PCM1702/1704K DAC - any interest?

[Gieseler Audio]

I still have a few PCM1702/1704K Burr Brown DAC chips  left so a Kompakt II using those chips is definitely a possibility.

These are true multibit R2R current output DAC chips with legendary status.

I'm just trying to gauge if there would be any interest in this?

 

Next question is deciding whether to go NOS or use the DF1704 digital filter which was designed to go with these DAC chips.

Unlike the TDA1541A which accepts I2S natively the PCM chips require either the matching digital filter chip or using shift registers 

to provide the correct input format.

I guess the sensible thing to do is build both versions & then do some listening tests.

Measurement wise the digital filter chips version wins by a country mile but from experience that does not necessarily 

guarantee the best sound.

However using a lot of shift registers which would be required can certainly impact the final sound quality for sure.

I think why my TDA1541A DAC sounds so good is the fact that I'm feeding direct I2S data out of the USB board straight into the DAC chip.

Anyway I think building both versions & doing some listening tests is the way to go.

 

Cost:

Due to the high value of the PCM1704K's that version would be around $2500.

The PCM1702's are lower in value so I think that version would be around $2000.

Any Thoughts? 

 

 

[frankn]

Hi Clay,

Did this project ever get off the design board?  
What currently is your best dac that accepts both USB and I2S (configurable?) ?  I’m using Innuos and a PS Audio CD/SACD player as inputs. 

[Gieseler Audio]

Hi Frank,

amazingly I have just started designing a PCB for it.

It will be an oversampling version using the matching DF1704 digital filter.

Pretty much a data sheet implementation but with upgraded power supplies & output stage.

I did think of a NOS version but that involves a lot of shift registers & that does degrade the sound.

I think that is why the TDA1541A NOS version sounds so good as there are no shift registers used.

Regarding my best sounding DAC, probably should wait until I have a PCM1704K version up & running and then I can do a careful comparison with the TDA1541A NOS Kompakt II

The TDA version does sound amazingly good so it is hard to imagine the PCM1704K sounding better but you never know.

 

[twwen2]

How about a PCM1704K Kompakt II with the upcoming tube output stage?

[Gieseler Audio]

Yes that is definitely something I will  be looking at

[frankn]

Hi Clay,

Any update on progress and are you in a position to be able to make a comparison of sound quality to your other products?  
 

Edited March 5, 2024 by frankn
Clarity

[Gieseler Audio]

Hi -  sorry I'm still very busy with development on the tube stage for the TDA DAC & not had time to get back to the PCM1704 design

[frankn]

Hopefully you will soon have some time to continue this project. Very interested in the outcome comparing it to your new tube dac. I’m interested in a DAC with (optimised) USB input to pair with my Innuos products.  

Edited May 29, 2024 by frankn
Add

[Gieseler Audio]

Well I have finally finished the TDA1541A tube design so yes I will certainly get cracking on a PCM1704K design again.

I have a few pairs of PCM1704K's left so it will be good to do something with them.

I also have a few PCM1702's which are very similar.

[Gieseler Audio]

I just want to get an idea what would be the most popular design choices.

 

1. NOS or regular oversampling using the matching DF1704 digital filter chip which I have?

I can do NOS but it does require using five shift register chips which I feel does have a slight negative impact on the sound. 
 

2. Normal all solid state design or passive I/V (resistor) and a tube output stage like I've just done with the TDA1541A design?

Obviously the tube version will cost a lot more, probably a bit over $3K

 

3. XLR balanced outputs  -  this will only be available on the solid state version 

 

My personal choice would be all solid state with the matching DF1704 digital filter.

The latest op amps I have been using sound extremely good & that combined with good power

supplies & nice Nichicon audio grade capacitors should sound very good. 

 

[THOMO]

The two best sounding DACs I have owned use PCM 1702s.One is a Krell KAV 300CD player converted to a USB input DAC by Mick Maloney [Supratek].Also his favourite DAC  and he has built and owned dozens of them.The other is the Accuphase DC 61 which uses  6 of them.

Edited May 30, 2024 by THOMO

[Gieseler Audio]

Thanks for the heads up  -   I have six new old stock PCM1702's so definitely on the list for 

for a nice DAC design.

