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Old 29th November 2011, 11:56 AM   #241
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Quote:
Originally Posted by Terry Demol View Post
Who says you can't use a transformer in 'current mode' ?
T
What I said was:
Quote:
Originally Posted by Russ White
In my opinion it is simply is not possible to run directly (even with resistors) into *any* transformer and keep the DAC in "current mode".
The Directly part is important.

Sure if you add some feedback from an active or passive device you can do it, but then you might as well not.

It is my understanding that you would also most likely need amplification after the ZF transformer in any case.
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Last edited by Russ White; 29th November 2011 at 12:10 PM.
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Old 29th November 2011, 12:14 PM   #242
Bunpei is offline Bunpei  Japan
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Quote:
Originally Posted by Joe Rasmussen View Post
No, there are no added 195R resistors, these represents the internal impedance of the ES9018 when used in Stereo mode.
I'm afraid that I'm quite a newbie on the topic of I/V stage or transformer stage design for ES9018 DAC chip. May I ask you some primitive or basic questions? I'd be very happy if any of you could kindly answer to my questions.

We always find +1.65V and 195R in Joe's schematic.
1. I understand that the value 1.65V is calculated as AVCC/2 (where AVCC=+3.3V). When we use Buffalo II with Russ' standard shunt type AVCC sub board, the actual voltage is a little bit higher. Is my understanding correct?
2. I understand that the internal output impedance value, "195R" is a result of summing up of four analog output sections in one side of one phase in the DAC chip.
- How was the "195R" originally derived?
- Is the value applicable even to "pseudo differential" mode output where only + and - outputs are involved? Is it also valid for "9 bit quantizer configuration"?
- Can we actually measure and confirm the "195R" by any means? Is the constant value "195R" valid for all the frequency range 10 - 200 kHz?
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Old 29th November 2011, 12:18 PM   #243
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Quote:
Originally Posted by Bunpei View Post
I'm afraid that I'm quite a newbie on the topic of I/V stage or transformer stage design for ES9018 DAC chip. May I ask you some primitive or basic questions? I'd be very happy if any of you could kindly answer to my questions.

We always find +1.65V and 195R in Joe's schematic.
1. I understand that the value 1.65V is calculated as AVCC/2 (where AVCC=+3.3V). When we use Buffalo II with Russ' standard shunt type AVCC sub board, the actual voltage is a little bit higher. Is my understanding correct?
2. I understand that the internal output impedance value, "195R" is a result of summing up of four analog output sections in one side of one phase in the DAC chip.
3. How was the "195R" originally derived?
4. Is the value applicable even to "pseudo differential" mode output where only + and - outputs are involved? Is it also valid for "9 bit quantizer configuration"?
5. Can we actually measure and confirm the "195R" by any means? Is the constant value "195R" valid for all the frequency range 10 - 200 kHz?
1. AVCC/2 is the more correct way to state this.
2. Ok
3. This is covered in numerous places even the datasheet.
4. Yes. Pseudo differential does not have any effect on the analog characteristic output impedance of the device. It is the same for any quantizer mode and pseudo or true diff as long as you parallel all four output channels. This is very easy to demonstrate on the Buffalo III with IVY-III or Legato. Just play something and switch between modes. You will notice the output volume stays the same.
5. Absolutely, and quite easily. Just play a signal of known amplitude across a fixed resistance and observe the output amplitude. The impedance of the DAC is the same regardless of frequency, but keep in mind that the DAC has a filter that could come into play but that is completely orthogonal to the output impedance.
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Last edited by Russ White; 29th November 2011 at 12:32 PM.
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Old 29th November 2011, 12:41 PM   #244
Bunpei is offline Bunpei  Japan
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Dear Russ,

I greatly appreciated and I am satisfied with your clear-cut answers!

Bunpei
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Old 29th November 2011, 01:28 PM   #245
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Quote:
Originally Posted by Bunpei View Post
Dear Russ,

I greatly appreciated and I am satisfied with your clear-cut answers!

Bunpei
No problem. Very glad to help.

One thing to remember is that while the output impedance is always exactly the same, the output signal amplitude at the + and - outputs (referenced to AVCC/2) will be different between modes. The thing to always remember is that when the two are properly summed (by the output stage) the differential result is the same amplitude in any case.

