Jump to content


Crown XTi input & output gains


  • Please log in to reply
31 replies to this topic

#1 Shep

Shep

    Power User

  • Members
  • PipPipPipPipPip
  • 28 posts

Posted 10 February 2012 - 09:03 AM

A couple of questions for those in the know...

I'm using my XTi 1000 for live bass & synth. as I cycle through different effects etc the input gain via my preamp can alter quite a bit, rather than hold constant. using system architect the input gain on the XTi tends to sit between -15db when dynamic/gentle parts are played right up to just under the cliping point. If I dig in real hard I occasionally (very rarely) hit the input clipping. Output gain rarely goes above -20db. Once or twice I have managed to light the -10db point for a split second, but thats it. So my questions...

1. What are the issues in clipping the input stage? On the rare occasions I have, I hear no audible difference and the input clipping seems to not effect the output gain in any way.

2. If I have a limiter activated, does this apply to input, output or both gain levels? How will I know if it kicks in (Does the front panel display anything, will is be audible)?

3. Whilst I have no issues with sound quality of the amp running at a relatively low output gain, are there ways to increase the output gain without increasing volume - after all, a correct gain level is considered to be the best thing overall for tone. As things do jump etc. due to my crazy effects set up I'd still be keen on keeping some headroom, after all clipping a 1400w amp at output (I'm running bridge mono) is never going to be a great thing for speakers.

Just in case it's needed, I have the following DSP in place...

Bridge Mono
High Pass Filter @ 35Hz (Butterworth 48db/Oct slope)
Output EQ = +3db @50Hz (Q=2.5) - This is maintain some low rumble when certain effects are very 'un-bass-y'
Limiter @ -3db

Thanks in advance for any input folks can give.

#2 dakos

dakos

    Admin

  • Members
  • PipPipPipPipPip
  • 759 posts

Posted 10 February 2012 - 05:27 PM

QUOTE(Shep @ Feb 10 2012, 09:03 AM) View Post
A couple of questions for those in the know...

I'm using my XTi 1000 for live bass & synth. as I cycle through different effects etc the input gain via my preamp can alter quite a bit, rather than hold constant. using system architect the input gain on the XTi tends to sit between -15db when dynamic/gentle parts are played right up to just under the clipping point. If I dig in real hard I occasionally (very rarely) hit the input clipping. Output gain rarely goes above -20db. Once or twice I have managed to light the -10db point for a split second, but that's it. So my questions...

1. What are the issues in clipping the input stage? On the rare occasions I have, I hear no audible difference and the input clipping seems to not effect the output gain in any way.
Yes, the speakers don't care who is clipping, the input or the amp, they still see DC and that does the same damage. One difference is that amp clipping can be more powerful then the input clipping. Clipping is clipping, audible or not, you must avoid it, if you can hear it that means you're already clipping hard. -15dB or -20dB is pretty low, why not push it up a few dBs, like 10dB so you never clip the input no matter what?

QUOTE(Shep @ Feb 10 2012, 09:03 AM) View Post
2. If I have a limiter activated, does this apply to input, output or both gain levels? How will I know if it kicks in (Does the front panel display anything, will is be audible)?
I presume you mean the limiter on the XTI, then it cares about the amps output.

QUOTE(Shep @ Feb 10 2012, 09:03 AM) View Post
3. Whilst I have no issues with sound quality of the amp running at a relatively low output gain, are there ways to increase the output gain without increasing volume - after all, a correct gain level is considered to be the best thing overall for tone. As things do jump etc. due to my crazy effects set up I'd still be keen on keeping some headroom, after all clipping a 1400w amp at output (I'm running bridge mono) is never going to be a great thing for speakers.

Just in case it's needed, I have the following DSP in place...

Bridge Mono
High Pass Filter @ 35Hz (Butterworth 48db/Oct slope)
Output EQ = +3db @50Hz (Q=2.5) - This is maintain some low rumble when certain effects are very 'un-bass-y'
Limiter @ -3db

Thanks in advance for any input folks can give.
If you have the limiter @ -3dB, you're basically running a 700W amp and not 1400W.
I didn't understand what is it you want to do gain wise, did you mean an explanation like this video?


#3 Shep

Shep

    Power User

  • Members
  • PipPipPipPipPip
  • 28 posts

Posted 11 February 2012 - 06:41 AM

dakos, thank you very much for your answers.

I apologise in advance if my further questioning shows how little I know in these areas - in fact, while your answer was very helpful, I think it has raised more questions than it answered for me. That said, I think a few clarifications will answer my immediate issues without me digressing too much!

