I have been updating my amplification recently to include 200 watts per channel to a 7 speaker surround system using my 990 and adcom amps. This might sound a bit unknowledgeable, but I am wondering about output using a variety of different rated amps. This is what I am using:

Adcom 555II for Left & Right (200WPC)
Adcom 555II for Rear L & Rear R (200WPC)
Adcom 545II for Side L & Side R (100WPC)
2Channel Adcom GFA-2535 bridged to (200WPC)

My question is this. I recently upgraded the 545's to 555's, and I am not seeing any significant increase in volume reachable through this change. I can turn the volume up to max, and it still isn't enough to blow me out of the room (believe me, it is still really loud but not to any distortable level). Does the 990 limit output of all imcoming amps to the lowest common demominator or to a specific point it knows won't start clipping the amps? Meaning, does the pre-amp limit output power to 100 WPC instead of allowing a higher output? Even when I change to a 2 channel mode to listen to CDs, etc., it still will not output a higher listening level than when I am listening to 7 channels.

Any clarification on input power to output levels would be hugely appreciates. I may just need an old school output primer. If I get another 200 watt amp, will the overall output power increase (if all of the amp channels are at 200WPC)?

Also, one other silly question. Does the surround back speakers deserve better power or do the surround sides? And if I were to upgrade speakers, would it be better to update the sides or the back speakers first? Just some additional musings.

Thanks so much! Brandon

It's not the preamp. When it comes to amps, doubling the wattage only adds 3 dB of SPL; that's why you're not noticing a significant change.

Typically in order to double the SPL in a given room you will need a 10 db increase. This means in order to double the output of your speakers at 1w you need about 8 watts to your speakers. Your speakers have a SPL rating of 88 db at 1W or at 2.83 volts which is the same thing into 8 ohms. It is typically somewhere between 85 to 95 db at 1W. For a 200 watt amp you get about a 24 db increase from the rated SPL at 1 watt no matter how you slice it. If your speakers are rated at 88 db @1W this means a max output somewhere around 112 db. If they start out rated at 98 db you get up to around 122 db. Both SPLs are very loud, but the second is twice as loud. Shear volume of SPL is not what you really are looking for. What you want is quality at high output. What larger amps really do for you is to provide margin to allow peaks to be reproduced faithfully without damaging equipment. The recommended power for your L/R speakers is 40-100 watts. If your are supplying them more than they can use they will eventually be damaged at max output. What sub are you using?

Considering that you are turning the volume of your preamp up to max, this means that if the gain of the two amplifiers are similar, you are not going to hear any increase in volume, no matter how much extra power one of them has.

You might try performing a calibration using the 75dB reference tone in the preamp. It sounds like it is calibrated way too low.

I am using a Boston Accoustics VR2000 Sub which is rated at 300 Watts and THX certified. I got it around 2000, and it's been a part of my setup ever since. It'a a huge sub that was top of the line for Boston that year.

Here's the description of the Boston VR2000 I found:
300 Watt THX powered subwoofer VR2000-Boston Acoustic's Flagship clean articulate bass with more power. 12" long throw polymer treated driver and fixed 80 Hz high pass filter, 40 to 100 Hz 24 db/octave 4 pole low pass filter. Variable crossover control, level control and polarity switch. AC-3/THX input bypass the lowpass and level controls.

Right now, I have the calibration set at 70dbB at -10 dB on the pre-amp, and the highest volume acheivable on the Outlaw is -1dB. Just watched a movie, and it wasn't too loud at that level--for most I would assume it would be.

Thank you guys for the replies. I think I will first try recalibrating the preamp. What'
s bizarre is that what I was using an Adcom preamp and the Adcom Amp, I could easily get to the clipping point when playing CDs (at around the 7 level of volume). However, it seems that since I have been using the Outlaw, I don't get anywhere close to that.

So, replacing the surround 100 watt amp with a 200 watt amp might allow me to increase the highest db level at the current calibration settings from -1 to say +2?

I do hope you realize that 99% of the time you are going to be actually using less than 10 watts of power from any amplifier. This is especially true if you use a subwoofer, since this region is where all the heavy power consumption is.

Buying a new power amplifier simply for more output level is not a very useful tactic. If you simply want more output, buy bigger and / or more efficient speakers.

i agree, its your speakers most likley. oddly enough i have a similar setup ampwise as you, i have two adcom 555's for the fronts and surrounds, a 545 for the surround backs, an outlaw 2200 for the center and an outlaw LFM-EX sub. my speakers however are larger: KEF Q5 frnts,Q3 surrounds, small dipole surround backs and an NHT M6 center. my system shakes the house and will make your ears bleed at +7 to+10. an adcom 555 is a very powerful amp.

I have multiple amps, SS including an Adcom 555 and an OA 750. MC 240 PP tube amps too. I agree that some tweaking of the preamp output on the OA 990 might be in order. All of my big main room speakers are horn loaded, ie. Klipsch Heritage, old line stuff-K horns, LaScalas, Heresy's. Horn loaded speakers are very efficient. At the SPLs you seek, you may damage your non-horn loaded spkrs. Most horn'd spkrs, regardless of manufacturer are in the 95-105 db/W range. BTW you can make these too, or buy them cheaper, if used - as I have done. At v high db output you WILL damage your ears if done for long. Pls keep this in mind. At an SPL of over 100 on my digital Radio Shack meter, I am only good for about 10 minutes of metal or rock. Then again, my place starts falling apart too. I have 2 dual 18" cabinet subs, they each have a separate 1000 w amp. For high SPLs you need either horn'd spkrs with good amps - but even 5 W SET tube amps would be fine, or less efficient spkrs with massive SS amps - like the 555s.
Just my 2 cents,

I noticed something similar when using my 990 with a Threshold S500e amp. It's like there is not enough gain coming out of the preamp to drive the threshold power amp properly. I switched to an Adcom 555II and there is plenty of gain with lots to spare.

What is that calibration with the refernce tone that you mention? I don't recall seeing anything about that when I did the setup.

The test tones that Altec is referring to are the built-in speaker channel calibration tones described on page 30 of the 990's manual (under the CHANNEL CALIBRATE menu).

Did you do the "auto setup" to set speaker distances and levels, or did you manually adjust the "CHANNEL CALIBRATE" and "DELAY ADJUST" menus?