Author Topic: DDDAC 1794-NOS 24-192  (Read 166524 times)

Offline twogoodears

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Re: DDDAC 1794-NOS 24-192
« Reply #120 on: December 17, 2012, 04:43:54 AM »
Hi Tuyen... yes, I confirm it was a VERY enjoyable day, indeed... the gentleman from Australia is named James Woodbridge, sure an Aussie, but living and working in Bonn, actually... a very curious and empathic kind of guy and a pleasure to chat with.
Cheers.
Stefano

Offline rhlauranna

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Re: DDDAC 1794-NOS 24-192
« Reply #121 on: December 17, 2012, 05:03:30 AM »
Quote from: tuyen link=topic=842.msg12339#msg12339 date=
Oh, please tell Mr Schick that I am still waiting for my tonearm!!$#@

Me too.. 15+ months and counting :-X

Good news! Just yesterday I talked personally to Mr. Schick, and he promised me that you will receive your tonearm till the end of this year !!!

How was the meet, Reinhard?

Stefano has posted some photos and info on his blog.  Looked really enjoyable.  Who was the person from Australia?!

http://twogoodears.blogspot.com.au/2012/12/eau-de-cologne-winter-2012.html

well, let me begin here:

http://killerdac.com/forum/index.php?topic=900.0

tuyen

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Re: DDDAC 1794-NOS 24-192
« Reply #122 on: December 17, 2012, 05:28:42 PM »
thank you guys.  Enjoyable read.  Photos from Stefano really helped paint the scene :)


Anyways, back on topic of the nice new DDDAC 1794 NOS.

Guy in UK has added tube output stage to it.  Seems to like it.



Having had the chance to fiddle with various output stages for the DDAC1794, I've decided to stick with the Broskie Cathode Follower. (I make no apologies for being a tube guy.)

One thing I have found is that there is a benefit to be had using the +/- output from the DAC. Although I have not tried a transformer, (don't have anything suitable to hand), I expect that the benefit would be the same. You could even consider the BCF to be a sort of poor mans "active" tube transformer, converting a balanced output to single ended, but step-down, 2:1. (So if you had 1.2V single-ended from using one of the outputs, you'll still have 1.2V SE using both of the outs via the BCF.) Aside from any on-paper arguments about CMRR and noise cancellation, the bottom line.... more focus and less grain combining the outputs, as opposed to just using one single ended output. (Of course, if you prefer opamps...... )

Although I was using a differential gain stage in front of the BCF, I've gone back to the 133R I/V resistors and am just using the BCF to obtain a SE output from balanced.

200V HT from Tom Christiansen 21st Century Maida Regulator to the tubes. Heater supply is regulated too. ECC88's, 220R cathode resistors.
50k grid stopper and feedback resistors. That's all there is to it really.

I also swapped my original "junk" 7812 reg that was powering the main DAC board for a Salas shunt. To be honest, I couldn't hear any difference. Then I tried an eBay reg module based on the LT1764, claiming 40uV of noise. Couldn't hear any difference with that either. So it has stayed in by virtue of being last into the circuit. (I've ordered another to power the WaveIO board.)

I'll put it all into a case over the Christmas holidays.

Offline ozcal

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Re: DDDAC 1794-NOS 24-192
« Reply #123 on: December 17, 2012, 07:01:49 PM »
Good stuff T . I have a BCF on the way to use with the A-gd dac.
Listening with my ears :)

Offline zenelectro

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Re: DDDAC 1794-NOS 24-192
« Reply #124 on: December 17, 2012, 07:51:39 PM »
thank you guys.  Enjoyable read.  Photos from Stefano really helped paint the scene :)


Anyways, back on topic of the nice new DDDAC 1794 NOS.

Guy in UK has added tube output stage to it.  Seems to like it.



Having had the chance to fiddle with various output stages for the DDAC1794, I've decided to stick with the Broskie Cathode Follower. (I make no apologies for being a tube guy.)

One thing I have found is that there is a benefit to be had using the +/- output from the DAC. Although I have not tried a transformer, (don't have anything suitable to hand), I expect that the benefit would be the same. You could even consider the BCF to be a sort of poor mans "active" tube transformer, converting a balanced output to single ended, but step-down, 2:1. (So if you had 1.2V single-ended from using one of the outputs, you'll still have 1.2V SE using both of the outs via the BCF.) Aside from any on-paper arguments about CMRR and noise cancellation, the bottom line.... more focus and less grain combining the outputs, as opposed to just using one single ended output. (Of course, if you prefer opamps...... )

Although I was using a differential gain stage in front of the BCF, I've gone back to the 133R I/V resistors and am just using the BCF to obtain a SE output from balanced.

200V HT from Tom Christiansen 21st Century Maida Regulator to the tubes. Heater supply is regulated too. ECC88's, 220R cathode resistors.
50k grid stopper and feedback resistors. That's all there is to it really.

I also swapped my original "junk" 7812 reg that was powering the main DAC board for a Salas shunt. To be honest, I couldn't hear any difference. Then I tried an eBay reg module based on the LT1764, claiming 40uV of noise. Couldn't hear any difference with that either. So it has stayed in by virtue of being last into the circuit. (I've ordered another to power the WaveIO board.)

