DAC plus Preamp or DAC-Preamp or DAC-Volume Control ?

Thanks, Ralph. How would I go about doing so?

You could take the amps to any competent technician, have them contact us (651-690-2246) and we can tell them how its done (instructions are below). Otherwise you could also ship it to us.
Any SET has an input tube. Normally the signal comes in on the grid of the tube. This is the center pin of the RCA connection and also pin 2 of the XLR that will have to be installed. Pin 1 of the XLR is the ground of the RCA.


Pin 3 is where its different- that is connected through a coupling cap to the cathode of the input tube. If the tube has a cathode bypass cap, the ground side of the cap is lifted and connected to pin 3 (and when the RCA connector is in use, pin 3 is connected to pin 1 via a jumper you place in the XLR connector). If the amp lacks a cathode bypass cap (which will be an electrolytic), you sort out the value needed and connect it between the cathode of the input tube and pin 3, with the plus side to the cathode.This connection is not balanced, but it **is** differential. The amp’s character doesn’t change, while being able to process both phases of the balanced connection.

Plan B: install an input transformer to make the conversion. At least with our preamps, plan A above sounds better.

@atmasphere  Thank you very much. I'll run it by both the amp's designer and Richard Gray, who is local to me and would do the work.

For clarification, are you saying:

Your Plan A (Post above) is superior to > Plan B (Input transformer) Both of which are superior to > What I am doing with the cable approach (Keeping Pin 3 'Open/Not connected')?

Thank you.

David,
Plan A option  per Atmasphere is a very intriguing proposition 
.Charles 

@david_ten

Your Plan A (Post above) is superior to > Plan B (Input transformer) Both of which are superior to > What I am doing with the cable approach (Keeping Pin 3 'Open/Not connected')?

I've listened all three ways. The transformer has to be pretty good to keep up- it tends to have less bandwidth and detail and this is measurable (at least its bandwidth and distortion is). I prefer to use the signal that is presented by the balanced source- it tends to be more accurate than if you only use one phase as in an adapter. This is probably because the single-ended connection is more susceptible to noise and the like.

I've been running this sort of connection for about 10 years in one of my prototype amps and have modified many amps with this connection since. I first read about it when researching some of the works of George Philbrick, who is often credited (inaccurately, but he was certainly an early pioneer) with building the first opamps, which were vacuum-tube.

Ralph, I will follow through on this. Your guidance is appreciated. Thank you.