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Old 8th December 2007, 08:09 AM   #1381
ttan98 is offline ttan98  Australia
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oettle,

it's not the cable problem.

The problem is overloading the 6 output stages. The o/p from CD player to high for the o/p stages. It sometimes overload the A & B inputs.

What I did was to attentuate A&B by 6db and o/p stages 1 to 6 by 6db. That fixes the problem.
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Old 8th December 2007, 08:23 AM   #1382
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by ttan98
The problem is overloading the 6 output stages. The o/p from CD player to high for the o/p stages. It sometimes overload the A & B inputs.

What I did was to attentuate A&B by 6db and o/p stages 1 to 6 by 6db. That fixes the problem.
Hi TT,
the 6db of attenuation will be appropriate for analogue inputs to the A&B channels. I found that my RCA connected CD player (unbalanced) required -8db at the input to avoid clipping.

But, with a digital input to channelA, one should not need to apply any input attenuation with the low level (500mVpp) that comes from the Spdif.

With both types of input (digital & analogue) the following stages must be set to avoid any clipping in the analogue output.
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Old 8th December 2007, 08:25 AM   #1383
oettle is offline oettle  Germany
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Hi ttan96,

There can't be any overloading caused by the digital input!!!
Might be you are amplifying the signal within the DCX? The sum of your input gain, EQs and output gain must never be higher than 0dB otherwise you loose resolution.

Frank
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Old 8th December 2007, 10:55 AM   #1384
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Quote:
Originally posted by oettle
Hi ttan96,

There can't be any overloading caused by the digital input!!!
Might be you are amplifying the signal within the DCX? The sum of your input gain, EQs and output gain must never be higher than 0dB otherwise you loose resolution.

Frank

Frank is right. The digital input can max be 'all ones' in the data word. That will light up the input LEDs if you use digital input. If you have set the DCX flat, (no lift in any equalizers etc) a digital max signal (all ones, but it has nothing to do with the actual voltage levels at the digital input of course) cannot clip the outputs.

Jan Didden
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Old 8th December 2007, 11:50 AM   #1385
Ryssen is online now Ryssen  Sweden
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My Roland M-1000 can amplify the digisignal,so I adjust it to 0db on DCX in.Then set DCX to 0db out.
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Old 9th December 2007, 07:50 AM   #1386
AR2 is offline AR2  United States
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Default My mods done

After I did my analog mods to DCX I was itching to do some more. So digital portion was ready to be worked on. I have been waiting and thinking what to do for a long time.

My set up was: Sony CD player XA20ES which is very good transport but it is supplied only with optical TOSLINK out. - SRC2496 which I used to input TOSLINK and to output AES/EBU out to DCX2496. That alone is not ideal set up and is great jitter generator with all cabling. Than from DCX I chopped all analog stuff after AK4393 DACs and sent it straight to 6 Lundahl transformers - one for each ballanced channel. After them I use digitaly controled relay attenuator, than XBOSOZ preamps and than amps.

My analog mod was wiring connected to X13 connector on the DCX analogue board and was messy. So the first thing to do was to sort that out. But first I wanted to mod my CD player so I could avoid SRC and send S/PDIF signal straight to DCX.

So I conntacted Scientific Conversion here in the Bay area that makes highly regarded digital transformers. Jon Paul who is main designer and owner is very cool guy who has helped me design new output for Sony. I installed new tranceiver 485 chip with Scientific's top of the line digital transformer SC937-02 and with termination for 75 ohms. Here is the link for you for that transformer:
http://scientificonversion.com/catalog.html

Thank you Jon very much!

After that I turned to DCX. I used Jan Diden's passive board to make my analogue connections cleaner. Jans board deals only with outputs and additional RS232 sub board is there for the PC control that I use all the time. That was great for me since it omits all of the inputs that I do not use at all but digital in only. I do use occationally C input for auto delay calibration, but I have second DCX that will be great just for that purpose when needed.

So I proceeded with that mod, did all the flat cables and volia - that was done. Next I got Neutrik RCA connector for my 75 ohm coax S/PDIF input, and smallest Monster digital cable to rout the signal. I used empty space on Jan's board to have cable secured and wired to 1 and 2 connector on X13.

Next in line was Transformer and AES/EBU 110ohm termination resistor replacement. In the place of original transformer which was through hole, I placed Scientific Converesion's small beauty which is SMD, but almost perfectly fits in the place of original transformer. That little guy, unlike original one is shielded and it provides shielding connector. I replaced 110 ohm SMD resistor with 75 ohm that is located on the bottom side of the DSP board. Scientific has through hole transformers, but Jon was clear that this small guy is just the best performer overall. So, that was done.

Lets have some pictures than I will continue.
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Old 9th December 2007, 07:57 AM   #1387
AR2 is offline AR2  United States
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Here is that little guy hiding behind OSCON cap. You could see how it perfectly fits in original holes. Two middle connectors are non contact ones.
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Old 9th December 2007, 08:15 AM   #1388
AR2 is offline AR2  United States
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Next on assembly line was replacement of dreaded CS8420 input chip that has all kind of problems. I also wanted to do clock mod as well, I was for a long time thinking what are my choices. Than Frank Oettle came with his great small board that deals with both all at once. That is a small square board in the place of original input chip. Frank's board houses and uses CS8416 receiver chip, highly regarded AD1895 192 kHZ Stereo Asynchronous Sample Rate Converter, each with its own low noise regulator, and on the top of that Ultra Low jitter clock! Board was fine to assemble and it connects through connector to the board. Connector is soldered in the place of CS8420, only on one row, where few small wires needs to be connected from a second row. That was hard! Additionally one wire is needed to bring regulated 9V from power supply. I was also doing power supply replacement from Stephane who made great boards for DEQ2496. Unfortunately that couldn't work for me since Frank's board needed nice stable 9V supply. So I was back to original Behringer power supply.
Here is the picture of Frank's board. Red wire is 9V supply from power supply connector.
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Old 9th December 2007, 08:31 AM   #1389
AR2 is offline AR2  United States
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Next was listening test to check what it does. I was very curious to hear if all jitter talk is really something that makes sense or I would need to have special ears to hear the improvement.
It is understatement to say that I was blown away. I just couldn't believe that such a difference is possible. I would rate this improvement equal to analogue mod when I removed all opamps and replaced them with Lundahls.

What immediately became noticable was channel separation and imaging. The hole sound unfolded nicely and it had whole another depth. The voices are dead centered and instruments are behind on the sides. Highs are much cleaner and with nice detail. The grain was gone. I was just amazed that such a improvement is possible. I really would like to hear if everyone else who did this mod found the same improvement.

I believe that simplifying digital line, using low jitter transformers, and than Franks board that obviously addresses several issues that existed did it. I am trilled!

Thank you Frank - great board!

I would strongly advise this mod, as long as you are comfortable soldering very small SMD parts. Frank provides assembled board, but you would need to do connector and wires soldering.

Here is one more shot - DSP board. I replaced all electrolythic caps with OSCONS - there were a lot of them. I also removed AK 5383 AD converters. Since I am not using analog in, there was no reason for them to just seat there and use power.
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Old 9th December 2007, 08:38 AM   #1390
AR2 is offline AR2  United States
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Here is the shot of OSCON bypass caps for DAC AK4396....
That is next.
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