Build thread for Diyinhk ES9018 DAC on Ebay

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Does a schematic exist for the I/V stage? I'm just curious as nowadays I'm designing I/V stages :) I rather suspect that if the LME49990 is being used for that function its almost certainly not the best choice for SQ owing to having an undegenerated low noise LTP input stage which IME are very susceptible to HF overload.
 
Hi,

There's one in the datasheet, looks like this, without the balanced parts (link to GLT's page):

iv.png
 
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Thanks - the problem there for the sound is connecting the DAC output directly to one side of an LTP (long-tailed pair - the opamp input stage). That's a recipe for some serious intermodulation distortion which doesn't show up on sinewave testing. But you'll hear it as digital harshness, loss of soundstage depth, glassiness in massed strings and general loss of dynamics.

I reckon that changing the input opamp to something that will overload less easily will pay dividends in SQ, I'll check out some suggested parts. The amps which sound best will avoid the LTP and will hence be CFB architecture which would mean some slight circuit board tweaking... :p
 
Yes using FETs is indeed a step in the right direction as they're not so non-linear when overloaded as bipolars are. I know that ADI has at least one part which has improved input stage linearity - one of Barrie Gilbert's innovations a 'multi-tanh input stage' - so I will see if that one is possibly compatible with this circuit.
 
Here's my first suggestion to try - this one doesn't need any circuit changes at all.

http://www.ti.com/lit/ds/symlink/lm6171.pdf

Notice on page13 its showing a simplified schematic - not the normal LTP input stage, rather internally its a current-feedback (CFB) amp. Hence no overload problems - lots of internal current available to handle huge slewing demands.

Here's a similar (looks better but only SO8 package, no DIP) part - LT1818 is the single - http://cds.linear.com/docs/Datasheet/18189fb.pdf

Ooops, forgot to mention that LT1818 is limited to 12V total supply, max.
 
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I've listened to LM6171 - I used them with LM6172 in AMB's Mini3. The signature is okay, if a little bright and over-detailed. However, their performance is below that of the DAC IC so they won't do the DAC justice. I preferred the sound from LM7322/LM7321. So ltp or cfp matters, but so does thd+n, signature, etc. I've grown to seriously dislike op amp rolling - compromises...

I have a list of op amps that are "good enough" according to their specs :

OPA627, OPA827, OPA1641, OPA211, ADA4627, AD8597, LME49990, LME49710

and I'm sure there are more.
 
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I've listened to LM6171 - I used them with LM6172 in AMB's Mini3.

Rather like saying 'I've used a Ferrari, for a spot of shopping, it wasn't that bad'. That application is just an amp it seems to me, I/V duty is more like a racetrack in comparison to small town driving :D

However, their performance is below that of the DAC IC so they won't do the DAC justice.

In terms of noise, I would agree. However that DAC's noise performance is way beyond what anyone can actually hear in a typical setup. In terms of distortion (in particular IMD) performance on complex tones (music for example) the normal amps do not do the DAC justice at all.
 
haha....... yummy... more mei jing... I tried LT1028 a while back - super bass ! No detail at all... "no salt and too much gravy"

It's a shame that many datasheets don't show internals - the ADA4627 sound as good as any I've tried in I/V stages, but I have no idea if they are ltp or cfp or ? input.
 
I did wonder about the change in their naming style from 8 to 4....and ADI have been very keen to push the ADA4627 as "upgrade" to 797, 8610, etc, on their site. Anyway, the 627 sound good so for sure I'll try them.

Are any on my list cfp ? Do you know any fet that are cfp ? Or is there a good workaround you know ?
 
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 :D

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...
 
The CFB ones tend to have very high slew rates right ? Like 1500V/us instead of the 50V/us ?

I've done so much op amp rolling in the past for I/V and buffers, that I'd much rather give up on op amps and use a discrete stage. However, there's quite a range of designs for this too so it hardly makes it any easier to choose. Any tips ?
 
Yes - right. As a general rule here the faster the slew rate the better the opamp is going to be at handling the overload conditions encountered in doing I/V.

As regards discrete I/V stages, I haven't yet exhausted all the possibilities offered by very wide bandwidth CFB amps. I'll only go discrete myself when I'm totally convinced no integrated solution will do the job adequately. I'm just lazy like that and a man's got to know his limitations. It would take me a seriously long time to learn analog design as well as the professional IC designers so I prefer to continue to scour datasheets for days on end looking for the right part :D Ask me again in a few months how its going... :p
 
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