[lsc04361]

Hi,
 
I was going to order an O2 amplifier, not sure which to choose for the custom gain options.
 
Default gain levels of Objective2 is 2.5/6.5x. And there are another options as well, which is 1.0/3.3x and 1.0/4.5x.
The 1.0/3.3x one is said to be optimal for 2.10VRMS DAC and the 1.0/4.5x one is designed for use of Mac products, which have a VRMS of 1.5.
 
My DAC is having 1.5 VRMS. So following these descriptions, the amp should be of the 1.0/4.5x gain options.
Given that I might not use the high gain output anyway (my headphones are of a somewhat low impedance), either 3.3x and 4.5x should be fine. But I still would like to know what's the difference between these options, and why the default low gain is set as 2.5x, while it seems to make more sense if its 1.0x as well.
 
Thanks!

 

[buke9]

Hi,

I was going to order an O2 amplifier, not sure which to choose for the custom gain options.

Default gain levels of Objective2 is 2.5/6.5x. And there are another options as well, which is 1.0/3.3x and 1.0/4.5x.
The 1.0/3.3x one is said to be optimal for 2.10VRMS DAC and the 1.0/4.5x one is designed for use of Mac products, which have a VRMS of 1.5.

My DAC is having 1.5 VRMS. So following these descriptions, the amp should be of the 1.0/4.5x gain options.
Given that I might not use the high gain output anyway (my headphones are of a somewhat low impedance), either 3.3x and 4.5x should be fine. But I still would like to know what's the difference between these options, and why the default low gain is set as 2.5x, while it seems to make more sense if its 1.0x as well.

Thanks!

Having low impedance headphones doesn't necessarily mean you don't need high gain. Sensitivity is also a part of the equation.

 

[MindsMirror]

It is extremely easy to modify the gain yourself. I would get the 2.5/6.5x which is the most versatile. In order to modify either of the gain options to 1.0x all that you need to do is clip the leg of two resistors. You can turn it into either 2.5/1.0x or 1.0/6.5x.
 
It seems pointless to me to include both a 3.3x and 4.5x option. If 3.3x is not enough for you, chances are 4.5x still won't be.

 

[GREQ]

Don't bother with the 6.5x gain option - the distortion levels are insane.
You're much better off getting a cheap tube/solid-state hybrid amp, such as the Bravo Audio Ocean, but only if you need that much power,

 

[lsc04361]

Thanks guys.
By the way, I wonder what will the amplifier did to the signal if its set to 1x.
I get the notion of having 1x option around that is to simply provide a low output impedance for some DAP or other source which has a relatively high output impedance. But if the amplifier amplified the signal 1x, how is the output signal of the amplifier differ from the line level which has been input to the amplifier?

 

[MindsMirror]

The job of the amplifier is not just to multiply the voltage, it also buffers the input, and supplies power to the output. The O2 has two pairs of op-amps. One pair is the input/gain stage, and one pair is the output (actually there's two dual op-amps in the output but that's not important). The input op-amps buffer the input signal and multiply it based on the gain setting. The input op-amps do not interact with the headphone. It is the output op-amps that delivers the power and provides the low output impedance to the headphone, which is unaffected by the gain selection.
 
If you're interested, the input op-amps are in a non-inverting configuration. You can read about that, and how the choice of resistor values determines the gain. That is what the gain switch does, switches some of the resistors in the op-amp circuit.

 

[lsc04361]

The job of the amplifier is not just to multiply the voltage, it also buffers the input, and supplies power to the output. The O2 has two pairs of op-amps. One pair is the input/gain stage, and one pair is the output (actually there's two dual op-amps in the output but that's not important). The input op-amps buffer the input signal and multiply it based on the gain setting. The input op-amps do not interact with the headphone. It is the output op-amps that delivers the power and provides the low output impedance to the headphone, which is unaffected by the gain selection.

If you're interested, the input op-amps are in a non-inverting configuration. You can read about that, and how the choice of resistor values determines the gain. That is what the gain switch does, switches some of the resistors in the op-amp circuit.

Thanks. I shall find more about the input op-amp. I get the part of switching between resistor for different gain, in a simplified physic point of view though lol.
It would be great if they can include 1x option in all settings, isn't it, so that headphones that are very efficient and sensitive can also use the same amp, without having unneccessary increase of gain, together with the extra noise and distortion.

 

[Smugsie]

Through laptops/computers/ODAC/dedicated DACs/daps with line out, 1x gain is all I need.

Even with classical music that go down to maybe -50db to -10db, my Sennheiser HD600 and AKG Q701 never go past 12 o'clock on 1x gain with the sources I mentioned above. I only go past 12 o'clock for 10 minutes for fun before I dial it back down to 9 o'clock or less.
Sensitive earbuds like my Sennheiser IE80 go to 7 o'clock and I can't go any lower before there's channel imbalance.

However with my android/apple phones I hit 3.3x gain on max volume in my phone and the O2, the volume was still quiet! It was only during that situation did I wish I had 6.5x gain.