QUOTE(dakos @ Feb 10 2012, 10:27 PM) View Post
Yes, the speakers don't care who is clipping, the input or the amp, they still see DC and that does the same damage. One difference is that amp clipping can be more powerful then the input clipping. Clipping is clipping, audible or not, you must avoid it, if you can hear it that means you're already clipping hard. -15dB or -20dB is pretty low, why not push it up a few dBs, like 10dB so you never clip the input no matter what?

I get ya. Nothing should ever clip. What I find odd is that my preamp is not clipping. My preamp has a peak light at the input and a VU meter on the output. My preamp input light flickers occasionally, pretty much as is suggested in most gain structure rulings but he output VU meter NEVER peaks. It tends to haver around -3db to 0 which i take is a good thing - however the output volume is only at about 35% to keep this at this level. The VU meter on the pre is clearly not as sensitive/accurate as the System Architect input meter for the XTi which sees that as the input running between the -15 and 0 as I mentioned in my 1st post. The little 'clip' marker above the input/output meters in SA - How far over 0 do you have to go for them to clip?

Your last bit, about upping the input by 10db - This really confuses me. Are we talking input of output. Surely adding 10db to -20db, brings me to -10db which is CLOSER to clipping? I'm unsure how this would help OR how I would achieve it without peaking my preamp?

Again, I apologise if the questions sound dumb.

QUOTE(dakos @ Feb 10 2012, 10:27 PM) View Post
I presume you mean the limiter on the XTI, then it cares about the amps output.

Excellent! This I understand! smile.gif

QUOTE(dakos @ Feb 10 2012, 10:27 PM) View Post
If you have the limiter @ -3dB, you're basically running a 700W amp and not 1400W.
I didn't understand what is it you want to do gain wise, did you mean an explanation like this video?

I did not know that regarding the limiter. Clearly I have some technical research to do! As it stands, as I can't get my output gain anywhere near that loud I suspect having the limiter on is achieving nothing but reducing my headroom it seems.
As for the gain, my apologies for not being very clear. Actually that video is very helpful in confirming that what I am doing is correct, however that only seems to help set the input gain of the XTi. I'm not using a desk so don't have the 'fader' to set at unity as in the video, but my 1st port of call is the input gain knob, which I set to the peak light flickering and then roll back slightly. I then set my EQ and then turn up the output volume on the preamp until the VU meter is flickering around 0db and not peaking (which as I mentioned earlier is at about 35% of max).
This corresponds to an input gain on the XTi which dynamically jumps from -15/-10 to 0 depending on the effects/dynamics of whats being played. Where I'm struggling is that corresponds to the output gain staying at -20db, or often, just lighting the 'signal' light and not even the -20db light. I assume this means things are not running massively efficiently. So how do I raise the output gain to an efficient level?

And one last time... Really sorry if I am being very dumb over all of this! smile.gif

Shep



#4 dakos

dakos

    Admin

  • Members
  • PipPipPipPipPip
  • 759 posts

Posted 12 February 2012 - 03:13 AM

Would be great if you write all the gear you have and how you connect and configure everything.

Fear not about stupid questions, we were all stupid once and probably still are smile.gif


#5 Shep

Shep

    Power User

  • Members
  • PipPipPipPipPip
  • 28 posts

Posted 12 February 2012 - 06:22 AM

QUOTE(dakos @ Feb 12 2012, 08:13 AM) View Post
Would be great if you write all the gear you have and how you connect and configure everything.

Fear not about stupid questions, we were all stupid once and probably still are smile.gif


Well... You asked for it...

Roscoe Century 3006 Fretless Bass >
Stageclix wireless receiver >
Input of SFX custom Loops Mixer >

----- Loops Mixer Channel 1 send > (THIS IS MY 'NOISE' CHANNEL)
--- Boss OC-2 Octave (#1, there's 1 in each channel) >
----- Input of Bypass Looper >
--- Zvex Mastotron (Bypass Looper switch 1) >
--- WMD Geiger Counter (Bypass Looper switch 2) >
--- Corvid Effects Myrtle Fuzz (Bypass Looper switch 3) >
--- FullTone Bass Drive (Bypass Looper switch 4) >
--- Moogerfooger MF-107 FreqBox [Moog EP-2 connected to Frequency & MP-201 connected to Mix] (Bypass Looper switch 5) >
--- Tone Factor Analogue Filter 442 (Bypass Looper switch 6) >
--- 3Leaf Audio Groove Regulator (Bypass Looper switch 7) >
--- Boss PN-2 Tremolo/Pan (Bypass Looper switch 8) >
----- Output of Bypass Looper >
--- Eventide Pitchfactor (Connected to Ernie Ball VP JR Pedal) >
--- Moogerfooger MF-102 Ring Modulator (MP-201 connected to Frequency and LFO Out patched to 12-Stage Phaser Sweep In) >
--- Moogerfooger MF-103 12-Stage Phaser >
--- Moogerfooger MF-108M Cluster Flux >
--- Moogerfooger MF-101 Low Pass Filter (MP-201 connected to Cut-Off and Mix) >
----- Loops Mixer Channel 1 return >

