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Review: NwAvGuy's O2 DIY Amplifier - Page 92  

post #1366 of 1550
Quote:
Originally Posted by Draygonn View Post

inb4 moved to SS

What is really impressive about this clairvoyant post is that it was post number 1337 :)
 

 

post #1367 of 1550

Move had already happened by then, unfortunately.

I think that people are reading too much into opamp rolling. Opamp rolling works on two principles:

 

1) That you know better than the designer/designer cut corners of some sort.

2) That audible differences will result even when neither opamp is seriously upset (Oscillation doesn't sound too great apparently...)

 

I can't see either of these statements holding true, the latter never being true IMHO if you are using a half-decent audio opamp and implementing it properly.

post #1368 of 1550

Hello guys,

 

I received my JDS Labs O2. I am using it with K501 and NuForce uDAC. I hear some distortion. Is it because of DAC or amp?

post #1369 of 1550
Quote:
Originally Posted by thehadi View Post
I received my JDS Labs O2. I am using it with K501 and NuForce uDAC. I hear some distortion. Is it because of DAC or amp?


Try using the lower gain setting, if you are not already doing so. Also, the NuForce uDAC(2) is not very good in terms of distortion, and it cannot output a full scale signal without clipping. In this particular aspect, even a decent onboard audio chip is better.

 

post #1370 of 1550
Quote:
Originally Posted by stv014 View Post


Try using the lower gain setting, if you are not already doing so. Also, the NuForce uDAC(2) is not very good in terms of distortion, and it cannot output a full scale signal without clipping. In this particular aspect, even a decent onboard audio chip is better.

 



Thanks for quick reply stv,

 

When i try low gain (x2,5), i think it's not enough for K501. And uDAC is first generation. uDAC(1).

post #1371 of 1550

The uDAC actually clips from its line outputs (yup, Nuforce are that incompetent) so that could be what you're hearing.

2.5X gain is plenty anyhow, looking at the sensitivity of your headphones. 6X gain is designed to be used with MP3 players and other devices with low voltage outputs and will result in clipping when used with a higher-voltage source. This is by design.

post #1372 of 1550

Thanks for reply. I think it's time to go from uDAC to another toy. Waiting my DX100 and new ODAC.

post #1373 of 1550

     Quote:

Originally Posted by Willakan View Post

 

I think that people are reading too much into opamp rolling. Opamp rolling works on two principles:

 

1) That you know better than the designer/designer cut corners of some sort.

 

I'm pretty sure modding the Fostex T50RP works on this principle, yes?  In the case of the O2 corners were cut from a price perspective, if not, it'd be 'spec'd out' with AD8620, or the like...

 

Quote:
Originally Posted by Willakan View Post

There are engineers that believe lots of things. None of these things have ever been produced under controlled conditions. I wonder why.

 

First you experiment, then you believe, then you test, then you look for hard data.

 

Most people stop at 2, or start at 4...

 

I came to this thread to check on 1...

 

post #1374 of 1550
Quote:
Originally Posted by kiteki View Post

I'm pretty sure modding the Fostex T50RP works on this principle, yes?  In the case of the O2 corners were cut from a price perspective, if not, it'd be 'spec'd out' with AD8620, or the like...


The T50RP was a good driver by a company that makes good OEM drivers, slapped into the first enclosure they could think of. It was never intended to be a reference design, they probably didn't even think about how good the driver was. It wouldn't be worth their R&D cost to research a good design and sell it for more.

 

The Objective2 is an amp designed exclusively for measured performance, and has had a considerable amount of R&D put into it to make sure it performs as well as it can for its design and cost.

 

Amps work with relatively simple electrical signals. Headphones work with complex sound waves and reflections, and are considerably more unpredictable. With an amp, you can compare opamp specs and measurements to see which works best with the design, and even less optimal designs will have fairly benign audible effects. With headphones, there are a nearly infinite number of tweaks that can be made to alter the sound waves to a very audible degree. Reportedly, the HD800 has been improved with a strip of t-shirt, and the LCD-3 improved with a piece of toilet paper.

 

See the difference?

post #1375 of 1550

 

I see the difference.

 

Most studios just buy the Fostex T40RP and leave it at that, ftr.

 

post #1376 of 1550

Just a quick question so I wont have to read trough 90 pages... is this O2 really that good if I just want a powerful amp to amplify whats coming from the DAC with colorations, but with lots of authority and power? Would it be an improvement over the Little Dot Mk5 for AKG Q701's?


Edited by derbigpr - 3/5/12 at 5:28pm
post #1377 of 1550
Quote:
Originally Posted by derbigpr View Post

Just a quick question so I wont have to read trough 90 pages... is this O2 really that good if I just want a powerful amp to amplify whats coming from the DAC with colorations, but with lots of authority and power? Would it be an improvement over the Little Dot Mk5 for AKG Q701's?

