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Old 11th November 2007, 12:33 PM   #1271
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I agree with you as well.

For the PSU, I posted this months ago.

# beween the switch mode PSU and a linear PSU on +15v (inside a DEQ).

http://www.diyaudio.com/forums/showt...050#post712050

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Old 11th November 2007, 01:28 PM   #1272
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Hi,

The standard DCX already has a PLL, SRC and clock as well and so itís already able to up-sample and re-clock any incoming data. So my mod isn't a new function at all (itís even not a new idea except the combination and improved supplies), but an improvement of the SRC and clock.

Because sound quality is always the sum of errors in the chain an additional SEC2496 won't improve something but would worsen it.

By sure Iím not aware of all PSU mods. For those I have seen I would recommend to make some SPICE simulation regarding PSRR and noise for the whole frequency band not only HF noise. Insert 3 simple 100ĶH coils (about 0.5 ohms) in the +/-15V and +9V rail between the PSU and DSP board and make the same measurements. Surprise, surprise you will end up in a similar result like the PSU mods. More relevant than HF noise is the noise in the audible frequency band (10 Hz to let say 40 kHz). The typical used voltage regulators have a PSRR of about 60 dB and get much worse above 1 kHz. Also output noise of these standard regulators isnít the very best. So there is plenty of room for new mods. I hope I wasnít too frankly.

Frank
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Old 11th November 2007, 03:38 PM   #1273
ergo is offline ergo  Estonia
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There is a lot of discussion here lately about if and how much any mod improves the DCX. In one regard the DCX is a very very good platform to learn about sound of different analog stages for example. As there is basicly ability to make the output into 3 times stereo output one can easily do a different analog stages for each output pair (or leave one pair for stock version) and then use the DCX as stereo DAC.

This is exactly how I started to do it - I figured that before I dive into an active crossover world at all I would try to make the DCX to be as good stereo DAC as possible.... so I experimented with passive analog stages, JFET followers, transformers, opamps etc etc. And at all times there was 3 different stages active on 3 output pairs and DCX configured FLAT. This way one can switch back and forth between these outputs that have a signal chain EXACTLY the same upto DAC chip output pins.

For all the sceptics here - try to mod one pair of outputs and leave the other stock - comepensate the levels - and A-B listen to those and say you will not hear the difference....... I'm very sure you will.

Ergo
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Old 11th November 2007, 04:07 PM   #1274
Ryssen is online now Ryssen  Sweden
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Quote:
so I experimented with passive analog stages, JFET followers, transformers, opamps etc etc.
What did you think?Wich sounded best to you?

Another question:Is there any sonical difference of tentlabs,Selectronic or http://diykits.com.hk/ oscillators,except for the price..
(I mean just the oscillator not the whole clock)
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Old 11th November 2007, 04:57 PM   #1275
ergo is offline ergo  Estonia
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Ryssen,

Well my feelings after all trials are following

* Passive mod is an upgrade compared to original output stage. The datasheet suggests it is able to drive even the passive preamp after it. In reality the one to one comparison to active stages gives afeeling in the end that there is a bottleneck there. The sound is clean and neutral but seems to lack some punch and energy that make music sound alive.

* Transformers (I tried Lundahl) are very good sounding, but as I'm also a kind of nerd and also look at objective measurements I never got the spectrum to look "clean" with transformers. Being a digital / analog mixed design device there is still a lot of RF energy in the DCX case and I was not able to shield the transformers well enough to keep all that out.

* Same comments as for previous apply for passive RLC filtering.

* Simple one stage opamp design is the one I have been using in the end. With shunt regulators on each opamp and simple RC before and after opamp it seems that the plusses are all there and I do not feel the "lack of punch" I mentioned before.

*****

So where I ended up was to have a RC filter, then a 6 channel ALPS pot and then a single opamp stage. All this inside the DCX case.

For current versions I have moved the 6ch APLS pot + opamp stage to separate box as I sometimes want to emulate the crossover with PC and LspCad and soundcard and there was the same problem with the lack of analog volume control....

So I can imagine that Jan's solution for analog stage is a very good one as it is very similar topology wise where I ended up.

