The Objective2 (O2) Headphone Amp DIY Project

[Blackbird7]

I've just completed everything and done resistor and voltage tests. Most of things are ok, but some values are different than expected.

In resistor tests R1&R2 should be 100-200, I've measured them 238. R5 should be 100K, I have it 109K. R25 should be 330K, but it's 316K.
As for voltages, when testing with AC, only difference from NwAvGuy test diagram is U4 pins 4 and 8. They should be 11.8V (+/-), but are 11.6V (+/-).
When I disconnect from AC, and try those pins with batteries only, they have 8.9V. It should be also 11.8V?

Are resistor measurements in acceptable values? Did I do something wrong?
It's DIY bought on Head'n'HiFi, and as I see, everything is as written in O2 BOM.

[sofaspud]

Looks like what you may be dealing with is nothing but component tolerance. R1 & R2 are current-limiting resistors only; their values aren't critical unless they are too low and allow excessive charge to the batteries. It looks like your other resistors are part of the engineering change for the power management circuit. I didn't implement that change and so will refrain from comments, except to say it has to do with the O2 turning on and off, not its actual operation. The voltages you show are fine. AC power provides a few more operating volts than battery power.
If these are the worst things you've found in the tests, get some cheap headphones for first power-up testing and listening. If that passes, plug in your favorite headphones and enjoy your new O2!

[BamboszeK]

I have two O2+ODAC combo in same enclosure and i have small problem with noise. At full volume, i can hear a noise with very sensitive IEMs.
With bare O2 without ODAC what i build before there is dead silent even at full volume. Well, it is insane level, i do not even tried to play music at this volume but i want just make sure that everything is ok.

I just found that:

here was some unconfirmed reports of hiss and hum from the odac installed on top of the o2..

from AudioPoutine ODAC Mounting kit instructions

[agdr]

Originally Posted by BamboszeK

I have two O2+ODAC combo in same enclosure and i have small problem with noise.

I've been wondering if putting something digital (noisy) that close to the audio input parts is such a good idea.

With the O2 powered up, try disconnecting the USB cable to the ODAC and then listen for noise again in your headphones with the volume and gain all the way up again. With the USB cable pulled out that cuts the power to the ODAC and should quiet all the digital stuff. Does the hiss go away like that?

[BamboszeK]

Disconnecting USB cable almost removes noise, but amp is not still dead silent like O2 without ODAC in enclosure. It maybe because ground traces in input jack are cutted so input "floats" and pull noise from air. I noticed that ground wire makes big difference in combo, bare O2 is dead silent even without it.

[agdr]

BamboszeK - interesting! You are right, without the inputs grounded the O2 will pick up some noise. In this case the O2 inputs would still go back to ground via the input circuit of the ODAC, but with the power removed there is no telling how much resistance to ground would be present in the ES9023 chip. A lot of additional resistance would increase the Johnson noise on the O2 input and that alone would bump up the background noise slightly.

Have you twisted each input wire together with a ground wire going from the ODAC to the O2? If not that would definitely be worth doing.

[BamboszeK]

At beginning, i want to thanks you for help. Yeah, input wires are twisted together, i've used standard cat 5e ethernet wires.
Summing, looks like mounting ODAC inside O2 decreases performance slightly, but mostly inaudible or imperceptibly in real use.
Ah, and one more small question. JDS Labs and NwAvGuy suggests slightly different wiring methods. I've used JDSLabs method 1, connecting to P1 with one ground wire.
http://www.jdslabs.com/pdf/Instructions_ODAC_DIY.pdf and http://nwavguy.blogspot.com/2012/05/...ay-update.html

[agdr]

Originally Posted by BamboszeK

Ah, and one more small question. JDS Labs and NwAvGuy suggests slightly different wiring methods. I've used JDSLabs method 1, connecting to P1 with one ground wire.

Yeah, it sounds like the ODAC increases background noise a little, but probably not enough to really be a problem.

On the wiring, I would recommend NwAvGuy's way of doing it using two wires. The twisted pair thing works because equal currents in opposing directions in the two wires produce equal electromagnetic fields around the two wires, but in opposing directions so they will cancel. Using the two wire approach ups the chances for getting equal but opposing field cancellation around the wires.

[Blackbird7]

Originally Posted by sofaspud

Looks like what you may be dealing with is nothing but component tolerance. R1 & R2 are current-limiting resistors only; their values aren't critical unless they are too low and allow excessive charge to the batteries. It looks like your other resistors are part of the engineering change for the power management circuit. I didn't implement that change and so will refrain from comments, except to say it has to do with the O2 turning on and off, not its actual operation. The voltages you show are fine. AC power provides a few more operating volts than battery power.
If these are the worst things you've found in the tests, get some cheap headphones for first power-up testing and listening. If that passes, plug in your favorite headphones and enjoy your new O2!

Thank you!
I did test and everything seemed ok, so I took my AKG K702 having doubts, can they sound better with O2. They sure can! I'm so glad I decided to try this DIY, after 15 years from last time I soldered something.
All in all, it went much easier than expected. At the end I realized that U5 and U6 are soldered too high, and had to re-solder them... They were extremely hot when doing that and I was scared I burnt them. But it seems they're not easy to kill. And then realized that outer battery is too high (by a hair) to fit into case. Doesn't bother me as I plan to use it as desktop amp for now.

[sofaspud]

Great to hear you're enjoying your tunes.
You could probably adjust the battery connector a little to get it to fit. It has a lot of metal mass, so what I do sometimes in those situations is remove as much solder as I can, then melt the remaining solder and use long-nose pliers to wiggle the part while the solder rehardens, which leaves the part loose.