----- Loops Mixer Channel 2 send > (THIS IS MY 'SUB' CHANNEL)
--- Boss OC-2 Octave (Marked Ch.2 in photos) >
--- Boss GEB-7 Bass EQ >
--- EBS Unichorus >
----- Loops Mixer Channel 2 return >

SFX Loops Mixer Output >
Boss DD-20 Giga Delay >
TS - TS Jack connection to EBS-1v2 rack preamp >
TS - XLR connection to Ch.1 of XTi 1000 configured as discussed >
Speakon - Speakon connection to Barefaced Big Twin T cab.

All pedal connections are made with George L's solder-less jack to jack connections and all pedal gain levels are set to keep the preamp input from peaking. Worth noting that the input and filter section peak lights on the preamp indicate 10db under clip, rather than that actually clipping.

Hope this helps.

Shep

Make sense? Thought not
_________________

#6 dakos

dakos

    Admin

  • Members
  • PipPipPipPipPip
  • 759 posts

Posted 13 February 2012 - 04:42 AM

Dear Shep,
I hope I understood your problem correctly...
Going over your systems specs took me some time but I think I figured out some of the picture...
Your preamp has a maximum output rating of 4dBm (that's 1.23V) and the amps input sensitivity is 1.4V (that's 5.14dBm or 4dBu). The second thing is that you have the amp gain knobs turned down by -15dB at the amp, that would mean you need allot more at the input side of the amp to reach the amps rated output. Since your preamp can't give more then 4dBm without clipping which is barely enough when the amp gain is open all the way, all the more when it's tuned down.

Bottom line... Push your gain knobs on the amp ALL THE WAY UP and see if you then able to light up that -10dB led on the amp.

#7 Shep

Shep

    Power User

  • Members
  • PipPipPipPipPip
  • 28 posts

Posted 13 February 2012 - 05:31 AM

QUOTE(dakos @ Feb 13 2012, 09:42 AM) View Post
Dear Shep,
I hope I understood your problem correctly...
Going over your systems specs took me some time but I think I figured out some of the picture...
Your preamp has a maximum output rating of 4dBm (that's 1.23V) and the amps input sensitivity is 1.4V (that's 5.14dBm or 4dBu). The second thing is that you have the amp gain knobs turned down by -15dB at the amp, that would mean you need allot more at the input side of the amp to reach the amps rated output. Since your preamp can't give more then 4dBm without clipping which is barely enough when the amp gain is open all the way, all the more when it's tuned down.

Bottom line... Push your gain knobs on the amp ALL THE WAY UP and see if you then able to light up that -10dB led on the amp.


dakos,

Thank you for the answer, and for answering with number rather than an 'in my experience answer'.

Just to confirm... You're suggestion is to turn the XTi up as high as possible, and turn volume down (if needed) with the output of the preamp. I shall try it this way over this weeks studio sessions.

I assume the next suggestion is to get my hands on a 'hotter' pre amp.

My main confusion over the subject is that on System Architect I can easily get the input gain bar all the way up with the preamp set as it is, my thought then was that if the input is as high as it's going to get, then surely the output should be pretty hot... My obvious lack of experience is showing!

Shep

#8 dakos

dakos

    Admin

  • Members
  • PipPipPipPipPip
  • 759 posts

Posted 13 February 2012 - 07:15 AM

Regarding the 'hotter preamp' that depends, after you turn the knobs up, would you need more volume? If you do, then a hotter preamp would be good as most pro grade preamps have +22dBu outputs and are able to push the amp to full power with ample headroom even when the amp volume knobs aren't at full power. Actually, since your pre has 1.23V, and the amp needs 1.4V for full power, that's wouldn't be such a big difference in volume (Sorry about the previous part, I confused two posts, the rest is still valid). So if you need more, the preamp is a good place to start...

I'm not using SA so I don't know what's going on there but the logic of things should be the same.

