I would like to ask if adding an optical input (TOSLINK) requires to add more components or will it complicate things for ODA/ODAC combo? I'm not sure if this was discussed before in forums/blogs.
Hi, there are no provisions on the ODA board for toslink or other optical input. You would have to use an external optical-to-RCA converter, something like this: http://www.amazon.com/Digital-Optic...qid=1409775476&sr=8-3&keywords=toslink+to+rca . If you wire the ODAC into the holes by the front panel 3.5mm jack and then run the toslink converter to the rear panel RCA jacks, your front panel input select switch will select between the ODAC (3.5mm jack position) and optical/toslink (RCA jack postion).
isn't "galvanic isolator" effectively synonymous with "transformer"?
not trying to be a dick, just wondering if a pair of $6.37 Edcor PC10k/10k interstage transformers would do the job of isolating the odac just peachy? Assuming you leave USB power and ground to their own devices.
not trying to be a dick, just wondering if a pair of $6.37 Edcor PC10k/10k interstage transformers would do the job of isolating the odac just peachy? Assuming you leave USB power and ground to their own devices.
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The big mystery is where the ground loop(s) or other interaction is coming from. If the problem is a ground loop between the PC and the O2 that Edcor on the output of the ODAC would do the job. But if the problem is some weird interaction between the digital signal lines in the USB port and the USB port's power lines, then something like that Saelig adaptor that isolates on the digital side is the ticket. I actually tend to think the problem may be the latter, something on the digital side. The O2's Triad power transformer is well isolated, at least according to the specs, so not much of a way to get a ground loop going through the wall socket.
That would be an interesting test to make on a PC/ODAC pair that is having trouble! A 1:1 audio transformer on the output vs. the digital side isolator.
Well, by definition, the power transformer will AC couple you to the power grid. And depending on various factors it generally does a pretty good job of isolating you from common-mode noise on the power feed.
but i don't have one of these amps, and don't have an odac, and haven't read the whole thread.
but i don't have one of these amps, and don't have an odac, and haven't read the whole thread.
It would be interesting for anyone having PC-ODAC trouble to unplug the AC cord, if they are using the O2 on AC, and see if the problem remains while running on batteries. If so the problem would pretty much have to be on the digital side.
I haven't experienced the problem myself either, just going by a bunch of posts I've seen about PC-ODAC trouble being solved by galvanic isolators, plus a few PMs and emails with some fairly technical folks who also ran into the problem.
I eventually did get an ODAC a few months ago just for sizing purposes. I'm really still holding out for OPC's DAC that he has had in the works for a while now. I'm expecting that will blow the ODAC right out of the water. 🙂
I haven't experienced the problem myself either, just going by a bunch of posts I've seen about PC-ODAC trouble being solved by galvanic isolators, plus a few PMs and emails with some fairly technical folks who also ran into the problem.
I eventually did get an ODAC a few months ago just for sizing purposes. I'm really still holding out for OPC's DAC that he has had in the works for a while now. I'm expecting that will blow the ODAC right out of the water. 🙂
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I am hearing noise with my in-ears with Objective dac/amp combo with volume turned up. And at max with gain switch toggled on, I think I can hear a power hum. I heard that Mayflower has a prototype of the ODA, hopefully they will sell some soon? But I wonder how they will keep up with all the new revisions you produce.
What voltage of wall transformer are you using with your O2? The 12Vac transformers allow the O2's +/-12Vdc voltage regulators to go into dropout (so they won't filter out hum) for anything but the very lightest headphone loads. But the flip side, with a heavy load on the O2, since he didn't heat sink the regulators anything higher than 12Vac would cause the voltage regulators to overheat.
Kind of a bad situation with the O2 there. Raise the input voltage to 14Vac or 16Vac to keep the voltage regulators out of dropout and then they overheat with a heavy load. That is why I heat sinked the voltage regulators on the ODA to prevent that problem
Mayflower does have a bare V2.1 board now, which is the latest revision. It sounds like he may be thinking about selling them at least. 🙂 If he or any of the other O2 sellers out there are able to find a source of cheaper panels the price could drop a bit. That $100 Front Panel Express charges for the set of front and back panels just makes people choke, and rightly so. Blank panels come with the case, just as with the O2 case. With a CAM milling machine those could be done essentially for free, for the cost of running the machine.
The existing V2.1 of my version of the ODA is probably going to be the last for the foreseeable future. It works great and there isn't any space left on the board to add more stuff. The next thing to come along at some point will probably be a top-slot (of the B4-080 case) accessory board that works with the existing ODA board. May have tone controls, cross feed, or other goodies on there along with ODAC mounting holes.
Here is something unrelated but may be of some interest to folks with an O2 headphone amp. I’ve posted some modern O2 part substitutions here, some O2 build mistakes to avoid here, and a couple of the easier modifications I've posted over the years here.
