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Old 8th January 2013, 07:17 AM   #21
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I prefer to put something passive (i.e. a filter) nowadays between the DAC and any active stage because the challenges are just too great for semiconductors unaided so I've moved away from active I/V. If you'd like to learn a bit more about passive filtering you could have a butchas at my thread over here : Digital that sounds like analog

As regards the TPA6120 yes its a good choice - I have whole tubes of ADI's equivalent to that which is AD8016 and planning to build a lowish-power poweramp with several of them paralleled
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Old 8th January 2013, 10:40 AM   #22
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Quote:
Originally Posted by abraxalito View Post
No, none on your list are CFB - none of the ones I've so far mentioned are true CFB either since they'd not work in the current circuit without mods. A particular point is that a true CFB amp can't have a feedback capacitor or it goes wild

No, don't know any FET ones which are CFB but I agree that would be an interesting avenue to explore if anyone's up for designing a discrete stage, looks like it could be good...
already done, Patrick aka EUVL/Papa/John Curl and their SEN/CEN variants are current conveyers/transimpedance stages with passive IV on the output. simple circuits, I just wish it didnt necessitate floating supplies/Batteries.

the thing for the ESS in stereo mode though is the input needs to be high transconductance/low impedance, low noise, as well as having the ability to handle the above average current of 16ma that you see from the 9018.

because of the above, jfets are difficult to choose, mosfets tend to need to be high current gain power devices... and the best candidates objectively end up being bipolar transistors.

this thread has some very interesting discrete circuits for ES901X too including some CFB types, one of which is a discrete AD844 variant.

Last edited by qusp; 8th January 2013 at 10:53 AM.
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Old 8th January 2013, 10:52 AM   #23
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A current conveyor isn't the same thing as a CFB amp. Current conveyors operate open loop from my (limited) understanding.

Yes what you say about ESS's requirements are reminding me of an earlier discussion we had where I said I was just too lazy to go there, coz ESS has made it too hard NOS is sooo much easier, but by no means a walk in the park all the same.
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Old 8th January 2013, 10:55 AM   #24
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yeah fair call on the actual SEN, but check the development thread there is a number of simple CFB designs discussed. also in the link I forgot to add is added now has a number of options including CFB

yep I think current conveyer must be open loop and gain depends on the device characteristics like transconductance etc but it seems a little bit of a grey area, but transimpedence amps dont have to be open loop of course

interesting and topical paper at ADi

Click the image to open in full size.

^^ CFB amp

Last edited by qusp; 8th January 2013 at 11:17 AM.
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Old 8th January 2013, 11:32 AM   #25
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Has anyone done any measurements with different op amps for the ES9018 ?

How about the AD844 in the I/V ? Too much THD ?

Last edited by KlipschKid; 8th January 2013 at 11:40 AM.
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Old 8th January 2013, 05:39 PM   #26
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KlipschKid, what do you plan to use for the 3.3v analog? which can be increased to 3.6v (like Buffalo) or even 4.0v based on specification
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Old 8th January 2013, 06:51 PM   #27
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I wouldnt push it to 4v, I use 3.65 as a happy medium
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Old 8th January 2013, 08:10 PM   #28
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3.8 is safe as shown here: ESS Support Downloads in the analog power consumption chart.

If using slower clocks, then you can probably use the higher voltages. Apparently, higher voltages result in better performance.

The white paper says:
"With 4.0V power supply greater than 133dB can be achieved"

There is also some indication that slower clocks could give you better performance:
ESS Sabre Reference DAC (8-channel)
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Old 8th January 2013, 08:24 PM   #29
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its not safe at the speeds I run and potentially shortening the life of the dac chip for an extra 1-2db max (they cant even tell you how much) when your chances of seeing the full standard 133db are already nil? doesnt seem worthwhile to me.

of course it potentially give better performance, its the analogue reference for the output, meaning you get more swing, higher DNR and the the output will of course have higher DC offset to match. AVCC/2

I tried 4v, found no audible difference vs 3.6, but settled on 3.65. and I certainly wouldnt be recommending people here send it 4v with a shunt reg, generally shunt regs do not have very stable voltage output vs temperature due to the tempco on the voltage references used, part of the reasons I pulled back back then. you could potentially send it 4.5v....

running at 4v is like running the clock at 125MHz.... well actually at least running at 4v has a marginal measurable benefit.
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Old 8th January 2013, 11:35 PM   #30
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Default Build thread for Diyinhk ES9018 DAC on Ebay

On another thread I wondered aloud about SSM2141

http://www.analog.com/static/importe...ts/SSM2141.pdf

is that device even worth any chatter? What with all the high-spec op amps being considered? {I'm not likely to use any op amps after the I->V anyway}.
I see it deployed on boards on eBay:

WZ 21B SSM2141 Balanced Unbalanced Board Balance Input Output Unbalance | eBay

and for various reasons I have some interest.
[modding Behringer DCX2496 which has AKM AK4393 differential out DACs]. SSM2141 reminds me of the Broskie cathode follower:

http://tubecad.com/Product_PDFs/BCF%209-Pin.pdf

though I have no idea what SSM2141 or the tube circuit would spec out at vs ESS reference design [or the better stuff being discussed HERE]. Anyone seen it used anywhere in real life?
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