............................. NOTE: If this unit does not sell in a couple of days, I will be editing the AD to include an iFi power supply. The price can be dropped, and the sound will still be as great as it was to begin with. Stay tuned........................................................................................ These units do not have a volume control. What I have done here is to put in what I would call a gain control. I say this because a buffer amp does not increase the volume, but is a 1 to 1 ratio or so in volume. I have found that putting this control in the circuit helps me keep from overloading these tubes (rare). You don't cut it back very much, so don't fret about too little gain. This product may be one the coolest that I have ever made to date, but it is Pete Millet that brought the design to us. Thanks so much Pete for your design! So it is based on a 'new' tube device made by Korg. Just call them tiny tubes. I couldn't take my eyes off them and wanted to get on it ASAP. I did, and I will just say, it is the power supply that makes this thing sound like it does. I mean to say, it sounds just fine, until you put a different power supply to it. I have tried switching supplies (not bad actually), battery supply (better), and the Pangea supply (OMG). So, these buffer units that I have been making vary by design, sound and experience (your experience, that is). If there is a more 'tubey' sound to be had, this is it. You like it you keep it. If it doesn't 'work' for you send it back in perfect condition and receive a full refund. Simple as that. Ask my customers. So far, I have not had a single buffer unit returned. 'Nuff said. To be clear, this sale is for one unit. I also made one more of these units, as you can see in the photos. It operates off of two 9 volt batteries. Inquire if interested. I won't be making anymore of these 'cuz in the near future, just look for a new product from this design in the form a headphone amp.