The Objective2 (O2) Headphone Amp DIY Project

[Twinster]

Sorry I meant P1 just beside J2. So yes I'll try to remove one of the ground wire and leave one RCA groung only. Thanks for the input.

Originally Posted by agdr

J1 is the DC power jack. That is why you have hum if you connected to the ground there,. There are some really big current spikes moving back and forth between the power jack and the filter capacitors.

The ground ring of the RCA connectors goes to the center (middle of jack, towards the front of the board) pin of J2, the input jack that you connect to your music source. And you should only use one wire, not two, or you risk a ground loop. Just run one wire from that pin on J2 to the ground ring on either RCA jack. The other RCA jack is touching the case with its ground ring, and you just grounded the case with your other RCA jack ground ring and your sanding, like MrSlim said.

If you just made a typo and really are connecting to J2 instead of J1 then the two wires, rather than one, may be the cause of the hum. Also try to route that single ground wire away from the area around the DC jack and 4 filter capacitors C2 - C5 to avoid hum pickup.

[agdr]

Originally Posted by swalter

Hello gents,

I would have a question regarding capacitors C6 and C7. The BOM states 1.0uF whilst the circuit diagram states 0.22uF. Which values are the correct ones?

Thanks, Stefan

The BOM spreadsheet is correct. I think RocketScientist posted once that he was having some trouble getting the schematic document updated on Blogger. The spreadsheet is dated Dec 2011 but the schematic is Aug 2011.

[swalter]

Thanks, so I will refrain from soldering the 0.22uF ones in that came with the kit and look through my parts stock at home for some 1uF ones instead.

Stefan

[agdr]

Originally Posted by swalter

Thanks, so I will refrain from soldering the 0.22uF ones in that came with the kit and look through my parts stock at home for some 1uF ones instead.

Stefan

That is actually a modification I came up with that RocketScientist adopted. If you already have the 0.22uF you are OK. The negative regulator chip U6 shows a 1uF in the data sheet which would help suppress oscillations under some odd circumstances. But if you put in the 0.22uF and your U6 isn't getting abonormaly hot, which would probably be the case 99% of the time, you are fine. If someone is buying the parts the first time though might as well get the 1uF since the price is about the same.

[swalter]

Originally Posted by agdr

...if you put in the 0.22uF and your U6 isn't getting abonormaly hot, which would probably be the case 99% of the time, you are fine...

I guess I use the 1uF then, better save than sorry Thanks for the detailed explanation!

[MrSlim]

Originally Posted by Twinster

Sorry I meant P1 just beside J2. So yes I'll try to remove one of the ground wire and leave one RCA groung only. Thanks for the input.

I've mounted the RCA's this way:

Colored isolating ring on the outside, Screw it down tight with nut #1 (if you use the part# RS specified you get 2), add the ground lug ring, then add the second nut. Throw away the the inside washer..

I also use a double ground, one to each RCA twisted tightly with the signal wire, with the RCA's right above the input connector, wires are about 1.5 inches long (with a 3 pin connector). I get no hum..

[Twinster]

So you also used a ground wire to each RCA jack.

My wires are about 2" long and I have also twisted them around the signal wire. Maybe I need to sand down more inodize paint and I'll redo the nut order like your.

Thanks again.

Originally Posted by MrSlim

I've mounted the RCA's this way:

Colored isolating ring on the outside, Screw it down tight with nut #1 (if you use the part# RS specified you get 2), add the ground lug ring, then add the second nut. Throw away the the inside washer..

I also use a double ground, one to each RCA twisted tightly with the signal wire, with the RCA's right above the input connector, wires are about 1.5 inches long (with a 3 pin connector). I get no hum..

[wendell c]

just finished my O2 and I had a question about charging, does the led light up when charging or when batteries are fully charged? thanks

[agdr]

Originally Posted by MrSlim

I also use a double ground, one to each RCA twisted tightly with the signal wire, with the RCA's right above the input connector, wires are about 1.5 inches long (with a 3 pin connector). I get no hum..

Good to know! Certainly can't argue with good results.

[Davey]

Originally Posted by wendell c

just finished my O2 and I had a question about charging, does the led light up when charging or when batteries are fully charged? thanks

The LED has nothing to do with battery charging. It just indicates whether the unit is on or off.

Batteries will charge if the AC wall-wart is connected, they won't if it's not.

Cheers,

Dave.