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Musical Fidelity X-DAC V2 Mod

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demiro
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Re: Musical Fidelity X-DAC V2 Mod

Post by demiro » 28 Aug 2009, 14:00

Those BlackGate, are together with polipropylen by-pass?
Thanks.

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DejanM
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Re: Musical Fidelity X-DAC V2 Mod

Post by DejanM » 28 Aug 2009, 17:25

demiro wrote:Those BlackGate, are together with polipropylen by-pass?
Thanks.
No, I didn't put any by-pass cap to BG Nx ... To get a better understanding of this change take a look at the output stage of this DAC:
X-DAC V2 Output stage.jpg
X-DAC V2 Output stage.jpg (48.08 KiB) Viewed 2306 times
X-DAC V2 Output stage.jpg
X-DAC V2 Output stage.jpg (48.08 KiB) Viewed 2306 times
We are talking here about C109 (10 uF, 20V) on the picture ...


demiro
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Re: Musical Fidelity X-DAC V2 Mod

Post by demiro » 28 Aug 2009, 19:24

Ok, sorry for my misunderstanding.
Thanks alot
:gnum

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Re: Musical Fidelity X-DAC V2 Mod

Post by DejanM » 28 Aug 2009, 20:19

demiro wrote:Ok, sorry for my misunderstanding.
Thanks alot
:gnum
It is nothing wrong with the idea to by-pass an electrolytic cap - on the contrary - it is something very often done - but normally I do not by-pass BGs Nx series ... They are quite good as they are and I am not sure whether by-passing will bring anything to their behaviour.

One thing more ... BGs Nx are non-polarised and the original tantallium cap was polarised, as you can see on the figure. So the usage of BG Nx is not quite correct here. Nevertheless, I went for BG Nx because they have an excellent reputation as coupling caps. But more correctly you would put polarised electrolytic here, something like Panasonic FM. I by-pass Panasonics with 0,1 uF Evox-rifa or similar. That would be an alternative approach ....


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Re: Musical Fidelity X-DAC V2 Mod

Post by demiro » 28 Aug 2009, 21:42

In my case I replaced the original OPAs using OPA2604. The are a bit cheaper than OPA2111, but they sounds good to. The BG NX series caps is hard to get in UK, so maybe I put the polarised electrolitc cap from Syno or Vishay... or Panasonic.

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Re: Musical Fidelity X-DAC V2 Mod

Post by DejanM » 28 Aug 2009, 21:49

demiro wrote:In my case I replaced the original OPAs using OPA2604. The are a bit cheaper than OPA2111, but they sounds good to. The BG NX series caps is hard to get in UK, so maybe I put the polarised electrolitc cap from Syno or Vishay... or Panasonic.
OPA2604 were the first replacement in this circuit. It was working ok but the difference between OPA2111 and 2604 is remarkable. Yes, there is a difference in price but it is worth every penny ...

I bought my BGs at:

http://www.partsconnexion.com/


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Re: Musical Fidelity X-DAC V2 Mod

Post by RIVIERA » 04 Sep 2009, 10:57

aktivni fndr filter posle iv op-a, strasno muti sliku,
probaj pasivni pristup, a ako si preradio na non-os mod
mozes i da ga preskocis...
isprobaj i override jednostavno, i uverices se?

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Re: Musical Fidelity X-DAC V2 Mod

Post by DejanM » 05 Sep 2009, 09:15

RIVIERA wrote:aktivni fndr filter posle iv op-a, strasno muti sliku,
probaj pasivni pristup, a ako si preradio na non-os mod
mozes i da ga preskocis...
isprobaj i override jednostavno, i uverices se?
Tesko je uraditi by-pass immitence kola jer su prva dva OPA u jednom chipu a druga dva u drugom. To bi bilo dosta budzenja ... Ideja je preci u non-os i jednostavno ceo taj izlazni deo premostiti ili jednostavnim otpornikom ili jos bolje trafoom.


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Re: Musical Fidelity X-DAC V2 Mod

Post by RIVIERA » 05 Sep 2009, 11:02

Pa da...
jako je nezgodno kada su dupli op.
*
nos radi uvek dobro.
Riv je ok
Cak i sa trafoom na izlazu
potreban ti je Riv, retko je dc primara odgovarajuci
da bi se dobio sto manji off-set na izlazu daca,
(to je jedna od tipicnih da ne kazem gresaka)
*
jako dobre rezultate daje neka vrsta folded cascode
sa bjt tranzistorima...
kolo je relatvino jednostavno, i moze se iskoristiti i postojece
napajanje koje snabdeva OP...
*
koji je dac unutra?


