Oppo 205 head amp’s “unity gain” & Lumin’s Leedh volume control:

[Gus141]

I’m not sure anyone can help me with this question due to the combination of gear and the use case, but does anyone know what a good “unity gain” volume setting is for the headphone amplifier on the Oppo UDP-205?

I want to use the near-lossless Leedh volume control on the Lumin U1 Mini streamer. The Lumin threads on various forums say to set “unity gain” on your amp and then control volume on the Lumin app.

I have the Lumin U1 Mini connected to the Oppo 205 via USB DAC input and I’m using this setup as a headphone streaming rig only. I like the DAC and built-in head amp of the Oppo 205, but my cans and IEMs (Sony MDR-Z1R and IER-Z1R) are too sensitive for the powerful Oppo head amp and I have to set between 24 and 34 on the Oppo volume for my preferred listening volume. So I thought that was too much digital attenuation in the ESS DAC chips and wanted to do the better Leedh volume control in the Lumin.

My understanding of “unity gain” is not good. But I figured a start would be to set the Oppo 205 head amp’s volume to 100 and adjust the Lumin’s Leedh software volume control to 34 (my max volume level usually on the Oppo): it was a little too loud, so I adjusted the Oppo down to 97 and it sounded the same as when I don’t use the Lumin’s volume control. So Lumin digital output fixed at 100% vol with the Oppo head amp vol at 34 = Lumin Leedh Processing with digital vol at 34 and Oppo head amp at 97.

Is that approach OK? Or is this more about voltage and measurements? I’ve also read many threads where their amp’s unity gain is at “12 o‘clock” on the volume knob. Since the Oppo 205 doesn’t have a volume knob that was no help ;-)

[And by the way, the Lumin’s Leedh processing sounded better to my ears than the Oppo doing the volume control.]

Thanks in advance for any and all guidance.
Cheers,
Gus

 

[DVDdoug]

but does anyone know what a good “unity gain” volume setting is for the headphone amplifier on the Oppo UDP-205?

You'd have to know something about the design. The amplifier is connected to the DAC internally so we can measure the signal out of the amplifier but we (probably) can't measure the signal directly out of the DAC so we don't know the gain.

Unity gain means no gain and no attenuation (the same as a straight connection). But in the case of a headphone amplifier or power amplifier, unity gain can mean current gain and power gain, but no voltage gain. Gain is amplification and a gain or multiplication of 1.0 is "unity".

None of this is critical unless you get noise or distortion or some audio problem.

The general rule of "gain staging" is to have the strongest signal through the signal chain that you can get without clipping (distortion) for the best signal-to-noise ratio, and attenuate at the last place you have an adjustment.

But convenience is also a consideration and usually there is no problem unless you attenuate and then re-amplify by a lot.

When you attenuate digitally you do lose resolution, but something similar happens with analog too because when you attenuate you lower the signal without lowering the noise of the following circuits/components. That makes a worse signal to-noise-ratio. But it's not problem if you're not hearing the noise...

When you hear the effects of low-resolution you hear quantization noise. But the quantization noise is normally so low that you can't hear it, again unless you re-amplify by a lot.

 

[Gus141]

You'd have to know something about the design.

Unity gain means no gain and no attenuation (the same as a straight connection). But in the case of a headphone amplifier or power amplifier, unity gain can mean current gain and power gain, but no voltage gain. Gain is amplification and a gain or multiplication of 1.0 is "unity".

None of this is critical unless you get noise or distortion or some audio problem.

The general rule of "gain staging" is to have the strongest signal through the signal chain that you can get without clipping (distortion) for the best signal-to-noise ratio, and attenuate at the last place you have an adjustment.

But convenience is also a consideration and usually there is no problem unless you attenuate and then re-amplify by a lot.

When you attenuate digitally you do lose resolution, but something similar happens with analog too because when you attenuate you lower the signal without lowering the noise of the following circuits/components. That makes a worse signal to-noise-ratio. But it's not problem if you're not hearing the noise...

When you hear the effects of low-resolution you hear quantization noise. But the quantization noise is normally so low that you can't hear it, again unless you re-amplify by a lot.

Thanks! Great info. This helps.

Cheers

 

[Gus141]

…
The general rule of "gain staging" is to have the strongest signal through the signal chain that you can get without clipping (distortion) for the best signal-to-noise ratio, and attenuate at the last place you have an adjustment.
….
But convenience is also a consideration and usually there is no problem unless you attenuate and then re-amplify by a lot.
….

I added the bolding above from pieces of your quote for emphasis. I think my desire to try out the Leedh Processing of the Lumin streamer without knowing the hardware design of the Oppo is not very scientific and likely just going to compromise what was already working (and convenient with the hardware remote of the Oppo).

When using Leedh processing early in the signal chain I’m likely over attenuating too early and over amplifying at the last stage (the headphone amp). Where as sending 0dB unattenuated digital from the Lumin streamer to the Oppo and letting the DAC and amp design work as designed, with a great hardware remote too, is likely the best choice to follow here.

Cheers