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Old 7th June 2013, 01:49 AM   #1
agdr is offline agdr  United States
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Default agdr's ODA headphone amp and O2 booster sales thread

This post is being split off from this thread in Headphones:

A version of an O2 Desktop Amp (ODA)

I'm doing a run of 10 boards and using two for test. The remainder are up for grabs. Just PM me to be put on the list. No money collected until I have the boards back, built one up and verified there are no problems and am ready to ship.

The details are in the post in the link, around $15.20 per 4 layer board plus shipping that either has tracking or delivery confirm. I'm taking any restrictions off how many boards per person. If all goes well on this run I may do a larger one later on.

I'll post status in this thread. Should take me a couple of weeks to get the extra 2 layers added, a week or two for fab, a few days for DHL to ship and a week or two for build and test.

Last edited by agdr; 18th February 2014 at 11:05 PM.
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Old 7th June 2013, 03:59 AM   #2
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One board for stereo setup, correct?

My headphones are AKG Q701. Will this headphone amp be excellent with them?

If all yes then I'll take one board

Thanks
Do
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Old 7th June 2013, 06:39 AM   #3
agdr is offline agdr  United States
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Quote:
Originally Posted by pinnocchio View Post
One board for stereo setup, correct?

My headphones are AKG Q701. Will this headphone amp be excellent with them?

If all yes then I'll take one board
That is right, just one board for stereo.

This amp should work very well for the Q701's. I have a pair of Shure SRH940's that have approximately the same impedance (44R vs. your 62R) and sensitivity (100dB vs. 105), and they work great. I also have a pair of AKG K550's, but those have a much higher sensitivity, 115dB/V, which only requires about 80mV of output swing. The Shures are in the ballpark with yours, with around 1.8Vrms of swing for full volume.

One of this amp's big things is vastly more current capability than a lot of amps, with those 3 paralleled dual chips (6 op amps in parallel) on each channel, for a total of about 320mA or so of current capability per channel to drive really low impedance, low sensitivity cans.

And on the other hand it has a high/low voltage switch on the power supply, so that in the other +/-16Vdc rail position it can power hard-to-drive cans in the other direction, high (600R) impedance low sensitivity models. In your case you would use the low voltage +/-7Vdc power supply setting. It is just a switch on the back.

The 4 position gain switch and optional bass boost may be useful, too, looking at the Q701 frequency response curve here:

AKG Q701 Quincy Jones headphones / HeadRoom Audio

And this is probably one of the few headphone amps out there with a dual-stage power supply that has LT317/337s as pre-regulators feeding LT1963A/LT3015 low noise LDO final regulators. That was sort of a byproduct of the LT1963A having a max input of 20Vdc and my wanting the amp to be able to use easy-to-find 24Vac transformers, but the net result is a tremendously low level of power supply ripple.

I'll put you down for a board. It is OK to change your mind at any time, just let me know, since it will be a few weeks. I'm mainly getting these boards to test adding a 3rd and 4th layer to some 2 layer Gerbers I already posted. I have to get a minimum of 10 boards, so I just decided to sell the extras. The boards are getting ordered regardless.

Last edited by agdr; 7th June 2013 at 06:43 AM.
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Old 11th July 2013, 09:21 PM   #4
agdr is offline agdr  United States
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The PC boards for this project are ready to ship to those who expressed interest. I'm going to cover the cost of US shipping - 1st class mail with delivery confirmation - so a total of $15 a board. These are just spare boards from a PC board fab run, so feel free to buy fewer boards than you indicated or cancel outright - no problem. I've got a waiting list of friends at this point for any extras.

Just send me a PM with your DIY audio name and your shipping address. I'll send you my paypal address. When the board(s) ship I'll PM you the postal service tracking number.

This thread in the headphones forum has the latest Bill Of Materials (BOM)

A version of an O2 Desktop Amp (ODA)

and I will post an updated set of build instructions there this weekend.

I'm still in the process of having a set of front and back panels fabbed, received, and verified. When I get that finalized I will also post those files for Front Panel Express and Proto Panel, along with the measurements to just drill the panels that come with the B4-080 box yourself. Proto Panel is still running their 1/2 price special this month, which looks like (haven't sent them out yet) will clock in at $10-$12 per panel (front and back) plus shipping. Please be aware that a rear panel is required on this project since the voltage regulators heat sink to it. In the build instructions I have building up and testing the power supply section as the first thing to do. If you don't have a rear panel yet I'm including a procedure to temporarily bolt a small heat sink onto the pre-regulators to allow it to run 10 seconds or so for testing purposes to verify the output voltages.

As promised I'm also making a donation to DIY audio right now.

Happy soldering!

Last edited by agdr; 11th July 2013 at 09:33 PM.
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Old 12th July 2013, 03:28 PM   #5
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What will be the price difference to ship to Canada, Montreal?

Thanks
Do
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Old 12th July 2013, 09:34 PM   #6
agdr is offline agdr  United States
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Quote:
Originally Posted by pinnocchio View Post
What will be the price difference to ship to Canada, Montreal?

Thanks
Do
I'll find out - please PM me with your shipping address.
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Old 16th July 2013, 02:03 AM   #7
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DACs : TPA Buffalo II + OPC's NTD1 I/V | TPA OPUS + IVY III Speakers : Jim Holtz Statements | Astasia SD | Tubasson Mark 2
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Old 27th July 2013, 04:42 AM   #8
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board has been received!

Thanks
Do
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DACs : TPA Buffalo II + OPC's NTD1 I/V | TPA OPUS + IVY III Speakers : Jim Holtz Statements | Astasia SD | Tubasson Mark 2
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Old 29th July 2013, 01:59 AM   #9
agdr is offline agdr  United States
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Quote:
Originally Posted by pinnocchio View Post
board has been received!
Good to hear! Now the fun part, you get to build it.

The first part is easy, if you are following the build instructions, the AC input power supply section. Big & easy-to-solder parts and no back panel need for this part (no voltage regulators yet). Even the two SMD resistors on the bottom are huge, 2512 sized. Then you can test just this part with your DMM as per the instructions.

I've added voltage warnings/reminders in the latest version of the build instructions. You will wind up with around +36Vdc on one rail input and -36Vdc on the other, so important not to get in contact with live parts on the top or bottom of the PCB while it is on and out of the case! And be sure to discharge those 4 large filter capacitors once it is off and the power cord is unplugged if you are going to be working on it again soon.

Please let me know if anything on the board or in the build instructions isn't clear or could be improved as you go through the build.

Last edited by agdr; 29th July 2013 at 02:01 AM.
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Old 29th July 2013, 03:19 AM   #10
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Don't worry about SMD, I've done plenty and I actually like them!

Thanks for everything
Do
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