iFi Audio Pro iDSD discussion thread
Feb 8, 2015 at 2:31 PM Post #376 of 2,994

EVOLVIST

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4) Passive Filtering and Discrete Analogue stage
The analogue stage in the iDSD Pro will be completely discrete, no Op-Amp IC's and in fact the actual discrete design will also not just be Op-Amp made discrete (and often worse than the best integrated ones) but will use something radically different, pure Class A (
beerchug.gif
) being among the features. Much of the circuitry draws its inspiration from legendary and exceptionally sounding studio equipment.
 
 
Not only that, but the DAC outputs will have a purely passive, CLC (Capacitor-Resistor-Capacitor) based lowpass filter to remove ultrasonic noise. Commonly the DAC outputs are filtered at least in part active. Often active filters struggle with the amount ultrasonic noise and RFI they have to handle and at a few 100kHz they often loose the ability to filter at all.
 
Not so for the iDSD Pro. Using passive CLC filtering provides the correct filtering out to many Megahertz, so that the following analogue stage is not required to handle ultrasonic noise and RFI outside it's ability to handle.

 
Hey guys, question for all (and the above quote is related to the iDSD Pro outputs): given these features, would you take this to mean that this would relate to the XLR outputs, as well, leading into, let's say a headphone amp?
 
I'm showing some of my lack of technical knowledge, being that I'm used to Op-Amps, but I've read a few articles to bolster my knowledge, concerning passive, discrete, amplification, sooooo...
 
What I'm trying to get at here, if I understand this correctly, if the iDSD Pro runs XLR outs without the use of Op-Amps, then the balanced signal going into my HP amp should not have the colorization intrinsic in most Op-Amp based preamps?
 
That's kind of been a problem of mine, for a while, even with the iDSD micro, that if I don't go direct, but instead opt for preamp mode, the signal going into my headphone amp is in some way colored by the preamp sound. I'm not getting the straight sound, in other words.
 
In a perfect world I would like to set my HP amp to unity gain and then control my volume with a transparent preamp. It sounds like this is what iFi is getting at here, or am I off base?
 
Feb 8, 2015 at 7:03 PM Post #377 of 2,994

john57

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When IFI stated that:
 
"not just be Op-Amp made discrete (and often worse than the best integrated ones)"
 
I find this to be true with another manufacturer DAC's The early version was all discrete and the sound was so so. When the next version uses op-Amps the sound quality improves.  It is harder to make good sounding discrete unit as compared to the best integrated design. I have no beef about Op-Amps or integrated class D amps.
 
Feb 8, 2015 at 8:16 PM Post #379 of 2,994

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When IFI stated that:

"not just be Op-Amp made discrete (and often worse than the best integrated ones)"

I find this to be true with another manufacturer DAC's The early version was all discrete and the sound was so so. When the next version uses op-Amps the sound quality improves.  It is harder to make good sounding discrete unit as compared to the best integrated design. I have no beef about Op-Amps or integrated class D amps.


I follow ya. Certainly. It's just to me, however, every time I go out of an Op-amp pre into an my Auditor, which offers their own proprietary SUPRA Ops, the combo either comes out sounding squeezed or too sibilant: just processed, like a form of double amping.

If I'm reading iFi right, a well designed discrete C-L-C analog outputs from the XLRs should cure this ill. But I don't know if I'm reading them right. :)
 
Feb 8, 2015 at 8:47 PM Post #380 of 2,994

john57

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I follow ya. Certainly. It's just to me, however, every time I go out of an Op-amp pre into an my Auditor, which offers their own proprietary SUPRA Ops, the combo either comes out sounding squeezed or too sibilant: just processed, like a form of double amping.

If I'm reading iFi right, a well designed discrete C-L-C analog outputs from the XLRs should cure this ill. But I don't know if I'm reading them right.
smily_headphones1.gif

From what IFI is saying at the last part for me is that the outputs should have filtered all the RF interference that the device may have pick up without effecting the audio range.  RF interference pollution is becoming more of a issue with all the wireless devices in the home.  
 
Feb 9, 2015 at 8:30 AM Post #381 of 2,994

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  From what IFI is saying at the last part for me is that the outputs should have filtered all the RF interference that the device may have pick up without effecting the audio range.  RF interference pollution is becoming more of a issue with all the wireless devices in the home.  

