Hello Doede,
I am presently building a V3 version and wonder what voltage value transformer to buy for the PSU. In any case it will be minimum 50VA as I already heard the effect of more power in the transformer on my current 8 decks DDDAC (V1 V2 mix).
As I had to tweak, with you help, the old PSU when I went to 8 boards, Today I prefer asking before buying my transformer. (Toroidy supreme audio grade in mind)
From PSU Building instructions:
Optional chokes
Suggestions are between 50mH and 1H – as long as the DC resistance is below 4 Ohm. This applies, when used with the DDDAC1794MK3 board (1 or 2 boards)
Maximum current output
The PSU can deliver easily 1A or more. But with the delivered heatsinks it is intended for maximum two DDDAC1794MK3 DAC boards, where redominantly the analog section (9 Vdc) is drawing up to 200mA per Board. Two boards are below 400mA and perfectly safe when a 12 Vac transformer is being used. For higher currents increase of heatsink size is necessary! This is DIY experiments…
My understanding:
A 4 Ohms choke will add 1.5 Volts ( 0,22 resistor out ≈ +0,1V) drop for 2 boards and 3,1V drop for the silly boys like me who may use 4 boards.
In the chapter about old PSU tweaking you stated a 5,5V headroom is needed.
Guessing it is still same requirement, needed headroom is 8,6V with four boards if I am correct.
My question is:
Will a "powerful" 2X12V transformer still do for the task when switching to 4 boards or do I need a bit more voltage?
Thank you for advising.
PS: The kits are a pleasure to build with amazing board quality. Thanks!
I am presently building a V3 version and wonder what voltage value transformer to buy for the PSU. In any case it will be minimum 50VA as I already heard the effect of more power in the transformer on my current 8 decks DDDAC (V1 V2 mix).
As I had to tweak, with you help, the old PSU when I went to 8 boards, Today I prefer asking before buying my transformer. (Toroidy supreme audio grade in mind)
From PSU Building instructions:
Optional chokes
Suggestions are between 50mH and 1H – as long as the DC resistance is below 4 Ohm. This applies, when used with the DDDAC1794MK3 board (1 or 2 boards)
Maximum current output
The PSU can deliver easily 1A or more. But with the delivered heatsinks it is intended for maximum two DDDAC1794MK3 DAC boards, where redominantly the analog section (9 Vdc) is drawing up to 200mA per Board. Two boards are below 400mA and perfectly safe when a 12 Vac transformer is being used. For higher currents increase of heatsink size is necessary! This is DIY experiments…
My understanding:
A 4 Ohms choke will add 1.5 Volts ( 0,22 resistor out ≈ +0,1V) drop for 2 boards and 3,1V drop for the silly boys like me who may use 4 boards.
In the chapter about old PSU tweaking you stated a 5,5V headroom is needed.
Guessing it is still same requirement, needed headroom is 8,6V with four boards if I am correct.
My question is:
Will a "powerful" 2X12V transformer still do for the task when switching to 4 boards or do I need a bit more voltage?
Thank you for advising.
PS: The kits are a pleasure to build with amazing board quality. Thanks!
Looks like their site is a bit erratic. Sometimes it works, sometimes it times out. Oh well.
Thanks for the feedback Tristan (and your patience with the small error in your kit
)You are correct with two boards. The double boards draw 400mA, hence the 1.5V drop with 4 Ohm choke.
Without choke, with a solid 2x12Vac transformer, you will have a (measured by me) headroom of 7,7V. so when using a choke with 1,5V drop there is 6,2 left over which is OK (!)
BUT.....
If you are now doubling the boards again to 4 boards, you are getting into the critical area of too little headroom (4.7V).
My suggestion would be, IF you want to go for 4 boards (like the "old 8-deck"), you should use two PSU.
In that case you could actually do a true 2x mono set-up "PSU1-2xboards-Right" and "PSU2-2xboards-Left"
But for now, you should be fine with a 50VA transformer 2x 12Vac
Just an interesting fact. You can use the Output connectors with the regulated voltage on the DAC board as an input for an alternative power supply (only valid reason I see is to just test and experiment a bit with alternate PSU or ultracaps for example...) The on board LT1763 is actually designed to use in this way too. If the regulator is used with battery backup for example, it acts like a diode and resistor of several 100k.
Datasheet says:
The devices are protected against both reverse input and reverse output voltages.
