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Old 16th December 2005, 05:52 PM   #1
morbo is offline morbo  Canada
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Default DCX2496 newbie - questions and 2nd opinion request

Hi All, I am about to receive a DCX2496 and am totally new to it. With that in mind, I have a few questions about integrating it into my setup. I have read a lot about how this can be done, and to narrow things down straight away, I'd like to give a bit of info as 'given', so as to avoid unneccesary discussion of it.

Given: active triamped system with:

Seas 27TBCG tweeters - driven by own amp with volume control (eventually replaced with pannasonic digital reciever)
CSS WR125 midwoofers - driven by own amp with volume control (eventually replaced with pannasonic digital reciever)
stereo sealed rythmik servo-subs driven with built in plate-amps (with volume control, damping/extension control, and non defeatable 2nd order highpass, max 160hz)

I want to integrate this triamped system as the L/R speakers in my home theater system, and have it pull double duty as a high quality (by my standards) reference 2 channel setup. I am not the 'golden ears' type, all of my sources, amplification, and cabling are marantz quality at best. I have no interest in any mods or upgrades to the DCX at this time. I intend to have volume control infront of the DCX (whether analog or digital), as illustrated below. I realize this is not ideal, but it is what will work in my system without major additonal spending. In the future I may go to a 2 channel only setup with the DCX, but for now I am stretching my budget enough with this purchase.


Proposed setup:

For casual listening/HT:


analog L/R preamp out from reciever -> DCX (via homemade RCA-XLR cable) -> tweeter amp, midrange amp, sub plate amps (via homemade XLR-RCA cable, attenuators?)

In this setup, input level is controlled by the 'master volume' from the receiver. I suppose I would set the highest level i would likely ever listen at as the clipping point on the DCX.


For serious listening (2 channel redbook)

coax digital out from CD player -> DCX (not sure how to do this) -> tweeter amp, midrange amp, sub plate amps (via homemade XLR-RCA cable, attenuators?)

In this setup, input level is controlled by the digital 'volume control' in the cd player. I'm not sure how much quality loss there is when doing this, I assume it will be less than an extra DA/AD conversion and passive volume control by the receiver.


Questions:

1. Since all my amps will have a volume control, do I need to attenuate the outputs from the DCX like I see people doing?

2. How can I get the coax digital out from my cd player to the DCX?

3. Does anyone see any glaring problems with this setup? Anything that obviously won't work?
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Old 17th December 2005, 03:05 PM   #2
AndrewT is offline AndrewT  Scotland
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Hi,
my power amps have a gain of 34db to 35db.
I have a set of attenuators of -30db after the DCX2496.
This produces a nice sound level into 89db sensitivity speakers.
Some would call it loud but I would need slighly louder for serious listening at realistic levels. Probably +6db to +10db in level.
Effectively the same as reducing my attenuators from -30db to -20db.
I can produce quiet listening by reducing the input from +8db to 0db on CD input but my other inputs are at +15db reducing to +8db for quiet listening. This difference between input levels and going from quiet to normal and back again is very fiddly.

I do not consider the proposal to use a digital volume control as optimum. Your effective 16bit input is being lost as soon as some attenuation is dialled in. I think this will be worse than analogue attenuators before the DCX.

A small analogue correction before DCX will probably be effective.
But I beleive that the majority of the level trimming should be done after DCX.

All this is only worthwhile as a system for developing an active xover for the fully active speakers. It is so easy to experiment.

As final parting shot. I felt that the quality of my stereo reproduction was poorer with DCX in line and very definately the bass was much reduced and this with only AE1s (130mmdriver) as the main speakers. I am running passive bi-amped just now until I find the time to develop the active 5.1 system.
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Old 17th December 2005, 04:06 PM   #3
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Quote:
A small analogue correction before DCX will probably be effective.
why would you want to do this?
As to the quality of stereo reproduction - I do not have the same experience, having run active both in analogue and digital format.

As to bass reproduction: I found that a lot of folks requesting more bass do not appreciate a clean, punchy bass without overhang or boominess that they identify with a "strong bass".

I cannot concur from my experience that bass reproduction is diminished by the dcx.

When measured through the deq rta, the bass is enhanced by the same level if I use analogue or digital x-over. I am talking only of the range below 25Hz, as my subwoofers are flat to that range and only fall offbelow that point.
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Old 17th December 2005, 04:26 PM   #4
AndrewT is offline AndrewT  Scotland
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Hi Audiokraut,
Quote:
Post #3
taken out of context.
Quote:
why would you want to do this?
I was not advocating major volume change before DCX.
Instead I recommend all volume change after DCX.

As an alternative use the major amount of volume change and/or correction after DCX and then a small attenuation to adjust between quiet and louder before DCX. The advantage being that the coarse but relatively fixed output settings are not easily adjustable (6channel) but the input side is fairly easy to adjust in the stereo (2channel) mode.
That is the (convenience) reason you would want to do this.
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Old 17th December 2005, 04:29 PM   #5
AndrewT is offline AndrewT  Scotland
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Hi Morbo,
you will have to decide for yourself if the DCX cuts off the bass compared to driving the speakers direct.
But do tell us what you find.
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Old 17th December 2005, 04:34 PM   #6
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Quote:
Instead I recommend all volume change after DCX.

Completely agree to that.
I have sourced my six gang pot's from thel in germany, the only reasonable priced ones I could find anywhere with relatively tight tolerances of 1 db within gangs.



Quote:
1. Since all my amps will have a volume control
How do you make sure that when changing volume that each amp gets attenuated by the same amount?
Very cumbersome. Use the advocated method.
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Old 17th December 2005, 11:21 PM   #7
morbo is offline morbo  Canada
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Thanks for your replies guys. With all due respect, as I said earlier, I want to do volume control BEFORE the DCX. Six channel volume controls, VCAs, etc etc after the DCX, are not an option for me. I know that is not optimal, but there is no other way to integrate into my HT system. I can do some fixed attentuation on the outputs if needed, though all my amps are receivers, and thus have a volume control on them already, which is why I asked if they are still needed.

I am not concerned about bass being limited. I have measurement gear and will be able to see if this is happening.

[quote]
1. Since all my amps will have a volume control

How do you make sure that when changing volume that each amp gets attenuated by the same amount?
Very cumbersome. Use the advocated method.

[/qoute]

Well I inteded to measure the output to get the right level. And what is 'the advocated method'?
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Old 19th December 2005, 08:22 PM   #8
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seeing as there is no way I can get all my filters designed and the parts ordered by xmas, I've decided to take the plunge and get a dcx. I fancy having one anyway!

I will be using it the same way as morbo, I read the long dcx thread and somewhere in the middle someone said that although not ideal this method is adequate. As a prototyping tool for filters that will eventually be hardwired there should be less concern about noise?

my AV amp will only be powering the surround channels, so I can turn them down -10db to increase the LR pre-amp output. (unfortunately I cant increase LR +10db because with phantom centre the centre stays at 0db)

I will reduce the gain at the input to the (chip)amps.

Can someone confirm that LT can be implemented on the dcx?

As its a 2way design, at least I only need to build 6 xlr to rca cables. Any tips for building? I guess I'll find a thread on that somewhere close.
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