The Objective2 (O2) Headphone Amp DIY Project

the computer is absolutely causing the noise. Computers are noisy, especially from the onboard sound card. I would not expect anything less than what you describe.
Using the digital output and going through your receiver's dac should improve or completely eliminate that.
I use a digital output from my computers onboard optical out into my schiit bifrost and the sound is totally silent.

you dont want to go through the receivers h/p out into the amp. someone correct me if im wrong.

the only other alternative that comes to mind is to buy another dac. I would suggesd the ODAC when it becomes available ;-)

congrads on the amp. Its a giant for sure!
I know right, what a piece of crap this onboard sound card. lol
Yeah I am using the digital output from the computer but if I use digital output, I can't get a line out to my O2 headamp. Apparently it says that Tape/MD out, VCR1, VCR2, MultiOutput (Zone2) do not output digital output, only analog. Which basically equates to not being able to use the awesome onboard DAC on the receiver. Like you said, I could buy a DAC so i can still use the digital out from my computer (as long as the DAC takes optical/digital in) and send it directly to the O2 but that means more money. On a super budget lol. The headphone out on the AV receiver is my only option but im not sure what that would mean in terms of SQ and signals and all that stuff.
 
I love this amp it's great and for the money sounds good. However, paired with my flat Shure SRH840 headphones, the sound is sibilant and even jarring with I hear cymbals and highs. Anyone else notice this?<br />
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The Shures impedance is not so high so if your laptops output impedance is too high then it would violate RS's 1/8 rule. Even an ipod would violate the rule for those headphones. That could somewhat mute the high frequencies. The O2 would correct that and give you the Shures true high frequencies. You may need to turn down the treble a little according to taste. Some people are very treble sensitive.
 
.... On a super budget lol. The headphone out on the AV receiver is my only option but im not sure what that would mean in terms of SQ and signals and all that stuff.

A cheap 3.5-3.5 connector would do it. That may not be the solution if the laptop really is producing distortion, but it may just be a lack of power. I get distortion from my laptop when trying to feed my high current headphones.

RS says any reasonably priced cable will do: expensive cables don't pass double-blind testing:ie. they really don't do anything.

Also BR777 is talking about noise rather than distortion. Which are you talking about? Noise is the background hiss.
 
A cheap 3.5-3.5 connector would do it. That may not be the solution if the laptop really is producing distortion, but it may just be a lack of power. I get distortion from my laptop when trying to feed my high current headphones.

RS says any reasonably priced cable will do: expensive cables don't pass double-blind testing:ie. they really don't do anything.

Also BR777 is talking about noise rather than distortion. Which are you talking about? Noise is the background hiss.

I'm going to go out and buy a 3.5-3.5mm cable and report back with it going directly from my computer line out and also trying the Denon's headphone out. Headphone out from the receiver will keep the DAC and digital signal so hopefully it'll work.


Sorry, I should go back and edit it. I meant noise when I wrote distortion. I know what distortion is but for some reason I chose the wrong word. It's noise like unwanted signals and just messy static type of noise. Gets louder with the volume on the headamp, gets worse when computer volume is higher than 40-50%. this is also on my desktop with a Z68 motherboard, not a laptop if that means anything. Just throwing it out there in case.
 
I got about 800 mVrms out of it running Rockbox 3.10 at a volume setting of +3 dB (using a fullscale sine), which should be just enough to clip an O2 at high gain when running on batteries. The original firmware should be about equally loud (assuming you have the volume setting on "High", which I suspect may not be the case right now - you shouldn't have to crank the volume with the M50s running unamped). Staying a few dB shy of full output should be fine.

What could cause a problem of not enough output? I'm running on AC with stock components that I know work, I'm running the clip at a very high volume(which is the same as a different clip so I know that isn't damaged) and I know I don't have any hearing loss. I really hope it's not damaged headphones though, I mean they don't sound like they're damaged and I don't think I've done anything that could cause damage lol.
 
I know right, what a piece of crap this onboard sound card. lol
Yeah I am using the digital output from the computer but if I use digital output, I can't get a line out to my O2 headamp. Apparently it says that Tape/MD out, VCR1, VCR2, MultiOutput (Zone2) do not output digital output, only analog. Which basically equates to not being able to use the awesome onboard DAC on the receiver. Like you said, I could buy a DAC so i can still use the digital out from my computer (as long as the DAC takes optical/digital in) and send it directly to the O2 but that means more money. On a super budget lol. The headphone out on the AV receiver is my only option but im not sure what that would mean in terms of SQ and signals and all that stuff.

