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Old 20th September 2012, 01:53 PM   #11
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Quote:
Originally Posted by doulos24 View Post
I used 56 ohm as my headphones are 55 ohm I also have 300 ohm phones
What headphones are those, AKG 240 Studio? Those are not very bassy if properly driven.

Have you tried the resistors in series to raise the output impedance? It should boost the bass similar to what your audio interface's headphone jack does but actually affects sound quality negatively.

Last edited by xnor; 20th September 2012 at 01:56 PM.
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Old 20th September 2012, 02:20 PM   #12
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Originally Posted by doulos24 View Post
they are are consistent with RMAA and when using voxenngo span and room eq wizard with an outside signal generator
Your measurements are almost certainly wrong.
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Old 20th September 2012, 09:54 PM   #13
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Quote:
What headphones are those, AKG 240 Studio? Those are not very bassy if properly driven.

yes they are the k240 studios
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Old 20th September 2012, 10:01 PM   #14
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Quote:
Your measurements are almost certainly wrong.
when you want to do a scientific measurment it's good to have a control to test against ,so when I Measure my headphone output on my interface it measures exactly as it says it should, but somehow my measurements on my amp are wrong?

let's do the math op amp thd .0008% a few top of the line passive components 1% resistors double sidded pcb meaure thd + noise about 4 times the opamp's self noise .0026% seems about right to me

from the same guy you sent a refrence from measuring a cmoy amp

Frequency Response+/- 0.1 dB ExcellentTHD 1 Khz 150 Ohms0.002% ExcellentTHD 1 Khz 15 Ohms0.030% GoodTHD 20 hz 15 Ohms0.028% GoodTHD 20 Khz 15 Ohms0.040% Very Good

Last edited by doulos24; 20th September 2012 at 10:21 PM.
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Old 20th September 2012, 10:36 PM   #15
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my bad I got the numbers wrong the thd of the chip plus noise is 0.00003% @ 2kohm, VS= 15V

http://www.farnell.com/datasheets/37248.pdf driving 600 ohms 0.00003%

Last edited by doulos24; 20th September 2012 at 10:41 PM.
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Old 21st September 2012, 12:25 AM   #16
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Do you really suppose that I am unfamiliar with the datasheet performance of an LME49720? This tells me you are lacking in imagination. This is an AUDIO forum.

It doesn't matter what it says in the datasheet, you have still to achieve those figures in your implementation. You cannot simply take these numbers and add a few % for passive components and expect to predict the performance of a given layout. This tells me how little you truly understand. Electronics is highly layout dependent. Perhaps you think these numbers were achieved on a piece of veroboard? Performance like that can be thrown away with one badly routed connection.

You have either not read or not understood the material in the link I posted. This suggests to me that you are unwilling or unable to learn.

3 channel or virtual ground amps are very unlikely to achieve performance as good as amps with a true ground, even one produced by 2 batteries. So unlikely that I am confident that your measurements are meaningless.

You posted a diagram with a 741 in it that is incapable of sourcing or sinking enough current to support one 56 ohm load, never mind two. This tells me you are a novice. You ignore the fact that a 741 has barely sufficient slew rate to be used in any audio application and claim that it makes no difference and say that you used a different opamp anyway. This tells me you are overconfident, inconsiderate and arrogant.

You asked for advice. Pay attention to what I have written instead of poking out your tongue.
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Old 21st September 2012, 02:19 AM   #17
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It doesn't matter what it says in the datasheet, you have still to achieve those figures in your implementation. You cannot simply take these numbers and add a few % for passive components and expect to predict the performance of a given layout.
few % for passive components oh you mean roughly 86 x the input distortion? that is 8600%

current draw of the lm741 is what? 20mA the entire circuit draws 13ma of current

that's 6.5ma for a single 56 ohm load you have to remember that the op amp is capable of driving 600ohms without taxing it or changing its distortion level.

Last edited by doulos24; 21st September 2012 at 02:35 AM.
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Old 21st September 2012, 03:15 AM   #18
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ok so my RMAA measurments are crap cause its a virtual ground lets test your theory I have a profire 2626 I/0 and it has its specs on file

THD+Noise

0.007% (-83.0dB), 1kHz, -1dBFS headphone out + instrument "DI" input

THD+N (min gain, no pad) 0.0014% (-97dB), 1kHz, -1dBFS so If i were to do a

loop back test my thd + noise should be just over .0020%

what did I measure????
Left Right
THD, % +0.0020 +0.0019
THD + Noise, % +0.0022 +0.0022
THD + Noise (A-weighted), % +0.0028 +0.0027

amazing!
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Old 21st September 2012, 07:05 PM   #19
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so here is the difference I was looking for, so I think I will try to improve this section on my next amp it makes it a little lean in the bass

Click the image to open in full size.
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Old 22nd September 2012, 12:11 PM   #20
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I don't think you have responded to what I wrote about output impedance.

The profire 2626 specs clearly state:
Headphone Outputs:
- Output Impedance: 75 Ohms

Have you tried putting 75 ohm resistors in series with the load? I'd suggest to EQ instead since a low output impedance means better control over the headphone drivers, but in the end it's your choice.
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