It finally happened at iFi

By this point in time, it is surely no secret that there was a shakeup at the top of iFi/AMR that lead to at least DIY guru and tech director Thorsten Loesch, leaving the company to start his own venture.  (I am very excited for whatever he brings to market next)

Insert problem numero uno.  Thorsten owns the intellectual property that is the backbone of iFi products, which is very distinct from the myriad other companies dependent on the big two of AKM and ESS.  Now that AKM is wounded and just hanging on after the unfortunate factory fire in Nobeoka, Japan, ESS has stepped to the forefront and many designs from a number of product creators are being reworked to accommodate a switch to ESS.  

No problem for iFi?  Since their backbone tech is built on Burr-Brown/Texas Instruments silicon?  Think again.  Mr.  Loesch still happens to own the intellectual property for a large portion of iFi tech.  If iFi wants to do something different, it has to be very different.  

Which brings me to this product.  The iFi GO bar.  

It looks to be a standard dongle DAC/headamp like we are familiar with from several audio companies.  All was looking mildly interesting to me until I saw it does NOT use the Burr-Brown DSD1793 chipset!!  Rather it uses an unspecified Cirrus 32-bit DAC.  Now, before I go all conspiracy theory here, perhaps it has something to do with power consumption, although the somewhat diminutive iFi iDSD Nano of nearly a decade ago ran off 5V USB power and could be used in portable fashion just fine.  

So here we have for the first time since the original iDAC was released in 2012, a product built on something other than the DSD1793 DAC.  (feel free to correct me if I am forgetting something in there that did NOT use a DSD1793)

But what about this 32 bit Cirrus Logic DAC, and how does it compare to the DSD1793?

​I believe we should start with iFi marketing jargon.  Up until recently 'Bit Perfect' was used to describe a type of PCM oversampling filter, or better put, lack of filter.  It denoted a mode in which the DAC operated in NOS (non-oversampling) mode over the 6 most significant bits.  The term become obfuscated a bit over time when it started being used to simply describe 'native' format conversion. (such as native PCM or native DSD)  And now the advertising for the Go Bar has once again defined 'bit perfect' as one of the onboard filters.  However, the GO bar advertisement DOES specifically state that DSD is converted in native form.  

iFi does not specify which Cirrus Chip is used.  Compared to the DSD1793, the Cirrus chips that would be candidates have TWO DSD modes. 

The first mode sends a DSD signal through a 'dsd processor' which will filter it into a multi-bit format.  Here volume control and level matching between PCM and DSD can occur.  The filter in the DSD processor has a 50khz cutoff for DSD64 files ala SACD Scarlet book.  (No information is available for the cutoff used with 128fs or 256fs.)  Then after processing, this intermediate format is sent to the same final Delta Sigma converters as PCM for final conversion and output.  

The second mode behaves more like the Burr-Brown DSD1793.  All the aforementioned DSP is avoided as the 1 bit signal stays 1 bit and 'bit perfect', if you will, all the way to the final switched capacitors which perform the final conversion.  

Finally, the Cirrus chipsets are fully Delta Sigma chipsets.   All PCM bits are converted via Delta Sigma.  Cirrus does not have the unique architecture that converts the top 6 bits via something similar to a R2R ladder.  With the iFi 'Bit Perfect' filter combined with DSD1793, the top 6 bits of any PCM file are truly the same as a Non-Oversampling PCM DAC.  Perhaps even a bit better because the conversion is done via 64 switches of thermometer code which allows for dynamic element matching and better linearity than a typical R2R DAC.  

In closing, iFi has a couple burning questions to answer here. 

1. How is volume control implemented for DSD?  The answer will be quite telling.  

2. Is there a mode that allows the chipset to send DSD direct to the switched capacitors, keeping with the iFi tradition of minimal DSP and 'native DSD' conversion?  


I will close that I am a big fan of iFi products, and not because they sponsor me or even provide products for me to review.  The truth is far from the case.   Never once have I received a loaner product or any financial compensation of any kind.   I just like their products.  They are unique and sound great.  They just 'click' with me.  

Will the Go bar 'click' with me?  I don't have a clue until I review it.  Which means one thing.  I have one on the way for just that!   Until next time, happy listening in this holiday season!

​
ERRATA:
Upon further examination of new iFi products, both the Go Link and the Uno both make use of ESS chipsets.  This is a whole new can of worms.  There is no way to bypass the internal DSP that converts DSD to multi-bit for volume changes, DSD/PCM max volume normalization, and sample rate conversion before it is re-modulated by the Hyperstream Delta Sigma DAC.  I guess we come full circle back to where it all started with the original iDac.   I am kidding, of course.  These are all valid solutions and iFi I am sure has made some great products here.  There is more than one way to skin a cat.  Ooops... can we still use such expressions these days without a woke cancel mob?  haha.  
​

---