Does using a rca to XLR adapter compromise power and dynamics of power amp?

Based on one of your other threads it appears that your Krell amp is an FPB 400cx. According to its manual it has a specified sensitivity (the input voltage required to drive it to its rated maximum power capability) of 2.71 volts. If your combination of AVR and source(s) can provide that much voltage you will be able to drive the amp to full power. Although given how powerful the amp is a bit of a shortfall may not matter.

There are a few balanced amps, BTW, such as certain Audio Research models which provide only XLR inputs, that will not work properly when provided with an unbalanced signal via an adapter. The result in those cases being a drastic reduction in power capability, as well as increased distortion. I don’t think that applies in this case, however, because on page 13 of the manual it states that:

A one piece RCA-to-XLR adapter is available from Krell Industries, to allow single-ended operation using the balanced XLR inputs.

Although the nature of the adapter is not defined I suspect it is essentially the same as other simple commercially available adapters, as opposed to being a transformer or some sort of active (powered) device.

What is likely to be a more ideal approach from a sonic standpoint, though, would be to use a Jensen transformer providing RCA inputs and XLR outputs, instead of a simple adapter. Their model PI-2RX (costing a little under $300), similar to PI-2XX shown here except with RCA input connectors, would probably be suitable. It would convert the unbalanced signals from the AVR to true balanced signals, as well as eliminating any ground loop issues that may be present.

Regards,
-- Al

Thanks very much, almarg.  Yes, the amp is Krell FPB 400cx, and the receiver is Denon AVR X5200.  I just looked at the X5200 specs and the only thing I could find that may be relevant is under the Analog section, where it reads:

Rated output:          1.2V

https://usa.denon.com/us/product/hometheater/receivers/avrx5200w

Now, my guess is that that is some sort of nominal output and that it can produce peaks higher than that.  Is that normally the case? 

With regard to the Jensen adapter, I looked at their web page, and it seems the primary selling point is to eliminate "hum and buzz".  I currently have none of either of those, as the system is dead silent until a signal is fed.

Looking at the specs on page 319 of the AVR manual, where the 1.2 volt figure appears, I would interpret that figure to be the output voltage the AVR would produce when it is used in conjunction with a line-level analog source and is provided with an analog input of 0.2 volts (note the reference to input sensitivity of 200 mv), with the volume control at max. Most modern analog sources will provide considerably higher voltages than that, and in response I would expect that the AVR would be capable of providing considerably more than 1.2 volts.

However I see also that if digital media are listened to via the AVR’s internal DAC the rated output voltage corresponding to 0 db (which would refer to the maximum possible value of a digital sample) is 2 volts. In that situation you would not be able to drive the amp to full power. But the difference between 2 volts and 2.71 volts is only 2.6 db. That is about a 26% reduction in maximum power capability, but is a fairly small difference from a subjective standpoint. And given the very high power capability of the amp you may never want to use that 26% anyway. Especially if your speakers have low impedance, as the amp is rated to provide 400, 800, and 1600 watts into 8, 4, and 2 ohms respectively.

Regards,
-- Al

OK, yeah, my speakers are rated 4 ohms and around 92db sensitivity.  I'm thinking I'm in pretty good shape with my current situation.  I just didn't know if the rca to XLR adapters would in any way limit the amp's ability to produce bass transients, slam, and impact.  But it appears that should not be the case.  Other factors, such as speaker cables and interconnects, may be the way to get the best out of the amp and to the speakers.

Correction to my previous post: "26%" should be "46%," although as I indicated that corresponds to a reduction of 2.6 db which is a small amount from a subjective standpoint.

Regards,
-- Al