Any issues to be aware of if driving SET from a balanced source?

George, I don’t know about the adapters you suggested, but IME most XLR to RCA adapters short the signal on XLR pin 3 to ground (XLR pin 1). That will be appropriate for many XLR outputs that are transformer coupled or "cross coupled" (as well as being appropriate when adapting RCA outputs to XLR inputs), but will definitely cause problems for **some** actively driven differential outputs. See this thread, for example.  And also note the following statement in the second Rane reference I provided earlier, pertaining to actively driven differential output stages:

Mark off even more points for potential distortion (depends on op-amps, and exact configuration), oscillation, and failure, resulting from asking one side to drive a short (the result of grounding one side for unbalanced operation). 

AJCrocker1, yes, use of an adapter cable will not be a suitable approach if the balanced outputs are referenced to a DC voltage. However, I have never encountered either a consumer oriented or a pro oriented XLR output that had XLR pin 1 referenced to a DC voltage, rather than to ground. And presumably likewise for the "S" of a "TRS" connector. If you are aware of an exception to that I would be interested in knowing about it.

Regards,
-- Al

I was assuming the XLR output was a standard affair, as I've never had problems using these from any xlr output sources to my single ended input product.

Cheers George

There are two ways to do it if you want the amp to really get the full benefit of the balanced source:

The first is with a high quality input transformer, which can convert from balanced to single-ended. Jensen is an excellent source for that.

The second is that it happens that any SET can properly receive a balanced signal, and while its reception won't be balanced by definition, it certainly can be differential by definition and so can process both phases of the signal. This is a very minor modification- the hardest part about it is sorting out where to install the XLR connector. The mod won't change the character of the amplifier.

The technique is simple- a coupling capacitor is used to couple the other half of the balanced signal (pin 3, if pin 2 is tied to the grid) into the cathode of the input tube. If the cathode circuit employs a cathode bypass capacitor, that cap will be the coupling cap. If the circuit does not, it has to be added. It really is that simple and works quite well- I've been doing it for years with a set of type 45-based amps.

Refer this to a technician and they will have no troubles doing the hookup.