how you might use batteries.

Attachment:
batterysupply.GIF


The terminal blocks are not well marked on this board. Please see the board outline above for indications of where power supply connections need to be made as well as input and output signals.
If you choose to use a different power supply EPO does sell a kit for a dual polarity linear supply that would be great for this headphone amp when coupled with a 12VAC dual secondary transformer.


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PostPosted: 01 Dec 2016, 15:21 
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Testing
Its going to be pretty hard to do this incorrectly so I don’t see you having any trouble. However, in the interest of safety, my safety, I will first absolve myself of any responsibility for your safety. Anything you do here is on your own and best judgement. I am simply giving my opinion and its up to you to either already know, or research, whether my description of the build, testing, and use of this device should be followed or if you even have the capability to proceed without hurting or killing yourself. You sure could kill yourself with the 120VAC that the input of your power supply will require unless you use batteries and if you put any part of your body somehow in electrical contact with the positive and negative rail it will hurt quite a bit and I suppose its possible this could also kill you. Consider yourself warned and proceed if you agree to NOT hold me responsible for your inept or perfect build and any damages to yourself or anything that you connect to this device.

Really you should wait a day after your build and then come back and review your assembly. Any mistakes I make I can usually find if I leave it alone for a while and come back with a fresh mind and eyes. Backwards capacitors really will explode and really could take an eye out. So, review after a rest.

If all parts are inserted and soldered correctly this circuit will JUST WORK. Once you connect power you will want to feel the tops of the opamps and the output transistors with your finger. If they are warm, that’s fine. If they are hot you should be looking for mistakes. There is no trouble shooting here. There is really only finding which part is in the wrong place or which part did not get soldered or got a cold solder joint. You should short the input Vin to V0 and measure for DC voltage on the output. I have never had more than 12mV of DC offset on the output and its almost always in the 3 to 4 mV range. Outside of this range is not alarming but numbers over 50mV would really have me wondering whats wrong here?

This is a very low distortion design and it is very fast. I have measured it as low as .0003% total harmonic distortion and at speeds up to 1.6MHz for sine waves but it operates best under 600kHz for square waves. It will drive 16 Ohms speakers at these specs and will drive headphones of any impedance. For headphones of 600 ohms it definitely needs the gain provided by the first stage of this circuit but would be fine as a current buffer into headphones from 32 to 300 ohms.
Have fun. Good luck and check out our other kits from EPO.

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PostPosted: 01 Dec 2016, 15:25 
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The copper is single sided although I did use a double layer pcb for a larger ground plane. You could etch a board from the following pic. Its 50mmx100mm



.
Attachment:
copper.GIF


Attachment:
silk.GIF


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PostPosted: 01 Dec 2016, 15:34 
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There it is. Please build it and let me know what you think. Jim Williams was just a genius and reading his App notes is pretty fun when youre in the mood for something like that. He appreciated audio but wasnt obvious about it. I infer that from the usefulness of some of his circuits when put to work in audio. This thing has great speed and super low distortion. He has another that I will post in the next few months that I got up to 25MHz and hundreds of V/uS before I broke it somehow. It would have gone faster if I had a faster source to drive it with!

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