Performance Features Ergonomics Value
www.soundandvision.com
I quote from their article. :"According to Denon, when Pre-amplifier Mode is engaged the receiver's preamp outputs can provide up to 4.8Vrms—more than enough to drive any outboard amplifier to full power. If you use the preamp outputs (which are always active) with their internal amps still connected, they will be limited to as little as 1.44Vrms, which is not enough to drive some external amps to maximum power. A third option would have been nice: disconnect only the three front internal amps to allow the use of external power for the critical LCR front channels, letting the other internal amps handle the surround and overhead effects speakers. (The only Denon AVR to offer full on/off control over each separate channel's individual amp is the AVR-X8500H.) "
I have not tested this - anyone up for the challenge with one of these to measure output with RCA cable connected with internal amp enabled
That information about the 1.44 V mentioned in the review you linked is very misleading, the writer should have posted a link to his source (he claimed it was Denon). If it was from Denon, then I dare say it was taken out of context.
The fact is, the preamp output did not clip at such lower voltage, but it would have increased distortions due to the feedback from the power amp, and it is the power amp that would begin to clip when the preamp output reaches about 1.2 V (give or take, typically..), so by 1.4 V, clipping could be quite severe.
However, only a % of the power amp's distortions would be fed back to the pre out so it really isn't that bad, except for the golden ears.
For some real figures, take a look of the test results by ASR, that HD mentioned:
Denon AVR-X3700H AVR Review | Audio Science Review (ASR) Forum
See that the green curve shows at preamp output 2 V, SINAD (reciprocal of THD+N) is still at about 77 dB, that is -77 dB THD+N, or 0.014%. That is quite respectable/acceptable, in fact better than some so called separate processor/preamp such as the Marantz AV7705.
On the graph, it says "Amps Off", "Amps On", that's confusing terms used by the reviewer (surely not intentionally). It would have been better if he used the term "amps disconnected", amps connected etc..
Even in preamp mode, the power amps are never turned off, but the signal input would be disconnected from the preamp output so there would be no signal to "clip".
The preamp output could actually reach as higher as 4 V or a little higher if you look at the curve provided by Denon to Gene (audioholics.com) in his review of the AVR-X3600H. Gene and Denon also have a you tube video in which Gene explained how the preamp output's distortions would increase due to the feed back from the internal power amp clipping, when the preamp output is higher than say 1.2 V or so.
So again, 1.4, or 1.44 V you quoted, were not the limit, it was just at the point when the preamp output distortions would increase significantly but still at reasonably low level, when the internal power amps would clip and the resulting distortions get fed back to affect the preamp output negatively. Yes it looks bad but if you put things in perspective, it is a matter of about 0.001% THD+N at 1.4 V, versus 0.014% at 2 V. At 2V pre out, a power amp with 29 dB gain (quite typical) would be driven to about 400 W into an 8 ohm load or 800 W into a 4 ohm load. Even at 1.4 V, a 29 dB gain power amp could be driven to about 195 W into 8 ohms or 390 W into 4 ohms. Hardly an issue for most people if 200 W is all they need, just have to stick with power amps that offer the typical 28 to 29 dB gain, such as power amps from Monolith, Outlaw, Marantz, Yamaha, Onkyo etc., there are many choices.