I appologize if i'm misunderstanding, but if your reveiver allows digital input, and contains a dac, it must output analog to something right? id be shocked if it will only utilize its dac for headphones

Your instructions saying that if you use a digital in you must use a digital out does not sound right - i get the feeling you are misunderstanding. If this were the case you would again be bypassing the dac in your receiver, and therefore there would be no point or usability with its dac.

it sounds like when you say distortion, you are really meaning computer noise.
going directly from your computer to your amp wont change that.

the connection you would want would be - digital out from your computer to digital in on your receiver, then analog out of your receiver into your amp.
i'm pretty sure you should be able to get this to work.

by the way if your instructions say it wont output digital to the various connections, that is correct, it would be analog b/c it uses the dac, then sends the analog signal to the various output channels.. this is how its supposed to work..

good luck
 
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Sorry, I should go back and edit it. I meant noise when I wrote distortion. I know what distortion is but for some reason I chose the wrong word. It's noise like unwanted signals and just messy static type of noise. Gets louder with the volume on the headamp, gets worse when computer volume is higher than 40-50%. this is also on my desktop with a Z68 motherboard, not a laptop if that means anything. Just throwing it out there in case.

RS did write that under some circumstances noise can be mitigated by amping through the O2. I can't remember exactly how it works but if I remember correctly: if the noise doesn't increase from the source as you increase volume than the O2 will help if the source is set to high volume. But I think you wrote that your noise increases at the source with higher volume even before putting through the receiver.

So you probably do need a better DAC. RS has some reviews of cheap DACs. One of them measures well enough but has an issue that is, if I remember correctly, corrected by putting through the O2. Probably too high output impedance, but I'm guessing because I haven't re-read the review.
 
I appologize if i'm misunderstanding, but if your reveiver allows digital input, and contains a dac, it must output analog to something right? id be shocked if it will only utilize its dac for headphones

Your instructions saying that if you use a digital in you must use a digital out does not sound right - i get the feeling you are misunderstanding. If this were the case you would again be bypassing the dac in your receiver, and therefore there would be no point or usability with its dac.

it sounds like when you say distortion, you are really meaning computer noise.
going directly from your computer to your amp wont change that.

the connection you would want would be - digital out from your computer to digital in on your receiver, then analog out of your receiver into your amp.
i'm pretty sure you should be able to get this to work.

by the way if your instructions say it wont output digital to the various connections, that is correct, it would be analog b/c it uses the dac, then sends the analog signal to the various output channels.. this is how its supposed to work..

good luck

Yeah that's what I thought, I mean why would it only allow the DAC to work for speakers and headphones?

Here is the manual quote under multi source (which is used to send signal to another power amplifier (in another zone/room).
"NOTES:
• The signals of the source selected in the MULTI mode are also
output from the VCR-1 and VCR-2/V.AUX recording output
terminals.
• Digital signals are not output from the multi source audio output
jacks."


At first I understood that statement that the multi source audio output does not SEND OUT digital. But then I thought about and wondered why they would even put that in the manual since all the connections for multi/preout/VCR recording is RCA Analogs. And when I tried using a digital optical signal from my computer, it did not work. No sound or output at all. I tried VCR1 output, VCR2 output with the recording function on, I tried MD/Tape Monitor out with it selected, nothing. Preout and multi out, nothing. Then, when I changed the input source to analog (using 3.5mm-to-RCA from my computer instead of the digital optical), it started working.

From what I understand, someone said something about tape loop and recording being a straight signal, no processing. No DAC, no tone control, just receive the analog signal and send it somewhere else. Which is plain stupid cause why not allow for the digital source to be converted by the DAC?



Anyway, I went out to Radioshack and about a 3.5-3.5 cable. So regarding the noise this is the current situation. The 3.5mm-3.5mm connected directly between my computer's onboard headphone out to the O2 Line-In gives me NO NOISE. Even with the computer volume at 100% and the O2 knob at 100%, I don't hear the noise. I just hear shuffling/scraping sound when I turn the volume knob though. I also hear very very very high frequency and quiet noise when the volume knob is at 100%. It's not easy to detect and it's reminiscent of tinnitus ringing.

When I use this 3.5mm to connect the O2 line in to the Denon's headphone out (like I wanted to do previously using the computer's digital out to the receiver), the sound quality is better. Obviously because I'm utilizing the Denon's DAC and getting digital signal. But, this creates hissing at around the 11 o clock position on the volume knob. It gets louder as the volume knob goes up.

Not sure what this is all about but I'm pretty confused now.
 
Anyway, I went out to Radioshack and about a 3.5-3.5 cable. So regarding the noise this is the current situation. The 3.5mm-3.5mm connected directly between my computer's onboard headphone out to the O2 Line-In gives me NO NOISE.



When I use this 3.5mm to connect the O2 line in to the Denon's headphone out (like I wanted to do previously using the computer's digital out to the receiver), the sound quality is better. Obviously because I'm utilizing the Denon's DAC and getting digital signal. But, this creates hissing at around the 11 o clock position on the volume knob. It gets louder as the volume knob goes up.


Not sure what this is all about but I'm pretty confused now.


no noise - great

some things you are saying aren't making sense.