In battery backup applications where the output can be held up by a backup battery when the input is pulled to
ground, the LT1763 acts like it has a diode in series with its output and prevents reverse current flow.
So in short, if there is no power at the input, you can add an external power to the “output” terminal of the board (3,3V and 8V of course)
In case of the DDDAC MK3 board, it is VERY important to have powered the digital side BEFORE you add power to the analog side!!
Without digital 3,3V the analog side of the PCM1794 consumes more power and gets very hot. Not sure if it will go defect, but better not try…
Datasheet says:
The devices are protected against both reverse input and reverse output voltages.
In battery backup applications where the output can be held up by a backup battery when the input is pulled to
ground, the LT1763 acts like it has a diode in series with its output and prevents reverse current flow.
So in short, if there is no power at the input, you can add an external power to the “output” terminal of the board (3,3V and 8V of course)
In case of the DDDAC MK3 board, it is VERY important to have powered the digital side BEFORE you add power to the analog side!!
Without digital 3,3V the analog side of the PCM1794 consumes more power and gets very hot. Not sure if it will go defect, but better not try…
Good question, I do not know why the PCM1794 is doing this, I only know that attaching only the analog side with no digital power, current draw goes up and hence the chip is getting pretty warm. On the DDDAC board itself there is a safety measure that the 8Volt regulator does NOT start, when there is no 3,3 Volt present. So no worries for the normal setup
Back to the situation where anyone would like to try another power supply, make sure both 3.3 and 8.0 volt are present at the same time. If the 8Volt is present a couple of seconds before the 3.3 V there is no issue. They just need to be there at (roughly) the same time.
Back to the situation where anyone would like to try another power supply, make sure both 3.3 and 8.0 volt are present at the same time. If the 8Volt is present a couple of seconds before the 3.3 V there is no issue. They just need to be there at (roughly) the same time.
ok checked.....
with 3.3 V present: normal analog current Ia = ~ 200mA (one MK3 DAC Board with 4x PCM1794) - regardless, if Va is 5 or 8 Volt.
but....
without 3.3 V present and powering from External power at the output terminals (see above...)
Va = 5V => Ia = 200mA
Va = 6V => Ia = 300mA
Va = 7V => Ia = 400mA
Va = 8V => Ia = 500mA
Not sure what this tells us, but one thing at least, if you power the analog side externally with anything above 5V, make sure 3.3 V is present as well at the digital side
Again (!) If you power the board through the normal input terminals, this cannot happen, as the Va only starts when 3.3V is present .... That is the way I designed it.
This whole story is just for those who want to experiment and know what they are doing
Idea for experimenting: Use a Battery Backup at the 3.3V? Use Supercaps, UC-Pure from Ian?
with 3.3 V present: normal analog current Ia = ~ 200mA (one MK3 DAC Board with 4x PCM1794) - regardless, if Va is 5 or 8 Volt.
but....
without 3.3 V present and powering from External power at the output terminals (see above...)
Va = 5V => Ia = 200mA
Va = 6V => Ia = 300mA
Va = 7V => Ia = 400mA
Va = 8V => Ia = 500mA
Not sure what this tells us, but one thing at least, if you power the analog side externally with anything above 5V, make sure 3.3 V is present as well at the digital side
Again (!) If you power the board through the normal input terminals, this cannot happen, as the Va only starts when 3.3V is present .... That is the way I designed it.
This whole story is just for those who want to experiment and know what they are doing
Idea for experimenting: Use a Battery Backup at the 3.3V? Use Supercaps, UC-Pure from Ian?
I already did some listening tests between the on-board solution with LT1763 and good old 3045 regulator. Also good, but still this somewhat clean/cold touch I personally do not like - but that is me - I want this very analog, vinyl kind of sound (without cracks and noise )
- I want this very analog, vinyl kind of sound (without cracks and noise )
What's going on with these Ground Lift switches?
I'd say the RCA outer ring always needs to be connected to GND. Also, I guess GND should always be connected to chassis / safety earth, possibly through a ground loop breaker.
https://sound-au.com/earthing.htm
https://en.wikipedia.org/wiki/Ground_lift#Safety
I'd say the RCA outer ring always needs to be connected to GND. Also, I guess GND should always be connected to chassis / safety earth, possibly through a ground loop breaker.
https://sound-au.com/earthing.htm
https://en.wikipedia.org/wiki/Ground_lift#Safety