Yet another happy art clean box user

[dynamowhum]

I have the panny xr57 reciever and using a behringer EP1500 for the bass deparment. Wasn't getting the power I needed and Thomas and Inu recommended the clean box to me. Well I just got it hooked up and folks I got to tell you it has made a huge difference. I have the clean box at the 12:00 position and I backed off on the EP from 32 to 18. Right now I'm listening to Neil Youngs Heart of Gold DVD and it is very nice indeed. Thanks guys.

[Landroval]

What's a clean box?

[ThomasW]

A line level shifter...used to match consumer output voltage to pro-sound input levels

[Inu_Yasha]

Glad to hear it worked for you dynamowhum. Are you running your sub off of one channel or bridging it? Also, what type of sub do you have again?

[dynamowhum]

Bridging the amp and I have 2 15" atlas subs from ascendant audio. I am beginning to think about a bigger IB though. It helps when you have a designated man cave.

[JonW]

Hey Fellas,

I was wondering at what point is it worth using one of these boxes?

My Crown K1 amp is running my sub. I've got the amp cranked up to 100%. And from the preamp-processor, I've got the sub level at 0 and the left and rights at -1. (Haven't done any room measurements yet- waiting to complete my 3 Modula MT's.) It seems I've got enough bass. And using a box like this (or the Rolls equivalent) would just allow me to turn the amp knob down some. Is there any audible benefit to that? Thanks.

[ThomasW]

I've got the sub level at 0

Whats the range? Is "0" the highest value or does the level go to +10 or something?

If it goes to +10 and you're on '0' it's fine. If '0' is full out then yes, you may benefit from using one of the devices.

[JonW]

Whats the range? Is "0" the highest value or does the level go to +10 or something?

If it goes to +10 and you're on '0' it's fine. If '0' is full out then yes, you may benefit from using one of the devices.

Right, the settings on the prepro max out at 0. With the sub at 0 and the left and right at -1, it seems I’ve got plenty of bass already. Presumably adding the box and having the ability to turn the amp knob down helps something?

So what benefit come from adding in the clean box?

[Inu_Yasha]

Right, the settings on the prepro max out at 0. With the sub at 0 and the left and right at -1, it seems I’ve got plenty of bass already. Presumably adding the box and having the ability to turn the amp knob down helps something?

So what benefit come from adding in the clean box?

What you're doing is the same exact thing I was doing prior to me getting the cleanbox. As Thomas told me in another thread, I was just creating distortion in the driver. When I got the cleanbox, I immediately noticed a difference in sound once I got everything calibrated. I'm running a RL-p15 on a EP2500 with my settings at 30db (3 o'clock) and almost full on the cleanbox; my prepro is at 0 (on +/-12db scale). Now the bass sounds a lot less strained and there's more clarity when I turn up the volume. I would definately recommend getting a cleanbox for your situation!

[JonW]

Thanks. Creating distortion, eh? Is that because the amp is trying to work maxxed out? But it’s not putting out much power. Hmmm… At any rate, it’s a cheap thing to try. Googling around looks like they’re just over $50. So I’ll pick one up and see what happens. Thanks.

[oxcartdriver]

JonW,you have adjustable gain control via a switch on the back of the Crown K1. What setting do you have the switch set to? There is a 31.55dB and 26dB gain switch.

I have a crown K2 set to the 32.88dB gain level running one RL-p15. I'm still awaiting necessary equipment to EQ the sub, but I'm curious about your setup and implications to my work in progress.

[soho54]

Creating distortion, eh? Is that because the amp is trying to work maxxed out?

No, the pre-amp(AVR) is creating the distortion trying to output a full level signal. If the pre-amp hiccups, it just sends it right on to the amp, which just amplifies the hiccup. You want everything in the signal chain the clip at about the same time.

Some pre-amps cannot output a signal with enough voltage to drive pro amps properly. The amp isn't harmed, but you kill the pre-amp which is trying to boost the signal to compensate. This causes the pre-amp to clip way before normal, and can make things sound... umm bad.