 
Right, but I'm more concerned with the first part, to wit:

 
4) Passive Filtering and Discrete Analogue stage
The analogue stage in the iDSD Pro will be completely discrete, no Op-Amp IC's and in fact the actual discrete design will also not just be Op-Amp made discrete (and often worse than the best integrated ones) but will use something radically different, pure Class A (
beerchug.gif
) being among the features. Much of the circuitry draws its inspiration from legendary and exceptionally sounding studio equipment.

 
I would assume, but don't want to presume, that this would apply to the analog XLR outputs being a discrete non OPA design, pure Class A? Meaning that connecting via balanced ICs to a headphone amp, the user would get the benefits of an all-discrete design, without any overt colorization intrinsic in running OPAs from one device to another OPA device.
 
If so, this would be something to truly cheer about, as a major feature, and not something that's just an extra $1000 with 2 extra DAC chips, a remote control, more I/Os and another "bit perfect" setting. Class A and a discrete design, for the HP Out, XLRs and RCA? I hope I'm reading this right; moreover, that this feature doesn't get lost in the wash when we're talking the benefits of the Pro series.
 
Feb 10, 2015 at 11:48 AM Post #382 of 2,994

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iFi...I hate to bug you, but might you know the answer to this query? Am I off base?
 

4) Passive Filtering and Discrete Analogue stage
The analogue stage in the iDSD Pro will be completely discrete, no Op-Amp IC's and in fact the actual discrete design will also not just be Op-Amp made discrete (and often worse than the best integrated ones) but will use something radically different, pure Class A (
beerchug.gif
) being among the features. Much of the circuitry draws its inspiration from legendary and exceptionally sounding studio equipment.

 
I would assume, but don't want to presume, that this would apply to the analog XLR outputs being a discrete non OPA design, pure Class A? Meaning that connecting via balanced ICs to a headphone amp, the user would get the benefits of an all-discrete design, without any overt colorization intrinsic in running OPAs from one device to another OPA device.
 
If so, this would be something to truly cheer about, as a major feature, and not something that's just an extra $1000 with 2 extra DAC chips, a remote control, more I/Os and another "bit perfect" setting. Class A and a discrete design, for the HP Out, XLRs and RCA? I hope I'm reading this right; moreover, that this feature doesn't get lost in the wash when we're talking the benefits of the Pro series.
 
Feb 10, 2015 at 12:06 PM Post #383 of 2,994
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I would assume, but don't want to presume, that this would apply to the analog XLR outputs being a discrete non OPA design, pure Class A? Meaning that connecting via balanced ICs to a headphone amp, the user would get the benefits of an all-discrete design, without any overt colorization intrinsic in running OPAs from one device to another OPA device.
 
If so, this would be something to truly cheer about, as a major feature, and not something that's just an extra $1000 with 2 extra DAC chips, a remote control, more I/Os and another "bit perfect" setting. Class A and a discrete design, for the HP Out, XLRs and RCA? I hope I'm reading this right; moreover, that this feature doesn't get lost in the wash when we're talking the benefits of the Pro series.

 
Hi all.
 
Give us a few days - as we speak, we are preparing some technical information on all of this.
 
And also preparing for the Retro launch at the same time too. And also the Bristol Show which is next weekend.
 
We wish to draw something up in-depth but without giving away our secret sauce.
eek.gif

 
iFi audio Stay updated on iFi audio at their sponsor profile on Head-Fi.
 
https://www.facebook.com/iFiAudio/ https://twitter.com/ifiaudio https://www.instagram.com/ifiaudio/ https://ifi-audio.com/ info@ifi-audio.com
Feb 11, 2015 at 7:33 AM Post #384 of 2,994

BillsonChang007

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Hi all.
 
Give us a few days - as we speak, we are preparing some technical information on all of this.
 
And also preparing for the Retro launch at the same time too. And also the Bristol Show which is next weekend.
 
We wish to draw something up in-depth but without giving away our secret sauce.
eek.gif

I feel like we are more excited about the product than iFi.. haha 
 
Feb 11, 2015 at 12:23 PM Post #385 of 2,994

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  I feel like we are more excited about the product than iFi.. haha 

 
Ha! Yeah, no doubt. For me the waiting isn't the hardest part; it's the not knowing the specs of what I'll be purchasing.
wink.gif

 
The product will come. It's the anticipation of the goodies in the box, though. Otherwise, it's all good. I have become a firm believer in iFi, so when they say it'll be special, I have little doubt of that fact. It's simply a matter of how special.
wink_face.gif

 
Feb 13, 2015 at 9:23 AM Post #386 of 2,994
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  iFi...I hate to bug you, but might you know the answer to this query? Am I off base?

