The Objective2 (O2) Headphone Amp DIY Project

[greenalien]

If anyone is interested, I have 10 complete O2 kits available for immediate shipment - UK only - see O2 Headphone Amp - Complete Kits (UK only)

[greenalien]

I have 10 complete O2 kits available for immediate shipment - UK only see O2 Headphone Amp - Complete Kits (UK only)

This offer has now been amended to include European Airmail shipping, at no extra cost, so long as you don't mind a UK mains adaptor.

[greenalien]

Sorry, but I've had to add an extra £2 to the EU shipping costs due to the cost of Airmail.

[gumleguf]

Any advice on configuring the O2 to match a set of Beyerdynamic dt770 600 ohm headphones?

[sgrossklass]

Nothing in particular. You just need to keep the gain stage out of clipping by choosing your gain settings accordingly, as outlined before.

People with sensitive headphones/IEMs and loud sources tend to drop low gain to unity, but your Beyers are firmly on the other end of the sensitivity spectrum.

[gumleguf]

Thanks, but I'm a hopeless newb to this. Would I be going for a higher gain setting e.g x6.5 or a lower gain setting e.g. x1 for my Bd dt700 600 ohm head phones? Or am I missing something and is it the output voltage I should be concerned about? I plan to use the amp at my office always connected to AC power.

[nezbleu]

Originally Posted by gumleguf

Thanks, but I'm a hopeless newb to this. Would I be going for a higher gain setting e.g x6.5 or a lower gain setting e.g. x1 for my Bd dt700 600 ohm head phones? Or am I missing something and is it the output voltage I should be concerned about? I plan to use the amp at my office always connected to AC power.

So why not build the amp as per the plans, and see whether you have any gain issues? The stock arrangement gives you a low gain of about 2.5x and a high gain of about 6.5x, selectable with a front-panel switch. If you are concerned order some extra resistors (values are on the BOM and schematic) and use the sockets, so you can try some different settings. Report your findings back here!

[unsopa]

Hello,

eventually I will build the objective2, when PCB-boards are easily available in europe. It would be my first headphone amp then. I'd like to experiment on a perfboard first, having a little experience building a few guitar-stompboxes in the past. Just for proof-of-concept I'm thinking of building the amp-part of the schematic first and the power-supply and power-management later.

Here my questions: Would it be possible to use temporarily two isolated 9V DC outputs of my guitar-effects power-supply for positve and negative rails of the o2 amp section?

Or would it destroy something? (that the technical specs will suffer I'm aware).

What would happen, if one of the both 9V-outputs is disconnected temporarily? Would my 300 Ohm headphone or the circuit be fried?

Please be patient, because I'm writing not in my language, thank you.

[agdr]

Originally Posted by unsopa

Here my questions: Would it be possible to use temporarily two isolated 9V DC outputs of my guitar-effects power-supply for positve and negative rails of the o2 amp section?

Or would it destroy something? (that the technical specs will suffer I'm aware).

What would happen, if one of the both 9V-outputs is disconnected temporarily? Would my 300 Ohm headphone or the circuit be fried?

If by isolated they mean each output is on its own transformer secondary (I did some searching but couldn't find a schematic for the unit on the net), it should work fine. Just hook two of the 9V outputs in where the batteries would normally be connected, being careful to get the polarities correct. If one supply disconnects that would be no different than one battery disconnecting - or shorting itself out, which happens - and that is what the O2 power management circuit takes care of. So no problem.

You will find out soon enough about the isolation. If they are not truely transformer-isolated you will get a nice spark when you hook the wires onto the center two battery terminal locations, that ties the "-" of one channel to the "+" of another. Won't hurt the O2 but the power supply may not be happy.

[unsopa]

Thanks, agdr,
but what I meant was to omit the O2 power management also and just to build the main amplification first and to get some first impressions. As far as I know the DCT 200 power-supply ist truely transformer-isolated and short-crcuit-protected. Under these circumstances - how big is the risk to damage the headphones by temporarily using just the 2 x 9V outputs on the rails of the amp-section?