dcx2496 shakedown

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Hi,
I have wired in -32db of attenuation in the output from the DCX.
Feeding a very short wire (15mm) into each of the Michell power amps(+33.3db), then into Acoustic Energy AE1s.
I can turn off the source and let my ears acclimatise to the lack of noise and when putting my ear to either the treble unit or the mid/bass the output is completely silent.
When these speakers are passively connected to a Cyrus 8 (+34.4db) they emit a slight hiss but this appears silent at 500mm.
Conclusion;- run the input into the DCX to just below clipping and then attenuate the output to achieve complete silence when required.
 
I think the guy with the singing polar bear avatar mentioned it a while back. A big plus is that it has a built in volume control that can be controlled by wiring up a linear pot and for some reason I got the notion that it supported unbalanced signals better than the Behringer and may even sound better.

There seems to be a lot of confusion about using the Behringer with normal home equipment. I have yet to find a clearly stated answer to what seem to be the most common question: how to use with unbalanced RCA connections. I'm hoping Davey comes back and answers my last post with "Yes."
 
Rane RPM26z

I was wrong about that avatar. Here are the comments I've read:
sfdoddsy
Thunau

There's another user who posted in the big DCX2496 thread that he had received the Rane on loand but he never posted his findings.

On the issue of volume control, having remote volume control is necessary for me. I hate having to get up to change the volume. I currently using relay volume controls in my two preamps and they were both about $100-150 each.

The idea of using three of these to control volume seems like too much of a pain and cost/complexity-wise seems high when compared to the Rane that could conceivably act as a preamp, crossover, parametric EQ, and volume control all in one box. I'd still have to make a remote linear pot to control volume but I think I could just modify one of my remote volume boards to do that easily enough.
 
On the issue of volume control, having remote volume control is necessary for me. I hate having to get up to change the volume.

So essentially you are spending an additional $700 for the Rane
just to have that pot feature. // ouch //

If you didn't need the remote volume, then I bet I can make
your loudpeaker work with the $120 Behringer analog crossover
but you want dipole and probably want some form of eq. // hehe // ..
 
Konnichiwa,

ultrachrome said:
I made a simple rca to XLR cable by bridging pins 1 and 3 per the Behringer manual (p20).

While general practice in Pro-Audio this is a terrible idea.

It actually makes one of the two halves of the output op-amp work into a very low load (60 Ohm) which causes it to thermally modulate the common die with signal and to modulate the common supply.

As you also need around 20db attenuation to interface the DCX to consumer standard Amp's, here is my suggestion for a "Balanced/SE" attenuating converter that does not cause the above problems and does not require a transformer (which is the other possibility - a 4:1 stepdown studio grade line transformer with +22dbu level handeling is ideal):

Make a box with XLR "Tails" and RCA Output Cables or Sockets (depending on taste)

Each RCA output pair receives two toggle-switches, one changeover and the other center neutral. These will become switches to select between the two polarities and -18/-12/-24db attenuation.

From pin2 & pin3 connect a pair each of 2K2 (1% or better) resistors in series to pin1 (ground).

The join between the two resistors for each polarity is connected to one of the two poles of the polarity selector. Thus at the flick of a switch the polarity of any given way can be inverted.

Further the "center neutral" switch connects a 2K2 resistor (-18db) or a 750R resistor (-24db) between the two junktions of the 2K2 pairs.

Now each output Op-Amp sees a sensible load of > 2K2 each and the load is reasonably well balanced (as long as Z-Load > 10K), you can simply resolve any polarity issues (be they in different makers Amp's, drivers etc.) at the flick of a switch and your full-scale levels are now:

-12db = 2.5V RMS
-18db = 1.25V RMS
-24db = 0.625V RMS

The same thing makes a neato passive "Pro -> Consumer" interface converter in dual channels. Switch and resistor quality matter, so don't skimp too much.

Sayonara
 
ultrachrome said:
Not really. Seems like the Rane is more the equivalent of a DEQ+DCX.
MSRP comparision is DEQ+DCX $600 v. RPM 26z $1000.

It's not the cheapest way go but it seems like the Rane holds the middle ground between the Behringer and DEQX solutions.

Cool............

but I don't see why you need so much horsepower for your design.
I don't see any real issues with the ribbon and PR midrange that requires a fancy EQ, simple level matching will do the job. The EQ you need for the dipole, does it require an expensive solution ? /hehe
You would think that even one parametric band is sufficient..... the
net result is an expensive volume control for your application. /heh
 
The Rane is worth the money if you need its features. Being able to draw your own signal path with its CAD-style interface is a big plus. And it's quieter than the Behringer. However, it won't eliminate the need for a volume control. You can control digital gain blocks with a pot but the analog gain is set and forget. It works great for optimizing your gain structure but it can't be adjusted on the fly. The best you could do is set up 8 presets with different analog gains and change to them with a switch. That's actually not too bad an option. Maybe 4 presets, 0, -10, -20, -30dB (-30 is the max attenuation with the analog control.) Pick one for the mood you're in and you could do the fine tuning with the preamp without losing much digital resolution.
 
Kuei Yang Wang said:
Konnichiwa,

SNIP


Each RCA output pair receives two toggle-switches, one changeover and the other center neutral. These will become switches to select between the two polarities and -18/-12/-24db attenuation.

