Parallels AD1865 DAC Built

This is a welcoming post in this year 2023.

During the last year holiday, which is last week, I spent lot of my time at home, tidy up my working space especially my desk for doing this electronic hobby.

I guess I will not make any DAC anymore. It is enough and I have experienced all kind popular vintage multibit DAC ever. But, somehow I still have a piece of AD1865 lying on my drawer unused.

And this how the idea of paralleling AD1865 DAC is came from.

Here it is.

Actually paralleling DAC IC is not a new things.

The first well known parallels DAC was came from the very first Accuphase DAC, they clearly stated it as Multiple Multibit DAC.

You can read it here

In short, multiplying DAC IC in double up quantities improve both signal and noise at the same time, but in total they will improve the signal to noise ratio and reduce errors.

SN ratio is cannot achievable by using high grading DAC IC. The higher grade such J or K grade will only improve the dynamic range, resulting from more accurate the resistors ladder inside the DAC circuitry, but not for the SN ratio. So this parallels DAC approach is improving in the are that a single DAC cannot do alone.

The greater effect is when 2 DAC IC are paralleling together, continue to 4, 8, 16 and so on but the result are follow by the law of diminishing return.

Since I have one AD1865 left, so why I don't do the same things?

The unit for this parallel DAC experiment is no others than my daily use integrated amplifier that use the LM3875 amplifier. This amplifier is having it's own DAC circuitry and the last update for the DAC inside this amplifier was exactly built on last year. I posted it on here

Unlike most of the integrated amplifier in the market, they put lots of function for suit many peoples wants. Somehow they are not specialized in one area, so they put lower performance on it. So most of the others function in the common integrated amplifier in the market are either degrading the sound quality or just a waste.

When I built an integrated amplifier like this, what I want is simplicity with high performance audio that suit my preference. It is more challenging to design an integrated amplifier to sound good because of the limited space inside.

As always I starting this experiment in a 10 cm by 7 cm universal board as required in the small space inside the amplifier case. It is point-to-point wiring on every pins of the components.

No dirty stacking job here.

No ugly piggy-back one IC on top to others IC.

It is all a clean job.

This is the size comparison between previous, a single AD1865 side by side with the parallels AD1865 DAC module.

They shared the same size and surprisingly the parallels board looks more simple.

Why?

The main reason is because I don't use op-amp.

I know op-amps are simple to use, well documented by the manufacture, low cost, low power required and easily available.

But some say the op-amps create their own sound signature and for the DAC will become the sound of op-amps itself.

So previously I did try not to using op-amps in my single AD1865 DAC here, just a simple resistor connected to the power amplifier directly. It works but the sound not that great, less punchy and slow.

The reason because a simple passive resistor as DAC current to voltage converter need a gain stage to boost up the output. The most popular one is using vacuum tube as I did on the post here.

But again, using tube is not suitable for this integrated amplifier application due to limited space inside.

So I keep using the same method, only using a resistor as the DAC current to voltage converter, then with 10nF low pass filter directly to the potentiometer as the amplifier volume control and then goes to LM3875 amplifier with 21x gain setting.

That's it!

No sound of op-amps, no coloration from using a vacuum tube as gain stage. It is all pure sound of the DAC itself.

The initial test for this DAC circuitry is working as planned. I using a headphone amplifier and listen it carefully. Guess what, parallels two AD1865 DAC sound completely different from what I heard before.

It is terrific!

This is a good sign of successful experiment and I can move forward to install it inside the integrated amplifier.

It doesn't take so much time to install this DAC module inside the integrated amplifier unit.

The transformer using here is high quality 12 VA EI transformer to make sure enough juice deliver to the parallels AD1865 DAC.

The audio signal output using 200 ohm resistor on each channel DAC, the voltage conversion is now become 400 mV.

Small enough if I compares to standard CD player output is around 2 volt.

The downside of this small DAC output is the amplifier volume level should be crank higher.

I don't care about it because I am not a high gain lover. Instead this is very good in theory because the potentiometer resistance is now more less resistance on the signal pass compares when on the high gain.

Previously on my 2 volt output DAC, the normal listening level is on 9 to 10 o'clock volume position. With this new parallels DAC, my listening level is only slightly higher, about 12 to 1 o'clock volume position.

Besides of this issue, the very important is how does it sound now?

In short, this Parallels AD1865 become one of the best sounding DAC I've ever built.

I can now fully understand the meaning on low level linearity on every DAC IC datasheet I have read before. For years I wondering what does it means, what is that and what the effect to the music?

And right now, with this parallels AD1865 DAC, I can feel what is the benefit of the low level linearity in the music.

It is not about detail, it is not about the sound-stage, not even about more bass or treble but it is all about every single note when the instruments, or music start or ends, focusing to the listener.

Every piano note, every guitar strings before and after they played on every single note are now listenable.

The tiny singer's voice when it start and finished on every music note are now deliver better.

It is very musical and enjoyable to listen the music now. It is just like a whole new experience listening to the same music again and again.

I live happily in this new year with this finding.

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