*****

As for clock - I have only tried the Tent XO - so unfortunately can not comment on Tent versus Selectronics issue.

I'm lucky in one more point - I have unmodified DCX2496 at work - so I can do comparisons between where I'm at with my mods compared to original one. Plus I have modified one DCX for my friend (where we modded the analog in and out but not the clock) so I have even a third midway modded reference.

Having done this since spring 2004 I'm pretty sure I'm not imagining the positive progress compared to stock unit - having listened to the unit in different homes and moods etc. But each has to travel their own way as not all mods are quaranteed sucess. Some trial and error is always good and educates a lot

Ergo
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Old 11th November 2007, 06:04 PM   #1276
AR2 is offline AR2  United States
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Man, you guys were busy during my night. Full page of answers.
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Old 11th November 2007, 06:44 PM   #1277
AR2 is offline AR2  United States
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Quote:
Originally posted by oettle
I wouldnít worry too much about this problem. Itís a minor one.
Thank you Jan and Oettle.
No I am not worried at all. It is just that I didn't do any clock improvements, and since I was getting ready I was trying to find out which one will be the best one to do.

I am very excited about Oettle's mod since I have ordered one. I have Behringer SRC and DEQ and DCX. I do not think it is good to stack more units one after each other since every unit in the chain and S/PDIF cable will bring more jitter.

To answer Oettle's question - my CD transport is pretty good one, it is Sony XA20ES. Very solid mechanism and tray with CD clamp, but unfortunately in the Sony style they have provided only optical out. Because of that I have to go through SRC. Regarding that I am researching how to mod my CD as well. I am thinking of inserting transmitter CS 8406 and appropriate digital transformer, so I could have AES/EBU output. That could go straight to my DCX with short cable which certainly will be much better than having several units. I just ordered my Sony schematic in order to see how to access the signal. Any advice here is welcomed.

Another mod that I will be doing is as I mentioned earlier, exchange of AK4393 DACs to AK4396s. I have two DCX units and on one one DAC died. So I will exchange that one first and see if there is any improvement. There is a lot written about these chips, but I do not expect any big improvement. We will see. I will document in pictures my surgery. I just got my hot air soldering station, so I feel no IC soldering is a problem: (Wait until I start screaming for the help)

What is interesting CS8416 in Oetl'e mod is 192 capable, as well as AK4396. I do not know if DSP is 192 capable or not, or if that matters. Question is: Is it possible to put throgh 24/192 signal after all this modifications. I will see, since my sound cards are capable of producing 192 digital signal, as well as there are modifications that are done to the SACD that allow that kind of digital signal to be sent out.

Anyway, I have a lot planned to do. I will be doing Power supply mod as well after I find the right transformer for 110v.

AR2
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Old 11th November 2007, 06:55 PM   #1278
Ryssen is online now Ryssen  Sweden
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Quote:
* Passive mod is an upgrade compared to original output stage. The datasheet suggests it is able to drive even the passive preamp after it. In reality the one to one comparison to active stages gives afeeling in the end that there is a bottleneck there. The sound is clean and neutral but seems to lack some punch and energy that make music sound alive.
This is exactly how i thought when I did this on my Emu1212 soundcard.The punch is there with a opamp after.

Thanks for the detailed answer.
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Old 11th November 2007, 07:51 PM   #1279
ergo is offline ergo  Estonia
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AR2,

The modding of the XA20ES should not be difficult at all - I have XB930 which is in many ways similar unit and I assume in you player the SPDIF signal comes out from the transport PCB also with a separate 3 wire connector that then goes to DA and analog PCB somewhere near the Optical out socket.

Basicly all you have to do is to use this signal and make a circuit after it to feed the 75 ohm coaxial digital cable. There are many circuits in this forum for that purpose just run a search and pick what seems best to you.

Ergo
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Old 11th November 2007, 08:02 PM   #1280
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Guys,

I have been looking into that optical input thing. Am I correct that those Toshiba optical S/PDIF receivers just need a +5V, you plug in the optical cable, and than at their output you have the 'electrical' S/PDIF?? Is that really all there is?

Jan Didden
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