So the key point here is the practical difference between amplitude at any single output and output impedance. Output impedance never varies, yet the individual components of the output signal can, but when summed it all works out the same in the end.

Cheers!
Russ
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Last edited by Russ White; 29th November 2011 at 02:51 PM.
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Old 30th November 2011, 04:16 AM   #246
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Quote:
Originally Posted by Joe Rasmussen View Post
Hi Terry

Shows you can do a lot with feedback. But as a wise man once said "all things may be possible, even lawful, but not all things are advantageous." Seems the guy's name was Saul or Paul or something.
Hi Joe,

It depends. In the ZFT's case, you don't necessarily have to use an opamp
with FB to get very low impedance at the DAC OP. You just need the ZFT to
feed a low impedance and the ZFT itself to have a very low winding
resistance. Can be sub 1 ohm if that is required.

They can be quite useful for various apps, Studer used to use them for
summing bus applications in consoles.

I thought about using a ZFT for Sabre but came up with better circuit
which uses finite resistance of DAC to cancel distortions in the I-V.

Quote:

Come around and listen to the Oppo 95 here, puts a smile on my face. Need two clocks though, makes a real difference.

Cheers, Joe R.
Thanks, am very busy ATM. Maybe we should blow froth off a few for xmas
WRT 2 clocks are you referring to 27MHz and audio div freq for the second?
Does Oppo 95 use 9018?

cheers
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Old 30th November 2011, 04:51 AM   #247
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Quote:
Originally Posted by Terry Demol View Post
Hi Joe,

I thought about using a ZFT for Sabre but came up with better circuit
which uses finite resistance of DAC to cancel distortions in the I-V.
Ahhh, sounds interesting, care to elucidate? - Suppose not.

Quote:
Originally Posted by Terry Demol View Post

Maybe we should blow froth off a few for xmas
WRT 2 clocks are you referring to 27MHz and audio div freq for the second?
Does Oppo 95 use 9018?
Got some nice German "bier" in the fridge right now.

Oddly enough, they have gone for 25MHz on the digital motherboard into the Meditek chip. There is also a buffer there from USB/eSATA ports (I have been able to 'trigger' it when no activity from the port as the HDD has gone into sleep mode) that is clocked (re-clocked really) from the 'master' clock. Our VSE guy in Munich, Ned says it almost certainly does the same off the transport.

Yes, uses ES9018 and have 80MHz on it.

Then transformer coupled 1:1 to XLRs, but has two 330R to ground from both phases of the DAC (stereo mode - 4 parrallel) and get a decent 1.3V RMS. Without the resistors in simple voltage mode, it sounds light in balance, but then firms up nicely.

Got 600+ albums, some 24 bit stuff as well, on a 2TB hard drive and yet only filled 1/6th of its capacity.

But watching movies on the 95 is a real hoot. Mate, the realism and IMPACT it has is HUGELY enjoyable. I am worried, is this thing also turning me into a videophile? Shock, horror!

Cheers, Joe
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Last edited by Joe Rasmussen; 30th November 2011 at 04:54 AM.
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Old 30th November 2011, 11:32 AM   #248
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Lets keep it on topic mates. Anything further off topic will be deleted. Fair notice.
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Old 30th November 2011, 11:45 PM   #249
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Quote:
Originally Posted by Russ White View Post
What I said was:

"In my opinion it is simply is not possible to run directly (even with resistors) into *any* transformer and keep the DAC in "current mode"."

The Directly part is important.
You said "directly into *any* transformer".

To me that reads a transformer connected 'directly' to the DAC OP with
nothing in between.

I don't see any mention whether any additional circuitry should / not be used
after the transformer.

Quote:

Sure if you add some feedback from an active or passive device you can do it, but then you might as well not.
a) The zero field transformer can reflect a sub 1 ohm impedance to the DAC
without the use of mixed (as they call it) feedback.

b) How can you add some feedback from a passive device?

c) Your "might as well not" suggestion is counter to the DIY spirit in this
forum.

My suggestion was to make people aware that the transformer itself can be
used in 'current mode' and hence reflect a very low impedance. I've done
it and it works.

T
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Old 1st December 2011, 12:01 AM   #250
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Quote:
My suggestion was to make people aware that the transformer itself can be used in 'current mode' and hence reflect a very low impedance. I've done it and it works.
Could you share a schematic or other details?
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