The Objective2 (O2) Headphone Amp DIY Project

[Etilletas]

I'm not sure I could build this then.

Tell me if I have this right: The O2 will have issues with extremely hard to drive headphones because the high gain necessary will cause clipping? But can this be fixed easily if you modify it?

It might be a valid criticism because it is supposed to be a "do it all" amp, but the critics (well, amb) is also saying the input will always clip, which makes no sense at all using the standard gain and a typical input right? He seems to be making a mountain out of a molehill just because NwAvGuy pissed him off.

Maybe a std. gain of 2x might be good just to be safe, but I wouldn't really know.

I'm sorry if us non-technical people are coming across as idiots, but we are just trying to understand, and I think this amp interests a lot of people who aren't that familiar with DIY.

Etilletas = Satellite (no DIY experience)

[Rembrant]

Originally Posted by Etilletas

I'm not sure I could DIY this then.

Tell me if I have this right: The O2 will have issues with extremely hard to drive headphones because the high gain necessary will cause clipping? But can this be fixed easily if you modify it?

It might be a valid criticism because it is supposed to be a "do it all" amp, but the critics (well, amb) is also saying the input will always clip, which makes no sense at all using the standard gain and a typical input right? He seems to be making a mountain out of a molehill just because NwAvGuy pissed him off.

Maybe a std. gain of 2x might be good just to be safe, but I wouldn't really know.

I'm sorry if us non-technical people are coming across as idiots, but we are just trying to understand, and I think this amp interests a lot of people who aren't that familiar with DIY.

Etilletas = Satellite (complete n00b as far as DIY goes)

The amp was made to be useful for sources that don't have a preamp out. Like portable devices and such. These guys are on about something because they can't blowtorch the input with 4vp from a preamp that they could either remove from the signal chain altogether, or simply attenuate. The loudness of this amp, at the right gain setting, would not require you to overdrive the input with any set of phones I can think of.

Why this happens.
The volume control pot was placed between the gain and buffer stages of the amp for various reasons. One of them being the opamp that was chosen for the gain stage. Ultimately, the attenuation could be moved to its own stage with buffers flanking but that would require at least two extra dual opamps and more board space etc. They could blowtorch that attenuation stage all they wish. There are always trade offs. This amps claim is superior performance at reduced cost. Not that one can't overload the input with a ridiculous amount of signal.

[RocketScientist]

Just to be clear, the O2 on AC power runs off 12 volt rails. The maximum input is 7/X where X is the gain factor. So with 3X gain it can handle 2.3 V RMS input which is more than most anything without a volume control can produce. If your source has a volume control, there's no issue at all.

It's also worth noting the input stage and output stage (at max volume) clip at the same level. And there are hardly any headphones on the planet that need 7 V RMS.

[maverickronin]

Those sorts of extra "hot" sources actually seem to be pretty popular over at head-fi which is why I think they're making a fuss about it...

[xnor]

Why not just simply set the lower gain to 2x so that there's no problem with hot nonstandard sources. I don't understand what all the fuss is about.

[RocketScientist]

Originally Posted by xnor

Why not just simply set the lower gain to 2x so that there's no problem with hot nonstandard sources. I don't understand what all the fuss is about.

I don't fully understand it either but I've decided to lower the default gain to 2.5X (8 dB) to provide some extra margin for rare sources. This allows up to 2.8 V RMS of input. I've already revised the article and the new resistor values will be in the revised design documents.

If anyone knows of realistic O2 sources, without volume controls, that have more than 2.8 V RMS of output, please post a link to the specifications here. And if there are such sources, the gain resistors can be simply clipped dropping the O2 to 1X gain and you could still drive the HD600s beyond an ear splitting 110 dB SPL with such a source.

[idjoel2000]

Originally Posted by RocketScientist

If anyone knows of realistic O2 sources, without volume controls, that have more than 2.8 V RMS of output, please post a link to the specifications here. And if there are such sources, the gain resistors can be simply clipped dropping the O2 to 1X gain and you could still drive the HD600s beyond an ear splitting 110 dB SPL with such a source.

dacmagic? 4.2vrms in balanced mode: Specifications / DacMagic Digital to Analogue Converter / Digital Music / Products / Cambridge Audio

CMIIW

[RocketScientist]

Originally Posted by idjoel2000

dacmagic? 4.2vrms in balanced mode: Specifications / DacMagic Digital to Analogue Converter / Digital Music / Products / Cambridge Audio

But that's 2.1 V RMS in unbalanced mode and would work great with the O2's unbalanced input.

[Upstateguy]

Originally Posted by maverickronin

Those sorts of extra "hot" sources actually seem to be pretty popular over at head-fi which is why I think they're making a fuss about it...

Originally Posted by RocketScientist

I don't fully understand it either but I've decided to lower the default gain to 2.5X (8 dB) to provide some extra margin for rare sources. This allows up to 2.8 V RMS of input. I've already revised the article and the new resistor values will be in the revised design documents.

If anyone knows of realistic O2 sources, without volume controls, that have more than 2.8 V RMS of output, please post a link to the specifications here. And if there are such sources, the gain resistors can be simply clipped dropping the O2 to 1X gain and you could still drive the HD600s beyond an ear splitting 110 dB SPL with such a source.

I just looked up my Stello DA100 and it has a 2.4Vrms output signal level. I've never thought of the Stello as being a "hot" source but it seems to be very close to the maximum with a 2.5 gain.

My Pico portable dac is listed as having an output of 2.84Vrms on the HeadAmp web site (maybe I'm reading it wrong). Link I never thought of the Pico as being a particularly "hot" source either and have plugged it into all my amps, both portable and desktop, with no problems.

My feeling is that there might be a few more 2+V sources out there then we realize, but I'll leave it to the EEs here to sort it out.

[idjoel2000]

Originally Posted by RocketScientist

But that's 2.1 V RMS in unbalanced mode and would work great with the O2's unbalanced input.

yeah but personally, i always use the balanced output using xlr-rca converter and feed it to my single ended amp since the balanced out sounds better than the single ended one and i'm pretty sure some members here are doing the same thing since it's covered in dacmagic mod thread somewhere in the Digital Line Level section in this forum

anyway, i was just trying to give some input