 

Yes, but maybe or maybe not by a significant or even audible amount.  If you go by the spec listed for the Little Dot Mk5, it claims 0.05% THD+N into 300 ohms at 100mW (5.48V rms) with the standard 1 kHz test tone.  Assuming that the O2 does similarly with 300 ohms as it does with 150 ohms and 600 ohms (a very reasonable assumption, considering the performance into 150 ohms and 600 ohms is very similar), it gets about 0.001% THD+N with the same test.  It depends on the design, but most amplifiers will have a harder time putting the same amount of power into a lower impedance like the ~60 ohms of the Q701, so the distortion could well be significantly higher than 0.05% just for THD+N when driving the Q701.  With real music, distortion is higher than for just a 1 kHz test tone, because of intermodulation products and so on.

 

100mW is actually a typical power input to a Q701 to play loudly, so that's not that much of a stretch.  Into a load like that, O2 should get between 0.001 and 0.002% THD+N...for what that's worth.  THD+N for a 1kHz input is just one benchmark out of many, so it's not particularly indicative of total performance, especially since the number alone doesn't tell you about whether the distortion is 3rd order harmonics, 2nd order, or what else.  Many more tests are on the designer's blog for the O2, if you want to look yourself.

 

They don't list the output impedance for the Little Dot, but based on the listed output power at different loads, it would seem like it's probably not negligible.  That would slightly alter the frequency response of those headphones and contribute to additional distortion when driving headphones as opposed to test resistors on the lab bench.  Still, we have a very incomplete picture of the type of distortion and the overall performance characteristics of the Little Dot, so it's hard to say if these issues would actually be audibly worse and whether the O2 would actually be a real upgrade for those headphones.  By the books, the specs indicate lower performance for the Little Dot, but the "how much" and "how" are not clear.


Edited by mikeaj - 3/5/12 at 6:16pm
post #1378 of 1550
Quote:
Originally Posted by mikeaj View Post

 

Yes, but maybe or maybe not by a significant or even audible amount.  If you go by the spec listed for the Little Dot Mk5, it claims 0.05% THD+N into 300 ohms at 100mW (5.48V rms) with the standard 1 kHz test tone.  Assuming that the O2 does similarly with 300 ohms as it does with 150 ohms and 600 ohms (a very reasonable assumption, considering the performance into 150 ohms and 600 ohms is very similar), it gets about 0.001% THD+N with the same test.  It depends on the design, but most amplifiers will have a harder time putting the same amount of power into a lower impedance like the ~60 ohms of the Q701, so the distortion could well be significantly higher than 0.05% just for THD+N when driving the Q701.  With real music, distortion is higher than for just a 1 kHz test tone, because of intermodulation products and so on.

 

100mW is actually a typical power input to a Q701 to play loudly, so that's not that much of a stretch.  Into a load like that, O2 should get between 0.001 and 0.002% THD+N...for what that's worth.  THD+N for a 1kHz input is just one benchmark out of many, so it's not particularly indicative of total performance, especially since the number alone doesn't tell you about whether the distortion is 3rd order harmonics, 2nd order, or what else.  Many more tests are on the designer's blog for the O2, if you want to look yourself.

 

They don't list the output impedance for the Little Dot, but based on the listed output power at different loads, it would seem like it's probably not negligible.  That would slightly alter the frequency response of those headphones and contribute to additional distortion when driving headphones as opposed to test resistors on the lab bench.  Still, we have a very incomplete picture of the type of distortion and the overall performance characteristics of the Little Dot, so it's hard to say if these issues would actually be audibly worse and whether the O2 would actually be a real upgrade for those headphones.  By the books, the specs indicate lower performance for the Little Dot, but the "how much" and "how" are not clear.



Yes, it appears that by specs O2 should do better. The biggest reason why I want a new amp for Q701's is I feel Little Dot doesn't work well with low impedance cans. It actually has high output impedance, not sure how much, nobody knows, but the fact is, Little Dot ships it with a little impedance adapter for low impedance headphones. I don't have that adapter since I bought mine second hand, but it says something.  It just sounds overly bright and thin, changes the sound that comes out of my sound card drastically.

post #1379 of 1550

Are we forbidden to mention that blog or simply forbidden to link to it?

post #1380 of 1550
Quote:
Originally Posted by khaos974 View Post

Are we forbidden to mention that blog or simply forbidden to link to it?



Not sure as I wasn't around during the whole banning thing, but one thing I will say is that as wide-spread as the O2 is becoming.. internet censorship of mentioning his name is cheesy and goofy. Like looking at some back water countries internet censorship policies.

 

 

I don't see what everyones problem is with the O2, as some here don't seem happy with it.  It drives my HD650's beautifully and sounds great. I'm happy with it in its stock configuration and don't feel the need to move on. I'm very happy with what I put together with my own hands for the price I did.

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