I run an EP1500 on my mains and sub, with no converters. The mains are 0db and the sub is -6db on a +/- 10db scale in the AVR. I have seen 113db peaks in moves on my RS meter uncorrected at my seat without clip lights flashing, so it is a gear specific problem. (single 12" sub, this will be remedied soon. :twisted: )

I do plan on trying a CleanBox out in the next month or two, when switching to some new gear. I'll post something if I notice a difference with the old stuff when I add the ACB. :T I'm expecting a possible extra kick in the seat from the low end.

[Inu_Yasha]

Honestly, look on ebay. I got mine shipped to my door for $33. I haven't had time to eq my sub as of yet bc of exams and the equipment not comming in as of yet. I can imagine that there are really high peaks in movies such as War of the Worlds! Trust me, get the clean box if you think you're running your prepro hot in order to compensate. You'll definately hear the difference!

[JonW]

JonW,you have adjustable gain control via a switch on the back of the Crown K1. What setting do you have the switch set to? There is a 31.55dB and 26dB gain switch.

I have a crown K2 set to the 32.88dB gain level running one RL-p15. I'm still awaiting necessary equipment to EQ the sub, but I'm curious about your setup and implications to my work in progress.

I'll check which setting I have it on, when I get home tonight. And I'll post here tomorrow with what I find.

[JonW]

No, the pre-amp(AVR) is creating the distortion trying to output a full level signal. If the pre-amp hiccups, it just sends it right on to the amp, which just amplifies the hiccup. You want everything in the signal chain the clip at about the same time.

I see. Perfect explanation- thanks.
So then it sounds like when I get a clean box, I should turn down the sub out level on the preamp. How do I know what the best combination of levels is for the preamp out, the clean box knob, and the sub amp knob?

Honestly, look on ebay. I got mine shipped to my door for $33. I haven't had time to eq my sub as of yet bc of exams and the equipment not comming in as of yet. I can imagine that there are really high peaks in movies such as War of the Worlds! Trust me, get the clean box if you think you're running your prepro hot in order to compensate. You'll definately hear the difference!

Excellent. I'll get one. And heck, this is a much cheaper way to improve sound relative to anything else that ever gets mentioned around here.

[dynamowhum]

Yes it is a good bang for the buck deal. Me likey.

[JonW]

JonW,you have adjustable gain control via a switch on the back of the Crown K1. What setting do you have the switch set to? There is a 31.55dB and 26dB gain switch.

I have a crown K2 set to the 32.88dB gain level running one RL-p15. I'm still awaiting necessary equipment to EQ the sub, but I'm curious about your setup and implications to my work in progress.

I had a look last night. To be honest, I forgot all about the switch. The two swtich options are labelled 1.4 V and 26 db. According to the manual, it's 31.55 db gain at 1.4 V sensitivity and 26 db gain at 2.65 V. I've got mine in the 1.4 V position. Sounds like you're doing the same.

[JonW]

No, the pre-amp(AVR) is creating the distortion trying to output a full level signal. If the pre-amp hiccups, it just sends it right on to the amp, which just amplifies the hiccup.

So now I'm wondering what the optimal settings should be.

I had a look at my preamp-processor (Audio Refinement Pre2-DSP). The range of levels for any channel are -12 up to 0. Right now, I have left and right at -1 and the sub at 0. It sounds like it would be better for me to lower things down from 0, to prevent distortion.

With a range of -12 <-> 0, would it be better to have each channel about -6, right in the middle?

If -6 is optimal, I could move the left and right to -6 and have the sub at -5. Then I'm all OK, with no need for the clean box. Or am I missing something?

[SteveCallas]

Assuming the amp being used is a quality amp, and the Crown K1 is, I'd set the processor output level as low as you can get away with. It comes down to whether the analog pre out stage of the processor will add distortion before the amplifier - my trust will go to the amplifier in just about every case. On a scale of -12 to 0, I'd aim for around -10 if possible. Adjust the amp gain to calibrate from there.

