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Using the AD844 as an I/V
Using the AD844 as an I/V
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Old 11th February 2019, 09:24 AM   #2241
diyiggy is offline diyiggy
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wow ! And seems also abble to drive headphones.



C4 & C6 with a foilded styren cap (or a silver mica) or a less good 5 mm pitch MKP (avoiding XR7) should be usefull to preserve the clarity of the previous stage.


And for the same purpose : C4+R10 / C7+R18 could be removed if one has an input cap on the pre or amp... (but headphone?)



Btw, just has been looking at your Lingdac shematic. Is this AD8017arz a sort of AD844/OPA860(/1) transconductance IC ? Or why do you prefer it over these last ones to stay in the thread topic (whether an embeded feedbackloop in it?)


Anyway, many thanks for that.
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Old 11th February 2019, 09:52 AM   #2242
abraxalito is online now abraxalito  United Kingdom
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Headphones can be driven yes - just need to check that the bias current is set (via R8 & R16) in accord with the impedance of the 'phones. Also since its classA there's a fair amount of power being dissipated in Q1/Q2/Q4/Q5 - the PCB layout (found on the lingDAC thread) has areas of copper on both sides to act as heat spreaders. One point I just noticed - the PSU is shown as +9V but in fact this buffer only needs 7V to swing 2VRMS at the output, so to keep the FETs as cool as possible its best to run only as high on the rail as needed to swing the full signal.

C4 and C6 are NP0 types, not X7R so no need to swap them out. NP0 are quite blameless as caps. Yes you could remove output coupling caps if you know the next stage has them - definitely do not remove when feeding headphones.

AD8017 is a current feedback amp with high output drive capability. I chose it mainly because its very cheap on Taobao, excellent bang-for-the-buck. AD811 performs slightly better SQ-wise but is more difficult to employ as its output doesn't swing as close to the rails, demanding more volts on the supply. It also runs very, very hot. Incidentally lingDAC only uses discretes in the OPS, its PhiDAC which uses the ADs.
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Last edited by abraxalito; 11th February 2019 at 10:00 AM.
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Old 11th February 2019, 10:02 AM   #2243
pistollero is offline pistollero  Portugal
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Quote:
Originally Posted by georgehifi View Post
Forget the AD844's own buffer it's not very good sounding. Come off the 844's pin5 to your own buffer, I found a "genuine" OPA627 to be exemplary, make sure it's genuine by getting it from an authorized TI distributor, as there are many fakes of these.

Forget the BUF03 in the pic that's the first one I tried, too dirty sounding great bass though.

Cheers George
Hello George, could i use this schematic for the pcm1702 instead of 1704?
are all the component values ok? use 3x ad844 or only 1?
i īm using lt1028 as i/v but i would like to try this alternative.
thks.
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Old 11th February 2019, 10:52 AM   #2244
diyiggy is offline diyiggy
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With good layouts I noticed NP0 in the final direct signal path gives subjectivly something not so neutral at ears (so in the listen frenquency range) : often too thin and a little brighty. Although it depends on the width of the traces on the pcb as well ! When I have choice I swap them for Panasonic PPS if SMD designs where the capicitance is notof an importance (serie signal)- Wima FKP2 (non metalized) are good too. or foilded styrens if vias (silver mica being a little too much brighty and thin as NP0 and not tin foilded styrens less good either). YMMV. I like AWG30 (or more little)width and short length output traces for some reasons before RCAs or any gears output stage (trying to have low mass serie contacts). As for the serie resistors I try to use cheap metalized Yageo which are very low noise or RD if not better RS Sussumu in the digital stage AND after.


Again YMMV, all being subjective at ears in the last details (but the Devil often in its for sure)
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