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Old 2nd October 2011, 11:33 PM   #491
qusp is offline qusp  Australia
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yeah thats all i use at the moment is a small computer fan to suck the fumes out the window for the reasons you state, i'll get a proper one one of these days
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Old 5th October 2011, 01:43 AM   #492
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Quote:
Originally Posted by regal View Post
The "high much power do we need" section on the website actually rules out a few popular headphones for the 110 dB peak recomendations. It would seem the most elelegant solution to the issue would be to use two boards full balanced, I think this would make it an amp that really would match/beat any other SS design for a fraction of the cost. It would basically increase the power between 2x to 4x (depending on the phones impedane/sensitiviy) and propably handle any dynamic headphone made.
For the very rare headphones that really need more than 20 volts peak-to-peak (7 Vrms) I would suggest a different amp than the O2. 99% of headphones I know of can hit 110+ dB SPL with the O2. If you're the 1% looking for hearing damage or own some really rare uber power hungry headphones, I would suggest looking into other amps. I cannot recommend the O2 for higher than a 24 volt (+/- 12V) supply or in balanced/bridged mode.
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Old 5th October 2011, 12:33 PM   #493
regal is offline regal  United States
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Originally Posted by RocketScientist View Post
For the very rare headphones that really need more than 20 volts peak-to-peak (7 Vrms) I would suggest a different amp than the O2. 99% of headphones I know of can hit 110+ dB SPL with the O2. If you're the 1% looking for hearing damage or own some really rare uber power hungry headphones, I would suggest looking into other amps. I cannot recommend the O2 for higher than a 24 volt (+/- 12V) supply or in balanced/bridged mode.
Hey I bought the boards not so quick to give up on it yet .

I am definately not looking for hearing damage but found your chart on "more Power" sept blog interesting and have given it a lot of thought.

Ok maybe I am not interpreting you chart for power requirements and recommendations correctly. You recommend 115 dB peak for listening to high dynamic range classical music. Very popular headphone: the Beyer DT880 would be "borderline" with this amp as 7vrms*7/600= 81 mW. Also the AKG Sextettes, Also the AKG 240-DF's, the AKG340's, many of the orthos

Maybe I am reading the chart wrong instead of using the 7vrms, would it make more sense to look at it from Vpeak to peak so instead of Prms on chart those are Pp-p? Or mabey there is just very very little music that requires these 115db peaks?

Not trying to stir controversy, just thought the chart was very interesting and deserved a little discussion as it applies to the )2.

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Old 5th October 2011, 01:18 PM   #494
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I believe you're looking at it right. I asked about this directly to rocketscientist a few weeks ago, and I suggested running in bridged mono mode with 2 boards in order to get twice the voltage swing as I am running K340s myself to get to the 115dB maximum in case I ever decided to need it (I'd have to be listening pretty loud compared to what I'm used to). He noted that it would be possible, but with certain side effects (inability to drive lower impedance headphones, increase in output resistance? - who cares you're driving high impedance headphones anyways. I think he also mentioned exactly "You also need a way to invert the input signal to half of each amplifier which means adding an op amp. " which I'm assuming is for single-ended setups since i am using a buffalo.

Quote:
Originally Posted by regal View Post
Hey I bought the boards not so quick to give up on it yet .

I am definately not looking for hearing damage but found your chart on "more Power" sept blog interesting and have given it a lot of thought.

Ok maybe I am not interpreting you chart for power requirements and recommendations correctly. You recommend 115 dB peak for listening to high dynamic range classical music. Very popular headphone: the Beyer DT880 would be "borderline" with this amp as 7vrms*7/600= 81 mW. Also the AKG Sextettes, Also the AKG 240-DF's, the AKG340's, many of the orthos

Maybe I am reading the chart wrong instead of using the 7vrms, would it make more sense to look at it from Vpeak to peak so instead of Prms on chart those are Pp-p? Or mabey there is just very very little music that requires these 115db peaks?

Not trying to stir controversy, just thought the chart was very interesting and deserved a little discussion as it applies to the )2.

thanks
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Old 5th October 2011, 02:45 PM   #495
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Regal, I backed off to 110 dB SPL in my reply for exactly the headphones you mentioned. Some of the AKGs (in the hard to drive high impedance versions) are also long since discontinued.