If -6 is optimal, I could move the left and right to -6 and have the sub at -5. Then I'm all OK, with no need for the clean box. Or am I missing something?

Ehh - the goal is to be calibrated to reference level if possible. This means that at a master volume of 0, depending on your test tones, your mains and sub should be putting out 75db or 85db. Calibrating everything to itself is definitely better than no calibration at all, but calibrating to reference will put you on common ground with everybody else.

Also, if you just lower the channel levels to -5 and -6 from 0 and -1, you'r enot really gaining anything, as you'll have to turn the master volume louder to get to where you were before with the same material.

[soho54]

JonW, this could take awhile. :B

It sounds like it would be better for me to lower things down from 0, to prevent distortion.

Most of the time, yes.

With a range of -12 <-> 0, would it be better to have each channel about -6, right in the middle?

Around there or lower if the amp allows. It depends on where the pre amp clips.

If -6 is optimal, I could move the left and right to -6 and have the sub at -5. Then I'm all OK, with no need for the clean box. Or am I missing something?

That is fine as long as you are still getting the max SPL you need from the speakers. When you lower the levels in the pre pro you are lowering the max volume you can achieve, without amplifying the signal even more with the amp. Since you are at the highest setting with the attenuation knob on the amp you cannot add any more juice.

I can't really give you hard numbers because I don't own the same gear. ( I hooked my laptop up to my AVR and played a test signal of 17hz, 22hz, and 100hz burst sine waves at 1/4 volume on the laptop. I turned the amp's knob all the way down, and the AVR all the way up until there was audible distortion was present. The good fuzzy kind. I then lowered the levels in the AVR until it sounded normal again. I keep doing this until I could reach a volume of +10db with no ill affects. I then took 2 db off for good measure and ended up around -3db on a +/- 10db scale.) I don’t recommend you do this, just trying to show that it is best to start in the middle and adjust from there.

Now this is the point where you have to decide if you want to calibrate the DVD input to the 85db standard, or not. This is a completely personal choice. Also notice I said DVD input, only the one input will be calibrated all the others will be different. I have no experience with your pre pro, so the next question is if it uses the THX (low)-db to (high) 0db volume indication scheme.

If you are not calibrating to a known level read part 1 and just pick a volume of around 75% of max.

1-Pop in Avia, turn it up to 0db, and adjust the pro amp, and the levels on the other speakers until you get 85db from them all with the tones at your seat. If you can’t get 85db at your seat something is very wrong. 2-Now turn on some pink noise and turn up the volume to make sure you can still get 105db from each individual speaker and 115db from the sub on the old Rat Shack meter. This is assuming your stuff can do these levels, if unsure use 100db and 110db instead. If you can't hit these numbers and the pro amp knob is at max (and you could before), you need the converter. 3-Once that is done throw in an action movie and play it at the loudest volumes you will listen at. If it all sounds good, and the amps are not clipping themselves to death you are done. If it still sounds off and a little bass anemic, try the converter.

Hope this helps. :T

[ThomasW]

Someone sitting next to me was ask about the relative distortion levels differences be low and high output settings on a standard sub out. And they stated, there's no difference in distortion regardless of the output setting.

I'll leave it to everyone's imagination as to who provided this info, and their qualifications to answer the question....:wink:

[Dennis H]

Someone sitting next to me was ask about the relative distortion levels differences be low and high output settings on a standard sub out. And they stated, there's no difference in distortion regardless of the output setting.

I'll leave it to everyone's imagination as to who provided this info, and their qualifications to answer the question....:wink:

Gee, I wonder who that was? But, Engineer Jon may not be familiar with all the cheap electronics out there and I can believe that some of them can drive the preamp into either analog or digital clipping. So we should accept real-world user experience as valid data. So there.