I'll put it all into a case over the Christmas holidays.


Tuyen,

You have making of incredible system now - but need to start thinking outside (or maybe inside) the box.

There are already tubes in pre amp, the pre amp is fully balanced - the dac is fully balanced.
 
It may not be looking at you but I can see it clearly, direct couple DAC OP, fully balanced, to the pre amp IP tubes.
It is very simple. 

You don't need broskie cathode fiollower - this converts bal to unbal, only to feed your pre amp which is balanced.

cheers

Z

tuyen

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Re: DDDAC 1794-NOS 24-192
« Reply #125 on: December 18, 2012, 12:40:07 AM »
Cheers Z. Makes sense.. I had thought about going down the same path.   Just saw that a guy had tubed the outputs and thought be nice to share someone's diy fun :)

The guy's advice pretty much aligns with yours:

Quote:
Originally Posted by tuyen 
Does that mean I can bypass the coupling capacitor? How about the R load resistors?


My advice would be, unless you know that the inputs to your pre are cap coupled, stick with the coupling caps on the outputs of the DAC.

The I/V resistors? The DAC has current outputs. You need to keep the I/V resistors.

Quote:
Originally Posted by tuyen 
PS. your temp setup looks really interesting Clive. How does the tube rectification/output stage compare to the standard passive IV output? Do you use a valve preamp as well? IE. will I benefit from going an active tube output stage like yours if I already am using a decent valve preamp?


Well, the BCF I'm using although active, isn't really active in as much as it doesn't provide gain. It just combines the balanced outputs into a single output for SE use. In your case, where you'll be using both +/- outputs into your pre, there is no need to add anything if you are happy with the concept of passive output from the DAC board.

The problem with adding active tube stages to DAC's is that without feedback, they better be very low distortion, or you end up in the situation, where the passive out has reasonably low distortion to start with, that you increase it just by adding a tube stage. And without using very high transconductance tubes, you'll probably be adding more noise to the output than is there with the passive out.

IMHO, there is a benefit from using the balanced outputs from the DAC. Without getting into any audiofool clichés, eg. "it seemed like a veil was lifted", I didn't find it subtle. If you have a balanced setup to start with, you don't need to do anything. If you are single-ended, then it is worth thinking about transformers or the BCF.

Offline dddac

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Re: DDDAC 1794-NOS 24-192
« Reply #126 on: December 27, 2012, 11:39:33 PM »
a quick response to the many posts where the modulator is questioned ....

also in the DIY forum, there are posts about questioning the working of the modulator. Of course I cannot look inside the chip to see what happens, but I can look outside....:) ( and listen for that matter)

when I look (measure) I see signals coming out as I am expect them to be. sine wave is sine wave, square is square, triangle is triangle. Even single pulses are a single pulse. fft analysis and linearity plots give no reason to suspect something is wrong.

on top the DAC just sounds great. also on 44.1 my listening experiences versus 192/24 should not be interpreted, that 44.1 SQ is not good. it is still top of the bill, it is just that 192 is so sweet :cool:




Offline ozmillsy

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Re: DDDAC 1794-NOS 24-192
« Reply #127 on: December 28, 2012, 09:59:43 AM »
Well, I've actually been doing some reading on sigma delta dac design to understand what the modulator step does.  

In a generic 1bit SD design,  the modulator accepts multibit data streams, and converts them to 1bit.  There is generally *always* a filter after the modulator, to remove the high frequency noise that is generated by the conversion to 1bit.

There is a trade off when performing the conversion, that needs to be understood.  As the word length is reduced, the sample rate increases.   This is pretty obvious, and I don't know why I didn't jump to that conclusion earlier.    

I've read a little bit about why oversampling is generally used in all SD designs.  Basically the oversampling pushes the data up further away from the inherent noise floor.  I haven't read how that helps any downstream processing, I haven't got that far.

I believe the PCM1794 chip is a multibit SD design.    I haven't gotten to that either, to understand what exactly the modulator does in a multibit design?  I think there are multiple 1 bit streams, but I'm not sure.

« Last Edit: December 28, 2012, 10:02:16 AM by ozmillsy »
It's all about the music,, not the equipment.

Offline zenelectro

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Re: DDDAC 1794-NOS 24-192
« Reply #128 on: December 28, 2012, 10:36:49 AM »
Well, I've actually been doing some reading on sigma delta dac design to understand what the modulator step does.  

In a generic 1bit SD design,  the modulator accepts multibit data streams, and converts them to 1bit.  There is generally *always* a filter after the modulator, to remove the high frequency noise that is generated by the conversion to 1bit.

There is a trade off when performing the conversion, that needs to be understood.  As the word length is reduced, the sample rate increases.   This is pretty obvious, and I don't know why I didn't jump to that conclusion earlier.    

I've read a little bit about why oversampling is generally used in all SD designs.  Basically the oversampling pushes the data up further away from the inherent noise floor.  I haven't read how that helps any downstream processing, I haven't got that far.

