That's indeed a problem.
Another idea is to put a small switching supply inside the O2 that would generate -12V from 12V DC input.
These days it could be made with one IC, one inductor, 2 caps and 1-2 diodes.
No more RFI problems and would have the advantage of accepting all small 12V DC adapters which are everywhere (at least around these parts).
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Well, I just like my toys sturdy. And chinese parts are often faulty or unreliable.
Not because they are chinese, but because you can get away with more stuff in china.
If a 14 year-old assembles a product, can you expect the same quality? no.
If your workers assemble product for 14 hours a day, they can't work as precise...
So if something is made in Germany, to me, it is inherently more trustworthy...
Since I upped my personal order for the PCB's to 10, I might actually tinker with one or two.
(Please, RS, do not tar, feather, shoot and drown me!)
I'll equip one with matching-spec fairydust-components, such as Mundorf and the like.
And then I'll have a blind test with me and my girlfriend. Blindfolds are always fun ^^
Btw, we are now at 40 kits. Even if not everybody follows through, we can still pull it off.
And thats 40 kits in essentially two days. We still have approx 14 days until the cutoff date for orders.
(Thats because of Ollies PCB timings. Placing orders before September 18th provides no benefits...)
Not because they are chinese, but because you can get away with more stuff in china.
If a 14 year-old assembles a product, can you expect the same quality? no.
If your workers assemble product for 14 hours a day, they can't work as precise...
So if something is made in Germany, to me, it is inherently more trustworthy...
Since I upped my personal order for the PCB's to 10, I might actually tinker with one or two.
(Please, RS, do not tar, feather, shoot and drown me!)
I'll equip one with matching-spec fairydust-components, such as Mundorf and the like.
And then I'll have a blind test with me and my girlfriend. Blindfolds are always fun ^^
Btw, we are now at 40 kits. Even if not everybody follows through, we can still pull it off.
And thats 40 kits in essentially two days. We still have approx 14 days until the cutoff date for orders.
(Thats because of Ollies PCB timings. Placing orders before September 18th provides no benefits...)
If you'd like to design such a supply, find room for it in the O2's enclosure, and solve the noise issues, you're welcome to. I talk about the trade offs of that method in the Design Details article (see section 2-20).
It adds cost, makes the power supply asymmetrical in terms of impedance, and most of all, adds noise--especially in the cramped format of a portable amp. Here's what the output of headphone amp the uses just such an approach looks like on a scope--note all the noise on the negative half of the audio output (blue waveform--the red waveform is the input signal):
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You're right about that... Without any further guarantees, "made in Germany" is a much better quality assurance than "made in China", especially if the thing comes from ebay, which is a totally uncontrolled import channel. But I made the remark because the modification ideas of fireworks are in my eyes a lot worse and more dangerous than than a dodgy Chinese adapter.
For anyone who has the ability to do level matched blind tests of the O2 against other headphone sources--especially those that can be expected to measure fairly well--I would very much like to know the result!
But it's not fair to use tubes, single-ended, Audio-GD, noisy amps, or other sources that measure poorly. As, better or worse, they will be much easier to pick out in a blind test.
That's interesting, thanks for posting. I also looked at what you wrote about the power supply.
About the noise: the switching supply I'm thinking of would have a switching frequency of at least 200kHz, maybe 500kHz or more. Even if a very small amount reaches the headphone cable it would just be blocked by its inductance.
Moreover, I would still keep the linear regulators you put in, so the -13 to -14V generated would still have to pass through the negative linear regulator. My guess is that the noise at the output of the circuit would be negligible, probably invisible on a scope when looking at the 1V output signal (way less than the resolution of an 8bit oscilloscope on that scale).
What do you (or anyone else) think ?
@fireworks: Its an interesting thought, but would you mind discussing it in the O2's thread?
I'd like to keep this here strictly GB related...
@Bahkata:
Right now we're at the 42 unit mark.
From here on out, prices won't decrease too much with additional orders.
I actually expect my 27/22 figures from the first post to be a pretty good ballpark estimate.
It all depends on the quantity, shipping (7 to 10€ for you, b/c of the heavy transformer and the case) and potential insurance for your order.
And as long as I don't "make" more than 1€ per kit, I wont adjust the prices as it will be lots and lots of work...
I'd like to keep this here strictly GB related...
@Bahkata:
Right now we're at the 42 unit mark.
From here on out, prices won't decrease too much with additional orders.
I actually expect my 27/22 figures from the first post to be a pretty good ballpark estimate.
It all depends on the quantity, shipping (7 to 10€ for you, b/c of the heavy transformer and the case) and potential insurance for your order.
And as long as I don't "make" more than 1€ per kit, I wont adjust the prices as it will be lots and lots of work...
The problem is mainly EMI. You can filter and regulate all you want, but the magnetic fields from the switching supply will still cross couple into the nearby audio circuitry. Noise is relative. The O2 has < 4 microvolts of noise at the output. That's the total RMS sum of all noise below 96 KHZ. We're dealing with audio so it's good to consider 16 bits of dynamic range (96 dB). That puts the noise floor at 16 uV referenced to 1 volt if you want to maintain at least 16 bit performance.