This issue has been discussed several times in this (admittedly long) thread. I believe the best solution is to use a different amp rather than turning the O2 into something it's not designed to be. I'm not sure yet, but my upcoming desktop amp might also be a better candidate for those needing more output voltage.

The main issue is a DIP8 op amp, like the 4556, cannot safely dissipate enough power with higher voltage rails when used with some headphones. And if an op amp fails it might take an expensive pair of headphones with it. Power dissipation increases as the square of voltage. So going from 12 to 15 volt rails increases dissipation over 50%. And bridging will increase it by a factor of 4X (2X per IC).

The best solution is to use an amp like The Wire, National LME49600 reference design, etc. using heat-sinked output buffers with higher dissipation capability.
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Last edited by RocketScientist; 5th October 2011 at 02:51 PM.
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Old 5th October 2011, 02:50 PM   #496
agdr is offline agdr  United States
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Attached - LT Spice sim of one O2 board set up for balanced output into 600R with 500pF in parallel for the headphone cable. Driven with out of phase 3.2Vpeak (2.26Vrms) with 2.5x gain, +/-12V supplies. That input level is as high as I could go in the sim to preserve a good waveshape with the balanced config.

Disclaimer(s): I can't claim to know squawk about balanced systems, never have messed with them much, so I may have mucked something up here. Also just to re-iterate RocketScientists' warnings about hearing and equipment damage! So not recommended that anybody actually do this, just academic curiousity.

The key is at the top of the plots. Green and red are the 180 degree out-of-phase 3.2Vpk inputs to the two channels. Dark and light blue are the 1st stage outputs of the two channels. Magenta is the difference voltage across the 600R load, which would be equivalent to putting a DMM or isolated scope probe directly across it - what the balanced headphone would see.

With the 3.2Vpeak differential input, the difference output shown is 15.6V peak = 11.0Vrms. All is sinusoidal, of course, if anybody hasn't seen it yet check out RocketScientist's good recent blog post on music power. That would be 202 mW into 600R.

The remaining two plots are the same thing done at 10Hz and 20kHz inputs.

Last edited by agdr; 5th October 2011 at 02:55 PM.
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Old 5th October 2011, 03:31 PM   #497
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I should also add I'm planning a future blog article to help dispel many of the myths surrounding balanced headphone gear. In most applications, balanced gear has more disadvantages than advantages and many of the alleged benefits are myths. But ever since publishing the 3 channel article I have received lots of questions about balanced designs.

On top of risking frying the O2's output ICs and damaging your headphones from the resulting DC, balanced (bridged) amps also require cutting the plug off the end of all your headphones or otherwise re-wiring them for a 4 wire connection. One would hope people would only do that for some really good reasons, but it turns out, those reasons are usually more mythological than real.
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Old 5th October 2011, 11:43 PM   #498
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but "dual mono" with 4 pin connector wired "balanced" headphone cabling is the shortest path to eliminating crosstalk "ground contamination" - for all the silence at head-fi when I point it out in "3-channel" amp threads
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Old 6th October 2011, 12:19 AM   #499
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Thanks JCX. There certainly is measurable benefit from using a 4 wire connection on a conventionally grounded 2 channel amp in terms of crosstalk. If the difference between say -65 dB and -85 dB crosstalk is audible is another question. But my main point above is a balanced amp forces re-wiring headphones. Being able to use only 4 wire heapdhones is a significant compromise without any objective evidence "balanced" circuitry offers meaningful performance improvements.

At least with a conventional 2 channel amp and a proper ground scheme you can have both 3 and 4 wire headphone connectors if you want to gain the crosstalk benefits of a 4 wire plug. But the 3 wire option goes away completely with a balanced amp.
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Old 6th October 2011, 04:30 AM   #500
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Quote:
Originally Posted by regal View Post
Hey I bought the boards not so quick to give up on it yet .
I have an idea for the power-mongers out there lusting after 115dBA that consider the O2 hasn't enough grunt. Why not fork off RS's design with your very own O3? Call it the 'Ozone' because where the O2 has just two paralleled 4556 stages in its drive stage yours will have 3. That'll allow you to raise the supply voltage to 15V without compromising the thermals too much.
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