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Re: Musical Fidelity X-DAC V2 Mod

Post by RIVIERA » 05 Sep 2009, 11:03

a da pcm69 pardon... :D


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Re: Musical Fidelity X-DAC V2 Mod

Post by RIVIERA » 05 Sep 2009, 11:37

umalo da zaboravim
Sa primenjenim samo Riv na izlazu daca,
dobija se 180deg phase shift
a to je neispravno
(prihvtljivo je u slucaju da posle signal ide na cevni preamp
single end single stage, koji u principu isto obcu fazu za 180deg
pa tako na amp dolazi signal ispravne faze...)
sa tim da interconect trba izmeniti da vruci kraj ne bi putovao kroz shirm...
*
Tako da je upotreba transformatora neophodna
da vrati fazu i naponski pojaca signal
medjutim povecace se i izlazna impedansa sa kvdratom prenosa step-up
ali mislim da ce to biti dovoljno da drajvuje capacitivnost kablova i ulaza preampa?
*
ako se koristi preamp koji obrce fazu trafo trba povezati protivfazno...
cheers
*
Riv je oko 120 do 100 oma
(previse male vrednosti mogu ostetiti dac chip)
pa je mozda najbolje da krenes sa vecim vrednostima za Riv
na pr 220 oma, i kontrolises temperaturu daca
mini hladnjak na dac chip nije los izbor
izoblicenja se drasticno smanjuju...
*
na izlazu posle Riv-a oko 100oma dobices oko 100-200mV
*
ovde karakter zvuka zavisi
od izbora trafoa
pa posle od izbora Riv-a
*
to su neka moja iskustva na ovu temu
:D


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Re: Musical Fidelity X-DAC V2 Mod

Post by RIVIERA » 05 Sep 2009, 11:41

izvinjavam se sto davim
ali jos nesto:
*
veoma osetljivo i pazljivo sa merenjima off-seta na dacu
ili bilo kojih drugih vrednosti,
zato sto ako se slucajno spoje nogice pipalicom instrumenta
95% se trajno ostecuje dac chip...
*
nisam siguran
ali mislim da je PCM69 redak dac chip
i nece ga biti jednostavno nabaviti
cheers

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Re: Musical Fidelity X-DAC V2 Mod

Post by DejanM » 05 Sep 2009, 16:34

Pa i to je jedan od razloga zasto zelim da uzmem jos jedan slican DAC (cena je oko 100 eura) i da onda uradim sledece:

- direktno da na nozice izlaznog signala PCM69 zakacim Lundahl LL1636 (N=20, R(primara) = 2,5 ohma; R(sekundara) = 790 ohma)
- ne stavljati izmedju dac chipa i primara trafoa nikakav filter (preporuka Audio Note)
- na sekundaru trafoa otocno staviti otpornik od 50K -> to ce da da izlazni nivo od ~2,2 V

Bilo bi interesantno cuti kako ce to da svira ... :D


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Re: Musical Fidelity X-DAC V2 Mod

Post by RIVIERA » 06 Sep 2009, 11:25

Sigurno dobro...
ali bojim se da ces spaliti dac chip sa 2.5oma dc res.
ako vec hoces da probas samo zato sto je neko na negde na netu rekao
onda
mozda umesto na ground spoji drugi kraj primara na
Vref, koji postoji na prvom OP-u?
tako ces smanjiti struju kroz namotaj...
*


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Re: Musical Fidelity X-DAC V2 Mod

Post by RIVIERA » 06 Sep 2009, 11:33

drugo
za 2.5oma dc
pretpostavljam da je trafo manji
sto znaci da je zica u primaru jako tanka
to vodi na zakljucak da je broj namotaja
manji,
sto dalje znaci da je induktivnost primara manja
iz toga proizilazi da je potrebna izuzetno niska
izlazna impedansa Req,
da bi se dobio pun niski spektar...
*
To je slucaj kod MC zvucnica koje imaju Req oko 16-20 oma
ali nije slucaj sa dac-ovima
*
nisam siguran, ali mislim da je Req daca oko 1-1.5K
tek sa Riv na izlazu Req opada i moze se smatrati kao
vrednost u paraleli...
a to je malo manje od Riv?
:?

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