- if you send a digital signal into your receiver, it should not output digital to anything, that would be pointless unless you were using the receiver as a digital passthrough which you would not be doing in any of your circumstances being discussed

-digital goes in, analog goes out. that is how a dac works. It is still hard to belive that the internal dac would not send its signal that came from a digital input, then converted to analog, to its various outputs. to have a dac only for h/p out doesnt make much sense.

- the signal coming out of your headphone amp is not digital. it is analog. if it were digital you would not hear music, probably some kind of screech or static or who knows what.
- this means that in a sense you are double amping - the receivers hp out has an "amp" and you are sending that signal to your o2. I dont know enough of the details, but i would think you'd get a cleaner and better sounding signal going from one of your receivers analog outs to your o2 amp.

someone with more technical understandings can probably do a better job of explainng stuff than i can.
 
no noise - great

some things you are saying aren't making sense.

-digital goes in, analog goes out. that is how a dac works. It is still hard to belive that the internal dac would not send its signal that came from a digital input, then converted to analog, to its various outputs. to have a dac only for h/p out doesnt make much sense.

most modern recievers have the digital-in set up so that you cannot copy the digital signal. digital copyright in effect here, and a real pain

Unfortunately that means no signal to the record outs from a digital signal.

The way he has it set up, though the headphone out, is the only way to use a reciever as a DAC, and yes he is double amping. You could lower the volume on the Denon and turn up the volume on the O2, you may find a sweet spot somewhere.

Else buy a dac and use that between the computer and the O2
 
most modern recievers have the digital-in set up so that you cannot copy the digital signal. digital copyright in effect here, and a real pain

Unfortunately that means no signal to the record outs from a digital signal.

The way he has it set up, though the headphone out, is the only way to use a reciever as a DAC, and yes he is double amping. You could lower the volume on the Denon and turn up the volume on the O2, you may find a sweet spot somewhere.

Else buy a dac and use that between the computer and the O2

So you are confirming my interpretation of the manual when it says that digital out is not supported, it means the digital IN from the computer? I mean what BR777 is saying makes sense also and I do not understand why they would only allow for the DAC to be utilized for speakers and headphones but not for any of the receiver outputs to record. If I use an analog in, I can record and output analog all I want, but if I use a digital in, then no output at all? it sure seems that way but it does not make sense to me either.



The hissing doesn't bother me since its only after 11 o clock and it's pretty freakin loud at that position I wouldn't go above that in normal use anyway. I think I'll just use the headphone out from the Denon AV receiver for the time being until I get a DAC. It actually is kind of nice getting the tone controls. It also makes the sibilance much less pronounced. Thanks for the input guys.
 
An option might be to use a grub dac. That is how I use one of my O2s with my laptop. I think the sound is excellent. I also think it would sound better than the sound card or headhpone outs.
The grub is a USB dac and a kit sells for about $35.00 so the investment is small. Just my $.02
 
Finally all done

Today I finally received my front panels from the group buy! They fit perfectly, look fantastic, and of course anchor everything in place nicely. (I also took the liberty of scraping off some of the paint around the lower right screw, so the ground wire from the input jack grounds the case and the panel)

Once again, thank you RS and everyone involved in the board group buy and the front panel group buy; this is a professional looking and sounding piece of kit!

side2.jpg

rig1.jpg
 
SUCCESS!!!

Wow, this thing is incredible! I just completed the build and all the testing. Worked first time out. I just sat here (1 AM) in a musical stupor listening to the Holly Cole Trio on my Grado's. Unbelievable! Horrible pics below from my cell phone. Thank you RS for an amazing design matched by your amazing generosity to all of us!!! Good night all!
 

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I put together a list of headphones that can make use of the O2's amplification and buffer capabilities. Compared to what a typical PMP can provide, the yellow indicates a headphone that needs more.

I spec'd everything to 115dB or max power handling, whichever is lower.

Everything can make use of the lower impedance. The only thing I'm not sure about is some of the ultra low impedance IEMs (UE600 and K3003) and the distortion performance of the amp. I only kept the K3003 on there for kicks and giggles. It's out of the price band of the rest of this stuff.

An externally hosted image should be here but it was not working when we last tested it.


So 26 of the 40 models I calculated need an amp, most of them needing a current buffer beyond what most amps supply, assuming most amps supply 35mA or less. The O2 can do up to ~140-150mA.

This is an abridgement of my larger spreadsheet with all the automatic calculations in it.
 
Yea, I can't imagine 1V thru Grado's even a breif transient, I hought .5Vrms was the edge of sanity with these drivers. I'm still scratching my head on the more power section of the blog. I brought up about how the AKG Sextettes need close to 200mW (almost twice the 115db number) yet the real world Grados are opposite (much less than the chart). I am glad RS published this 'cause its an important issue.

Possibly the ratings/specs for sensitivity are not such a good tool for estimating power needs because the manufacturers test methods are all over the map and more of a sales/marketing number than a meaningful (say NIST traceable ASTM) spec?