Looking for input on this gain structure I am working on

So I borrowed an older O scope from a friend and am trying to setup gains but some things just don't seem to add up.

I am running an Onkyo 3009, into an SMS1, into 2 EP4000's.

Step 1. Put 60hz test tone into Oppo and hooked up scope to sub output from Onkyo. I am having a really tough time trying to read this thing as it doesn't ever appear to square off.
Here is the wave with sub out at +12 and volume at 0. It looks like it might barely be clipping but it's hard to tell. I can't imagine the Onkyo putting out almost 20 volts unclipped.


For comparison, here is the sub volume at -2.5, volume on SMS at +28 and +32. That certainly appears clipped.



Here is the SMS1 output at a setting of 22 with sub out at -2.5.


At this level, the EP4000's gains are running wide open. SMS volume of 24 puts them into clip, so I backed off to 22.

So my final gain structure is Onkyo MV 0, Sub out -2.5, SMS1 +22, and EP4000 gains maxed. Does this appear correct? If that is I originally set them up very cool as Aud set sub gain at -12.5 and I had SMS1 at 15 with EP4000's at 1/2 gain.

This also goes against what most people say about driving the EP4000 to clipping. The EP4000 input sensitivity is 1.5v. So I should be able to clip the amp with a 1.5v signal, yes??? Then why does it take a 3.5v signal from my SMS1 to drive it to clipping? If I remember correctly I am feeding about 1.49 volts at -2.5 from my 3009 to the SMS1. So the SMS is boosting the signal 2 volts via the volume control, up to the 3.49v to drive amps to clipping.
Edited by bass addict - 2/12/13 at 11:03pm

The other interesting thing that I'm finding is that others had mentioned the SMS having it's input voltage clipped at around 1 volt or so. I outputted 5 volts to it and measured the output and it wasn't clipping. The only thing that appeared to cause a clipped signal was boosting the SMS's volume up too much, yet I have never seen anyone talk about that????

OK, well that confirms that. 20 volts is crazy non clipping output.

I'm still curious why it takes 3.5 volts to clip the EP's. Shouldn't it be much less than that with zero attenuation?

Hmmm, I decided that just to double check measurements I'd download the 60hz tone off of HTS forum. I burned this one (which is MP3), and it shows much lower voltage readings (13 volts compared to 20 volts max from Onkyo) than the 60hz sinewave from Bass Mekanik that I dl'd off of I tunes. Any reason maybe an MP3 version might not output 0dbs signal? I can't imaging Bruce's would not be accurate. I think I'll stick with the hotter readings from the original disc just to be on the safe side.

OK, maybe this Flu I have been fighting the last few days has taken a toll on me, but unless I'm missing something, there was absolutely no reason to setup a gain structure.

Maybe it has more to do with guys who's subs are under performing because there is no way I will ever be even close to clipping either my outputs, SMS1, or amp.

As mentioned earlier, my sub out was at 0, with SMS on bypass and at volume 22. Gains on EP's had to be wide open to reach clip point.

Well I just went through and EQ'd the SMS1, and to get the levels even close to matching up with the mains, I had to back the sub out to -10 and the volume on the SMS was only at 3.

So I run through and eq everything (I'll post some graphs for input later), and re run Audyssey. Final setting is sub out at -13, SMS at 13, and gains on EP's at 20. At these settings it would be impossible to clip the EP's. I will meter the subs to see if they need to be bumped up, but it won't change much in the grand scheme of things.

Am I missing something, or is this a good thing from going overkill???

I haven't played with the mini, so I can't make a direct comparison. They each have their pro's and con's. If you don't want to screw with REW, the SMS1 is a nice all in one kit. I like some of the features it offers such as sub volume control on the fly, and separate eq options for music, movies, etc.

I will be using REW alongside it, but it's nice to know it's not required if one so chooses to forgo that option. While my xt32 does a pretty good job with the rest of my speakers, it does some weird things in the sub world, so I'm glad to have this. If you check out my build thread you can see some comparison graphs with Audyssey and the SMS.

As far as the EP statement; that is in correlation to the number on the gain knobs on the front.

Well here are the known factors.

1) The Onkyo can output up to 20 volts without clipping
2) No matter how many volts I output, I did not see the SMS1 clipping the input signal (as has been stated in other threads)
3) The SMS1 will clip the output signal at a volume level of 28 and above
4) It takes a gain structure of 0 db output, and volume level of 24 on SMS1 to clip EP4000, and that requires gains full open.

So what is the relevance of any of this?

Calibrated sub levels (in my case) require sub out at -12, SMS1 at 16, and EP4000 gains at app 1/4. So setting up a gain structure is absolutely worthless in this case as I'm nowhere near clipping any of the signal chain. It sounds like the only way a gain structure would come in handy is for guys who run too little of a sub (or amp) for the room size???? Or am I missing something here?

Agree'd. The only way I would think you would ever attain setting gains at max, is if you had a pretty weak sub out signal on your AVR. I think most cases would require attenuating the gain to some degree. Like I mentioned, I can't even get close to half as I only have about another db of output I can back out of my receiver before bottoming the sub out.

No, just means you have a lot more headroom. In the past I have been able to maximize gains a little better. With my current build, as I've just found out, there is no way I am ever going to get even close to maxing out the chain.

It's all about voltage. Your amp gains are just attenuating the voltage to a certain point. If it takes 3volts to clip your amp, you can either get there by +10 sub out and the gains fully attenuated, or 0 sub out and gains wide open (just using random numbers). It really doesn't matter how you get there (as long as output signal is not being clipped). As mentioned, gains are not volume knobs.


True, but that's why you set gains with a 0dbs signal. That is the highest signal that will be output from your player, so as long as you don't send the amp into clipping with that, you are good to go. Now eq'ing will effect this so one needs to exercise caution and re check levels after any major eq sessions.

I agree Wayne. I set the volume for close to unity at 16 (unity is 15) and called it a day.

The volume is for the output. What I found interesting is many claimed the SMS would clip the input above 1.5v or so, and they made no mention of clipping the output. I found just the opposite. I couldn't detect any clipping of the input, regardless of voltage (I didn't go to the extreme here), but the output did clip at around 5volts. I'm not sure why the volume can be run up to around 50, as that is well past the onset of clipping, regardless of input voltage.