 
Hi,
 
As promised....please bear in mind that we can only discuss so much as we have to walk a fine line between informing our customers and not giving away our secret recipes.
wink_face.gif

 
Kind regards
 
iFi Skunkworks.
 
 
 
 
To filter actively or to filter passively, this is the question (part 1)

Some interesting questions have been raised around the subject of the filter circuitry for the iDSD Pro and the amplification stages. It is a complex subject.
 
So please bear with us as we do our best to inform you on the course we have taken and the reasons behind.
 
There is a whole lotta tech speak to crunch through - and it may seem heavy going. So if you suffer from insomnia, you may wish to bookmark this.
 
Without further ado…
 


Why filter the signal at all?

First, we must understand that a DAC-Chip will produce substantial supra-sonic output (which we justly may call “digital distortion”) in addition to the Audio signal we want. Just how this looks like depends on many factors. Rather than looking all options, let's focus on the BB DSD chip we use in iFi products.

It has a core that runs normally at a speed of around 11.3MHz to 12.3MHz. This is a very high speed. This is the speed at which the elements in the core switch. As the process is switching, it creates higher frequency components reaching much higher than main switching frequency.

This switching is one of the processes that produces this noise outside the audio band, the others are related to sample theory and produces what is often called “images”. Simply said, the actual audio signal is “mirrored” around the sample rate in a frequency plot, hence the name mirror images.
 

 
Source: http://defenseelectronicsmag.com/site-files/defenseelectronicsmag.com/files/archive/rfdesign.com/images/digitalpll-Figure03.jpg

Most audio circuitry cannot handle such supra-sonic signals, they are too fast and cause distortion to our audio signal. So what we require with any DAC is a filter that so to speak “strains out” the unwanted noise and leaves the audio signal. And ideally it gets all the noise and leaves the audio totally untouched.

In the real world ideal filters do not exist. A filter that removes the supra-sonic noise will have impact on the audio range and will introduce either phase-response variation, transient-response variation or both.
 
 

 
Source: http://www.electronics-tutorials.ws/filter/fil82.gif

We have to sail between the Scylla of insufficient filter selectivity (too much noise gets through) and the Charybdis of excessive filter impact on the audio (we filter out most noise and pad a lot of distortion the music). But filter to some degree we must, so we must chart a course that will hopefully take through instead being wrecked on rocks of Charybdis or sucked into the chaotic whirlpool of the Scylla.
 

 
Next time: Part 2: How to filter Digital Audio
 
iFi audio Stay updated on iFi audio at their sponsor profile on Head-Fi.
 
https://www.facebook.com/iFiAudio/ https://twitter.com/ifiaudio https://www.instagram.com/ifiaudio/ https://ifi-audio.com/ info@ifi-audio.com
Feb 13, 2015 at 10:43 AM Post #387 of 2,994

EVOLVIST

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Hi,
 
As promised....please bear in mind that we can only discuss so much as we have to walk a fine line between informing our customers and not giving away our secret recipes.
wink_face.gif

 
Kind regards
 
iFi Skunkworks.
 
 
 
 
To filter actively or to filter passively, this is the question (part 1)

Some interesting questions have been raised around the subject of the filter circuitry for the iDSD Pro and the amplification stages. It is a complex subject.
 
So please bear with us as we do our best to inform you on the course we have taken and the reasons behind.
 
There is a whole lotta tech speak to crunch through - and it may seem heavy going. So if you suffer from insomnia, you may wish to bookmark this.
 
Without further ado…
 


Why filter the signal at all?

First, we must understand that a DAC-Chip will produce substantial supra-sonic output (which we justly may call “digital distortion”) in addition to the Audio signal we want. Just how this looks like depends on many factors. Rather than looking all options, let's focus on the BB DSD chip we use in iFi products.

It has a core that runs normally at a speed of around 11.3MHz to 12.3MHz. This is a very high speed. This is the speed at which the elements in the core switch. As the process is switching, it creates higher frequency components reaching much higher than main switching frequency.

This switching is one of the processes that produces this noise outside the audio band, the others are related to sample theory and produces what is often called “images”. Simply said, the actual audio signal is “mirrored” around the sample rate in a frequency plot, hence the name mirror images.
 

