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Old 29th November 2011, 05:28 AM   #941
qusp is offline qusp  Australia
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yeah thats why i mentioned it =) i have other balanced headamps too, but even the bal-se wire is a VERY strong contender and not at all out of place in such a high end rig.

do remember running balanced you will have 3v point to point output from the sabre
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Old 29th November 2011, 05:32 AM   #942
qusp is offline qusp  Australia
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Quote:
Originally Posted by RocketScientist View Post
@ethanolson, the short answer to that question is most DIYers design "blind" without proper test equipment and using only heavily biased sighted listening as their guide. They very often think they hear things that don't really exist as has been demonstrated countless times in blind listening tests. if you throw a bed sheet over the equipment, without changing anything else, the benefits they think they hear magically disappear. So it's easy to see how they think adding an op amp stage to a DAC chip improves the sound when in reality it might make the performance a bit worse.
haha please realise that this is an area where RS really doesnt know what hes talking about. to get the 120db voltage out spec quoted in the datasheet, there is also a specific voltage out schematic. just connect the output of the sabre directly to an amp input and you'll be lucky to get 100db vs 135db with a proper low impedance IV stage. now of course RS will say you cant heard the difference, but to me thats a pretty extreme difference and you may as well use an ipod if you are happy with that.

it doesnt have a 'current mode' or a 'voltage mode' the higher the impedance seen by the output the more like a voltage source it looks, the lower the impedance seen at the output (preferrably biased to AVCC/2) the more like a current source it looks

RS i have no problem with your engineering approach, this is why i like ackos products as in his day job among other things his company privately contracts to supply RF and control systems gear to the australian defence force. you'll excuse me if i dont mind trusting his skills and measurements.

its probably better to do a little research about the gear you make dismissive comments about. opc's mosfet IV i use (among a few others) as well in the development phase, did some of the most exhaustive measurements with the AP that ive seen on this dac chip and passive resistive IV (which is better even than connecting direct) was pretty ugly by comparison. the THD +N and DNR is fairly profoundly affected by the impedance and/or transconductance of the next stage

Last edited by qusp; 29th November 2011 at 05:51 AM.
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Old 29th November 2011, 06:07 AM   #943
qusp is offline qusp  Australia
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for the D1 IV, so then after those measurements over 30 different mosfets were tested to find the highest gM part it was discovered that up to a point the supply voltage used improved the gM, so thus we have an IV stage that runs at +/-50v and dissipates roughly 50W.

i tested >150 of the chosen mosfet at the circuits operating point for VDS and gM at 3vrms 1khz sine wave input (to match the sabres output) and sets of fets for the GB were selected. I built a differential input instrumentation amp to amplify the measurements taken across gate to source at as close to the same temperature as possible and used 3 x DMM and an old HP voltmeter. each DUT was placed in a replica of one phase of the D1 circuit and operating points were matched to what would be used

still sound like fumbling in the dark?

Last edited by qusp; 29th November 2011 at 06:13 AM.
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Old 29th November 2011, 06:32 AM   #944
sofaspud is offline sofaspud  United States
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Quote:
It's amazing how much better they sound amped... and I'm a quiet listener.
Headphones (or IEMs or whatever) are more ubiquitous now than in the glory days of Walkmans. And I often get the urge to say that... headphones sound soooo much better amped it ain't even funny.
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Old 29th November 2011, 12:53 PM   #945
sgrossklass is offline sgrossklass  Germany
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"Amped" is far too general a term though. An amplifier is, after all, not a magic black box that'll make cans sound better no matter what. That's not how things work in the real world. And whenever "better" comes up, the inevitable question arises - compared to what? Headphone outputs vary widely, too.

Ultimately it comes down to analyzing a headphone's needs (required voltage and current levels, tolerable noise and output impedance) and matching that to whatever the source has to offer. If this works out well across a wide range of headphones, we have a good amp there.
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Old 29th November 2011, 01:51 PM   #946
ethanolson is offline ethanolson  United States
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@sgrossklass, I believe the higher current availibility is to account for a fuller sound, though it may also be some distortion that I like. I haven't measured it to really know.

You are right about raising the question of "better than what?" Better than the same headphones from my iPod without the amp. My laptop has lots of juice so compared to straight out of the port, there isn't much change... other than the hiss. My DAC stage really helped improve the sound there.

I've had the distinct pleasure of listening to the NuForce uDac2-HP before I knew about RS's blog and I made the determination within 2 minutes that it was worse than straight from my computer... other than the hiss. So there are differences that are audible to me... but I don't know if it's because the headphones can "breath" better or if there's some distortion at play.

My current amp can supply (much more than) the needed 125mW into my headphone's 55-120 Ohm impedance range and it was with this amp that I actually had the realization that something there is helping me hear more and I really like it.
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Old 29th November 2011, 01:57 PM   #947
ethanolson is offline ethanolson  United States
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Oh, I forgot to mention that my interest in the O2 stems from the fact that it's well understood because it is well measured and it has a great damping factor. These are things I just can't say one way or the other about my current setup.

But I have even greater interest in the ODA because I no longer listen to music from any portable devices and don't think I will again for many years.
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Old 29th November 2011, 02:55 PM   #948
RocketScientist is offline RocketScientist  United States
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Quote:
Originally Posted by qusp View Post
haha please realise that this is an area where RS really doesnt know what hes talking about. to get the 120db voltage out spec quoted in the datasheet, there is also a specific voltage out schematic.
I was (perhaps mistakenly) answering the question in general terms not for a specific DAC. I certainly wasn't trying to criticize any specific designer. Ethanolson's question was:

"Why does everyone have I/V stages for their ESS DACs?"

Because ESS doesn't make their datasheets public I've only seen data on a few ESS DAC chips. But the ones I've seen have an output stage built into them and their DNR spec is at the output pins of the chip--not after an external IV stage as you suggest. The application circuit in the datasheet does not show an op amp stage after the DAC.

Adding an op amp onto a DAC that already has an internal output buffer stage isn't likely to improve much besides perhaps the ability to drive unusually low impedance loads or provide a higher voltage output if desired. Adding gain after such a DAC isn't likely to improve the DNR as you suggest.

Certainly if a DAC chip is designed to be followed by an IV stage, or has a high impedance output, you should use an op amp stage. And it may well be some of the ESS chips are in that category. I was assuming Ethanolson was referring to the ones with built-in output buffers.
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Old 29th November 2011, 03:06 PM   #949
Jokener is offline Jokener  Germany
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Just because they came up, are you planning on testing an ESS-based DAC anytime soon?
Or would you consider doing so if someone (i.e. me) offered to send you one to test?
I am really curious about these little buggers and can't find many measurements on them...
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Old 29th November 2011, 03:17 PM   #950
RocketScientist is offline RocketScientist  United States
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@Jokener I will be publishing some ESS DAC measurements but I'm not sure when.
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