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Old 21st October 2011, 05:45 PM   #541
MrSlim is offline MrSlim  Canada
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Quote:
Originally Posted by Turbon View Post
Thanks MrSlim, I'll check it out but tubes? what are they for? buffering?. I need no amplification since I'm going for the O2 but still, I'll look into them.

Hmmm, sorry - the grub dac looks intressting... But, the input is limited to 16/48 on usb. I am more in search for 24/96 as a minimum without amplifier.

Brgds
Well, then you should be looking here: Yoyodyne Consulting/Audio Hardware

The YC-USB9023 is available now, for less than $100.. with variations to come...

JD
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Old 21st October 2011, 07:08 PM   #542
Turbon is offline Turbon  Sweden
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Yes!

Thanks JD - just what I was looking for!

Brgds
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Old 23rd October 2011, 03:07 PM   #543
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I'm ordering the parts from the BOM list. I have question for the Gain resistors R19,R23 and R17,R21. What are the most typical values to use at these locations?

Thanks.
SB
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Old 23rd October 2011, 04:08 PM   #544
MrSlim is offline MrSlim  Canada
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NwAvGuy(RocketScientist) specifies 2.5x and 6.5x as the "standard" gain values..
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Old 23rd October 2011, 04:40 PM   #545
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Tx
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Old 24th October 2011, 01:22 AM   #546
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I wonder if it's possible to use a 24V AC adapter in O2. Yes, I did read the max voltage should be 20V AC.

Since the caps (470uF/35V) and both MC7812ACT & MC7912ACT are all capable to handle 35V, I thought 24V should be ok. Have I overlooked sth?

Pls advise. Thanks!
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Old 24th October 2011, 03:12 AM   #547
agdr is offline agdr  United States
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Quote:
Originally Posted by dumbears View Post
I wonder if it's possible to use a 24V AC adapter in O2.
I think the regulators would cook.

Lets say 24VAC winds up around 30VDC after the half wave rectifiers and filter caps. Ignoring line voltage fluctuations and transformer regulation increase with light loads, that would be (30VDC - 12VDC) * 0.1mA = 1.8W each with 100mA loading. But there are no heatsinks on the regulators, no space for any, and they butt right up against each other.
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Old 24th October 2011, 04:34 AM   #548
agdr is offline agdr  United States
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dumbears - something here that you could try. Lol - similar to a suggestion I got jumped on about in another thread recently

+/- 15v AC required for balancing converter board

You could try adding 6.2V or so zeners in series with the rectifier diodes to knock the voltage down to level that isn't so close to the voltage regulator maximum. The resulting power dissipation is more in line with what the un-heatsinked voltage regulators can handle. The zeners then share in the dissipation.

24VACrms = 34VACpeak = 68VACpeak-peak, of course. The first plot is with a 220mA load, around the max the O2 can handle, producing about +/-18VDC going into the voltage regulator chips. The second plot is with a 22mA load resulting in about 24VDC going into the regulators. The picture is how to make it work. Solder the rectifier to the zener, then stuff the free leads in the holes where the rectifier would otherwise go.

6.2V 3W zeners like this would work just fine

1N5920BG ON Semiconductor Zener Diodes

that one has a DO-41 case like the 1N4002. Zeners tend to be noisy, but at 6.2V and below the breakdown mechanism is primarily zener, which is vastly quieter than zeners above 6.2V which are primarily avalance breakdown. See the max noise denisty column in the datasheet here to get a feel for it -

http://www2.microsemi.com/datasheets/sa5-27.pdf

after 6.2V the noise density jumps from 5uV/sqrt(Hz) to 40uV/sqrt(Hz)
Attached Images
File Type: png O2 with zeners circuit 220mA load.png (35.2 KB, 321 views)
File Type: png O2 with zeners plot 220mA load.png (22.3 KB, 319 views)
File Type: png O2 with zeners plot 22mA load.png (20.0 KB, 318 views)
File Type: jpg IMG_1209.JPG (96.8 KB, 283 views)

Last edited by agdr; 24th October 2011 at 04:43 AM.
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Old 24th October 2011, 06:02 AM   #549
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I think the 24VAC would work, but as the headphone output was increased the regulators would trip their thermal protection circuits and shut down to cool.
Basically, any AC supply capable of 1) overcoming the dropout voltage of the regs and 2) not causing excessive reg power dissipation will work.
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Old 24th October 2011, 06:56 AM   #550
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Agree with this:If you are genuinely interested in the O2 as a DIY project, then it's up to you to set the output level of your source correctly or in lieu of being able to do so, then set the input gain of the O2 correctly
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