PCM1738e Question?

[georgehifi]

Excuse my ignorance with digital, but i've been hearing alot about stacking (paralleling) dac's. Can a PCM1738e be stacked? and what advantages do you get?

Cheers George

[georgehifi]

Can anyone help? Ithought i'd give you a look at the output stage of the circuit as well.

George

[Charles Hansen]

When you are using current-output DACs (eg, PCM1738, PCM1704, AD1862, etc) then you can stack them and the currents will add. Each time you double the number of DACs the signal will increase by 6 dB, while the noise will only increase 3 dB. Thus there is a net increase in S/N of 3 dB each time you double the number of DACs.

However, remember also that the drive circuitry will also be presented with increased loading. This is probably most critical for the master clock. The increased loading *may* increase the jitter...

[georgehifi]

Thanks for answering Charles, i was begining to think that nobody knew this dac, i've posted the other half of the circuit, can you tell if whats driving the dac can do it easy, without having a hard time, i know that you can not read the chip numbers but i can on my circuit if you need to know them, just tell me which ones.

Cheers George

[Charles Hansen]

It looks like the DAC can be driven by two sources:

1) SM5819 DSD -> PCM converter, or;

2) CS8420 sample rate converter.


In my opinion, neither way is the best way for good sonic results. SACD will sound better by sending native DSD data to the DAC, and PCM will sound better by sending the original data rather than guesses created by the SRC chip. In addition, the master clock is sent through a MUX which will add jitter.

The bottom line is that there are many more meaningful ways to improve this device rather than adding mulitiple DAC chips. That said, there may be some small gains to be had by adding more DAC chips. The only way to know is to try it. This DAC is relatively low cost, only about $5. So it won't cost much to try.

Normally the multiple DACs were achieved with through-hole parts, which makes it very easy to install. The PCM1738 is only available in SMT, so it will much more difficult to add more DACs.

Good luck!

[georgehifi]

Thanks Charles you just scared me of it when you said smd, (53yro eyesights shot) i did'nt bother looking at it when i did my other mods.
I've replaced the 2x NE5532's after the dac with 4xad825's on browndog boards, that made a nice change, then i direct coupled the output, but first i had to trim out the dc offset in the discreet output stage, now it holds steady at 1 to 2 mv.
BTW that output stage is said to be so strong it can drive
4 to 6 watts rms almost good enough for a pair of efficent horns. (who needs amplfiers)

Thanks again for your help, George.

BTW here's the power supply very unusual

[Charles Hansen]

Just out of curiosity, what brand and model of DAC is this?

[georgehifi]

It's the Musical Fidelity AC3-24, the 4 big chokes on the power supply from what i've been told were left overs from the Nuvista amps, they had to use them up somewhere, the transistors on the output are BDX33 and BDX43 Darlingtons TO-220 package run in class A . This thing is massive in size and weight as much as some poweramps. It does 96khz and 192khz switchable.
Thought it would interest some, sure does sound good.
Some extensive measurments done here, very good jitter and what not.
http://stereophile.com/digitalsource...61/index6.html


Cheers George