A NOS 192/24 DAC with the PCM1794 (and WaveIO USB input)

Multiple boards v ONE

This is something worth considering.

AS with paralleling any component there are drawbacks whether it is a tube, an FET, resistors, capacitors - there are many who conceptualize that this leads to a "confusion" in the sound.

When it comes to resistors many feel two of the same value can be advantageous but any more than that can bring problems. With caps, in the signal path it is generally considered ideal that ONE is best and if your cap needs a bypass you need another capacitor. Speaking ideally, of course.

Multiple DACs bring the advantage of greater output energy and this is good to have if it will eliminate a gain stage but there has to be a downside.

I am wondering if one board might be the best for purity. Multiples would probably bring more vigor to the presentation at the expense of a little confusion in the finer details.

Maybe two could be the best compromise? I wonder if one is good would THREE be best? Sticking with odd numbers ...

I am still waiting for parts that I accidentally had sent to my old address. What an idiot! So my project is not going anywhere at this point.

Thanks to SUPERSURFER for pointing out (have to admit to being hardheaded) how close the PS bypass caps are to the pins of the DAC for a superior position for regulators. I assume he is going to use the input pin of the regulator as his entry to the 3.3 V regulator from his outboard raw supply? I think I am going to use the onboard position for storage caps and modify the board for power entry. Seems it would be neater than having to deal with a cap "in the air" but I tend to agree it is good to get caps away from PCBs.

Certainly something to think about. Maybe someone will be able to compare a "perfect" one board implementation to a standard four board? I know no one who cares about DIY audio (or audio in general) so it won't be me.
 
This is something worth considering.

AS with paralleling any component there are drawbacks whether it is a tube, an FET, resistors, capacitors - there are many who conceptualize that this leads to a "confusion" in the sound.

When it comes to resistors many feel two of the same value can be advantageous but any more than that can bring problems. With caps, in the signal path it is generally considered ideal that ONE is best and if your cap needs a bypass you need another capacitor. Speaking ideally, of course.

Multiple DACs bring the advantage of greater output energy and this is good to have if it will eliminate a gain stage but there has to be a downside.

I am wondering if one board might be the best for purity. Multiples would probably bring more vigor to the presentation at the expense of a little confusion in the finer details.

Maybe two could be the best compromise? I wonder if one is good would THREE be best? Sticking with odd numbers ...

I am still waiting for parts that I accidentally had sent to my old address. What an idiot! So my project is not going anywhere at this point.

Thanks to SUPERSURFER for pointing out (have to admit to being hardheaded) how close the PS bypass caps are to the pins of the DAC for a superior position for regulators. I assume he is going to use the input pin of the regulator as his entry to the 3.3 V regulator from his outboard raw supply? I think I am going to use the onboard position for storage caps and modify the board for power entry. Seems it would be neater than having to deal with a cap "in the air" but I tend to agree it is good to get caps away from PCBs.

Certainly something to think about. Maybe someone will be able to compare a "perfect" one board implementation to a standard four board? I know no one who cares about DIY audio (or audio in general) so it won't be me.


Hi Rick,

I agree with you on parallelling up. I don't like two tubes in parallel. But I did not notice that using more dac boards in parallel brings a less open/transparant sound(as it does with tubes). I do prefer to put 4 dacs in parallel.

I can tell you guys in about a week how my new dac boards will be build (I'm just waiting for the last ordered item to arrive). But I can tell you it will be quite modified in the supply section!
I would guiss putting the Vdd shunt at the dac pins would bring a worthwile improvement.

Regards,
 
@James, if possible could you post a picture of your current DAC board lay-out? I'd be intrested.
It's all a little messy again at the moment and currently running wifi, which I need to move the aerial out of the case for ideally...

IMG_20140604_114353.jpg


IMG_20140604_114408.jpg


IMG_20140604_114417.jpg


IMG_20140604_114430.jpg

Cheap Tekdevice 3.3v regulator on the mainboard.

I've got most of the bits ready to build a new unregulated 12v power supply like Stefan has. I'm just waiting for the chokes to arrive.