[chasw98]

Nice discussion, but so far no one has said anything about the peak capability of a preamp. If your test is going through with pink noise at 0 db to provide an output of, say, 2 volts to the power amplifier, and the amp is driven nicely with some headroom (say 10 db) at 2 volts, what happens when "dynamic" music comes through your system? For instance a piece of music is playing along at -20 db and a peak of cannon blasts (Telarc 1812 Overture) comes through at +10 db (a 30 db peak). You know your preamp will handle 0 db just fine, will it handle +10 without distorting? Now this is all relative and it depends upon the circuitry in your preamp as to how much headroom it has. But if you are running the relative levels of your preamp at a lower setting and still able to push your power amp to full output, then you have some added headroom. The clean box will allow you to run your preamp a bit cooler (lower level) and with the clean box added gain push your power amps to full output. Next week the discussion will center around signal to noise ratio and what happens when you run your amps and preamps at too low a level where noise can be a problem. My thoughts tonight.

Chuck

EDIT - In the studio and live sound world, the ideal situation is to have maximum gain with best S/N at all points in the chain from mic preamps to power amps and all equipment in between. This also applies to a home system these days where you look at the output of a source going to an input that amplifies and then goes to another input that amplifies, etc., etc.

[ThomasW]

Dennis,

Word from the side of the table says that op-amps typically clip at 8 volt drive levels. Output is quite linear up to the point just before clipping. 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...:wink:

[soho54]

Output is quite linear up to the point just before clipping.

This seems to follow what I am saying. There is no problems at one volume point and then wam, purple haze fuzz the next. :B Lower the channel levels and you get a few more volume points until electric lady land kicks in.

It sounds just like the faint noise the older cheap AVRs make while playing a DTS track. JVC sucks.

Maybe I should have made that more clear, and that I started at +10db.

[ThomasW]

This seems to follow what I am saying

Pre-amp line level voltages max out at approx 2 volts. So the op-amps are just loafing along at the max drive level of the pre-amp.

[SteveCallas]

Measuring the distortion of the analog subwoofer preout at various increasing voltages - sounds like a test Ilkka could knock out in a few minutes. Unless someone else here can give it a go, I'll see if he would be interested.

[soho54]

That is all well and good, but that just means the op-amp isn't causing the problem. I have no idea why it is there, only that in my case it was.

Are you trying to tell everyone to crank the levels to +10 now?
I'm confused here. Setting the equipment for max clean headroom per device is the norm isn't it? I know in live sound it is. (In my live sound applications anyway.) Why the resistance?

[ThomasW]

Measuring the distortion of the analog subwoofer preout at various increasing voltages - sounds like a test Ilkka could knock out in a few minutes. Unless someone else here can give it a go, I'll see if he would be interested.

It's possible that testing by Ilkka would be interesting. However, he fellow at the side of table has $250,000 worth of test gear in his lab. So perhaps we can trust his information that in this particular situation, the output level is irreverent to distortion, and let it go at that.....

Are you trying to tell everyone to crank the levels to +10 now?...I'm confused here.

The point is, getting all fixated on have any specific output level as 'ideal' isn't necessary.

[SteveCallas]

It's possible that testing by Ilkka would be interesting. However, he fellow at the side of table has $250,000 worth of test gear in his lab. So perhaps we can trust his information that in this particular situation, the output level is irreverent to distortion, and let it go at that.....

I don't doubt what he says, I'm sure he's very well studied on the subject, I'd just like to see some numbers and correlations. Irrelevant means different things to different people :B

[Dennis H]

Digital clipping on the LFE channel is quite possible depending on how the receiver designer implements things. DD spec calls for the LFE channel to be recorded 10dB low and boosted 10dB in the receiver. If that boost and/or the channel trims are done in the digital domain I can see some clipping happening. Of course, if all receivers were done the "right way", Jon wouldn't have to build his own DACs and amps.

If we're going to measure the distortion, it would need to be on the unit in question. I don't think there's any generic answer for all designs.

[SteveCallas]

If we're going to measure the distortion, it would need to be on the unit in question. I don't think there's any generic answer for all designs.

Valid point, but consider this:

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...

If they are pretty linear up to 8 volts, then as was said, just about any processor would give us a good general idea.

[JonW]

Thanks for all the discussion and explanations. Jacob, that all makes sense.

