McIntosh MR78 Question

Although experimenting with both alternatives might be worthwhile, I suspect that the best approach will be to use the MR78’s fixed outputs.

I took a look at the schematic for the MR78, which is provided in the service manual that can be downloaded at hifiengine.com if one is registered there. It shows that its volume control mechanism is a two-section 10K pot (potentiometer), one section being used for each channel, with each section wired between the fixed output for the corresponding channel and ground.

So the output impedance of the MR78’s variable outputs will vary as a function of the setting of its volume control, and will probably be relatively high for many or all of the settings that would be used. Which doesn’t sound like a good recipe for driving the low input impedance of the Audioengine speakers (10K for the models that are currently offered), or for driving the capacitance of the interconnect cables (especially if they are long).

Regards,
-- Al

P.S: I subsequently found the owner’s manual for the MR78 online, and in it a statement that "the load impedance connected to the Front Panel Controlled jacks should not be less than 47,000 ohms." That would seem to pretty much clinch what I said in my previous post.

Regards,
-- Al

Very informative, I have a lot to learn in terms of electronics. Thanks for the information Al.
-Richard