One thing that's amazed me this week is the difference in sound between different I/V resistors. I had another DDDAC here this weekend I was working on which was a 2 deck with 8 x shunt regs and 2W Audio note I/V resistors. I was comparing the 2 side by side using the same power supply, same I2S from the pi, same interconnects, everything. I wanted to know if it was worth my while to upgrade to 2 shunted decks. I expected the same sound with a slight increase in the airyness and resolution I'd get from a more accurate solution, which I did hear to a fairly subtle extent, but what I also got was very confusing I have to say... My I/V resistors are Rhopoint Squaristor GG102 which I chose after reading this thread:
What I experienced was a different sound between the 2 as though it was a different mix of the track playing. A particular example was Barfly by Ray Lamontagne, which I know very well and tend to use for testing.
With my Rhopoint equipped DDDAC, the main vocal was VERY clear and separate in the mix, as I'm used to. With the Audionote equipped DDDAC, the main vocal was further back into the mix, yet the drums were more accentuated than with mine. I certainly hadn't expected the elements to mix around like that and it's hard to say which I would prefer as it would totally come down to favourites for individual tracks..


As for my next move, I'm wondering if there's any good reason why I shouldn't run 4 decks, but powered off 1 set of 4 shunt regs, skip the VB+ wire for 3 of the decks and link them to the shunted deck using the holes of the electrolytics I would remove around the DAC chips. I'm sure that 4 times as much load is still well within the power output of each shunt and whilst it might not be quite as perfect as a load more separate regs, I can only imagine the differences will be negligible. What do you guys reckon?
 
Hi Stefan,
due to the parts I have at hand I'm thinking about the following power architecture. Could you, please, point out drawbacks if any. 1 or 2 DAC decks: 2 x Salas 8v shunts to power analogue (1 transformer); 5v separate power supply for a mainboard 5v need (1 transformer); main power 6,5v with 3,3v shunts for a clock, spdif, and a digital part of the DAC(s). (I have 3,3 v shunts at hand with maximum input 6,5v). What do you think?
 
Hi Stefan,
due to the parts I have at hand I'm thinking about the following power architecture. Could you, please, point out drawbacks if any. 1 or 2 DAC decks: 2 x Salas 8v shunts to power analogue (1 transformer); 5v separate power supply for a mainboard 5v need (1 transformer); main power 6,5v with 3,3v shunts for a clock, spdif, and a digital part of the DAC(s). (I have 3,3 v shunts at hand with maximum input 6,5v). What do you think?

Hi,

Please note that I have NOT tried this myself, I am only advising from experience.
I expect you will solder out the lf80 regs and connect the salas directly? Salas uses kelvin wires, if you connect these on the board where the lf80 was you will have good regulation.
If you want to experiment with the effect you can first use one board with the lf80 and the salas as raw supply, than later change to connection as I wrote above.
Than we would also be interested to hear the results from you!

Regards,
 
... What do you guys reckon?

Hi James, very intresting pictures. I’m surprised you've taken out C27/C29 and C18/C19&C32/C34. I’m thinking about upgrading these. I would test to by-pass R2/R4 and L1/L3 and also L2/L4 & R1/R3.
As for your shunt question. I’m personally thinking about two sets of shunts, one per two boards (not four). Have you done the math on the power consumption, they might run pretty hot with one set for 4 boards?
 
Hi, maybe this can help concerning the caps.

Before I modified my boards I asked Guido Tent about the caps behind the shunt regs.

This is what he replied:

I reccomend not to hace capacitors behind the shunts so better leave them out. This is only possible if the shunts are close to the chips. If they are more than few cm away, than a small nice film cap close to the DAC chip is fine.
I also bridged L2/L3 and R2/R4, both an improvement. I left R1/R2 unbridged because it didn't made a big difference and I was afraid the 3,3 V shunts would become to hot because of the higher voltage.

Regards
 
After reading the application sheet @ TENT LABS and

the posts here, especially SUPERSURFERS, I have come to the belated conclusion that these are the way to go.

The simplicity these allow makes them the obvious choice. I wish I had paid better attention earlier on.

One can basically eliminate all of the caps and resistors on the board and feed these direct from your raw supplies, one for each voltage, of course, with no need to mess around with PCB - just feed the input with your supply wire. So simple and elegant.

I NOW see SUPERSURFERS logic and agree his way is THE way.

My stupid address mistake has been advantageous in that I have time to correct my plan and to use these.

