Review: ZERO 24 BIT/192KHz DAC/Headphone Amp/Pre-Amp - Page 501

Ok, solved the offset problem with 2 pots, 2M5ohm, and 2 resitors, 1Mohm, to the + inputs of the output amp. Each adjustable. So now the offset is about 1mv. Now the DAC is completely DC coupled, no caps. in the audio path. The HDAM Earth is seated on sticky tape. The sound is very nice. I am comparing it with my Buffalo/Opus DAC. I don't use a headphone so the difference is very hard to hear. Speakers are not like headphones.
The housing of the Zero is really ugly/tastless. The Zhaolu 2.5 DAC I have is even uglier. I think I will rehouse it. The headphone amp. of the zero is far too hot. I disconnected it.

One more noob question:

Is it advisable to turn the Zero off when I'm not using it? Will it overheat if I leave it on overnight to burn-in?

You'll have to check the manual for the Juli as to what you can do with it.

Have a read of the FAQ in my sig. Normally, only the DAC section is in operation, with output going straight to the rear RCA jacks. If the Preamp button is pressed, the output goes through the amp/pre-amp section as well, controllable with the volume knob. If headphones are plugged in and the Preamp button is pressed, the ZERO becomes a headphone amplifier. With headphones plugged in, no sound comes out of the RCA jacks.

It wont overheat, no. I've left it on for many hours with no problems. I wouldn't put other gear on top of it though so it can have some ventilation as it does get quite warm.

Does the zero not use a phase locked loop to track this offset? Are you using that resistor network as an offset resistor to generate an offset voltage which is coupled between the inverting input of the op amp and the op amp's output? OR is this an Andrea solution. Prickly Pete, comments?
EDIT: would the HDAM not overheat by being encased in thick tape?

Thanks for the reply, Curra.

Do you think it would be alright if I left my Zero to burn-in overnight? I have 20 min pink noise alternating with 2 min digital silence.

Thanx Currawong.

There is no PLL for the offset. This is just a pot between +&- 15V going over a 1Mohm resistor to the + inputs , pin 3 and 5, of the output buffer.
And yes, the HDAM gets a bit warm. Will redo it.

OPA627 in head-amp?

Hi,

I have soldered version of OPA627AUs free after purchasing HDAM Earth. Is it possible to use these OPA627AUs in Zero head-amp instead of one LT1364? Anyone tried this combination?

Thanks,
Stanley

@Stanley:

You can, but you'd need 4 627s total - 2 each on 2 adapters. I don't remember the details but I'm pretty sure people have tried this and found it less than exciting...

I don't commend through this way to keep the output pot at 0VDC.
Why had DC level in there?
Because AD1852 is a single power supply chip, those output Pin of AD1852 have half power voltage, there are 2.5V.
But all those Pin don't have completely same voltage, maybe +out Pin had 2.53V,and -out Pin had 2.47V. The output analogy circuit is a difference amp, in this DAC is use a OP-IC to do that.
The output level of difference amp =VIn+ - VIn︳, in this case, output level=2.53-2.47=60MV.

Why I don't commend add a 1M ohms and adjust resistor to keep output DC at 0V?
These resistors will change the impedance of Vin+, then let the difference amp been un- balance, the distortion will grow up.
If clear to say this , it need a lot of words , but unhappily, my English is very bad. I hope you can guess and mean what I said.

Most amp had input couple cap or DC serve circuits, so I think, less than 100MV DC at DAC output , most amp will safe to work. You can test the DC level of the amp output pot , if near 0V, it work well.

Hmmmm further investigation (explanation ) WRT to dc offset would be warranted and appreciated.

This goes above my head at the moment but I do understand the concepts and why too much offset is a bad thing. It would seem though that the design of the Zero revolves around it pluses and it's minuses as does any design where certain compromises to topology must be compensated for or enhanced.

I have noted no ill effects from the stock arrangement as I believe Kingwa is correct in saying some offset if low enough is harmless and is present in a lot of designs...then again it's equally intriguing to see a learned new member of the Zero club redesign the circuit topology somewhat to arrive at a new configuration

This thread is certainly loaded with great information.

I marvel at the comments about a chassis being ugly...at this price point what do you expect ? It's functional and it serves the purpose, that's good enough for me...however if one spends money on a new chassis that's also really cool IMO...so...it's up to the individual once again

Either way I'm learning loads from you guys and loving it

Peete.

I started readin this BIG thread. What headphones does NOT fit this amp?
Can i buy whatever can i want and it will sound great?I Read the first ten pages and from that it seemed to fit most phones. so is there any no no?

EDIT. Or any specs? I mean - 32ohm = 600mW F.eks

Audio-gd, I respect your comments but think about it, 100mv offset x50(=gain power amp)=5 volt offset when volume is at the highest level. This happens when I test the system. The protection shuts off at about 800mv DC on the speaker output, so no solution.
Either way, if you use an offset integrator you connect a high ohmic resistor to the + opamp input also. Also think like this: the impedance at the + input is low=HF filter + impedance from the DAC chip =about 1k....so what does 1M do.....nearly nothing just offset the +input to match the - input. My Opus/Buffalo/Zhaolu/Elektor2000 are all DC coupled also. No problem. They don't need the offset adjuster BTW.
Soundwise= no difference but now I can crank up the volume to max. This is so cool. DC coupling is so accurate!

interesting modding bgt
i wish i had the time and ability to do the same =| probably just going to settle for a HDAM upgrade.

Can I suggest discussing mods to the zero in the Zero mod thread?

shampoosuicide: Should be no problem burning it in overnight. I gather just leaving it on, regardless if music is playing or not will burn it in. The more fun way, IMO, is to just listen to music through it and enjoy the change in the sound, but each to their own.