Both of my Onkyo's an 886P and an 806 will dump over 10 volts out of the SW output with less than 1% thd. Actually if I remember right they start clipping at around 12 volts. Anyway it is enough to clip the input of a DCX2496 which is a "pro" piece of gear while still being clean. The output stage on the DCX clips at about the same time with no gain applied inside of the DCX at all. My bottom of the line, many years old Pioneer 517k will even put out over 5 volts before clipping. There are a couple of audio mags and sites that test receiver or pre pro output stages. You don't need your particular model to be tested just something of the same brand and somewhat close to get a good idea. Manufacturer's aren't going to radically change that part of their design between units in a family. I'd be very surprised to see any modern reciever or pre-pro incapable of a clean
4 to 5 volts out the SW jack. That is enough to work with most any amp.
The main problem is that most people do not understand gain structure or spend any time at all optimizing it.This
Rane article is a good read.
The more and more powerful your system gets, with higher sensitivity and output headroom the more important it is to start paying attention to gain structure. In general you want to use as much gain as early as possible in the chain to minimize noise and hum. Basically you should take the time to measure what type of signal level your front end unit and any EQ units behind it are capable of producing or accepting cleanly, in addition to what your amplifier input sensitivity control should be set to to match up with them. Otherwise you may end up with a much higher amount of noise from your speakers and mismatched gains that produce clipping in the electronics well before the amplifier produces full output. All it takes is: A couple of hours of time, hacking up a cheap cable or two, a signal generator, a spectrum analyzer and a dmm really. Oh and unplug all the speakers. Basically you want to give the amplifier the hottest signal that is still clean that you can. The amplifier should clip first but it should only be just prior to the electronics before it in the chain. Otherwise you are either limiting your output headroom or you are increasing the noise in the system more than needed.
For example my system is easy.
886P SW channel = >12volts clean and clips the DCX input before it distorts itself.
DCX can accept right around 12 volts which clips the input
DCX output can produce right about 12volts prior to clipping. Both the input and output at 0 gain clip at just about the same time.
The K10 takes 6.34v input to produce clipping at it's lowest sensitivity setting. I have much more clean voltage than that available so the amplifier clips first which is what we want so I use this setting.
Using a signal that produces clean output from the 886P into the DCX, but that is just below clipping the DCX input stage and output, but results in heavy clipping of the K10 amplifier input.... I then lower the DCX output section level until it is just below clipping the amp input and then raise it back up until it produces solid clipping, but just into it instead of 6dB into it. At this point the 886P is producing a clean signal that is very hot. The DCX input is accepting as much as it can cleanly and the output is then attenuated some which means it is also clean at this level, which then runs into the amplifier input, which is set at its least sensitive setting and produces moderate clipping of the amp. The amp clips first before anything else in the chain and the signal is as hot as possible throughout the chain to the amplifier. After this point you should not touch any gain other than that in the front end receiver in the chain otherwise you will change the relationship between units.
If EQ is used in the receiver it does not matter and won't affect anything. However if you use EQ like I do, in a unit after the receiver, you may want to account for that by looking at the max amount of cut used which in my case is around 12dB at 45Hz. What that means is that with a 45Hz signal the input to the DCX will get clipped before the output into the amplifier produces clipping so that you will not be able to reach full power from the amp at that frequency range without readjusting the gain in the unit supplying the EQ
, upwards to account for the amount of cut. However many times such as in my case a cut is used to pull down a large peak in the response. Full output at amp clipping at 45Hz in my room would produce something near 145dB at my seat which is more than I ever intend to use or need. So the loss of 12dB of headroom there is no big deal to me and I just leave it alone.
My main channels are a similar deal. I have an Emo XPA-5 for them which only takes about 1.5volts or something like that to produce full power. Meanwhile the 886P produces less clean voltage from the main channels than the SW channel but it is still way more than the EMO needs. The DCX can still spit out 12 volts give or take. Since the Emo is a fixed sensitivity and the 886 and DCX both have many times more voltage potential than needed I simply run a 60Hz sine wave into the 886P and run it into the analyzer and push it to just below 1% THD. Then noting the voltage with my dmm and the SPL level recorded inside of the spectrum analyzer I then switch to the internal pink noise used for calibration and without touching any of the volume levels or input trims I note what SPL the pink noise is with the spectrum analyzer and take note of the output level of the channel being used for the pink noise. I know that this signal is a -30dB level from what would produce REF level. I compare the SPL from the 60Hz sine that produces just under 1% thd and that recorded by the -30 pink noise signal. The setting of the channel trim and the master volume setting for the 60Hz max clean sine wave, along with the spl recorded by the analyzer can be compared against the SPL recorded by the analyzer for the pink noise at the same channel trim. This will tell you what the maximum output the main channels can be set at to avoid clipping at REF level. Allowing you to use maximum signal strength from the receiver or pre-pro. In my case the 886 will be just below clipping at +8.5dB with a signal 30dB over the pink noise and the master volume at 0dB. From there the XPA-5 gain is fixed and the 886 is capable of putting out much more than it takes to clip the XPA-5. Also the XPA-5 has no clipping indicators and I'm not set-up to measure voltages as large as the amp will put out so I use the manufacturer's input sensitivity rating and measure the output from the DCX while putting the max clean 60Hz signal from the 886 through it. Then the DCX output stage is adjusted to produce the manufacturer's specified input voltage needed plus some just to make sure. From there plug the speakers back in and adjust the speaker levels to 75dB using the pink noise and adjust using only the channel levels in the receiver. If using EQ account for it the same way as outlined with the subs above.
That's just how I do it. YMMV. Anyway if you really want to get this stuff right you need to dig out a volt meter and a spectrum analyzer.Edited by Ricci - 10/15/12 at 12:24pm