Soruce:
C:%5CUsers%5CCOMPUT~1%5CAppData%5CLocal%5CTemp%5Cmsohtmlclip1%5C01%5Cclip_image001.jpg


Most audio circuitry cannot handle such supra-sonic signals, they are too fast and cause distortion to our audio signal. So what we require with any DAC is a filter that so to speak “strains out” the unwanted noise and leaves the audio signal. And ideally it gets all the noise and leaves the audio totally untouched.

In the real world ideal filters do not exist. A filter that removes the supra-sonic noise will have impact on the audio range and will introduce either phase-response variation, transient-response variation or both.
 
 

 
Source:
C:%5CUsers%5CCOMPUT~1%5CAppData%5CLocal%5CTemp%5Cmsohtmlclip1%5C01%5Cclip_image002.gif


We have to sail between the Scylla of insufficient filter selectivity (too much noise gets through) and the Charybdis of excessive filter impact on the audio (we filter out most noise and pad a lot of distortion the music). But filter to some degree we must, so we must chart a course that will hopefully take through instead being wrecked on rocks of Charybdis or sucked into the chaotic whirlpool of the Scylla.
 

 
Next time: Part 2: How to filter Digital Audio

 
Wow!  Thank you. This is exactly the nerdy stuff that most of us like.  Keep 'em coming...and good luck at the Bristol show!
atsmile.gif

 
Feb 13, 2015 at 1:20 PM Post #389 of 2,994

EVOLVIST

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Can you give us little more detail or direction on iDSD Pro? Like external dimension, connection interface, power supply. etc? Thanks.

 
Preliminary data posted in this very thread:
 
iDSD mini PRO    
Fully-Balanced DAC (USB/SPDIF/AES-EBU/Bluetooth)   
Formats:44.1/48/88.2/96/176.4/192/352.8/384/705.6/768KHz PCM   
 2.8/3.1/5.6/6.2/11.2/12.4/22.4/24.8MHz DSD   
 DXD   
Filter:PCM: Standard/Minimum Phase digital, Bitperfect 1, Bitperfect 2; selectable  
 DSD: Standard/Extended Range/Minimal analogue, selectable   
 DXD: Bitperfect Processing, fixed analogue filter   
DAC:Quad Core Dual Mono Bit Perfect DSD, PCM & DXD DAC by Burr Brown in current output mode (4-DAC Chip; 8-Channel; 16-Signals)
Clock:                            Ultra low jitter Crystal Clock (rms jitter < 300 Femtoseconds)   
Analogue Stages:Balanced fully discrete Class A - Non-Feedback I/V conversion by single BISS Supertransistor
 Balanced fully discrete Class A - Non-Feedback Line output buffer using J-Fets and BISS Supertransistors
 High Speed current mode Class A Headphone Buffer with balanced fully discrete Class A - Non-Feedback input buffer using J-Fets and BISS Supertransistors
Volume Control:Balanced 4-Way precision analogue by ALPS, Remote Control, can be bypassed for Line Outs
Audio Path passives:Tantalum Oxide Thin Film thin film surface mounted resistors,   
 TDK high stability C0G surface mounted capacitors   
 Panasonic PolyPhenylene Sulfide stacked film surface mounted capacitors  
 Elna Silmic II Electrolytic Capacitors   
Input: (selectable)USB 3.0   
 compatible with iPhone,iPod, iPad and Android Devices USB-OTG#   
 SPDIF RCA/Optical (only PCM up to 192KHz)  
 AES-EBU Balanced   
 BNC SPDIF Unbalanced   
 Bluetooth with aptX   
Audio System Support:PC - ASIO 2.2, WASAPI, Kernel Streaming (KS), Directsound   
 Mac - Core Audio   
OutputXLR True Balanced Audio (Output adjustable 4/10V @ 0dBFS [+14dBu/+22dBu])  
 Audio RCA (2V/5V @ 0dBFS)   
 6.3mm Headphone 4V/10V maximum output   
 Headphone Output Power 4,000mW/16R max.   
Dynamic Range:TBD   
THD &N (Line)TBD   
THD &N (HP 100mW)TBD   
Output Power (16R):> 4000mW   
PowerSource:External DC 14V (compatible with 12V Battery systems)   
Power Consumption:< 15W   
Size:220mm x 62mm X 210mm (W X H X D including feet, knobs and connectors)
 

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