The Objective2 (O2) Headphone Amp DIY Project

[CrustyD3mon]

Originally Posted by pby

Have you tried Farnell? You can try uploading the BOM, though it'll take a day. The b2 case seems to be listed as US stock so you may want to try ebay to avoid the fee.

I don't try anything yet...only have searched the case in ebay...but i can't find nothing there....i'm searching for B2 enclosure or B2-080SI but nothing...

The components....what is the BOM that you refer?

Thanks

[ethanolson]

Jokener hasn't posted since New Year's Eve. Something's up. I hope it's not terrible.

[pby]

BOM is the bill of materials. The farnell version is included in the resources documentation.
ebay.co.uk has a few b2 enclosures at reasonable price, but you'll have to enquire about shipping to portugal.

[jfrana]

There seem to be no solder bridges. (The solder is not great, but nothing seems to be bridging and everything seems secure.)

I retested resistances -- resistances are all right.

I retested voltage. I believe all the diodes tested correctly. But there was some funky stuff -- pin 4 and pin 8 of U4 do not drop below 1v with a battery removed. -- The details page indicates that this means broken MOSFET. Additionally pin 2 of U2 is near -11.8v instead of -8.4, this indicates that U2 is broken (or maybe Q1 or Q2).

I retested the headphones (for the heck of it) with the AC and without batteries. Everything sounds nice. and the volume knob attenuates the right channel but not the left -- could this be due to U2 or the MOSFET being broken, or must something else also be improper?

[agdr]

Originally Posted by jfrana

Additionally pin 2 of U2 is near -11.8v instead of -8.4

Suggestion: start with figuring this one out first. -11.8V is essentially the negative rail (negative power supply) voltage with the unit running on AC power.

The chip pins are numbered counter-clockwise looking at it from the top, starting with the "dot" in the upper left corner being pin 1. Check that you are measuring the right pins.

With the power switch on and the headphones unplugged, measure between ground (the metal shell of the gain switch) and pin 8 of U2, then between ground and pin 4 of U2 and see if you get the 12.0Vdc and -12.0Vdc rails, +/-0.2Vdc or so with the O2 running on AC. Be very careful on the IC not to short pins together when measuring! Helps to have the DMM test probe resting on the edge of the plastic IC socket to stabilize it at each pin. If you are using batteries do all these measurements once for AC plugged in, with the batteries out, then again with the AC unplugged and the batteries in. In the case of batteries the U2 pins 8 and 4 should read somewhere around +8.4Vdc and -8.4Vdc, +/-1.5Vdc or so depending on battery charge level.

Then measure ground to pin 2 of U2 again for both cases (AC only and batteries only) and see what you get.

What you are testing here is the condition of your power supplies going into the mosfets, along with the U2 pin 2 reference voltage divider.

Maybe RocketScientist will log on and jump in here.

[urshurak776]

Hi all,

My amp is done and sounds amazing. The only issue I am having is with the batteries. I have tried 2 different sets including the blue Tenergy 250's RS recommended. After keeping the amp plugged in for around 24 hours I only get about 10 minutes of battery time before the amp does the low power "stutter." All is well when i plug it back in. I guess my amp is not charging? Everything checked out IAW the testing section. Any ideas?more info

Thanks,

Todd

Update: now it stutters even with power plugged in. The weird thing is it is intermittent. It stutters, then corrects itself......ahhhhhhhh

[urshurak776]

I'M AN I-D-I-O-T!!!!!!!!! It only happens when using Pandora..........

[FloridaBear]

Originally Posted by urshurak776

I'M AN I-D-I-O-T!!!!!!!!! It only happens when using Pandora..........

Ahh..."Buffering..." It's interesting that plugging it back in appeared to fix the problem. A strange coincidence there!

[MrSlim]

Originally Posted by urshurak776

I'M AN I-D-I-O-T!!!!!!!!! It only happens when using Pandora..........

PEBCAK

[agdr]

Originally Posted by Nikon1975

Would it be possible to feed the amp with DC, mainly to charge the batteries. I don't mean necessary on the onboard AC connector, I could tap someware and add an extra DC input.

RocketScientist probably has a slicker way to do it, but I've just posted one way here:

O2 amp CRC, diode, cap, and heatsink mods

I wrote up this reply and then realized it was essentially a modification. I'm trying to keep mods out of the main O2 thread here, so I stuck it in my mod thread instead.

Good luck! Please post a picture if you build it.