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Review: NwAvGuy's O2 DIY Amplifier
Feb 27, 2012 at 12:50 AM Post #1,291 of 1,550
The 2step is using the same opamp in my Leckerton UHA6S that I actually prefer over the O2 for sheer transparency so I couldn't comment on the 2step not having heard it.  I hear it's a slighter warmer sounding tonality compared to the step1. 
 
Its best to consider the size and objectives of the two.  The O2 is more headphone oriented and transportable/stationary.  Others are more IEM, easier to drive oriented portable solutions.  Though the Stepdance1 tries to have it both ways so I think that's a fair comparison.  
 
Feb 29, 2012 at 9:00 AM Post #1,292 of 1,550
Is there any reason the ODA version of the amp could not have the option of being built with a variable gain control (as in a pot) instead of just a switch?  I would think that would give it even more versatility, all the way from super sensitive IEMs at 1x, all the way to extremely low sensitivity headphones runing from a low voltage source at the full 12X (though I doubt there are many situations where that much gain would really be necessary in a desktop version. . . not likely to be using an ipod with a desktop amp, but you never know).  With the desktop version it could be on the back of the amp by the inputs and out of the way.  I don't really know how that would affect performance like noise, etc.  I could be totally wrong though....
 
Feb 29, 2012 at 11:39 AM Post #1,294 of 1,550
Quote:
firev1 said:
Gain stage requires 2 resistors of equal values in parallel, with pots, this cannot be done
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It can definitely be done with stereo pots. Of course, it will only be roughly "equal value" with typical potentiometers.
 
 
Feb 29, 2012 at 12:08 PM Post #1,295 of 1,550


Quote:
lukeahale said:
Is there any reason the ODA version of the amp could not have the option of being built with a variable gain control (as in a pot) instead of just a switch?  I would think that would give it even more versatility, all the way from super sensitive IEMs at 1x, all the way to extremely low sensitivity headphones runing from a low voltage source at the full 12X (though I doubt there are many situations where that much gain would really be necessary in a desktop version. . . not likely to be using an ipod with a desktop amp, but you never know).  With the desktop version it could be on the back of the amp by the inputs and out of the way.  I don't really know how that would affect performance like noise, etc.  I could be totally wrong though....
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I've actually asked him about this before, here is the answer I got:
 
 
Quote:
NwAvGuy said:
Aksel, Meier has done some interesting things. My personal opinion is he keeps trying to re-invent the wheel when there's no need to. His "virtual ground" arguments, for example, make no sense to me. See my Virtual ground article for lots more about that topic.

If you're talking about his "portable amp" with the LM6171 output stage. His use of the volume control in the feedback loop is very noise prone. When the pot becomes noisy (dirt/wear on the track/wiper) that "noise" in the pot will cause the amp to briefly go to full volume. The effect will be to make the pot wiper noise massively loud.

It's also Audio Design 101 to never run DC through a volume control. To do so just about guarantees you'll get noise when adjusting the volume. But that's what Meier has done.

He's used really high value resistors in that circuit so the Johnson Noise is probably off the chart. The pot in the feedback loop is likely a band-aid to try and reduce all the Johnson Noise. 

And if you're talking about the Corda 2Stepdance. Near as I can tell it uses a stepped attenuator with CMOS switches to control the volume. I can almost promise that solution is much less linear than a simple volume control. Doug Self has written about all the issues with using CMOS switches for audio. That amp almost certainly has noise issues looking at the PC board. The DC-DC converters and digital circuitry are just too close to the audio circuitry. It also has losses in the DC-DC converter which shortens battery life. I do like the option of two different rail voltages.
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Mar 1, 2012 at 12:12 PM Post #1,296 of 1,550
Through the aid of some posters on this forum and receiving a PM from another member, I was able to get my items sorted out.  After removing the front plate, it was easy to see where the metal wires of "4" of the resistors on the right side were rubbing against the aluminum case.  These were straightened out and then trimmed with one of my smaller side-cutters.
 
Also, I didn't have the ground wire from the input terminal to my case.  I soldered a ground wire, sanded off a slight amount of the black paint on the inside of the front cover where the screw would mount --- and, where my wire connection would be applied to the case.  The front panel was re-installed and everything was tested.  I'm now back in good shape. 
 
This is one fine amplifier. 
wink.gif

 
Mar 1, 2012 at 6:51 PM Post #1,297 of 1,550
Indeed it is.   I'm glad you got yours back ip and running problem free.
smily_headphones1.gif

 
Mar 2, 2012 at 4:35 AM Post #1,301 of 1,550


Quote:
eric_c said:
Didn't he say the DAC can be placed inside the O2? It just replaces the battery compartment.
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Yep. It's held in between the back panel and the spring pressure of the battery terminals, a case slot on one side and a mounting hole on the other that lines up with one on the O2. 3 shielded wires connecting them, and it's done.
 
Mar 2, 2012 at 5:52 AM Post #1,302 of 1,550

it is not a plug and play, you need a little DIY skills. From what I have read we can order the ODAC with an external case, I might either do that or simply get the ODA+ODAC once they both come out, (from the looks of things it might be end if this year)
Quote:
eric_c said:
Didn't he say the DAC can be placed inside the O2? It just replaces the battery compartment.
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