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Old 5th December 2011, 08:12 PM   #1201
billyk is offline billyk  United States
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Thanks folks, I looked harder and saw that it would not work that way. I edited my previous post.
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Old 5th December 2011, 08:16 PM   #1202
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Originally Posted by konga View Post
Can you have both the 3.5mm input jack and an external jack connected to P3? Would I need to cut the traces to ground as mentioned in the documentation.

I'm thinking I can maybe fit a pair of rca jacks in the rear of the b2 case next to the batteries.
I think you mean P1 and/or J2? But yes, you can have both if you cut the traces under J2 as shown. Just don't try to use both at once (which would have one of your sources fighting with the other source--the O2 won't care but it won't sound very good and could even damage one or both sources).

@cusp et al, let's hopefully get back to the rational side of things here and leave CSA to his own self induced misery.

@jokener, I wouldn't take the "let's make a deal" bait. Your original deal was more than fair.
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Last edited by RocketScientist; 5th December 2011 at 08:19 PM.
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Old 5th December 2011, 08:21 PM   #1203
qusp is offline qusp  Australia
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done, i'm off to bed, if he carries it on i'll just put him on ignore, no loss
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Old 5th December 2011, 08:25 PM   #1204
NicMac is offline NicMac  Italy
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Originally Posted by Alexium View Post
@NicMac: it didn't occur to me... Great idea! Would you advise any specific picture?
I can't find the picture right now, but I'm sure we are quite a few around to take one for you
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Old 5th December 2011, 08:26 PM   #1205
Jokener is offline Jokener  Germany
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@RS: I must admit I am tempted. MythBusting has always been a fun thing to do.
And I am sure I can find them unicorns that you have mischieveously hidden in that particular unit.
But 80€ for a broken amp... 50€ was fair indeed. More than fair actually, it included the "lets drive a point across"-fee.
@CSA: what would justify the 80€?
I mean, shipping is $13, the parts are $30 and the PCB is $10... 50€ are equivalent to almost $70... ... ...
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Old 5th December 2011, 08:33 PM   #1206
dewardh is offline dewardh  United States
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Why don't we focus on the things we can all agree on . . .

Originally Posted by cheapskateaudio View Post
I should point out that I'm far from being an expert on electrical circuits.
and that CSA's headphone amp doesn't work very well . . .

and be done with this silly distraction ? ? ?

The O2 works fine when built to spec, sounds as good as anything out there, and is cheap and easy to build. CSA built something that isn't an O2 (which is why he won't post pictures) and is having problems with whatever it is.

That really should be the end of it . . .
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Old 5th December 2011, 08:36 PM   #1207
agdr is offline agdr  United States
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Originally Posted by RocketScientist View Post
I think you mean P1 and/or J2? But yes, you can have both if you cut the traces under J2 as shown. Just don't try to use both at once (which would have one of your sources fighting with the other source--the O2 won't care but it won't sound very good and could even damage one or both sources).
It may be possible to use one of the "3B" jacks (no switch) for J2 instead and avoid cutting traces, if I'm looking at the artwork correctly.

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Old 5th December 2011, 08:37 PM   #1208
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Originally Posted by Willakan View Post
I simply assumed that 3X gain would be appropriate for the K702s and now have an amp which requires very careful volume knob usage!
I found that 1x and 1.6x are where it needs to be to prevent a thermal meltdown in current-model studio-quality AKGs. It also provides enough range to make your favorite PMP's output turn into deafness.

Isn't it amazing how we all somehow still think that AKGs are hard to drive? I was very surprised when I found how loud the K272HD got. My laptop drives them too loud at 18% volume. My TouchPad, iPad2, and iPod Mini all have room to spare on their volume meters and the phones are loud enough.

We're entering a new era with AKG. They're releasing a new "closed" flagship the K550 with lower impedance and higher sensitivity. Their latest IEMS are 8Ohm 125dB SPL.

I'm still not exactly sure how I'd tweak an O2 for something like that. With 8 Ohm impedance there's such a narrow voltage window with low THD+N and I'm not sure it's even "acceptable." I'd like to see measurements. The DC offset would be higher than we'd want because we'd keep the damping maximized with low value resisters. The gain would have to be something wild like 0.5x to even dare plugging them in. And so on...

Fortunately, they're $1K so nobody has anything to worry about... until the technology gets commoditized. So we have some time to engineer.
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Old 5th December 2011, 08:42 PM   #1209
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Originally Posted by qusp View Post
not on the same page it doesnt, changing your story of your view of the amp from a good value and nice sounding amp to a pile of junk you had to 'fix' to make it rise from the level of vaguely musical rectal murmurings for dramatic effect makes you either a troll or a genuine insane person, which would you prefer?
You're forgetting that A) I initially was convinced by people (dogmatic types) that my amp was simply revealing how horrible and harsh my sources were. And that B) the performance of my first amp degraded over time. And that C) the performance of my second amp also degraded over time. That led me to the v-regs getting hot, something that was born out repeatedly. I tack soldered input bypass caps on both v-regs and U5 got cool but u6 got hotter, I decided to wait for the correct parts (tantalum caps) before proceeding further. The change in temps from adding those input bypass caps indicates that those were needed. But since I didn't have the right values or type I can't draw firm conclusions there.
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Old 5th December 2011, 08:47 PM   #1210
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@ethanolson, interesting. I wasn't aware of some of that. Some of the AKG changes might be the Harman influence. 8 ohm headphones are a bold move. I wonder if they're planning on their own amp/source to go with them?

I can certainly measure the O2 into 8 ohms at those sorts of levels. It might do better than you might think and the 0.5 ohm output impedance is still low enough. But lots of amps, even many expensive ones, are really going to fall on their face with an 8 ohm load.
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