Thanks, SUPERSURFER!
 
the posts here, especially SUPERSURFERS, I have come to the belated conclusion that these are the way to go.

The simplicity these allow makes them the obvious choice. I wish I had paid better attention earlier on.

One can basically eliminate all of the caps and resistors on the board and feed these direct from your raw supplies, one for each voltage, of course, with no need to mess around with PCB - just feed the input with your supply wire. So simple and elegant.

I NOW see SUPERSURFERS logic and agree his way is THE way.

My stupid address mistake has been advantageous in that I have time to correct my plan and to use these.

Thanks, SUPERSURFER!

Any diagrams to explain this mod please?
 
I think SUPERSURFER is ahead of my schedule

and I have no way to draw these clearly but I will give an explanation of my thinking which I think is similar to SUPERSURFER's.

Simply (?) two raw supplies - using TENT's guidelines he says 7 to 10 volts input voltage to the 3.3 volts regulators. I will use a resistor input (10R ?) after the rectifiers with around 3K uF cap to ground followed by a choke (.3 H, 11 ohms) another 3K uF of capacitance then likely an RC filter ( 10R and maybe 4500 uF capacitance) with a 7 volts transformer and a full wave rectifier the DUNCAN tool predicts just over 8 volts - the low end of Tent's recommendation but should be plenty. The leads from this supply connected directly to the 3.3 volts regs mounted per SUPERSURFER to the bypass cap "hole" that connects to the Vdd input of the DAC (I need to look at the board to tell you which is the one).

The positive lead from the 3.3 volts raw supply to the input of the reg - the output of the reg to the above mentioned hole in the PCB - the negative lead from the raw supply to the ground leg of the regulator AND to the ground point on the side of the board.

The more I think about this I thought one could get by without PCB surgery but I realize now the the +power trace must be cut. I have read Tent be of two minds about an input cap to the regulator. In the application notes he recommends 10 uF but I think earlier in the thread someone said he said none was needed. That would be preferred. If one elects to use an input cap this could be placed on the DAC board just be sure you cut the trace before that capacitor. OR you could have the cap attached to the input wiring to the reg and it would float above the board. I tend to think it is better to have the cap float.

I would retain the caps and resistors for the 8 volts supply on the board. There are three places where power enters the Vcc part of the board so one cannot be quite as elegant with the regulators input. The more I look at it one is stuck with having more path length that one would want, ideally, for the regulator. One can use any one of the three bypass cap "holes" for the regulator output but will need to run a wire to the other two and with these two it would be a good idea to use the bypass caps. One should be able to get away without the bypass cap at the input one uses for the regulator output. Again, I need to take a look at the board to tell you which one I will use. I know it will be the one that goes to pin 23 of the DAC. I am writing at work and do not have the board in front of me.

For the raw supply, extrapolating from Tent's recommendations one should use between 11.5 to 19 volts for the 8 volts regulator. Using a 12.6 volts transformer I would make it very similar to the other supply - but I would not use the last filter within the raw supply but use the filter on the board for this part of the supply. Bypass R1 - use 10R at R2. Bypass the inductors with lengths of wire and the 8 volts regulator - easily done when it is removed - just solder a wire across the two small pads. This will give you approx 15 volts at the input of the regulator.

I will attempt some kind of drawing. I know this sounds far more complicated than it really is.

This way the raw supply for the 8 volts reg will enter at the VB+ pin and ground would be attached at the ground point along with the ground wire from the 3.3 volts raw supply and from this same point the 3.3 volt raw supply ground. Daisy chained from here will the the wire to attach the 3.3 volts regulator ground pin.

First draft. I hope it makes some sense. I (and I hope others) will fill in blanks in time.
 
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I will follow you guys and I ordered 4 TENTs regulators for my 1 board DAC :)
Guido was very nice, he understand himself that my order was for the Doede DAC and he will send them tailored for... nice!
I have a silly question... In all the pictures that have been sent from you I see that the shunt are installed in the component side of the board. I will use the old motherboard and between the motherboard and the DAC board no component are installed. So, is plenty of room to install the shunt but nobody use it... maybe have some contraindication?
The connection should not be a problem as the space... if some millimeters more are needed I can use higher standoff. Maybe the hot dissipation?

Regards,
Enrico