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Old 9th June 2013, 08:39 AM   #461
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Quote:
Originally Posted by Zoran View Post
f
When I asked Dustin Foreman long tme ago about the Riv issues.
He said simply, put whenewr you want gnd, or +Avcc, os some +Vref in between...
So this dac has no classic output stage like old type models where the offset is have to be low.
Indeed so, I figured this out very quickly.

So surely there is an advantage to consider, pulling it to ground and have a "real" ground rather than faked one - and makes potential direct coupled circuits possible. At least more easy to do.

Is there something like a "virtual earth" that is Zero Ohm? Any signal there would indicate not. So is a "virtual earth" really "near earth"? If there is a signal there, then that signal (as a thought experiment) could be amplified.

So why not explore that... use very Low Z passive - is that not also "near earth" but without some of the negatives.

Looking at the parameters required for "voltage" drive and applying it to "current" drive, this in rounded off numbers is 10:1 or better. Preferably better, of course.

This is what I am doing and trust me, it works. Sounds very good indeed and lots agree.

Cheers, Joe
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Old 10th June 2013, 07:33 AM   #462
Zoran is offline Zoran  Serbia
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Yes, the dac has mosfet devices on the output
probably cascoded, and probably non-complementary type
because of the single supply of avcc +3.3V
for this pins I put Vref style of power (Jung variation with ad797, one for each channel)
So it is possible to tap the right value from avcc to exact match offset on the riv-s...
other way Joe explained
third way is to extract surrent to external I-to-I device and then convert.
.
the interesting q can be of the issue of amplification and nature of the amplification
1. Riv one level not amplified, 1:1 intersage - out
2. low riv - amplification active - interstage 1:1 optionally - out
3. low Riv - no gain - interstage step UP, passive amplifications - out
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Old 11th June 2013, 06:53 AM   #463
Zoran is offline Zoran  Serbia
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output impedanse or internal resistance of the generator, of each current output
is about 800ohm litlle bit less, so 4 outputs merged is about 200ohm litlle bit less.
that is for the 9008 chip but it is the same for the 9018.
it is not lets say referenced to ground, but rather this is internal resistance of the generator. so if we have current source conected to ground or some potential, that is R
connected ot the ither side.
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Old 11th June 2013, 07:06 AM   #464
Zoran is offline Zoran  Serbia
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LL1674 have 2 secondary coils. So You can run it in parallel and reduce the transfer ratio,
and voltage if You think that is too much.
unfortunatly in the datas some parameters from importance is ommited
like Lp inductance of primary
inductance of secondary, coupling factor
and capacitances...
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Old 22nd September 2013, 10:40 PM   #465
TNT is offline TNT  Sweden
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Q to Joe... The grounding of the middle-point of the 2 resistors R as oppose to use just one (2*R) resistor.. what gain is at hand here and whats the working of the earthing?

//
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Old 23rd September 2013, 09:53 AM   #466
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Quote:
Originally Posted by TNT View Post
Q to Joe... The grounding of the middle-point of the 2 resistors R as oppose to use just one (2*R) resistor.. what gain is at hand here and whats the working of the earthing?

//
Several. For one thing, it gets rid of the 1.65V offset and means that it is easier to get rid of capacitors in the signal path. The offset voltage becomes and offset current of 2.1mA per phase. The other is the much lower Z. If you don't ground the midpoint, the termination impedance becomes the Z of the other phase, so you are no longer using the DAC in current mode.

BTW, you can certainly try both, but I suspect I know which you are going to like after listening. Sabre DAC sounds better in current mode, a more fully fleshed out balance and not lightweight as it sounds when in voltage mode.

Cheers, Joe
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Old 23rd September 2013, 05:03 PM   #467
TNT is offline TNT  Sweden
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Thanks!

Just to be clear... is your description valid for the situations in the picture?

ess_traf.jpg

BR //
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Old 23rd September 2013, 11:17 PM   #468
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Originally Posted by TNT View Post
Thanks!

Just to be clear... is your description valid for the situations in the picture?

Attachment 372781

BR //
Looks about right.
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Old 24th September 2013, 12:04 AM   #469
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Diagram A is correct as far as the way the ESS dac and resistors are connected to the transformer.
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Old 24th September 2013, 07:37 PM   #470
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Quote:
Originally Posted by ihear21khz View Post
Diagram A is correct as far as the way the ESS dac and resistors are connected to the transformer.
But you don't like whats going on at the secondary side?

//
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