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Author Topic: Purely speculative - Rag, Yggy, Theta - how tech development affects sound, etc.  (Read 1867 times)

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OJneg

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But in general, a MOSFET amp can have a simpler output stage with fewer paralleled devices...which is good, because paralleled devices are always a sonic compromise. The more devices, the bigger the compromise. Yes, even when "matched."


Does this also apply to dacs which stack a bunch of chips together? (a big generalization I realize)

Going to depend on the chip. With current output DACs that are well matched I wouldn't be afraid of paralleling them. Someone else could provide some insight into any negative side effects (there's always pros and cons in engineering)
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Solderdude

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But in general, a MOSFET amp can have a simpler output stage with fewer paralleled devices...which is good, because paralleled devices are always a sonic compromise. The more devices, the bigger the compromise. Yes, even when "matched."


Does this also apply to dacs which stack a bunch of chips together? (a big generalization I realize)

Usually this was done to improve linearity.
The older 16 bit ladder DAC chips had problems with linearity (you were lucky to get 14 bits real resolution out of them).
It is VERY hard to make the MSB with such a tight tolerance compared to the LSB.
Paralleling those chips averaged out the errors of many chips (and increased the total output current) and linearity got a bit better.

In some low noise pre-amps some parallel input transistors, in this case the theory is that the noise (being random) doesn't 'add' as much as the signal which is common for these devices and thus effectively increasing S/N ratio.

For power amps it is needed to spread currents, or power dissipation (less heat/chip), over more than one device for technical reasons.

The O2 uses 2 IC 'halves' to increase output current.
I once made a power amp with a load of (high current) opamps in parallel.
Simply to increase output power and spread heat dissipation.

Just for the fun of it and because I had the parts lying around.

You can also parallel lots of tubes to increase output power


So there are plenty of reasons to parallel devices.
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Armaegis

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The reason I asked about parallel dac chips was due to reading about the DDDAC1794 project, and this note here... http://www.dddac.com/dddac1794_other.html
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ultrabike

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I actually got curious about them op-amps. What ya guys think of this one:

http://www.ti.com/lit/ds/symlink/lme49726.pdf
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Solderdude

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A nice theory that assumes jitter in each component either varies or is linearly spread among the chips.
Of course it is just HIS theory because he needs to explain something that he heard and appears to be getting a lot of 'heat' from others.

It would be nice to see actual shots of the final risetime with say 1, 10, 60 or 240 chips showing jitter, caused by DAC chips having different 'trigger points' AND slew rate improves with more (TDA1543) chips used.
It must be one hell of a clock and data driver being able to 'charge' the capacitance of so many paralleled DAC chip inputs/wiring not to mention the local decoupling and power supply which would be a real pain to get right with so many 'switches' switching at the same time :D
I would love to see the RFI emission that DAC shows.

Anyway... The spread that is in there will not be linear (as per his explanation drawing) but Gaussian BUT the jitter caused by the DAC chips NOT 'switching' at the same time will be improved for sure.
Too bad this jitter is much smaller than the jitter coming from the drivers that supply the clock (my assumption)

So yes... he may well perceive an improved SQ with more chips.
The question remains WHAT that would be causing.
I reckon it would be VERY EASY for such a DAC pioneer to show some real life scope pictures showing the improvements.
Now lets hope his scope also always 'triggers' at the exact same level  :)p17

Having more chips in parallel also creates other problems such as power consumption, power supply decoupling, the current needed to charge capacitances, length of wiring.
The higher the frequency goes (1794 is oversampling) the more problems you get in return.
Therfore I think it is impossible to predict how multiple 1794 DAC chips in parallel will yield a more accurate signal / affect subjectively determined SQ.
Most likely it will be an improvement to those that do.
But as with everything to get more (real) improvement you need to double the amount of chips every time you want more 1-2-4-8-16-32-64-128 etc.

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Solderdude

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I actually got curious about them op-amps. What ya guys think of this one:

http://www.ti.com/lit/ds/symlink/lme49726.pdf

Very nice, alas only suited for 5V supply rails (+/- 2.5V) so great for low voltage DAPs that need to drive 8 Ohm or 16 Ohm loads.
Can't be used for +/-5V or higher supply voltage rails.  :-[
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Marvey

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On DAC linearity. I'd suppose better linearity correlates to better SQ.

I hacked up a DCX2496 (digital EQ with 6 channels) and paralleled the 3 AKM chips' output.  This seemed to increase resolution from a subjective POV.

Would be interesting to measure DAC linearity. Plot X vs. Y where X is code (let's start at 16-bit) and Y it output voltage. Might be an interesting measurement.
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Anaxilus

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Just injecting a caveat here.  One of the problems with many making a subjective claim of 'better' IME is that they often just mean different (i.e. I now hear more of this but have lost that in doing so).  It's human nature to perceive new=better.  One needs to frame comments in context of how experienced is the listener, how clearly do they communicate, is there an agenda, how much are they being paid or compensated, what do they stand to gain, etc.  That way we can better parse what is valuable data from the chaff for constructive dialogue. 
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Just injecting a caveat here.  One of the problems with many making a subjective claim of 'better' IME is that they often just mean different (i.e. I now hear more of this but have lost that in doing so).  It's human nature to perceive new=better.  One needs to frame comments in context of how experienced is the listener, how clearly do they communicate, is there an agenda, how much are they being paid or compensated, what do they stand to gain, etc.  That way we can better parse what is valuable data from the chaff for constructive dialogue. 

Yep, that's one of the reasons our dev cycle is much longer than it used to be.

You do have to sit back, listen, test, and get perspective on new products, especially since, as designers, we're so close to them. It's thrilling when you first fire something up and have a listen...but you may be too close to the product to be impartial at that moment in time.

It's not unusual for us to intro something 18 months after first fire-up now. But there's a lot of stuff that's been on the burner...
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Kunlun

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Just injecting a caveat here.  One of the problems with many making a subjective claim of 'better' IME is that they often just mean different (i.e. I now hear more of this but have lost that in doing so).  It's human nature to perceive new=better.  One needs to frame comments in context of how experienced is the listener, how clearly do they communicate, is there an agenda, how much are they being paid or compensated, what do they stand to gain, etc.  That way we can better parse what is valuable data from the chaff for constructive dialogue. 

Yep, that's one of the reasons our dev cycle is much longer than it used to be.

You do have to sit back, listen, test, and get perspective on new products, especially since, as designers, we're so close to them. It's thrilling when you first fire something up and have a listen...but you may be too close to the product to be impartial at that moment in time.

It's not unusual for us to intro something 18 months after first fire-up now. But there's a lot of stuff that's been on the burner...


By the way, you mentioned having an epiphany a little while back. If you explained what it was, I missed it. Could you share it?
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