Originally Posted by
xwing1 
I thought I'd repost this, as it is a Problem for which I found a Solution, which seems common to all Onkyo preamps, and at least some Denons too:
PROBLEM: ONKYO TX-NR905 PREAMP OUTPUT VOLTAGE TOO LOW FOR OUTBOARD AMPLIFIER
My Onkyo 905 used as Preamp into my new Earthquake Cinenova Grande 7 channel amplifier does NOT make movies loud, indeed LESS loud than the internal 905 amps did (!)
It is clear that the output voltage of the 905 Preamp Outs is too low for the input sensitivity of the Cinenova. Earthquake's tech "Fadi" says their amp is designed to Industry Standard 1.9V max input needed, though "Industry Standard" is, as Jack Sparrow the Pirate says, 'More a Guideline than a Law'.
I could not find the rated output of the Onkyo 905 preamp, but some other Onkyo was rated to only 1V, which clearly wouldn't be enough based both on the VOLTAGE, and now in my EXPERIENCE.
The speaker volume output goes up until the Onkyo is at around 81%, after that it barely goes up if at all, seems to have maxxed out the curve of [volume setting vs preamp output].
--Does anyone KNOW the preamp out rating of our 905's?
--Can the 905 preamp out voltage be INCREASED by some potentiometers inside it etc? (YES I have maxxed out the "Cable/Sat Intellivolume" at +12dB in the 905 menus. I am using DirecTV satellite into the 905).
--I am trying to solve the problem on BOTH ends, I hate to have to send this 140 pound amp BACK to Earthquake for adjustment...
--IMHO Onkyo (and maybe Denon too, this was reported by a Denon owner who ended up SELLING his Denon and the Cinenova when it wouldn't go loud) have inadequate preamp out voltage CAPABILITY.
I got the Cinenova in order to NOT have to worry about amp clipping or distortion at loud volumes into my new PSB Synchrony 1 seven speaker home theater setup. I use an old reliable Velodyne ULD18II subwoofer and am directing an appropriate amount of the low freq's to it.
The 905 sounded good, but at high volumes I could detect some hardening/edged sound suggestive of amps-in-mild-distress; rather than beat it, I elected to get a bigger amp. Since the Cinenova is rated at 300Wpc 8 ohms, 600Wpc 4 ohms and my speakers are a nominal 4ohm load, the (well over) doubling of wattage should give me at least 3-5dB more headroom and without clipping worries. I have shut down the 905 (and got it to give very nasty strange popping-noises-of-distress) at high volumes with it set to "6 Ohm" so put it on "4 Ohm" but as tests show, this seems to limit output wattage to around 55-60 Wpc...NOT the ideal way for me to run my new home theater.
I have been impressed with the technical KNOWLEDGE of some people on here, and thanks in advance...
JT
ps the Onkyo definitely does strange things by removing significant bass to the sub vs. my old Yamaha RXV1050 receiver, especially/most notable in Direct or Pure Audio mode...separate issue
-->>EDIT/UPDATE: Onkyo Technical Support says preamp is rated up to 1V output only, and is not adjustable! This makes it a poor match for the Cinenova and likely other amplifiers as well. I am working with Earthquake to see what can be done to adjust the input sensitivity of the Cinenova amp to best match the output (dis)ability of the Onkyo 905...
I found a source listing some common preamp maximum output capabilities:
"- some receivers' preouts (~1V RCA)
- some highend, megabuck 2 channel preamps (30+ V XLR)
- Parasound Halo C1/C2 prepros (8V RCA, 16V XLR)
- Aragon 2 channel preamps (8V RCA, 16V XLR)
- Aragon Soundstage & Stage One prepros (7V RCA, 14V XLR)
So, yes, the 1V preamp output of our Onkyo 905's is substandard and suboptimal, and I am suffering for it.
-->>EDIT/UPDATE #2 10/25/2008: "Fadi" at Earthquake is being VERY helpful, and understands the problem (he is NOT the usual know-nothing "Janitor" one gets at company help lines!).
He is sending me a set of 7 resistors, and has Emailed me very high quality ACTUAL pictures showing how to take the unit apart, which resistor to change, and how to do it. I am good with soldering and moderate electronic work so I am the "test subject" for this. I will be making the resistor change to increase the amp's input sensitivity. I will be using a Radio Shack dB soundmeter and checking the exact dB difference at some reference volume settings on my 905, to document the difference in my setup.
HIGH PRAISE to Earthquake for their Customer Service and technical help so far!!! Onkyo's Janitor was at least able to get me the preamp out voltage max and no help on adjustment...LOL
-->>EDIT/UPDATE #3 12/28/2008: I swapped out the 7 resistors Earthquake sent. The speakers now play 5 to 5.5dB louder using the exact same Onkyo white noise test for the front 3 speakers, all else exactly the same. Readings via usual Radio Shack sound level meter, at about 13feet/couch listening position. I am now able to drive the Cinenova amp into light clipping on some things. IMO the preamp should be able to overdrive the amp into hard clip, to assure the preamp has the RANGE to fully utilize the amp on all sources/materials...and assure you are getting your (big) money's worth out of the amp, getting all the Watts it can properly produce. Fadi at Earthquake said they would likely incorporate this mod in future production runs, as it clearly will happen with ALL Onkyo products which ALL seem to have only 1V output max on preamps; some Denons at least are the same. I suggested a switchable input sensitivity as some amps have.
I still notice a rare harsh crackle/clip sound from the Onkyo at high volume bursts/levels at times. It happened well before the Cinenova upgrade, the Cinenova was certainly not clipping; so something, whether the preamp, or some processing glitching, is causing that. It doesn't happen except with Onkyo pumped up around 75-85% volume, and I don't think a processing glitch would do this, unless it involved the electronic preamp volume control.
