DPA little bit dac modding (7350 dac, ym3623b receiver) - diyAudio
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Old 27th March 2005, 07:58 PM   #1
ash_dac is offline ash_dac  United Kingdom
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Question DPA little bit dac modding (7350 dac, ym3623b receiver)

Hi,


Firstly, most of the components are surface mount so I cannot do much with my soldering skills.

My thoughts were to replace the capacitors with some higher performance ones.

There is a 11.2896mhz crystal on a ym3623b receiver which confuses me somewhat after looking at the 3623b datasheet.

Anyone know why this clock isn't 16.9344 Mhz ?


Regards,


Ashley
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Old 28th March 2005, 12:44 PM   #2
JohnW is offline JohnW  Hong Kong
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Hi Ashley,

The Xtal on the YM3623 is only used to clock the receiver when there’s no input signal - on a good design; this clock is "Muted" during "Lock" conditions to prevent beating (interference) between the recovered clock and the "start-up" clock. The YM3623 does not do this by design; normally an external "Kill" circuit (a diode between the Xtal clock and the "Lock" line) is implemented.

The best upgrade you can perform is to clock lock the unit - using the "Deltran" output - which provides a 256fS clock to the transport.

The LM358 are not in the direct audio path - but lower the impendence of the internal VREF sources within the SAA7350 – so don’t worry about there quality – elsewhere on the board you will find 5524 / 32 which form the LPF / output buffer – these could be upgraded.

The YM3414 is not that great a digital filter - if your skilled - you could replace with a PMD100 / 200 HDCD filter which will elevate your Little Bit to new levels.

John
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Old 28th March 2005, 05:09 PM   #3
ash_dac is offline ash_dac  United Kingdom
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Hi John,

Thank you for the clarification. I have opened it up again, and found one NE5534.

Why only one NE5534 ic ?

*there is another ic with code TI740X but i am not sure what this does*


Regards,


Ashley
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Old 28th March 2005, 06:03 PM   #4
JohnW is offline JohnW  Hong Kong
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Hi Ashley,

The device marked "TI740X" I suspect is the second channel's 5534 - your most likely reading the date code instead of the Part # - the part # may be obscured by flux...

John
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Old 28th March 2005, 06:44 PM   #5
ash_dac is offline ash_dac  United Kingdom
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Cheers John,

Makes sense about the NE5534!

The unit unfortunately does not have a clock out on the back connectors to lock with the player. But i don't see why the clock couldn't be fed back, and this could explain why the 11.2896 crystal is in there! (feed to Phillips based player)

How would i create a circuit to feed back a 11.289mhz signal?

Is the 256fS the 8X oversampled signal?


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Ashley.
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Old 28th March 2005, 11:21 PM   #6
JohnW is offline JohnW  Hong Kong
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Hi Ashley,

I’m sorry I thought that the Little Bit had a “Deltran” (Clock) output. Adding such a feature is not really a simple DIY job. The original Deltec / DPA clock-feed to the transport operated at 256Fs (44.1 KHz x 256 = 11.2896MHz). The reason the Little Bit uses the 11.2896 Xtal is not because it was important for correct operation of the DAC – but Rob Watts (the unit’s designer) uses this frequency Crystal for the Deltran function on other designs – so had this frequency to hand.

256Fs (11.2896MHz) is the Master clock frequency used in Philips I2S based CD players / digital audio chipsets.

Operating the early Toslink TX and RX devices at 11.2896MHz was beyond there rated Spec. resulting in increased clock Jitter, however as CD player servo chipsets are tolerant to Jitter in significant amounts – this is of little consequence.

On designs I developed for Pink Triangle and Cambridge Audio, I used 128Fs (5.6448MHz) for the Clock-Lock, this allowed operation of the Toslink TX & RX devices within there specified limits, and also easy clock division / multiplication of both 256 (divide by 2) and 384 (divide by 3) Master clocks commonly used in both European and Asian CD players.

I believe that Arcam used 96Fs for there Clock system – however I cannot confirm this.

If you want to develop your own clock-lock system, then I recommend you use a 128Fs clock. The Little Bit requires a 384fs (16.9344MHz) internal Master clock, which you can then divide by 3 for the Clock-Lock output.

You can use a simple L/C overtone circuit to multiply the clock from 128Fs to 256Fs or 384Fs, depending on your transport requirements.

If you do Clock-Lock, then use optical I/Os (Toslink) for the SPDIF & Clock, thereby affording EMI isolation between the DAC and CD transport – however the Little Bit is an EMC nightmare in its own right (can you watch TV with your unit powered?) – Deltec / DPA designs where REALLY poor from an EMC perspective.

FYI 8x oversampling operates @ 44.1KHz x8 = 352.8KHz

John
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Old 29th March 2005, 01:21 AM   #7
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Quote:
Originally posted by JohnW
I believe that Arcam used 96Fs for there Clock system – however I cannot confirm this.

Hi John

Speaking of Arcam and clocks - any chance you could look at my questions/ideas?
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Old 29th March 2005, 05:15 PM   #8
ash_dac is offline ash_dac  United Kingdom
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Hi John

Cheers for the detailed notes.

Yeah, I did notice that when I had the little bit on i got lines on my screen. I put it down to an over active imagination

Does the EMI spread out everywhere, into the environment, down the spdif cable and into the transport, etc?



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Ashley.
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Old 29th March 2005, 07:47 PM   #9
JohnW is offline JohnW  Hong Kong
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Hi Ashley,

Yes, the RF energy is radiated "everywhere", units directly connected to the DAC via audio, SPDIF data and even though the mains cabling are directly effected - its by no coincident Deltec / DPA digital products gained significant audio improvement when used with Deltec RF mains filters - these attenuated the RF getting into the units, and also transmitted to the mains supply from the units...

Fin, get Skype working and contact me - it’s much easier to discuss your options.

Cheers,

John
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Old 29th March 2005, 07:55 PM   #10
JohnW is offline JohnW  Hong Kong
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Ashley,

I had personal experience of RF & Deltec products - there distributor in HK had a load of duff units - and after Deltec had gone under, he approached me to repair them - mostly duff input IC's damaged by earth leakage currents.

While repair these units, the neighbor on the 3rd floor below, used to complain about bad TV reception while I tested the units!

John
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