Replace PCM1738 with PCM1792

[voodooless]

I'm looking at "upgrading" my (SA)CD-player with a new DAC chip. It now features a PCM1738. Not at all bad, but I guess, it would be fun to put another one in. So I looked and I guess PCM1792 could be the right candicate. I looked at the pinout, and it should not be to hard to make an adapter board

• PCM1738 -> PCM1792
  AGND1 18 -> 19
  AGND2 27 -> 24
  /CS 14 -> DGND
  BCK 6 -> 6
  DATA 5 -> 5
  DGND 8 -> 8
  IoutL+ 25 -> 25
  IoutL- 26 -> 26
  IoutR+ 17 -> 17
  IoutR- 16 -> 18
  Iref 21 -> 20
  LRCK 4 -> 4
  MC 13 -> 12
  MDI 12 -> 11
  MDO 11 -> 13
  MUTE 15 -> DGND
  /RST 1 -> 14
  SCKI 7 -> 7
  SCKO 10 -> -
  Vcc1 23 -> 23
  Vcc2 24 -> 28
  Vcc3 28 -> 15
  Vcom1 19 -> 22
  Vcom2 20 -> 21
  Vcom3 22 -> -
  Vdd 9 -> 9
  ZEROL 2 -> 1
  ZEROR 3 -> 2
  AGND3L 27
  AGND3R 16

All in all doable I guess. Also, the internal registers are virtually the same. The only thing that bothers me is the current output. The 1738 has +/- 2.48 mA, but the 1792 has +/- 7.8 mA. What exactly would be the influence of this on the output circuitry? I guess the level would be a bit higher, but that can simply be fixed. What else should be taken care of?

 

[jerome69]

According to TI, the replacement for PCM1738 is PCM1796.
I don't think, you should have an improvement of the sound, because these chips seems similar ?
The improvement can come from the digital filter, if better in the PC1792 ?
Your upgrade should work if the DAC is standalone.

It should be better to make your own external DAC with a CS8416 and a PCM1792 or a SM5865 ? isn't it ?

 

[voodooless]

Well, yes, the dac's are quite similar, as is the PCM1796, but is has more ripple, more THD and less stopband attenuation. PCM1792 has better THD, better ripple and an even deeper stopband, and also dynamic range is larger. If I want a replacement, then I would want at least a significantly better spec then the 1738, and the 1796 will not give me this. The 1792 however will.

External DAC is useless since this is a SACD player, and I still want to be able to playback DSD stuff.

 

[jerome69]

For me the distortion of these chips are extremely low 0.0004%. The stop band of the oversampling, ok, is better for the PCM1792, useful only for the PCM low rate 44.1 or 48kHz. For the DSD, the sampling frequency is high (>100kHz), no problem with the oversampling filter.
Perhaps I am wrong ?

Ok, Give us the result about the change 😉

 

[voodooless]

Well, I use the thing for both DSD and PCM, and on both the filters are equally important, not just the stopband, but specially the passband ripple, meaning that if there is less ripple, there is also less pre-echo.

Anyway, since I'm not sure what the higher current output is going to do, I don't want to make de swap yet. Making an adapter board is probably going to be challenge on it's own, specially since there is very little room in the player. Maybe I should just be glad with what I have now 😀 It doesn't sound bad, at all 🙂

 

[finneybear]

Or you can just piggyback two 1738 together. This will give you a output current a bit higher than 1796s. Not the 1792 level yet but 1792 is very demanding on the power supply so the swapping job is not just a plain swapping.