On one hand, I can see how distortion might creep in if levels are set too high. And, indeed, some people report clearer bass with the Clean Box. On the other hand, I can see where we are all working in the linear output range shy of distortion. So there would be no benefit from a Clean Box.

Everything all makes sense, but seem somewhat contradictory.


Thomas-
Send greetings to he-who-designs-speakers-cloaked-by-the-darkness-of-night.
:later:

[ThomasW]

Valid point, but consider this:


If they are pretty linear up to 8 volts, then as was said, just about any processor would give us a good general idea.

Whatever floats your boat.

The typical distortion at anything under 8 volts is ~.001% for cheap 'generic' op-amps. For premium op-amps it's ~.0001%. And the distortion is primarily just 'noise'.

So, whatever output level one chooses for the sub out setting, distortion just isn't an issue

[soho54]

On one hand, I can see how distortion might creep in if levels are set too high. And, indeed, some people report clearer bass with the Clean Box. On the other hand, I can see where we are all working in the linear output range shy of distortion. So there would be no benefit from a Clean Box.

There is more to it than cleaner bass. Check this link out for more on the Home/Pro levels. +4/-10 Skip down to the "What does this discrepancy really mean to my levels?" part at the bottom.

[SteveCallas]

The typical distortion at anything under 8 volts is ~.001% for cheap 'generic' op-amps. For premium op-amps it's ~.0001%. And the distortion is primarily just 'noise'.

Thomas, this is referring to consumer gear and not pro gear, yes?

[ThomasW]

Regarding op-amps, if no one tells them, they don't know where they're being used....:wink:

Just so no one's confused, op-amps are a bit different than the output devices used in power amps

[SteveCallas]

Regarding op-amps, if no one tells them, they don't know where they're being used....

Lol, I gotcha. I thought perhaps there were different grades used.

[JonW]

There is more to it than cleaner bass. Check this link out for more on the Home/Pro levels. +4/-10 Skip down to the "What does this discrepancy really mean to my levels?" part at the bottom.

Jacob- Thanks for the link. Interesting. So this says that the distortion issue is probably real. And that a gain box would help (for the sub). Which contradicts what Thomas (and an unnamed expert) are saying. Maybe I should just buy one and try it out?

And it also brings me back to wondering if I should lower the prepro output level of my regular speakers which are powered by a regular amp without a knob. Sure, I'll get less volume, but maybe less distortion from the prepro. I can just crank up the volume to compensate. Hmmm... I'll have to calibrate the whole system once I get the 3 extra speakers completed. Then maybe fool around some and see what I find.

[chasw98]

Jacob- Thanks for the link. Interesting. So this says that the distortion issue is probably real. And that a gain box would help (for the sub). Which contradicts what Thomas (and an unnamed expert) are saying. Maybe I should just buy one and try it out?

And it also brings me back to wondering if I should lower the prepro output level of my regular speakers which are powered by a regular amp without a knob. Sure, I'll get less volume, but maybe less distortion from the prepro. I can just crank up the volume to compensate. Hmmm... I'll have to calibrate the whole system once I get the 3 extra speakers completed. Then maybe fool around some and see what I find.

Jon:
I have to thoroughly disagree. If you do a search on that article for the word "distortion" it is only mentioned once. And when it is mentioned it is in reference to driving a 600 ohm load. To keep it simple, "consumer" -10 gear driving a 600 ohm load is similar to you trying to drive a .1 ohm load with your home amplifier that is meant for a 4 or 8 ohm load. As the article says there are not many pieces of 600 ohm balanced gear that you will find these days. Almost all current pieces of equipment have such a high impedance that just about anything can drive anything else, balanced or unbalanced, -10 or +4. What you are trying to do is fit the window of gain + noise from the sending piece of gear to the gain + noise receiving piece of gear. For example, if your home preamp can only deliver between .1 and 1 volt output and the receiving piece of gear (your "pro" amplifier) wants to see between .5 and 2 volts of signal, then you are limiting yourself to a .5 volt "window" so to speak in driving the amp. Obviously if you can boost the signal from the sending piece of gear into the optimum range for the receiving piece of gear, you will end up with better signal range and lower signal/noise. When you do not match levels you could end up driving the preamp (sending piece of gear) into distortion as you try to make the amplifier (receiving piece of gear) play louder or loud enough. Calibrated levels between pieces of equipment that are from different genres (pro vs. home) will help optimise level matching and S/N ratios therby providing optimum dynamic range with low noise. Most pieces of equipment these days have such a wide band of gain and such low noise floors that you do not need to worry about it, though. What Thomas and the "unnamed" engineer are saying is that distortion is not really a factor unless you are running at ridiculous levels such as +15 volts out and the power amp is turned up to 1 on the scale of 10. That is a mismatch and you will hear the distortion.

