[diditmyself]

I just got my 2009 Zero DAC with OPA627 on the DAC output. I wonder what tricks I should use to make it better.

1. The "treble killing" capacitors in parallel with the output? Do they really affect the sound, and if so in a negative way? If they are 22 pF (maybe they're 2.2 nF) as claimed in some of the modding posts here, they shouldn't affect the audible spectrum since the cutoff frequency is very high. If it's connected to an amp with 10k Ohm input impedance the cutoff frequency would be 800 kHz. What do you say, do they really worsen the sound?

There seem to be a lot of filtering caps around the opamp as well. Has anyone tampered with them?

2. Is the DAC opamp really necessary? The output impedance of AD1852 is spec'd to 65R. Isn't the AD1852 a voltage output DAC? What would the drawbacks be if I bypass it? DC offset? If I bypass it, where should the negative output go - just leave it as is? I think this is how Lampizator does it.

3. Are there any coupling caps to be upgraded?

4. Are there any decoupling caps that should be upgraded?

Other suggestions?

 

[FallenAngel]

1) Not sure, but I don't think there are parallel caps on the output, maybe series and they're DC blocking caps - without them you'll see some DC on the output, which you should remove before amplification.

2) Not necessary, but you need balanced to unbalanced conversion, or use half the signal. Should still cover DC blocking.

3) Of course, I think there are 3 coupling positions on the Zero.

4) If you want, though not as important as coupling.

Other suggestions : before dumping a lot of money into "upgrade", consider that the price of the DAC+upgrades may land you a better DAC.

 

[diditmyself]

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif before dumping a lot of money into "upgrade", consider that the price of the DAC+upgrades may land you a better DAC.

That's why I started this thread. Not to do any nonsense placebo mods with expensive parts, or risking instability. Removing unnessecary parts will be first on the list. But I want to be sure that they really are unnessecary. Replacing inferior active parts will be second and inferior passive parts third.

The cap on the output have to be in parallel. People are cutting it, not bypassing it. Besides, it's far to small to be a coupling cap. It's there for stability, like a zobel, or to filter out high frequency noise. The question is if it's necessary or not. The perceived increase in treble could be instability or imagination.

If for some reason it's not feasible to bypass "everything" (just using a polypropylene cap), I was thinking of replacing the DAC opamp with an open loop class A JFET buffer. I think the offset can be removed this way, and I hopefully don't have to use coupling capacitors.

I've read the very long threads of modding the Zero, but I'm not sure if I can trust all reports of dramatically improved results by adding large caps with long leads. The risk of introducing inductance and risking instability seems high. Besides the same guys use HDAMs with crazy long leads. Not only long leads but they're omitting the ground connector with faulty operation and enormous crosstalk as a result.