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I don't even know what wall transformers ARE, lol. I mentioned how I fixed the noise floor in the past, right? I turned the Windows setting to 24bit mode and somehow that fixed the noise floor problem. My active powered monitors, Krk Rokit 6s, exhibit some serious ground loop issues unless I use a ground loop isolator. Seems like the power around my house isn't all that good. Does the ODA allow for balanced connections? And are the low-volume-knob-channel-imbalance issues fixed?
Maybe if I go all balanced, I could eliminate all problems? Say: My HD800s use a balanced TRS connection (I believe), which I can connect to ODA so it's all balanced. The Rokits can be connected to a sub that accepts TRS and then connected to the ODA. But then, the ODA has to connect to the computer via USB and that can still cause some ground loop issues, I think. It's all so confusing, lol. It still reads like Greek to me. ODA's gotta be a more complicate piece of electronics compared to the O2/Odac, so aren't there more areas to screw up? I just hope if I buy an ODA that everything is done correctly, because my OCD is going to act up hardcore if say, a small mistake in assembly increase the noise floor by 0.01% even though it's inaudible. 😀
Well, I heard that Tyler has a prototype of the ODA because he told me so himself. However, I don't see the bare pcb for sale on his website:
https://www.mayflowerelectronics.com/product-category/diy-products/
I'll be watching Mayflower's website to see what he comes up with and at what price. I wonder if JDSLabs will do something.
Anyways,
Thanks.
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For some reason I've lost the ability to edit my post.
Also for some reason I keep thinking the ODA is an improved O2 and Odac.I *just* realized entire unit is just the amp. So to have a full unit, somebody needs to stick an Odac to the ODA. (This just demonstrates why I should not be the one to assemble the ODA, lol.)
Also for some reason I keep thinking the ODA is an improved O2 and Odac.I *just* realized entire unit is just the amp. So to have a full unit, somebody needs to stick an Odac to the ODA. (This just demonstrates why I should not be the one to assemble the ODA, lol.)
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Yeah the forum here only allows 30 minutes of edit time. I get tripped up by that all the time. 🙂
The ODA is a desktop version of the O2. So no batteries, but a lot of additional jacks and more ouput current, gain settings, better power supply, etc. It has measured slightly better (36%) in THD+N on the one dScope measurement that has been made so far. That one was at 15R load.
The is space in the ODA for an ODAC on a top slot board, but until that combination has been dScoped to make sure no digital noise gets into the analog I'm suggesting that folks use an externally boxed ODAC for now. 🙂
Whoops, I didn't scroll up and see that you had posted twice. 🙂 I only read your second post. Sorry about that. 🙂
Here are the rest of the answers. As for balanced wiring it mainly helps with hum pickup through the air, such as from fluorescent lighting and running the audio wiring near power wiring. The "balanced" terms comes from the fact that the electronics on the end of the balanced line is set up to cancel out any signal that appears the same on both wires ("common mode" is the tech term). So if you are picking up hum from lighting both the audio wires get the same amount of induced hum and it gets cancelled out.
Balanced wiring *may* help with ground loops through the wall outlet but only as a by-product, sort of a lucky accident, since one of the ways to cancel out balanced noise is with a transformer at the end of the wire. The transformer also provides galvanic isolation between primary and secondary which would break the ground loop. But if the balanced electronics are transformerless you may still get ground loop issues.
The ODA isn't balanced, just single-ended, and I don't have any provision to use it with balanced inputs. For that I would suggest taking a look at OPC's "Wire" headamp here: http://www.diyaudio.com/forums/vend...jects-available-here-bal-bal-se-se-lpuhp.html He has a balanced version. I think that AMB might also have a balanced version of his b22 amp on his site at amb.org.
But back to your ground loop issues through the wall socket with your Rokit 6s speakers. Most likely the solution is simply a galvanic isolator between your PC and your ODAC, like this one USB2ISO USB 2.0 Galvanic Isolator Adaptor ($59.95) : Saelig Online Store we were talking about a few posts back, that not only isolates the digital signal lines but also the 5V power. If that solves it, and it probably will, the problem is a design flaw with the ODAC. It seems a few people are having that problem.
No need to go with balanced wiring. Balanced is really only needed in recording studios and sound stages where the microphone lines and audio line-level lines are immensely long. At least that used to be the case in years past before wireless. These days everything probably uses wireless transmitters to avoid the long cable runs.
NwAvGuy goes into the balanced vs. single ended issue at some point in his blog postings. His summary is what I just wrote, plus he noted that balanced *adds* electronics vs. single ended, and every stage of amplification along the way adds a little noise. In other words, unless you are wiring up a soundstage, you will be better off with single ended in a home environment.
Balanced headphones and balanced headphone wiring is sort of a different animal. Here the goal isn't to cancel out noise pickup because the impedances involved are usually too low for that to be a problem. Rather the "balanced" headphone wiring gives you two separate ground wires, one for each channel. In a typical non-balanced headphone a single ground wire can be used for both cups, which means that signal sent to one channel cause a little voltage drop over that common wire and can be present in the other channel if the headphone drivers are very sensitive. But non-balanced headphones can also be wired with separate ground that are only hooked together at the TRS plug to minimize that effect. In the case of the ODA your two separate ground wires in the headphones will get connected at the TRS jack, but by having separate wiring in the cable you have avoided 95% of any common ground wire crosstalk.