[frankn]

Can you design it so the user can choose (switch) between NOS and O/S ?

 

[Gieseler Audio]

I was thinking about that  -  I could probably do it using jumpers.

 

[Jventer]

On 31/05/2024 at 9:22 AM, Gieseler Audio said:

Thanks for the heads up  -   I have six new old stock PCM1702's so definitely on the list for 

for a nice DAC design.

@Gieseler Audio I am a novice, but Clay if you go for the effort in doing such a dac would it be possible to buy more chips?

[Gieseler Audio]

It is very hard to still track down new chips and in the case of the PCM1704K they are very expensive 

$200 to $300 each 

[THOMO]

4 hours ago, Gieseler Audio said:

It is very hard to still track down new chips and in the case of the PCM1704K they are very expensive 

$200 to $300 each 

I have owned Audio Gd DACs using PCM 1704.They sounded really lifeless and boring.So whatever they did was not the right approach.A friend suggested their  fully discrete output stage designs were not good.

[Gieseler Audio]

Well I finally finished the pcb layout and boards have now been ordered.

There is a lot more layout involved when using  older DAC chips as there is a digital filter chip plus 

two DAC chips vs a single chip in a modern design.

I ended up using the DF1704 digital filter as it was designed to go with the PCM1704's and there were

a lot of very good sounding CD players that used that combination.

I should have one up and running in a couple of weeks.

Stay tuned!

 

Edited June 18, 2024 by Gieseler Audio

[Gieseler Audio]

Well finally all finished & sounding very nice.

The DF1704 is a little unusual with its clocking requirements but fortunately 

Amanero have special firmware to suit it so once the USB board was flashed with that all good.

There is just a small issue with the S/PDIF inputs so hopefully I can sort that shortly.

So it is PCM only (no DSD) and will handle all sample rates up to 192K

 

 

Edited July 3, 2024 by Gieseler Audio
More info

[Gieseler Audio]

Unfortunately I couldn't solve the coax/optical input problem.

Currently for all my DAC's I'm using a new Amanero special SE version board which allows for S/PDIF input as well as USB.

This reduces a lot of circuitry and saves having to do I2S switching which is better for sound quality.

The Amanero Combo384SE uses special firmware which enables the S/PDIF inputs.

Now  the issue is with PCM1704 DAC chips the Amanero also needs special firmware to work correctly.

There is no way to combine these two Amanero firmware's so my only option for this DAC is to build a fully separate S/PDIF receiver stage and I2S switching relays to select between USB and coax/optical.

This is no problem but it will increases the complexity/cost and build time.

Bottom line is this first unit (above photo) will only ever work with USB so I will be heavily discounting it.

Please PM me if interested.

 

I have now started design on a new board which will have the separate S/PDF input section but it is going to take a while.

 

 

 

Edited July 16, 2024 by Gieseler Audio

[Gieseler Audio]

Update!     

 

Initially I had a input problem but I've just fitted  a new release Amanero USB board and the problem is totally solved.

 All inputs are now fully functional -  sample rates from 44.1K to 192K tested & working fine.

The problem must have been the firmware with the older USB board I was using.

However I'm still keen to try a non oversampling version so hopefully that will happen soon.

[David A]

CHP use PCM-1704 dac chips in their dacs, though i'm not sure about the dual mono dac option boards for the D1.5.

[frankn]

Kompakt DAC II PCM-1702 NOS landed and running. Will give it several days and then provide some feedback. 

[frankn]

I’ve now made a couple of comparisons between the Kompakt II PCM1702 NOS and my DirectStream mk1 DAC. 
IMHO the differences are truly very small. I am happy listening to either. 
I think The Kompakt is a smidgeon brighter in mid-to-top end.  Detail, presentation, separation are extremely close on both. 
With more time and relaxed listening I will probably refine my opinion but initially very good overall.  
I did record a video demonstrating the sound through the system as I swapped between the two playback chains but I cannot load here as the format isn’t supported. I’ve sent it to Clay and he might be able to reformat/post, or comment. 

[MrBurns84]

Please do @frankn