#9 Shep

Shep

    Power User

  • Members
  • PipPipPipPipPip
  • 28 posts

Posted 13 February 2012 - 07:50 AM

QUOTE(dakos @ Feb 13 2012, 12:15 PM) View Post
Regarding the 'hotter preamp' that depends, after you turn the knobs up, would you need more volume? If you do, then a hotter preamp would be good as most pro grade preamps have +22dBu outputs and are able to push the amp to full power even when the knobs aren't at full power. Actually, since your pre has 1.23V, and the amp needs 1.4V for full power, that's wouldn't be such a big difference in volume, so if you need more, the preamp is where I would start...

I'm not using SA so I don't know what's going on there but the logic of things should be the same.


Volume is fine. I don't need more. I was more concerned about the gain structure and its effect on the overall tone of the output signal after watching millions of videos on gain structure.

My main reason for moving from a traditional 'bass amp' to a pre amp and power amp was to have much more power for the very low frequencies I boost. As I play live drum & bass/dubstep/electronic music my sound has a fair amount of 40-50hz in it, which, wile many bass amps will happily reproduce, boosting them by much uses a massive amount of available power from the amp and I found I was often clipping the output of the amp into distortion. The crown has given me a massive increase in available power with which to boost these frequencies without struggling (though not as much more than I thought given your explanation of the limiter!).

Shep

#10 Deromax

Deromax

    Power User

  • Members
  • PipPipPipPipPip
  • 99 posts

Posted 13 February 2012 - 02:17 PM

The gain structure optimization is mostly to minimise noise in a sound reinforcement system or when recording.  In the case of a musician rig, I think it's of less importance to try to lessens the noise, since the ambiant noise in the venue will be way higher anyway.  What is most needed in my opinion, is clean headroom.  Having the amplifier attenuators at a high position, maybe even maxed out, will cause the pre-amp to run at a slightly lower level, hence with better headroom available if you boost some frequencies and/or decide to play stronger notes!

Pro-sound consoles have great headroom and hot output, but musician preamps often seems to have weaker output, as this subject is a recurant question on various internet forums!

#11 dakos

dakos

    Admin

  • Members
  • PipPipPipPipPip
  • 759 posts

Posted 13 February 2012 - 02:37 PM

Regarding my advice to you then yes, my suggestion is indeed to turn the XTi volume knobs up as high as possible, and turn volume down (if needed) on the preamp. Let us know how it worked out for you.

As for the rest, Deromax wrote it nicely smile.gif


#12 Shep

Shep

    Power User

  • Members
  • PipPipPipPipPip
  • 28 posts

Posted 13 February 2012 - 03:47 PM

Thanks for the reply guys. I'm in the studio Wednesday this week so will follow your advice!

Thanks again

Shep

#13 Shep

Shep

    Power User

  • Members
  • PipPipPipPipPip
  • 28 posts

Posted 15 February 2012 - 11:10 AM

Ok...

Just had a rehearsal. With the power amp attenuator much higher and the Pre amp out put turned down a little to compensate I am now constantly lighting the -20db light an the -10 is lighting more regularly when using effects like envelope followers and sub octave effects. So I'd consider that a success.

However. On a couple of occasions I have had the -10 light lot and a sudden flash of the red thermal light along with a nasty pop from the speaker. It seems to be certain notes with a certain effect, do I assume a resonant frequency that's driving too hard. When running SA, the clip light on the software control panel is lighting, but on the amp front panel just the thermal light flashes, no sign of the clip light... Is this due to the limiter being on and indicative of the limiter kicking in?

Either way, the speaker did not like it!

#14 Deromax

Deromax

    Power User

  • Members
  • PipPipPipPipPip
  • 99 posts

Posted 15 February 2012 - 08:43 PM

You could try to enable a high pass filter at around 30 Hz (per your bass cab specs) and lowering the limiter threshold.  Try it one dB at a time, starting at -1 dB.

What is the current position of the input attenuator?  Do your input signal in SA is below clip?

#15 dakos

dakos

    Admin

  • Members
  • PipPipPipPipPip
  • 759 posts

Posted 16 February 2012 - 01:18 AM

QUOTE(Deromax @ Feb 15 2012, 08:43 PM) View Post
You could try to enable a high pass filter at around 30 Hz (per your bass cab specs) and lowering the limiter threshold.  Try it one dB at a time, starting at -1 dB.

What is the current position of the input attenuator?  Do your input signal in SA is below clip?
He already has a HP filter and the older XTIs only have -3dB, -6dB and -12dB settings...
The sound you hear is the thermal limiter engaging, it was described by many as "shattered glass"...
Take a little load of the amp or adjust the fans to "full speed" setting, see which works better for you.