I believe the PCM1794 chip is a multibit SD design.    I haven't gotten to that either, to understand what exactly the modulator does in a multibit design?  I think there are multiple 1 bit streams, but I'm not sure.


Oz,

All modern SD DACs use multibit modulators.  There are different ways of arranging the bits. There are a few white papaers around will see if I
can a few up for you. The 1794 is advanced segment which approaches the bits a different way. All of these MB SD chips work at
very high frequencies, many MHz.

FWIW I think currently the Sabre has the most advanced moodulator - and the most linear DAC.

It's not as easy to work with though as the 1794.

The other thing WRT Sabre is that you can actually change many settings, even the number of bit's. There are many hidden settings.
The reason is this: the Sabre is basically an FPGA which is very programmable. You can disable oversampling, run I2S direct,
make your own filters etc etc.

I've been playing with spice to optimise a few OP stages that will work with Sabre that don't use opamps.
There are quite a few options, some that use tubes, some transformers.

cheers

Z

Offline ozmillsy

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Re: DDDAC 1794-NOS 24-192
« Reply #129 on: December 28, 2012, 11:44:03 AM »
Yeah, I was aware the Sabre can be programmed for different multibit operations, up to 8bit for 2ch I believe.

What I don't understand is whether it is 8bit PCM,  or is it 8 x 1bit streams.

Did you see the new Teac DSD dac that uses dual mono PCM1795 chips.  It's getting some good comments.

It's all about the music,, not the equipment.

Offline rhlauranna

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Re: DDDAC 1794-NOS 24-192
« Reply #130 on: March 09, 2013, 10:02:57 PM »
it's always interesting to hear what other people think and discover:

http://www.computeraudiophile.com/blogs/mbrennwa/dddac1794-no-ordinary-dac-329/

Offline rhlauranna

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Re: DDDAC 1794-NOS 24-192
« Reply #131 on: June 14, 2013, 07:18:14 PM »
o.k., here are the latest results in testing/listening to the different DDDACs..

so, if you are interested, you might want to have a look here:

http://www.audio-creative.nl/projecten/

http://www.audio-creative.nl/muziek/goto-hoornsysteem-het-beste-luidsprekersysteem-ooit/

(this is in dutch, but don't worry, you may use the google-translator)

and here

http://twogoodears.blogspot.de/

enjoy
« Last Edit: June 14, 2013, 07:22:56 PM by rhlauranna »

Offline springcreek

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Re: DDDAC 1794-NOS 24-192
« Reply #132 on: June 17, 2013, 03:42:24 PM »
Will order mine in the next week or two...thanks Reinhardt  ;D

Offline kajak12

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Re: DDDAC 1794-NOS 24-192
« Reply #133 on: June 17, 2013, 07:36:01 PM »
Will order mine in the next week or two...thanks Reinhardt  ;D
I will hear tuyens this coming weekend
still discovering the link between electronics and audio reproduction.so much to learn and so little time

Offline ozmillsy

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Re: DDDAC 1794-NOS 24-192
« Reply #134 on: June 18, 2013, 09:18:46 AM »
I will hear tuyens this coming weekend
On your system?     I find it difficult to judge someone elses front end component, on their system, as I typically dont know their system well enough.
It's all about the music,, not the equipment.

Offline kajak12

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Re: DDDAC 1794-NOS 24-192
« Reply #135 on: June 18, 2013, 07:20:37 PM »
I will hear tuyens this coming weekend
On your system?     I find it difficult to judge someone elses front end component, on their system, as I typically dont know their system well enough.
not on my system but on joness99 comparing it with 20k+ cd spinners and emm labs dac/transport combo
still discovering the link between electronics and audio reproduction.so much to learn and so little time

Offline springcreek

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Re: DDDAC 1794-NOS 24-192
« Reply #136 on: June 19, 2013, 09:12:17 AM »
Cool love to hear your impressions  8)

Offline rhlauranna

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Re: DDDAC 1794-NOS 24-192
« Reply #137 on: June 24, 2013, 02:51:58 AM »
yes. and for those who feel interested in the combination of different output transformers, please read the latest part 5 from Triodedick here:

http://www.audio-creative.nl/hifi/dddac-1794-nos-diy-dac-deel-5/

enjoy

and just in case, that you might want to get it in your mother tongue, don't forget the google translater
« Last Edit: June 24, 2013, 02:56:44 AM by rhlauranna »

Offline kajak12

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Re: DDDAC 1794-NOS 24-192
« Reply #138 on: June 24, 2013, 09:18:46 PM »
Cool love to hear your impressions  8)
Tuyen never showed he had family business to attend.
still discovering the link between electronics and audio reproduction.so much to learn and so little time

Offline springcreek

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Re: DDDAC 1794-NOS 24-192
« Reply #139 on: June 26, 2013, 07:42:17 PM »
Bugger, oh well maybe next time Mario...I'm really keen on hearing what you think of it. My concern is that it might be a tad dry and not as rich or liquid as 1541/1543 chips with valve outputs and vintage chokes.