Originally Posted by bigguyca
Since the same question is posted in multiple threads here is my answer from the SR8012 thread. It doesn't seem a good idea ask the same question in multiple threads; that aside.
One item to consider is if you will believe you'll want to use external amplifiers during the life of the product. The SR8012 will be a better choice to drive external amplifiers since it has much more robust RCA outputs due to having buffers on the outputs of the volume control(HDAM's).
Another obvious option is the Denon X6500H (or X6400H). It is very similar to the SR8012, with many identical components, but lacks the HDAM buffers and likely has a somewhat less robust power supply.
The three AVR's; the X6500H, SR8012 and X4500H, are the three obvious candidates to consider in the upper end of Denon/Marantz AVR's. The three units share components, especially power amplifier modules, but have key and important differences in features and capabilities, with price being the complicating factor. Any of the three can be the best fit for a given set of requirements, none are bad or even average choices, unless you need all the channels that the X8500H provides. Owners of each of the units seem to be happy with their purchases.
Having buffers on the volume control outputs, and thus the RCA outputs, is an important feature if the owner of the AVR will be using external amplifiers from the AVR.
Originally Posted by Surge2018
I have never heard of buffers on the volume control outputs as being a benefit for using external amplifiers. Can you explain? I use a Kondo amp for the main L/R channels.
I selected the Denon8500H not because I needed 13 channels - I actually only run 6 channels! I chose it because of the quality of the DACs and the power supply — these have a big influence on sound quality.
Output buffers are common on higher end consumer equipment and pro equipment. Buffers are rarely mentioned in advertisements or specifications, they are a boring technical detail and not easy to explain. Marantz HDAM's are a notable exception and are well publicized. The buffers serve two purposes: providing an appropriately low output impedance (often 50 ohms RCA, 100 ohms XLR, in pro equipment, higher in consumer equipment for a variety of reasons), and the ability to drive lower impedance loads, that is the buffers have more current capacity, which makes them better voltage sources. IC opamps are the most common.
Yamaha uses output buffers in the preamp outputs in their CX-5X00 series AVP's and RX-AX0X0 series AVR's. These buffers are implemented with IC opamps vs. the discrete HDAM buffers. HDAM's are effectively used to implement opamps with current feedback instead of the more typical voltage feedback.
That said, you are using a tube external power amplifier that has a very high input impedance. The specifications for the Kondo amplifiers list input impedances of 70k to 100k ohms. It is very easy for about any RCA output to drive this high impedance, so you are good to go. For an example of much lower RCA input impedances see below.
While this doesn't relate your installation, there is another side to the high impedances generally encountered with tube equipment. Again looking at Konda equipment, the Konda preamplifiers are rated to drive loads, that is the RCA inputs of power amplifiers, where the power amplifier has an input impedance of 20k ohms or more.
Looking at these measurements of an Emotiva XPA Gen3 power amplifier from Stereophile:
The RCA input impendence was measured at between 14.5k ohms and 9.5k ohms depending on frequency. This means a Konda preamplifier, that wants to "see" a minimum of 20k ohms, driving the Emotiva power amplifier is not a good combination. Clearly the Konda preamplifier is designed to drive the 75k to 100k ohm input impedance of a Konda power amplifier.
An IC opamp output buffer (committing the sin of using transistors) could be added to the Konda preamplifier and the output impedance lowered to say 50 ohms. Somehow it seems unlikely that will happen. Alternatively Emotiva could increase the RCA input impedance of the XPA Gen3 to a more typical 30k to 50k ohms.