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I've tried to snatch AD samples, and their support played me like a fool...yes I own all the opamps you mentioned

no, they didn't "agree" to ship it to you, it means the chips were shipped from their warehouse to your local agency...but either they got lost between the latter and you, or they didn't find you "worthy"(not convincing enough application?)

using National parts because they're "free" and dismissing AD/LT because they're not...humm, none of these companies runs a charity business

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I have two of the LT1028ACN8, but I need to use a single to dual op-amp adapter, right?

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Yep that's right. You can get them on Ebay if nowhere else.

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Hi,

I don't use parts just cos they're free. But I'm not a wally - if a company is happy to send me samples for free then I'm not about to pay. Who would ?

Unfortunately, most of the time, the parts I want aren't in the samples programs.

I just realised I had already bought two LT1028 and I haven't even tested them ! Doh ! They're sitting in a tray waiting for an adapter which I completely forgot to get.

I think I should do a parts clear out at some point. It's getting silly how much I've got. I have complete parts for 3 Mini3's in a tray too and quite a few op amps I forgot about.

So you don't rate the AD797B then ? That's strange cos to me it seems like one of the most natural and pleasing op amps I've heard. I guess we all have our own personal faves.

check out majkel's thread OP for his impressions, and the last pages for mine if you like: http://www.head-fi.org/forums/f6/aud...-v-2-a-397691/

basically 797B has a true X/Z SS, but PRaT is very low...and the SS in the X axis is not as wide as 1028A IME.

1028A has a triangular shaped SS, so no need for crossfeed to get a phantom center channel on headphones, low end bass is eye popping(497x0HA ph34r ), mids are as creamy as a Burson and the trebles are slightly rolled off...which is fantastic for headphones use.

you can read RS impressions here: http://www.head-fi.org/forums/6402627-post77.html

I would very much agree w/ both majkel and RS...797B has an amazing Z SS, but all the rest lacks IMHO

OTOH 1028CS8 is a clear step down from ACN8 in my DAC, HUGE step down I'd say.

1028AC is a PRaT killing machine...if you check the PCM1794 datasheet, they actually advise to use 1028 as LPF, figures!

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now you just needs to add links to where those mods are explained for total noobs like me and we too can reach modding nirvana!

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I don't suppose you could throw-in what he's missing so far?
That is after-all the focus of this thread!

What would be awesome is if it could evolve into a How-to for every mod!*
Or at least an Index that points to other threads/sites that outline each mod.


*I guess many would be repetitions of the same sort of thing.
And some would be much more difficult than others....

Hi,

It's exactly why I started this thread - because there are too many posts to find anything; I can't. So I dunno how anyone is going to find out what and how to do it.

Just IMO here is my preference for mods in order of sq improvement :

1) Replace xo - reasonably easy; hardest thing was getting the old xo off without hurting the board. Very noticeable improvement everywhere and for everything - much better definition.
2) Replace feedback caps - very easy if you've already upgraded the decoupling caps and mounted them from the other side - this creates the necessary space around the op amps. Better caps would be Relcap RTE but they are even bigger.
3) Upgrade the -12v line with a 7912 - for me this was very easy to do. modest improvement.
4=) Remove or short output coupling caps. Quite easy. I initially replaced the output caps with BG NX but recently tried it w/o any. A clear improvement but not a great leap up. Be careful and check dc offset after doing this to make sure it is safe to connect up. More than 20mV DC is a sign something is not quite right and more than 50mV and you've got a problem somewhere. Ideally you should have just a few mV.
4=) Give the card a good linear supply - lm317a is fine for this. No need to go mad. also very easy for me. slight difference.
6)Upgrade decoupling caps - not much difference and quite difficult because of the through-hole solder on the large ground plane - needs lots and lots of heat and a v good soldering iron. But if you don't, it's harder to do step 2 !

Here is a photo of the feedback cap change - I simply de-soldered the smt caps and replaced them with Vishay MKP1830. I think I chose 3.3nF as opposed to the original 2.2nF. It reduces the bandwidth (but this has no audible effect) and gives a much more natural sound with slightly less distortion, especially in the upper frequencies.




Here are photos of the regulator upgrade and psu. The smt res on the underside is replaced with a 120K thin film and a 7912 is used to regulate the -12V line. The inductor just below the 7912 must be removed. You can read about it in this thread, together with some discussions about external linear psu :

page 1 http://www.head-fi.org/forums/f46/ma...ssence-426049/
page 19 http://www.head-fi.org/forums/f46/ma...9/index19.html








Here are some photos of the xo upgrade, and you can read about it in this thread :

page 1http://www.head-fi.org/forums/f46/up...ce-stx-433533/
page 7 http://www.head-fi.org/forums/f46/up...33/index7.html




And for the output coupling caps, just remove or short the two gold caps in the left of this photo



Hope this helps.

Wow great post, thanks heaps for that!
I'm some time away trying some of these, but I will do some eventually!

holy crap Thoppa your the man, I was about to send you a PM to ask what exactly you had done to you ST as I'm in the process if slowly modding mine.

I'm using the AD797BZ in the buffer and LT1364 in the I/V, then i by-passed the DC coupling caps on the RCA out which i've found made a huge difference to the highend dynamics (like removing a thin "copression" off the topend) i'm now looking for the next mod and liek you say have been scouring the forums to pick up each scrap of info I could.....

Looks like the TCXO will be my next port of call as removing Jitter is a huge step for Digital sources.....

Thanks,
Synth

Hi,

I'm quite willing to believe that removing the original Nichicon would have a more noticeable effect than the smaller steps I took to get there, so I've probably placed it too low, but nevermind...... But for me, definitely that Vanguard tcxo had the most effect.

I don't there is anything left to try really. Maybe upgrading the feedback caps in the buffer circuit, but they are poly~ already.... but if anyone has tried anything I'd love to know.

I think next up is to look at the noise on/from the mobo. Probably beyond my abilities tbh.

Instead of creating an external PSU; do you think creating some kind of filter circuit that plugs into the molex then to the card could clean things up a little bit?

The card has cleaning circuit on it, however a filter may be an idea for some as the cleaner the better.
The OP boosted the voltages on the card according to the first post so he would require an external supply.
If you wanted to follow his modding you would also need the external linear supply.

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If you are using an atx supply and want to knock down the high frequency noise, then yes, you could use some filters.

You'll need three 100uH 5A toroid coils and four 0.1uF y-rated caps. Connect one coil in series on the earth line and one coil each on the 5V and 12V lines. The caps go from the 5v to earth and 12v to earth, one cap before the coil and the other after.

This will create pi filters on the 5V and 12V and also a simple filter on the ground. If you do a google, you can read up more about pi filters.