So anything greater than 16 uV is arguably undesirable. And I seriously doubt you can get the EMI noise from a DC-DC switcher stuffed into a small portable amp below 16 uV. So then it comes down to how audible you think ultrasonic noise can be. The harmonic rich ultrasonic content forms beat frequencies within the audio band. They clearly show up on the dScope's spectrum. The question is how audible are they?
Ultrasonic noise also corrupts measurements as it raises the noise floor of the amp. Many of the O2's distortion measurements are already noise limited. A switching power supply would raise the "floor" much further.
It's not a compromise I'm happy with when it's entirely avoidable but others might find it acceptable. It would be more practical in a larger amp and I'd probably use a (expensive) DC-DC module that's already been engineered for minimum EMI/RFI. It's a lot of work to get the EMI/RFI low when you're starting from scratch (and even some commercial designers have a hard time as my scope trace above shows--that noise is only 20 - 30 dB below the audio signal. That's relatively awful.
So anything greater than 16 uV is arguably undesirable. And I seriously doubt you can get the EMI noise from a DC-DC switcher stuffed into a small portable amp below 16 uV. So then it comes down to how audible you think ultrasonic noise can be. The harmonic rich ultrasonic content forms beat frequencies within the audio band. They clearly show up on the dScope's spectrum. The question is how audible are they?
Ultrasonic noise also corrupts measurements as it raises the noise floor of the amp. Many of the O2's distortion measurements are already noise limited. A switching power supply would raise the "floor" much further.
It's not a compromise I'm happy with when it's entirely avoidable but others might find it acceptable. It would be more practical in a larger amp and I'd probably use a (expensive) DC-DC module that's already been engineered for minimum EMI/RFI. It's a lot of work to get the EMI/RFI low when you're starting from scratch (and even some commercial designers have a hard time as my scope trace above shows--that noise is only 20 - 30 dB below the audio signal. That's relatively awful.
Indeed, and I agree that if that's the best one can do, then it's not worth it. But I'm hoping for much better.
As per Jokener's request, we should continue in the O2 thread.
Maybe the mods can move the few posts related to a switching power supply for O2 onto that thread ?
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"Quantity: 1 - 41.72€ / kit (incl shipping)
Quantity: 10 - 20.72€ / kit (free shipping)
Quantity: 20 - 19.63€ / kit (free shipping)
Qunatity: 50 - 16.37€ / kit (free shipping)
Quantity: 100 - 15.02€ / kit (free shipping)
As you can see, the sweet spots are 10 and 100 kits. I expect more than 10 orders, but less than 100 (happy to be proven wrong btw)."
Aren't the sweet spot 10 and 50 ? Is there something i am missing ? i was waiting for the 50th joiner so we would again have a significant drop --> ~3euros
Quantity: 10 - 20.72€ / kit (free shipping)
Quantity: 20 - 19.63€ / kit (free shipping)
Qunatity: 50 - 16.37€ / kit (free shipping)
Quantity: 100 - 15.02€ / kit (free shipping)
As you can see, the sweet spots are 10 and 100 kits. I expect more than 10 orders, but less than 100 (happy to be proven wrong btw)."
Aren't the sweet spot 10 and 50 ? Is there something i am missing ? i was waiting for the 50th joiner so we would again have a significant drop --> ~3euros
@castlevania: Those are the prices from the Mouser cart.
Additional costs such as import tax (19%) will come on top of this.
And the sweet spots depend on personal preference, which is why posted the prices.
When we get closer to the end and before I collect the money, I can announce final prices.
But you can be assured I won't make a lot of money with this, especially not if you consider the hours (more like a weekend) I will put into sorting/bagging/tagging/documenting everything.
And it will always be cheaper than ordering individually. A lot cheaper.
As for expected quantity, we should end up significantly above 50kits.
Maybe closer to the 100 unit mark.
(That's ~8000, as in eight THOUSAND, individual components...)
Good times, noodle salad.
Additional costs such as import tax (19%) will come on top of this.
And the sweet spots depend on personal preference, which is why posted the prices.
When we get closer to the end and before I collect the money, I can announce final prices.
But you can be assured I won't make a lot of money with this, especially not if you consider the hours (more like a weekend) I will put into sorting/bagging/tagging/documenting everything.
And it will always be cheaper than ordering individually. A lot cheaper.
As for expected quantity, we should end up significantly above 50kits.
Maybe closer to the 100 unit mark.
(That's ~8000, as in eight THOUSAND, individual components...)
Good times, noodle salad.
I'll post the CAD-pictures of my OEM case on monday after work.
But the cases for the GB are the ones from the shop...
After all, I have not made any yet, it's an unproven design and it takes me 30 minutes to 1 hour to build a case...
But you're welcome to send me a private message later when the pics are posted.
We'll figure something out...
I don't have a supply for the Eneloops and they're not available at the vendors for this GB.
But you can find them on Amazon or in a local electronics store, if they carry quality products...
But the cases for the GB are the ones from the shop...
After all, I have not made any yet, it's an unproven design and it takes me 30 minutes to 1 hour to build a case...
But you're welcome to send me a private message later when the pics are posted.
We'll figure something out...
I don't have a supply for the Eneloops and they're not available at the vendors for this GB.
But you can find them on Amazon or in a local electronics store, if they carry quality products...
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