As for the wall-plug ground loop issues I can make a few suggestions there too. 🙂 If you house or apartment is new enough to have an actual ground wire going to the grounding pin on each wall outlet, one of the big culprits can be lack of a proper ground back at your circuit breaker ( or fuse if old) panel. There should be an 8 foot long copper-covered steel rod pounded into the ground within a certain distance of the panel (specified by national and your local electrical codes), then a certain size grounding wire going from that to the panel.
I would take a guess that some huge number of electrical breaker panels, like maybe 30%, have just that little bit done wrong. Such as a pipe being used for ground and it turns out that pipe has a dielectric (plastic) anti-corrosion fitting at the house entrace, or water softener, or hot water heater, which makes it useless for grounding, unless properly bypassed with a wire across the dielectric fitting which is usually forgotten. Or, one of my favorite finds, many of the setscrews inside the electrical panel are all slightly loose. If I open up a panel that is 20 years old I can practically guarantee that I can get 1/4 to 3/4 turn more of tightening on the larger power wire setscrews and most of the neutral and ground screws. Thermal expansion works them loose over time unless they were *really* cinched down by the installing electrician.
So to summarize, get a licensed electrician in when you can to verify grounding on your main electrical panel and make sure all the screws are nice and tight. That will go a long way to helping with odd grounding problems around the house.
I'll send you a PM right now with some more ODA information. 🙂
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In terms of ground loop, it's not THAT big of a problem for me because for the Rokits: I have a ground loop isolator. (I want to just use my new fancy-looking cables from Monoprice, but it won't work with the isolator, so I was thinking of picking up a cheap isolator with female to male.)
And for the headphone, there's no problem, just with my earphones, but that's only with volume up a bit more than I would use, and I don't use in-ears with Objective normally, I use them with my cell phone for on-the-go-use.
I'll go look for the breaker... I don't know where it is in my house, LOL.
Me thinking about ODA is mostly for extravagance's sake, but hoping it'd magically fix all my issues too.
And for the headphone, there's no problem, just with my earphones, but that's only with volume up a bit more than I would use, and I don't use in-ears with Objective normally, I use them with my cell phone for on-the-go-use.
I'll go look for the breaker... I don't know where it is in my house, LOL.
Me thinking about ODA is mostly for extravagance's sake, but hoping it'd magically fix all my issues too.
Sounds good. That isolator should do the job. In reading what I wrote above I should have been clearer that the electrical panel grounding stuff won't help with ground loops, the isolator is the solution there, but rather just in suppressing noise and for safety. I've run into that issue of proper electrical panel grounding so much over the years I tend to go off on a tangent. 😀
If you wind up getting an ODA and find it sounds better (than the O2) it is likely due to the power supply and higher output current drivers - even if much of that current capability is not being used with a particular set of cans. I'm only 50% on the measurements thing, unlike NwAvGuy who seemed to be 100%. I tend to believe what I saw attributed to Nelson Pass once, that it is possible for an amp to measure well but sound bad. Good measurements are a great starting point, but I tend to believe that a really good power supply is a big part of good sound, as is having excess current capability in the output stage. But that is just my two cents, of course. 🙂
I don't expect to hear a sound quality improvement. I'm getting it a) For teh bling b) For the cool clipping LED, and C) Lower noise floor.
Although, if I do get an ODA, I need to think of a way to put it on the desk so it doesn't take up too much space but is still easily accessible for the volume wheel. I have the O2/Odac under my monitor but I really don't think ODA will fit.
Life is so hard.
Although, if I do get an ODA, I need to think of a way to put it on the desk so it doesn't take up too much space but is still easily accessible for the volume wheel. I have the O2/Odac under my monitor but I really don't think ODA will fit.
Life is so hard.
One can never have too many headphone amplifiers! 😀
Here is how the O2 and the ODA cases stack up size-wise:
Attachments
No additional word yet! 🙂 I know he is really busy with his day job stuff though.
It will really be interesting to see what he comes up with for the half-volume control THD+N on the O2 amp. Just the Johnson noise alone, the "N" part, is guaranteed to increase given the O2's 10K pot. That would be 5K, or 1.27Vrms of additional noise injection in the signal path at room temperature. The ODA's 1K pot reduces that to .40Vrms at room temperature for the 500R half-pot resistance. That is a 67% reduction in noise generation in that resistor that is right in the middle of the signal path.
It is really interesting that NwAvGuy never published a half-pot THD+N number. He may just have missed the whole issue, including that source-resistance input distortion op-amp effect. I found an interesting app note from Linear Technology on the problem: http://cds.linear.com/docs/en/design-note/dn84f.pdf . For several of the LT op-amps he has graphed there 5K on the input would already but up a ways on the THD output curve, especially at the higher frequency end of the audio spectrum.
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