The Objective2 (O2) Headphone Amp DIY Project

[Splatem]

@xaurot
I will be testing a replacement MOSFET for Q2 in about two weeks, and will let you know if it fixes the problem I am seeing.

@jayce996
Have you looked on eBay? The O2 BOM lists alternative part numbers which you might be able to find with cheaper postage on the bay.

[QRikard]

For europe you could check farnell or elfa for example which might have the parts and probably cheaper shipping.

[swalter]

Hi,

if you need single spare parts you can also shoot me a PM, I buy all the parts in high quantities and am able to offer them to you at lower prices than mouser farnell & co. if single parts are required. Postage will be moderate is sent by letter mail in a bubble envelope

Stefan

[lorriman]

I need some clarification on RS's low power option which I intend to build next. He writes :

"You might also consider doubling the values of all six gain resistors and cutting the compensation capacitors in half to reduce the loading on the first stage."

All six gain resistors? I thought there were only four. Looking at the BOM I can see R3, R7, R19, R23, R17 and R21 are mentioned in some respect to gain resistors. Are these the ones? I know it seems obvious but I've learned the hard way not to make optimistic assumptions.

The compensation capacitors: I have no idea what these are. Which C numbers are we talking of here?

thanks

[sgrossklass]

You've got 6 gain resistors because there are two gain settings.
Rf = R16/22
Rg = R17/21 + R19/23

The caps are C19/20, in parallel to R16/22. Aim for same RC time constant.

An exact factor of 2 probably won't be feasible, but 2.2 should be.

BTW, I would actually recommend doing this. Low-power parts tend to have current-starved output stages which will be happier when loaded less. Gain stage noise usually is significantly attenuated anyway.

[sofaspud]

I know you already know this, but you'd be better off referring to the schematic instead of the BOM. Some of the resistors "are mentioned in some respect to gain resistors" on the BOM only because they are the same value. The gain resistors are R16, R17, R19, R21, R22, and R23. The compensation capacitors are C19 and C20.

[everlong]

Where do you guys buy 15-20V AC adaptor(EU plug preferable)? Anyone got a link to one that works with the O2?

Edit: Found one: http://www.kjell.com/sortiment/el/st...1000-ma-p44208

18V or 15V, the same or would 18V give more power?

[lorriman]

Originally Posted by sofaspud

I know you already know this, but you'd be better off referring to the schematic instead of the BOM. Some of the resistors "are mentioned in some respect to gain resistors" on the BOM only because they are the same value. The gain resistors are R16, R17, R19, R21, R22, and R23. The compensation capacitors are C19 and C20.

Thanks for that sgrossklass and Sofaspud.

In the meantime I'm listening, on my bed in my dimly but warmly lit room, to my O2+Odac with a nice bourbon and the 800 CD collection of my off-the-beaten-track-musical-taste flatmate. Here's raising a glass to Wigwam "Dark Album" which I've just happily barged in to.

[fenderf4i]

Are there any differences in the B2 and B3 enclosure other than the height? Is the PCB the same hight from the bottom of the enclosure on both cases? I'm looking to order a custom front panel for a B3, and am wondering if I just increase the height of the template for the B2 enclosure in the FPE software if it will fit the input/output etc correctly?

[ramsfan6239]

For a higher impedence headphone, like senn 650's, what would be a good gain for desktop only?