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Old 27th November 2013, 10:57 PM   #3071
Zen Mod is offline Zen Mod  Serbia
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that isn't I/V stage ( in any way or measure ) , as AR2 is using xformer right now
Sabre's output is looking into DC coupled balanced Jfet buffer ( sky high input impedance ) so it's working in pure voltage mode ;
after that , Lundahl xformer connected as 1:2 .

xformer for any sort of I/V is simply impractical there , tnx to sissy nature of Sabre output - halfway between voltage and current output realms

(I'm feeling all the time as riding that ship , while sitting in Heechee chair )

I'm not even going to comment approach of resistive loading of Sabre's output , translating it to voltage strong as fly's fart , then amplifying it again zillion times

it's either pure voltage route .... or non-compromised active I/V conversion route , last one with I/V input impedance lesser than 2R
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Last edited by Zen Mod; 27th November 2013 at 10:59 PM.
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Old 28th November 2013, 05:23 AM   #3072
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But isn't actually:

"resistive loading of Sabre's output , translating it to voltage strong as fly's fart , then amplifying it again zillion times"

=

"non-compromised active I/V conversion route , last one with I/V input impedance lesser than 2R"

where fly's fart is what You get at 2R

?
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Old 28th November 2013, 08:20 AM   #3073
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nope

one thing is if you load it with few ohms (in form of plain resistor) to convert current to (tiny) voltage, then introduce voltage amplification of zillion db

other thing is if you load it with active I/V ,having few ohms (0 as wishful hope) of input impedance ..... which role is exact and linear transfer of DAC output current to I/V stage output node - which is exact place of I/V conversion
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Old 30th November 2013, 08:07 AM   #3074
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The i2s output voltage at the WaveIO isolator is 2,6V and the i2s voltage after the dualXO board is 1,6v. Does this mean anything!?! Might this be the problem for my distorting DAC?!? I didn´t try the PCM board yet!

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Originally Posted by iancanada View Post
Hi apoo,

I got exactly the same issue when I test my PCM1794 and TDA1541A running from my PCM board at 384KHz.

I solved the problem by replacing the USB interface with other one.

Please refer the follow link for details:

Drive NOS AD1865/62,PCM1704/02/63,TDA1541 from FIFO: Universal I2S-PCM driver board

Please let me know for any progress.

Regards,

Ian
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Old 30th November 2013, 08:12 AM   #3075
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If a 2 pole sees an impedance (resistance), does it matter how it was achieved from the source point of view, and can the source know?

//

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Originally Posted by Zen Mod View Post
nope

one thing is if you load it with few ohms (in form of plain resistor) to convert current to (tiny) voltage, then introduce voltage amplification of zillion db

other thing is if you load it with active I/V ,having few ohms (0 as wishful hope) of input impedance ..... which role is exact and linear transfer of DAC output current to I/V stage output node - which is exact place of I/V conversion
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Old 30th November 2013, 01:55 PM   #3076
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imagine this :

case 1 : DAC - resistor - 40db voltage gain stage - buffer , to have 1Vrms per leg

case 2: DAC - I/V stage without active voltage gain - buffer , to have 1Vrms per leg

which one is better , from signal energy preservation point of view ?
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Old 30th November 2013, 02:00 PM   #3077
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Buffer = 1:1 ?
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Old 30th November 2013, 02:25 PM   #3078
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roughly , yes ; voltage gain slightly under 1 , current gain - as you manage it

though , I/V stage , when properly done , is having current buffer role ; to clarify more - it's relocating position of I/V resistor away from DAC chip itself , while not contributing at all in output current

so , you can see it also as voltage gain stage
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Last edited by Zen Mod; 30th November 2013 at 02:29 PM.
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Old 30th November 2013, 02:29 PM   #3079
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So into almost 0 ohm, the chip outputs 1 volt?
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Old 30th November 2013, 02:35 PM   #3080
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yes , and no ;
if you say - chip outputs through I/V stage , then yes

my last iteration , still waiting for proper tests , is having 1.15R differential dynamic input impedance (so 0R575 per leg) ; output swing set to 2Vrms differential
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