Yet another happy art clean box user

[Ilkka]

Interesting issue for sure. I'll take some measurements tomorrow.

[SteveCallas]

Interesting issue for sure. I'll take some measurements tomorrow.

Excellent.

[JonW]

You pick a volume setting say 0db or some number 75% of max and make that 85db on the Rat Shack meter with the levels, and amp gains.

OK, right. I guess I forgot about that. Haven't ever actually done it with my system. But I will some day.

Interesting issue for sure. I'll take some measurements tomorrow.

Yes, excellent.

You wouldn't actually be solving anything, just lowering your max headroom. If you set your main channel levels to +12 and need your master volume at -20 to reach a level you like, lowering the main channel levels to 0 would require you to set your master volume to -8 to get to the same levels. Raising the channel levels and raising the master volume level is one in the same when you can't adjust your amp gain.

Exactly.

But this part confuses me:

In the case of your subwoofer, you can adjust amp gain, so lowering the channel level and increasing the gain on the amp essentially gives your op amp more dynamic range and less chance of distorting or clipping.

I’ve already got the sub amp knob up at 100%. And the pre-pro sub channel output at the max. Adding a clean box would allow me to either lower the amp gain or lower the channel level- or a little bit of both. But they’re both maxxed out already. So how would a clean box help? I guess not at all, if you don’t think there’s any distortion coming into play.

Off topic, but if I were you, I'd swap the amp you bought for your surrounds with the one you are using for your mains if you haven't done so already :T

I have, indeed, fooled around with that a little. Not enough to say anything definitive yet. I did the swap comparing two songs and the two amps. On one song, the PS Audio (150 W) seemed a little clearer. And on the second song, the Adcom (200 W) seemed a little clearer. I called it a draw because I couldn’t tell if I really heard a difference or it was the placebo effect. You know how the old sighted testing things goes.

[SteveCallas]

I’ve already got the sub amp knob up at 100%. And the pre-pro sub channel output at the max. Adding a clean box would allow me to either lower the amp gain or lower the channel level- or a little bit of both. But they’re both maxxed out already. So how would a clean box help? I guess not at all, if you don’t think there’s any distortion coming into play.

You've got both maxed out because you aren't really able to calibrate to anything without an spl meter. They may not even be calibrated against each other, but it seems you've found a balance you like. Knowing that your speakers have a relatively low sensitivity, and knowing that the K1 has a relatively low sensitivity, if there were distortion to be experienced by maxing out channel levels, your situation would likely be a prime candidate, as the low sensitivities are working against you. Based on Ilkka's results, we'll have a better idea. Once you get those speakers done, I can stop by and we will get everything measured and calibrated.

On one song, the PS Audio (150 W) seemed a little clearer. And on the second song, the Adcom (200 W) seemed a little clearer. I called it a draw because I couldn’t tell if I really heard a difference or it was the placebo effect. You know how the old sighted testing things goes.

If anything, I'd hope our earlier tests show that all competent amps will sound the same. I suggest using the Adcom because it is more powerful.

[ThomasW]

You've got both maxed out because you aren't really able to calibrate to anything without an spl meter. They may not even be calibrated against each other, but it seems you've found a balance you like.

And fundamentally that's what it's all it's about

Knowing that your speakers have a relatively low sensitivity, and knowing that the K1 has a relatively low sensitivity, if there were distortion to be experienced by maxing out channel levels, your situation would likely be a prime candidate, as the low sensitivities are working against you.

The Crown K1 input sensitivity is 1.4V for full output (33dB gain) or a fixed gain of 26dB to match other amps. That's not particularly low.

FYI one member of the Crown K Series development team is sitting right there ->->->.

Based on Ilkka's results, we'll have a better idea. Once you get those speakers done, I can stop by and we will get everything measured and calibrated.

So Ilkka's flying down to measure Jon's processor? That's dedication. If he's measuring another brand, those measurements aren't relevant to the situation.

I'd hope our earlier tests show that all competent amps will sound the same

So you're saying a Krell 300cx, will sound the same as an Ayre MX-R?

[SteveCallas]

So Ilkka's flying down to measure Jon's processor? That's dedication. If he's measuring another brand, those measurements aren't relevant to the situation.

The results won't be 100% directly applicable, but it should give us a pretty good idea if distortion from processor analog pre outs is something that needs to be considered or not. Based on your earlier comments:

So regardless of the cost of the preamp, any of the current crop of production op-amps are just loafing along at line levels. As a result distortion is a fundamentally a non-issue...

it would seem one processor is just as good a "test subject" as another. There's either going to be some relevant amount of distortion or not.

So you're saying a Krell 300cx, will sound the same as an Ayre MX-R?

If they're not developed to purposefully alter the signal in some way, and they're being run within their respective limits, yes.

[ThomasW]

The results won't be 100% directly applicable, but it should give us a pretty good idea if distortion from processor analog pre outs is something that needs to be considered or not. Based on your earlier comments

The only test applicable to this thread is whether or not Jon's processor has enough drive to power a K1 without the addition of a CleanBox.

If they're not developed to purposefully alter the signal in some way, and they're being run within their respective limits, yes.

I suggest you not "bet the farm" with that assumption.

[JonW]

Hey fellas,

I don't have anything more to ask at this point. Being as it seems to be a tad unresolved. But I appreciate all the input and discussion. Thanks. :T

-Jon

[Ilkka]

Okay, here are the results. AVR used was NAD T743. Signal used was 50 Hz 0 dBFS sine wave played through a normal DVD player. NAD's sub out can be adjusted from -12 dB to +12 dB. Master volume was set to 0 dB (around reference level with normal speakers) (max is +6 dB). Absolute THD values can be a little bit lower (meaning 0.1% is actually 0.01% etc.), since there was some induced noice present. As you can see, the output started to clip above +7 dB or ~5.5 V.

