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Old 12th October 2005, 04:19 PM   #1
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Default DCX2496 RCA-XLR Connection

I know this issue has been discussed many times before here. I tried to understand, but I am still confused. To make summery, please confirm if following my understanding is correct:

-AA- Background -My application:
----------------------------------------
Same as Newform namely:

(a) DVD RCA Digital Out
I
(b) DCX XLR Digital in
I
(c) DCX XLR Analogue out
I
(d) Amplifier RCA Analogue in (Panasonic XR45)

The panasonic 6 Channel digital Receiver acts as Multichannel amplifier and Multichannel Volume control.


-BB- My Understanding / Question ?
------------------------------------------
(a)-(b) Digital Connection:
1. This can be just RCA/XLR connection using simple RCA/XLR contactor plugs "it will work"

2. Better yet, (reduced hum??) , would be to use for example Neutrik Digital Audio Tranformer/Adapter, converts 110 Ohm balanced AES/EBU (XLR) to 75 Ohm unbalanced ?

(c)-(d) Analogue connection:
1. Here also simple RCA/XLR plugs can be used. But, in this DCX analogue output end, care must be taken NOT to connect pin 1 to 3 on the XLR outputs. Pin 1 goes to RCA shield and pin 2 goes to the RCA center. XLR pin 3 is unused and unterminated.

2. In my case, since the Panasonic receiver will do the Volume control, it will NOT be required to add attenuators after the DCX ?


Have I understood correctly?

LageB
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Old 12th October 2005, 09:36 PM   #2
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I just wanted to comment on the fact that you are using the XR45's analog inputs.

I found that using the inputs on my Panny receiver (xr25) caused a serious drop in sound quality compared to the digital inputs. The beauty of the xr series of receivers is the ability to keep the signal digital all the way through the amp. I've found the A/D converters to be pretty much junk. The sound from my DCX straight to an analog 6 channel amp (a cheap one at that) was much much better than that from the analog inputs of the xr25.
You do still have to worry about attenuation though.

As for the rest of your questions, excluding the AES/EBU connection, I have my DCX connected as you have it.

I was unaware that you shouldn't have 1 and 3 connected on the XLR though, I'll have to do some reading.
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Old 14th October 2005, 12:33 PM   #3
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Hello dunderchief,


I have nothing to compare with. I have only used the XR-45 with analogue in, which I thought sounded pretty good. But again, without refererence it is hard to tell. I am sure XR-45 is better with Digital all way, but, with the DCX I have no option.

As for my original question You wrote "you have to still worry about attenuation though". Could you clarify what you mean?

Any other here, who can comment on my Understanding/Question in my first post thanks?


Thanks
LageB
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Old 18th October 2005, 08:03 AM   #4
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Ok,
By browsing further in various Forums, this is what I could deduct to be the conclusion regarding DCX XLR/RCA connections, without using transformers. Any objections?

(a)
Do NOT use conventional XLR/Plugs (such as http://www.merconet.nl/leverings_omv...rca/xlrrca.htm )

Instead, make your own cables with following mods

(b) DVD RCA Digital Out --> DCX XLR Digital in

"Thorsten Mod"
--------------
Pin on RCA connects to Pin 2 XLR, Sleeve on RCA connects to Pin 1 &
Pin 3 together. Connect a resistor of 220 Ohm across Pin 1 & 2.

Above mod is to reduce reflections which cause jitter.

(c) DCX XLR Analogue out --> Amplifier RCA Analogue in

"Davey Mod"
-----------
RCA plug at one end and XLR other end. But, in this DCX analogue output end, care must be taken NOT to connect pin 1 to 3 on the XLR outputs. Pin 1 goes to RCA shield and pin 2 goes to the RCA center. XLR pin 3 is unused and unterminated.

Above to avoid that DCX doesn't auto-increase the gain by 6db internally.


Have I got it right now?

LageB
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Old 18th October 2005, 08:33 AM   #5
AndrewT is offline AndrewT  Scotland
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Hi,
I too found that DCX2496 does not increase the gain by 6db when pins 1 & 3 are shorted together.
I did not need the extra voltage output so no problem, it just caused confusion on my part understanding what DCX was doing.
Instead I have terminated pin three with the same resistance as pin 2, i.e. 10k to ground for both pins, to reduce/match loadings on the DCX output stage.

By the way, at Odb in digital domain you will have almost 5Vac coming from pin 2. Will your amp accept this at line in?
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Old 18th October 2005, 09:29 AM   #6
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Ehr.. Sorry for my primitive questions but please be kind:


(1) Analogue out:
I thought increase gain would be good thing, to increase s/n ratio or something. If I have 6dB increase - what does it mean in terms of Voltage increase?

(2) 5Vac out from DCX (to consumer amp in):
Actually, when you mention it, my amp often displays "overflow" Does it mean that DCX out Voltage in is too high? This is the case when using normal XLR/RCA adaptor-plug.

Disconnect pin 3 seems like very bad idea in my case then ?


LageB
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Old 18th October 2005, 01:26 PM   #7
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Hell AndrewT again,


Maybe I read your post incorrectly. I understand the trick is to disable 1-3 connection to avoid the 6dB boost gain on DCX output. My previous post therefore does not make sense - sorry. It should read like this instead:

(1) Analogue out:
I thought decreased gain would be good thing, I read somewhere that decreased gain on DCX output would increase s/n ratio for Amp. A 6dB increase/decrease - what does it mean in terms of changed Voltage output?

(2) 5Vac out from DCX (to consumer amp in):
Actually, when you mention it, my amp often displays "overflow" Does it mean that the DCX out Voltage is too high? I have been using using normal XLR/RCA adaptor-plug.

Disconnect pin 3 seems to be a good idea then ?


LageB
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Old 18th October 2005, 05:20 PM   #8
AndrewT is offline AndrewT  Scotland
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Hi,
I am afraid your english is losing me.
-6db = half voltage and +6db = double voltage.
I needed -30db after DCX for my power amps. So the -6db due to leaving pin3 loaded as if it was feeding a balanced input was not a noise issue. In fact my power amp outputs are completely silent when no signal is fed to DCX.
I found that shorting pin3 to pin1 did not increase the voltage on pin2 contrary to what I had read.

I would be surprised if your amp could take 5V if the volume was turned well up. But many amps have an attenuator before any active stages that allow unlimited inputs without overloading the voltages amplifiers. However your 6 channel amp is using some kind of electronic attenuator and may not like large voltage signals. I do mot know what overflow means but again I suspect you are getting close to an answer - overload of input stage?
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Old 2nd May 2006, 08:27 AM   #9
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Default im confused bout xlr.

hi sorry if i sound stupid but i need help im currently usin phono jacks to connect my mixer to my amp. is it worth changin to xlr, will i get better sound quality? wot will happen if i use xlr to phono,will it make a difference. if someone could help me id be really grateful. thanks.
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Old 2nd May 2006, 05:55 PM   #10
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I use;

SPDIF out source -> RCA to BNC cable -> Canare SPDIF_AES transformer -> DCX digital input.

http://home.pacbell.net/lordpk/cable...S_Transformer/
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