[soho54]

JonW, what chasw98 said. :B

One other thing is my post is tailored to your pre pro to pro gear situation. Also the distortion I am talking about is not something that gets gradually worse as you turn things up. It is in effect a ceiling, which once you hit bad things occur. It sounds like a DSP hard clipping in digital effects processors.

My point was that if you used conservative levels setting and could not get that output you needed you need with the pro gear, you need the Clean Box. Yes you could crank the levels up but when you do that you risk lowering the ceiling to a point you might come across.

If you have a non-adjustable amp on the mains you need to adjust the levels to calibrate them to 85db first. Then do the sub.

Hope this clears things up.

[JonW]

Well, despite your best efforts, you guys are being quite helpful.

Almost all current pieces of equipment have such a high impedance that just about anything can drive anything else, balanced or unbalanced, -10 or +4.

Right. The way things are set up now (no clean box) actually seems to work fine, near as I can tell.

What you are trying to do is fit the window of gain + noise from the sending piece of gear to the gain + noise receiving piece of gear. For example, if your home preamp can only deliver between .1 and 1 volt output and the receiving piece of gear (your "pro" amplifier) wants to see between .5 and 2 volts of signale, then you are limiting yourself to a .5 volt "window" so to speak in driving the amp.

Makes perfect sense.

Obviously if you can boost the signal from the sending piece of gear into the optimum range for the receiving piece of gear, you will end up with better signal range and lower signal/noise.

Right. So where is that optimum? But maybe it sounds like finding that optimum range is something I need not worry about:

Most pieces of equipment these days have such a wide band of gain and such low noise floors that you do not need to worry about it, though.

So keep everything as is (no clean box, sub level maxed at 0, left and right almost maxed at -1) and that’s all?

Also the distortion I am talking about is not something that gets gradually worse as you turn things up. It is in effect a ceiling, which once you hit bad things occur.

Interesting. I didn’t realize that.

My point was that if you used conservative levels setting and could not get that output you needed you need with the pro gear, you need the Clean Box. Yes you could crank the levels up but when you do that you risk lowering the ceiling to a point you might come across.

Idunno. The sub sounds fine to me now. But maybe it is distoring a little and would benefit from lowering the levels? I don’t know.

If you have a non-adjustable amp on the mains you need to adjust the levels to calibrate them to 85db first. Then do the sub.

But you’d adjust to 85 db with the volume, correct? And that doesn’t help the output levels? So I’m back to being confused about the optimal preamp output levels.

[soho54]

Idunno. The sub sounds fine to me now. But maybe it is distoring a little and would benefit from lowering the levels? I don’t know.

If it sounds fine leave it alone. :B

But you’d adjust to 85 db with the volume, correct? And that doesn’t help the output levels? So I’m back to being confused about the optimal preamp output levels.

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.

[soho54]

I edited my post #20 some, try reading it again. It hopefully makes more sense this time. Here is a post by Ed Mullen that might help. Levels

[SteveCallas]

And it also brings me back to wondering if I should lower the prepro output level of my regular speakers which are powered by a regular amp without a knob. Sure, I'll get less volume, but maybe less distortion from the prepro. I can just crank up the volume to compensate

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. 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.

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