Portable MP3 players from Sony have dedicated volume buttons. You will find buttons or slider switches marked "VOL" with "+" and "-" indicators that raise or lower the playback volume, respectively. If you are listening to your Sony MP3 player and find that the "+" button does not raise the volume, and the volume is not already at the maximum (typically, level 30), take these steps. The exact menu wording and button navigation will vary by model.
Check the "Hold" switch, if your player has one. If "Hold" is engaged, pressing the "+" volume button, or any other button, will have no effect. Instead, switch off of "Hold."
Turn off AVLS. Sony recommends using its Automatic Volume Limiter System to protect your ears. To raise the volume beyond the AVLS limit, find the setting in the menu and switch it to "Norm" from "Limit."
Switch to manual volume mode. Various Sony units include a feature that adjusts or normalises volume automatically so tracks have a consistent volume even if they were encoded at different volumes. If you've ever had an unusually loud track follow an unusually quiet one in a play list, you will appreciate this feature. Check menu settings for "Preset," which limits you to Low, Mid or High instead of numbers 1 to 30.