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-   -   The Objective2 (O2) Headphone Amp DIY Project (http://www.diyaudio.com/forums/headphone-systems/193977-objective2-o2-headphone-amp-diy-project.html)

RocketScientist 14th August 2011 06:46 PM

Quote:

Originally Posted by idjoel2000 (Post 2671848)
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

A normal XLR to RCA adapter will only use half the balanced output and the voltage drops to 2.1 V RMS. If you tried to tie the two "hot" balanced outputs to the RCA to get 4.2V, half the balanced output from each channel would be shorted to ground inside the amplifier.

Arius 14th August 2011 06:51 PM

Likewise, I was just trying to give some guidance to the folks here who are unable to grasp basic math or comprehend the O2's superbly detailed documentation.

Joel and USG: Why point out to others how many volts your source puts out?

Line outputs that follow CD Redbook standard puts out 2V typical. Diff outputs are 4.5V typ.

If you are genuinely interested in the O2 as a DIY project, then it's up to you to set the output level of your source correctly or in lieu of being able to do so, then set the input gain of the O2 correctly.

Again, you've pointed out how your source might overdrive the O2 in default 3X gain. None of you have bothered to ask how to change the gain to 1X or 2X, or after reading this forum and the O2 docs stated that you will, I can only assume you do not possess sufficient skills to DIY this project.

idjoel2000 14th August 2011 07:08 PM

Quote:

Originally Posted by Arius (Post 2671883)
Likewise, I was just trying to give some guidance to the folks here who are unable to grasp basic math or comprehend the O2's superbly detailed documentation.

Joel and USG: Why point out to others how many volts your source puts out?

Line outputs that follow CD Redbook standard puts out 2V typical. Diff outputs are 4.5V typ.

If you are genuinely interested in the O2 as a DIY project, then it's up to you to set the output level of your source correctly or in lieu of being able to do so, then set the input gain of the O2 correctly.

Again, you've pointed out how your source might overdrive the O2 in default 3X gain. None of you have bothered to ask how to change the gain to 1X or 2X, or after reading this forum and the O2 docs stated that you will, I can only assume you do not possess sufficient skills to DIY this project.

well, rocketscientist asked for input, i was just trying to give one.. :p

personally i already quite understand and pretty much know what to do with my pcb when it shows up on my door

SpaceTimeMorph 14th August 2011 07:36 PM

Quote:

Originally Posted by Upstateguy (Post 2671847)
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.

The Stello DA100 only outputs 1.2 Vrms. The Stello DA100 Signature is listed as 2.4 Vrms but it doesn't specifiy whether or not this is balanced output... do you know which it is?

The pico is a DAC+HPA, the 2.84 Vrms quoted is max output from the amp section. Turning down the volume on the pico would allow for less voltage here.

Etilletas 14th August 2011 07:45 PM

Quote:

Originally Posted by Rembrant (Post 2671258)
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.;)

Thanks, that makes sense. So, say I wanted to use a higher gain setting for 600 ohm headphones - All I would have to do is reduce the volume of the source? i.e. set my Music Streamer II to like 50% instead of the usual 100%?
I think I could live with that. :cheers:

Limp 14th August 2011 07:50 PM

Quote:

Originally Posted by Upstateguy (Post 2671847)
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.

That is the Pico DAC/Amp you're linking to. If this is what you are going to use as a source there is no problem, as it has a pot for you to attenuate those 2.84Vrms.
I have the Pico DAC myself, and plan to use it with the O2. If I read the WM8740 specs correctly, and these are applicable for estimating analog outputs, it should only be about 2Vrms, tops, so no problem.
(please, anyone, correct me if I'm talking non-sense here)

Upstateguy 14th August 2011 07:52 PM

Quote:

Originally Posted by Upstateguy (Post 2671847)
<snip>
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.
<snip>
.

Correction: I think the2.84 figure is for the amp/dac

Steve Eddy 14th August 2011 08:00 PM

Someone should compile a database of sources with their 0dBFS output levels.

I'd do it, but I gotta... mow the lawn. Yeah, that's the ticket. I gotta mow the lawn. A really really big lawn. It'll take me weeks. :D

se

RocketScientist 14th August 2011 08:27 PM

Quote:

Originally Posted by Etilletas (Post 2671949)
Thanks, that makes sense. So, say I wanted to use a higher gain setting for 600 ohm headphones - All I would have to do is reduce the volume of the source? i.e. set my Music Streamer II to like 50% instead of the usual 100%? I think I could live with that.

I'll put some thought into making the article more clear. But it's best to work backwards from your headphones something like this:

Say you're going to use the Beyer DT880-600's which are the most voltage hungry cans I could come up with. They need about 5 V RMS to hit a seriously loud 110 dB SPL (the math is shown in the Gain Settings section).

Next you want to consider the source. The Music Streamer II specs list a "somewhat hot" 2.25 V RMS.

Then you figure out the gain: 5V Out / 2.25 V In = 2.2X to hit 110 dB SPL. So the default Low Gain setting of 2.5X will push the Beyer's past 110 dB at 0 dBFS.

You can also check for the maximum gain with the MS II if you want. For AC power that's 7/2.25 = 3.1X.

So if I was going to use the 600 ohm beyers with the MS II DAC, I'd aim for 2.5X - 3.0X and leave the DAC at full volume.


If you needed extra gain for something that was recorded/ripped way below normal levels, you could simply turn down the DAC volume, set the O2 to full volume, and use the 6.5X High Gain mode of the O2. Operated at max volume the output stage will clip before the input stage. Which means you get the full 7+ V RMS with no input clipping--plenty to ruin your hearing even with the voltage hungry 600 ohm Beyers.

To sum it up: Even using the default gains the O2 should work just fine with the 600 ohm Beyers and the HRT MS II DAC.

Upstateguy 14th August 2011 08:47 PM

Quote:

Originally Posted by Arius (Post 2671883)
Likewise, I was just trying to give some guidance to the folks here who are unable to grasp basic math or comprehend the O2's superbly detailed documentation.

Joel and USG: Why point out to others how many volts your source puts out?

Line outputs that follow CD Redbook standard puts out 2V typical. Diff outputs are 4.5V typ.

If you are genuinely interested in the O2 as a DIY project, then it's up to you to set the output level of your source correctly or in lieu of being able to do so, then set the input gain of the O2 correctly.

Again, you've pointed out how your source might overdrive the O2 in default 3X gain. None of you have bothered to ask how to change the gain to 1X or 2X, or after reading this forum and the O2 docs stated that you will, I can only assume you do not possess sufficient skills to DIY this project.

LOL, my post was answering RS request for numbers just like joel's was.


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