DCX2496 into Quest 3004

[Drizt]

Hi Guys,

Im just after some clarification on what I intend on doing.

I want to EQ my new subs with the Behringer DCX2496 and feed the Quest 3004 amp to drive the subs.

I hear that the DCX outputs pro levels and that this will need to be accounted for when feeding an amp.

The Quest amp has trims on the front but the manual says to use the gain switch on the back for this. The options are 1.4V, 26dB, 32dB.

I know the 1.4V is a sensitivity setting and the other two are relative gains.

I have asked this question elsewhere and im getting conflicting answers.

If anyone here can give me some help that would be greatly appreciated.

 

[event horizon]

I hear that the DCX outputs pro levels and that this will need to be accounted for when feeding an amp.

That depends entirely on the level you feed the DCX2496 😉 If you feed it well above line level then you can output higher "pro" levels.

I have one here that i haven't used yet, i intend to use the thing to replace the crossover in a pair of Yamaha NS1000Ms & go active using a Parasound HCA1206. Frankly i don't think there could be much arguement on which will have the lesser amount of distortion 😀

Don't forget that each output can be attenuated in the DCX itself, if i was you i'd run the power amp with the attenuators turned up full so there is no attenuation & adjust the gain in the DCX. At standard line level that'd give you a heck of a lot of headroom After all whatever you feed the thing will ultimately be punted out to the sub amp, turn the volume up from your pre amp & the input & thus output of the DCX will increase.

I'd use the 1.4V (26db) setting.

 

[Drizt]

Thanks for the explanation mate, greatly appreciated.

Ill be using a Behringer MX882 to mix signals and set levels (it can change the levels to whatever we need) going into the Behringer DCX.

Does that change your suggestion at all?

 

[event horizon]

Does that change your suggestion at all?

Not really no, just keep the gain in any equipment that feeds the DCX low so you aren't feeding ridiculous levels (like +15db) to the DCX. It's all about the line level you feed the thing that determines the output, as long as nothing is cranked for gain in each stage then you shouldn't have any problems imo 🙂

 

[Drizt]

Not really no, just keep the gain in any equipment that feeds the DCX low so you aren't feeding ridiculous levels (like +15db) to the DCX. It's all about the line level you feed the thing that determines the output, as long as nothing is cranked for gain in each stage then you shouldn't have any problems imo 🙂

Fair enough.

I had been told that the DCX works best with pro levels? Apart from mixing signals I had put the MX882 on the list as it could boost the levels from consumer to pro for the DCX. But in reality is that sounds like it won't be needed?

I had thought the DCX output pro levels even if you fed it consumer levels? Not so ?

 

[Drizt]

I'd use the 1.4V (26db) setting.

Sorry just saw this bit.

The 1.4V sensitivity setting is different to the 26dB fixed gain setting. Are you saying use the 1.4V setting and if that doesn't work well then switch to the 26dB gain setting?

 

[Drizt]

Not really no, just keep the gain in any equipment that feeds the DCX low so you aren't feeding ridiculous levels (like +15db) to the DCX. It's all about the line level you feed the thing that determines the output, as long as nothing is cranked for gain in each stage then you shouldn't have any problems imo 🙂

Ok, just going to run something by you to see if I have a good handle on it.

Scenario 1 (NO EQ):
If we gave normal pro levels (+4dBu) to the DCX and applied NO eq, then the DCX would output pro levels (+4dBu) which would mean selecting the 1.4V sensitivity gain setting on the Quest 3004. This would mean that +4dBu would be the highest output coming from the DCX (representing 100% signal). Is that right?

Scenario 2 (With EQ):
Lets say I use 6dB gain at 20Hz to extend the bass output of my sealed Maelstrom-X subs. With the same pro levels in, would the DCX now output +10dBu (+4dBu + 6dB gain) as its maximum output for a 100% signal strength for a 20Hz tone ? So if the Quest was set to 1.4v and it recieved a +10dBu signal it would cause clipping ?


I have been told that the actual voltage output at "0dB" varies depending on the standard. I believe 0.775V is the Consumer standard and 1.2V or higher is the Professional standard. Now I will just have to read up on what that all means. Hopefully I can make some sense of it and post back for anyone who is interested.

EDIT: Found this PDF which explains it better than me trying to summarise it -> http://www.proaudiosystems.co.uk/do...ures relevant to loudspeaker controllers..pdf

 

[AndrewT]

if your DCX is passing a signal that reaches 0dBfs then it is on the point of clipping before the signal gets out of the DCX.
The red LEDs are there to help you avoid that.

If you add +6dB to part of the frequency range and that signal is more than -6dBfs then that signal will clip. The red LEDs will light up.

If you add +6dB to part of the frequency range and that signal is below -6dBfs then it may not clip. The red LEDs will tell you.

The solution if clipping is occurring is to turn down the DCX adjusters to avoid clipping the signal inside the DCX.

0dBfs is +22dBu ~=9.75Vac=13.8Vpk

Do not use the adjusters as volume controls. Keep the signals passing through the DCX as high as possible and just below red LED clipping on all channels.

Add passive volume control AFTER the DCX.

 

[Drizt]

Thanks for the help.

I had to look up what 0dBfs was. Its the highest possible value for a system. So in the DCX's case that is +22dBu.

0dBu on the other hand is relative to reference voltage (consumer is 0.775V).
And pro levels are at +4dBu (or ~1.22V if I read it right).

