Digital to analog audio converter - volume output adjustment

[Mad Professor]

Good day all.

I have been asked to look into if it is possible to adjust the volume output on a optical digital to analog audio converter.
The unit works as expected, but even with powered headphones plugged into the converter the volume output is below the desired level.

I have had a quick look inside the unit, as it seems that it is using a 4558 Dual Operational Amplifier, for the headphone output.

Now I have never done any work with op-amps before so I am not really sure where to start.

I will try and take some pictures and get them up here asap.

Can you please advice.

Thanks for your time.
 
Best Regards.

[Richard Crowley]

I have been asked to look into if it is possible to adjust the volume output on a optical digital to analog audio converter.

Assuming by the rest of the message that by "adjust" you actually mean "increase"?  Likely many of us think of "adjust" as meaning user-controlled variable attenuation.

The unit works as expected, but even with powered headphones plugged into the converter the volume output is below the desired level.

Do the headphones work at a proper level when connected to other things?
Do other things connected to the D/A converter operate at a proper level?

I have had a quick look inside the unit, as it seems that it is using a 4558 Dual Operational Amplifier, for the headphone output.

It may be premature to hack that circuit when the problem may be elsewhere. From the symptoms you have disclosed here, we can't tell where the problem may be.  And since you have not revealed what any of the pieces are, we are limited to pretty much shooting in the dark.

[Bassman59]

Good day all.

I have been asked to look into if it is possible to adjust the volume output on a optical digital to analog audio converter.
The unit works as expected, but even with powered headphones plugged into the converter the volume output is below the desired level.

The output level is likely limited by:
a) DAC power-supply rails
b) amplifier current-source ability
c) headphone impedance.

[Richard Crowley]

Good day all.

I have been asked to look into if it is possible to adjust the volume output on a optical digital to analog audio converter.
The unit works as expected, but even with powered headphones plugged into the converter the volume output is below the desired level.

The output level is likely limited by:
a) DAC power-supply rails
b) amplifier current-source ability
c) headphone impedance.

The Mad Professor said that he was using "powered headphones".
His vague description does not allow us to determine whether the 4558 is in the DAC or in the "powered headphones".
There isn't half-enough detail here to allow any kind of decent response to the questions.

[linux-works]

leave the dac alone and simply add a good phones amp.

diyaudio and headfi are places to look for ideas on phones amps.