[ThomasW]

If you're getting 0.1% distortion at -12dB there is a problem. Either the receiver is defective or the noise floor of the measuring systems is quite high.

BTW are these voltage measurements 'peak' or RMS?

[JonW]

Holy cannoli. Isn’t 7% distortion really high when your output level is at about 85% of the max possible?

[Ilkka]

If you're getting 0.1% distortion at -12dB there is a problem. Either the receiver is defective or the noise floor of the measuring systems is quite high.

The receiver is not defective, though NAD's are famous of their humms and hisses. My system isn't built to measure electronics but speakers/subwoofers instead, so you can't expect 0.001% THD levels. Unshielded cables already pickup all sorts of noises.

BTW are these voltage measurements 'peak' or RMS?

RMS

[Ilkka]

Holy cannoli. Isn’t 7% distortion really high when your output level is at about 85% of the max possible?

Do notice that the signal used was 0 dBFS. You won't usually find that kind of levels from an audio CD or DVD.

[ThomasW]

Do notice that the signal used was 0 dBFS. You won't usually find that kind of levels from an audio CD or DVD.

Yes. Saw that immediately.

So others understand, with Ilkka's 0dBFS setting, the sub out clips at a point where there's 4 times more output power available than is needed to drive a K1 at full rated output..

At this point both Jon and I'll bail from this part of the discussion. He tends get a little 'testy' addressing 'straw-man' scenarios. My goal is to keep him in a good mood, since he's actually here designing the on-wall crossovers for the 'Missions Accomplished!' projects.... :T

[SteveCallas]

Well, at the very least, I'd say there is definitely a relationship between higher channel levels and increased distortion levels. Thanks for the testing Ilkka.

Jon, what master volume level do you typically listen at? When you get all five speakers going, with movies, you'll probably want to set the master volume a little louder than you would with 2 channel music listening.

[Ilkka]

Well, at the very least, I'd say there is definitely a relationship between higher channel levels and increased distortion levels. Thanks for the testing Ilkka.

I'd say it's just the opposite. My AVR is capable of outputting over 5 V before clipping. When do you see such levels being asked during normal program material and which amp needs such levels (normal input sensitivity is in 1-2 V range)? I'd say it's pretty safe to adjust one's sub out as high as possible (or at least up to 0 dB level). You won't see any additional THD.

[dynamowhum]

Thomas what ever you do keep Jon happy! I really want/need those non ported designs.

[chasw98]

My goal is to keep him in a good mood, since he's actually here designing the on-wall crossovers for the 'Missions Accomplished!' projects.... :T

Surprised you have been here this long. I remember reading somewhere that you had a very fine, smooth bottle of Mexican Tequila waiting for an occassion. Go keep him happy! :T ;x(

[ThomasW]

He's chained to a very heavy butcher block table...:wink:

[JonW]

Jon, what master volume level do you typically listen at?

The typical range is about -45 to about -5. -45 when it’s background music for reading and -5 when I’ve come home from a long, frustrating day of work. More typical for when I’m just listenting to music is about -30 to -15. I forget how high the prepro can go, something like +10 for volume (but -12 to 0 is the range for channel levels). I do notice that when watching movies in 2.1 I have the volume generally higher, maybe around -18 or so.

He's chained to a very heavy butcher block table...:wink:

So he can watch you post and harangue us. I see. Sounds like quite the vacation for both of you. :P Now go away and do something fun like work on speakers.

[JonW]

Well, at the very least, I'd say there is definitely a relationship between higher channel levels and increased distortion levels.

I'd say it's just the opposite.

OK, I remain confused about this matter. And I’m sticking to that. :P

[Inu_Yasha]

Wow, this discussion has really taken a turn... I'm not too sure what to believe; this topic almost reminds me of the topic of speaker cables making a difference. Some say it does (myself included to an extent) and others say it doesn't... It's all relative I guess.

IMHO, in your case JonW, if spending $30-50 won't hurt you too bad, I would just go ahead and get a cleanbox and see if it helps. At least you'll have some extra headroom if you ever want/need it.

[SteveCallas]

OK, I remain confused about this matter

There is a relationship between higher channel levels and more distortion, but unless you have your sub channel level at max and listen at reference levels, the distortion probably won't exceed 0.1%. So you should be fine.

[Ilkka]

Everything depends how much voltage your sub out jack can output before clipping. If it's below your pro amp's input sensitivity, you will definitely need a clean box or similar pre amp.

THD is a completely different matter. We would need to test many different AVRs in order to say anything definite. There can be some cheap units which can output some excessive THD if subwoofer level is maxed out (especially if the range goes above 0 dB).

[soho54]

Nice to see that Ilkka's numbers match my experience. :T

[JonW]

Wow, this discussion has really taken a turn...

Yup. But I appreciate everyone's help.

Maybe I'll calibrate the system once my Modula MT's are done. And see where things stand at that point. Certainly I'm happy to spend the $50 if it would help at all.

[Inu_Yasha]

Like I sad Jon, check ebay, I got mine for $33 shipped to me. For me, it made a world of difference; I didn't believe what the others down at AVS told me about it making a difference at first, but once I got the cleanbox and tested it, it really lived up to what others told me. Even dynamowhum agrees