Review: NwAvGuy's O2 DIY Amplifier

[wje]

Quote:

Just curious if there is any sonic differences between the portable and desktop version?

You've brought up a good question.  Isn't the desktop version supposed to also provide the DAC, too?   I do realize the portable version can be adapted with the DAC by removing the batteries to make space.  However, I would hope that the desktop version would allow for a bit more power --- to drive more difficult orthodymanic headphones.  But, given that the desktop is being created by the same designer, I'm sure there should be minimal if any, sonic differences as that seems to be one of the goals of the objective - to keep the sound as pure as it was received, then to amplify it and pass it on.
 

 

[vkvedam]

All
 
If I feed the O2 with a DAC's line out at 2.1 Vrms does it cause the O2 to clip on low gain and volume dial set at 10'O clock position (On batteries)? I have observed it yesterday after having tested with an Arcam rDAC outputting a 2.1Vrms signal in to the O2. Am I doing something wrong? But I could only hear the clipping in high frequency region, to be precise only with one album [Karftwerk - Tour De France Soundtracks] and on tracks 'Prologue' and 'Etape 2'. The recording doesn't have clipping for sure. Is there a way to get around it?
 
Thanks
Ven

 

[uelover]

Quote:

You've brought up a good question.  Isn't the desktop version supposed to also provide the DAC, too?   I do realize the portable version can be adapted with the DAC by removing the batteries to make space.  However, I would hope that the desktop version would allow for a bit more power --- to drive more difficult orthodymanic headphones.  But, given that the desktop is being created by the same designer, I'm sure there should be minimal if any, sonic differences as that seems to be one of the goals of the objective - to keep the sound as pure as it was received, then to amplify it and pass it on.
 

I read that there are different variant to the desktop version, one that provides a DAC and another that doesn't but will include 1/4inch plug as well as RCA inputs.
 
I have zero diy skills and since no one is currently selling the ready made desktop version, I ended up ordering the portable version one, compromising with a 1/4inch to 3.5mm adapter plug as well as a 3.5mm to RCA cable.
 
Hopefully the sonic difference will be minimal and if there is any, it will be due to the adapter plugs that I am using and not the circuitry itself. =)
 

 

[uelover]

Quote:

All
 
If I feed the O2 with a DAC's line out at 2.1 Vrms does it cause the O2 to clip on low gain and volume dial set at 10'O clock position (On batteries)? I have observed it yesterday after having tested with an Arcam rDAC outputting a 2.1Vrms signal in to the O2. Am I doing something wrong? But I could only hear the clipping in high frequency region, to be precise only with one album [Karftwerk - Tour De France Soundtracks] and on tracks 'Prologue' and 'Etape 2'. The recording doesn't have clipping for sure. Is there a way to get around it?
 
Thanks
Ven

Now you have just raised an important point. I am gonna connect the O2 to my desktop DAC which outputs at a fixed line level (not sure what is the Vrms).
 
Seems like I do need to find out more on how to get rid of any clipping should the situation calls for it.

 

[stv014]

Quote:

Originally Posted by vkvedam /img/forum/go_quote.gif
 
If I feed the O2 with a DAC's line out at 2.1 Vrms does it cause the O2 to clip on low gain and volume dial set at 10'O clock position (On batteries)?

Yes, on batteries, a 2.1 Vrms input can potentially be clipped even with the default 2.5x low gain setting. This is not fixed by reducing the volume, because the clipping occurs in the stage before the volume control. You need to reduce the gain to at most 2x by replacing two resistors, unless you can reduce the output level of your DAC.
 

 

[vkvedam]

Quote:

Yes, on batteries, a 2.1 Vrms input can potentially be clipped even with the default 2.5x low gain setting. This is not fixed by reducing the volume, because the clipping occurs in the stage before the volume control. You need to reduce the gain to at most 2x by replacing two resistors, unless you can reduce the output level of your DAC.
 

Thanks for that! Just tested it on AC and it doesn't seem to be clipping. Any specific reason?
 
Cheers...

 

[stv014]

Quote:

Originally Posted by vkvedam /img/forum/go_quote.gif
 
Thanks for that! Just tested it on AC and it doesn't seem to be clipping. Any specific reason?

 
Simple: when powered from AC, the supply voltage is higher. With batteries, the clipping level is at about 5 Vrms, while AC increases it to about 7.
 

 

 

 

[vkvedam]

Quote:

 
Simple: when powered from AC, the supply voltage is higher. With batteries, the clipping level is at about 5 Vrms, while AC increases it to about 7.
 

 

 

In that case my line in signal is only about 2.1 V RMS and why is it still clipping?
 
Thanks...

 

[palmfish]

Quote:

In that case my line in signal is only about 2.1 V RMS and why is it still clipping?
 
Thanks...

Maybe your headphone impedance has something to do with it? A lower impedance headphone would require more current to drive.
 
OTOH, my Denons are low impedance and my O2 has no trouble driving them on battery or AC. Of course, I've never turned the volume control past 9:00 because it's just too loud.

 

[uelover]

Quote:

Maybe your headphone impedance has something to do with it? A lower impedance headphone would require more current to drive.

Isn't the clipping is due to the input gain being too high? Headphone impedance wouldn't matter since the clipping happened before the output stage.

 

[stv014]

Quote:

In that case my line in signal is only about 2.1 V RMS and why is it still clipping?

 
Because it is amplified to 5.25 V by the input stage, and that is higher than the 5 V where the distortion starts to rise steeply due to clipping. Also, if the batteries have lower voltage (e.g. not fully charged), then the maximum output voltage without clipping is even less.
 

 

[Twinster]

I'm currently testing the Desktop version of the O2 that I just finish building with a friend and it sound the same as the portable version. The only differences is the taller case and input/output & volume control mounted on the back/front plate.
 
I've been listening to the O2 source by a DACport/Foobar with my T1 and I'm very impressed with the combo. I'm still discovering/getting use to the T1 sound (just 1 week) but I'm amazed that the O2 with the 2.5x gain can drive the 600 ohm Beyer to very good quality level. I think the slightly warmish from neutral DACport is just a good match for the O2 and T1 signature.
 

 
I'm definitely going to look at the upcoming ODA / ODAC combo.  

 
Quote:

Just curious if there is any sonic differences between the portable and desktop version?

 

 

[Crazy*Carl]

Is this the new design from Voldemort, or is it just the same O2 with different mounting locations for everything?

 

[vkvedam]

Quote:

Maybe your headphone impedance has something to do with it? A lower impedance headphone would require more current to drive.
 
OTOH, my Denons are low impedance and my O2 has no trouble driving them on battery or AC. Of course, I've never turned the volume control past 9:00 because it's just too loud.

Well I was driving my HE-5LEs which need about 9-10'O clock-ish amplification. For my Denons I don't go past 9'O clock on the dial.

 

[vkvedam]

Quote:

 
Because it is amplified to 5.25 V by the input stage, and that is higher than the 5 V where the distortion starts to rise steeply due to clipping. Also, if the batteries have lower voltage (e.g. not fully charged), then the maximum output voltage without clipping is even less.
 

Thanks again. So even if I am on AC and if I use a higher gain it's going to clip in that case because it's only OK up and till 7 Vrms. So I've got to use it in low gain and AC power to avoid any clipping whilst at home at least.