So many terms and concepts to get a handle of. Can get a pretty complicated for a laymen like myself.

Thanks for everyone for taking the time thus far. Im sure ill need more help along the way though, sorry guys.

if your DCX is passing a signal that reaches 0dBfs then it is on the point of clipping before the signal gets out of the DCX.
The red LEDs are there to help you avoid that.

If you add +6dB to part of the frequency range and that signal is more than -6dBfs then that signal will clip. The red LEDs will light up.

If you add +6dB to part of the frequency range and that signal is below -6dBfs then it may not clip. The red LEDs will tell you.

The solution if clipping is occurring is to turn down the DCX adjusters to avoid clipping the signal inside the DCX.

0dBfs is +22dBu ~=9.75Vac=13.8Vpk

Do not use the adjusters as volume controls. Keep the signals passing through the DCX as high as possible and just below red LED clipping on all channels.

Add passive volume control AFTER the DCX.

 

[AndrewT]

if you input a digital signal of a modern highly compressed CD into the DCX much of the signal will be at +21.9dBu for much of the time.
If all the EQ is flat and all the filters are flat then the output of a "modern CD" will be +21.9dBu.

If you add any high Q filtering or +EQ then the internal signal will be above +22dBu. The avoid this you must reduce the DCX gain until the maximum signal in every channel is <+22dBu. This will give you regular peak signals that are 13.8Vpk.
This will overload most domestic equipment.
You must add passive volume control AFTER the DCX.

If you input an analogue signal extracted from a "modern CD" then you must try to maintain maximum unclipped signals through the DCX.
If you reduce the analogue input using the DCX -15dB gain control you will ruin the signal to noise ratio at the output.
You will also ruin the signal to distortion ratio at the output.

 

[Drizt]

if you input a digital signal of a modern highly compressed CD into the DCX much of the signal will be at +21.9dBu for much of the time.
If all the EQ is flat and all the filters are flat then the output of a "modern CD" will be +21.9dBu.

If you add any high Q filtering or +EQ then the internal signal will be above +22dBu. The avoid this you must reduce the DCX gain until the maximum signal in every channel is <+22dBu. This will give you regular peak signals that are 13.8Vpk.
This will overload most domestic equipment.
You must add passive volume control AFTER the DCX.

If you input an analogue signal extracted from a "modern CD" then you must try to maintain maximum unclipped signals through the DCX.
If you reduce the analogue input using the DCX -15dB gain control you will ruin the signal to noise ratio at the output.
You will also ruin the signal to distortion ratio at the output.

Thank you again. All very helpful information. Ill be using analogue inputs, and using the MX882 to up the levels to what the DCX desires.

If I wasn't planning on 'Summing' some inputs on the MX882 then I could have just used the MX882 to both up the levels on the way in to the DCX and then down the levels on the way out of the DCX. But by 'Summing' in the MX882, if I did try to use it both pre and post DCX then I would create a feedback loop.

Hmmm, perhaps I should find a really cheap device that can do Summing..... Or just buy two MX882's, but that would seem a waste.

 

[Drizt]

Actually, perhaps I can just use the one MX882.

Each input can be set to split or mix mode. I thought the whole unit was either in split more or mix mode, but seems it can be done on an individual channel basis.

So I could do...

Main inputs, are the LPF (40Hz and below) output from my active main speakers.
Input 1 could be the LFE channel which gets mixed into both the L & R main outputs.
Set the main output levels appropriately for the DCX.

This could then be feed into the DCX .
The output from the DCX could then be feed back into the MX882 on channels 3 & 4.
Set those channels to 'split' mode (so that they don't get summed to the main outputs and create a feedback loop).
Set the output levels to what is appropriate for the inputs of the Quest 3004.

Work out the appropriate gain or sensitivity on the Quest.

I 'THINK' thats how it could work.

If I wasn't planning on 'Summing' some inputs on the MX882 then I could have just used the MX882 to both up the levels on the way in to the DCX and then down the levels on the way out of the DCX. But by 'Summing' in the MX882, if I did try to use it both pre and post DCX then I would create a feedback loop.

Hmmm, perhaps I should find a really cheap device that can do Summing..... Or just buy two MX882's, but that would seem a waste.

 

[Drizt]

snip...

I was wrong again... this is getting repetitive, me making mistakes that is

I can't use the 'sum / mix' functionality if I want to do level matching on the outputs of the DCX as it would create a feedback loop. I 'think' 🙄 I was right the first time.

I 'think' I have to scrap the idea of combining the Low Passed (40Hz and below) from the L & R mains with the Home Theatre LFE channel.

Summary:
Input 1). could be a copy of the LFE (use a splitter cable from my Integra DHC-9.9), which I put in 'mix' mode, adjust gain for DCX input, and output straight out of Output 1.

Input 2). could be a copy of the LFE (use a splitter cable from my Integra DHC-9.9), which I put in 'mix' mode, adjust gain for DCX input, and output straight out of Output 2.

Input 3). this would be the L output from the DCX. Here we would lower the voltage to the whatever is needed by the Quest 3004 for the Left channel input.

Input 4). this would be the R output from the DCX. Here we would lower the voltage to the whatever is needed by the Quest 3004 for the Right channel input.

Damn, I hope I have it right this time.. talk about a merri-go-round in my head 😛