From pin2 & pin3 connect a pair each of 2K2 (1% or better) resistors in series to pin1 (ground).

The join between the two resistors for each polarity is connected to one of the two poles of the polarity selector. Thus at the flick of a switch the polarity of any given way can be inverted.

Further the "center neutral" switch connects a 2K2 resistor (-18db) or a 750R resistor (-24db) between the two junktions of the 2K2 pairs.
SNIP

Sayonara

I have tried to get this description down on paper, but I dont get it!:scratch: Could anybody please help me draw the circuit.

DVC Keld
 
Davey said:
Yes, I understand this is different than what is recommeded by Rane and Behringer.
I don't know how much clearer I can say it....don't connect pin 1 to 3 on the outputs. Pin 1 goes to your RCA shield and pin 2 goes to the RCA center. Pin 3 is unused and unterminated.

Davey.

So I just got around to doing this to the output cables and it didn't seem to affect the output level at all. It was supposed to lower the output, correct?
 
Hi,
can I try?
Connect 10k to pin 3 and another 10k to pin 2.
Connect 200r between the two free ends of the 10ks, this forms a pi network that balances the outputs from the DCX.
Connect the screen to the far end of the 10k from pin 3. This is now your ground for the next stage.
Connect an RCA phono to both ends of the 200r. The ground (pin 3 10k) goes to the ground of the RCA and the hot end of 200r (pin 2 10k) goes to the input of the RCA.
you now have a source impedance of 200r to drive a cable and input greater than 2k.
attenuation is about -34db. 270r gives about -31db, 470r gives about -27db.
 
AndrewT said:
Hi,
can I try?
Connect 10k to pin 3 and another 10k to pin 2.
Connect 200r between the two free ends of the 10ks, this forms a pi network that balances the outputs from the DCX.
Connect the screen to the far end of the 10k from pin 3. This is now your ground for the next stage.
Connect an RCA phono to both ends of the 200r. The ground (pin 3 10k) goes to the ground of the RCA and the hot end of 200r (pin 2 10k) goes to the input of the RCA.
you now have a source impedance of 200r to drive a cable and input greater than 2k.
attenuation is about -34db. 270r gives about -31db, 470r gives about -27db.

I'm going to try this tonight. I have just enough parts on hand to do two cables with 220r and four with 470r. If I understand you correctly, the 220r will have a little less than-34dB of attenuation.

I'll use that on my woofers which are currently boosted to +15dB compared to my mid and tweet which are -13dB. It should allow me to bring the the levels closer together and allow me a little wiggle room.

As soon as my 12AT7s arrive, I'll swap them and a couple resistors into my grounded grid. Sure wish my foreplay was still operational. Seems like this would be a perfect use for it.
 
I ended up building Kuei's interface unit which has worked well although I opted to not include the polarity selector.

At the time I didn't have any 750Rs on hand and other things to do so I just lived with it in -18dB mode.

But I finally got tired of the hiss and tried 540R (maybe it was 560R) to quiet things further but still not enough with 100dB/W drivers.

I want to try smaller values for more attenuation but I don't really understand how to determine the attenuation by the resistor value nor how low I can go in value.

Can anyone shed some light on this?

Thanks.
 

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Hi,

ultrachrome said:
I want to try smaller values for more attenuation but I don't really understand how to determine the attenuation by the resistor value nor how low I can go in value.

Can anyone shed some light on this?

You can safely go down to a dead short.

Why not get a 1K adjustable resistorfor testing and turn it as low as you need?

Apart from that, if you look, the attenuation progresses in appx 6db steps with each step halving the value (to nearest preferred value), so halve the 750R to 390R for around 24db attenuation.

What Amplifier(s) are you using?

Ciao T
 
That's easy enough to follow. Thanks.

I'm using an Adcom GFA-545II (150W @ 4ohm) for the woofers and four channels of a Panasonic XR45 receiver for the midrange and tweeter.

The panasonic replaced an AKSA55 and BrianGT LM3875 amps. That setup was too clumsy to move.

The volume control on the Panasonic is quite useful for helping match with the woofers and the convenience outweighs any SQ issues. Also allows me to easily adjust the relative woofer level to suit my mood.

Currently the Panasonic volume is set to -18dB. In the DCX my woofers are at +14dB and my Mid and tweet are around +6dB. So about 26dB difference between the woofers and mid/tweet.
 
Konnichiwa,

ultrachrome said:
I'm using an Adcom GFA-545II (150W @ 4ohm) for the woofers and four channels of a Panasonic XR45 receiver for the midrange and tweeter.

Interesting, how do you like the pannie?

ultrachrome said:
Currently the Panasonic volume is set to -18dB. In the DCX my woofers are at +14dB and my Mid and tweet are around +6dB. So about 26dB difference between the woofers and mid/tweet.

Wow, that is a lot. Try getting the woofers back to no gain, the add pads (fixed) for 26db on mid and tweeter. As long as the Pannie is quiet by itself (easily tested by shorting the inputs and turning the volume all the way up), it shuld be quiet after the DCX, it has around 110db S/N, so if it hisses you have miles too much gain.

Ciao T
 
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