hello everyone,
I'm trying to have better understanding on the chokes subject. Choke input is the target.
Lundahl says that best mode for psu is common mode for better rejection.
I guess, that since this mode requires a cap before input to the choke, then it should be mounted as a second in line right?
And here comes another question. Lundahl actually refer to single tranny and full bridge rectifire (as I can see on their drawings). In such a configuration that would make sense to me, as the negative comes back to the bridge and is partly reutilised giving the other half wave, and it's ok to smooth it on the way back (this is just my rookie's logic).
But, what if we connected choke to centre tapped tranny, and used two diodes full wave rectifire? Is the common mode still best solution? I saw some posts saying about dirty negative, especially when grounded.
Could anyone shed some light on it, or correct me if I was wrong please?
Thanks in advance
I took the liberty to contact mr Lundahl for the answer to the question, and he let me to post his answer on this forum.
Lundahl drawing.jpg - DivShare
An externally hosted image should be here but it was not working when we last tested it.
"Please see attached a schematic for PSU with chokes connected for common mode rejection (The circles with arrows indicate that the choke halves are connected). The C1 can be omitted, but is often used. Should be a fairly small value cap, compared to the electrolytic cap C2 between chokes.
Please notice that it is important with current balance in the two choke coils. For this reason the grounding point is placed to the right of the second choke.
Yes, I agree that with double diodes/center-tapped transformer, the connection becomes questionable and the benefits are not obvious.
- Per Lundahl"
PS,
can you see attached photo? I placed link in case you don't.
Attachments
Thanks for sharing
Thanks for being interested
I do not have completed my dddac yet and it will take some time. I just started this project as I needed a valid dac to my newly constructed speakers. As you know I’m totally green in that matter but trying to learn fast, and this forum is a great inspiration to it. Of course I took mine from supersurfer, as most of the people here. Just follow the leader
!! There is not much things done yet as Im waiting for crucial part which is a case. I ordered one from hifi2000. Big case with radiators in order to house whole powering lines including my HTPC newly built for that purpose (fanless, no moving parts- 100% ssd) gigabyte based APU – I’m very opened for advices in that matter. Whole power comes from one big premium audio toroidal transformer from polish factory TOROIDY.pl and is encapsulated in steel can and epoxy resin. 500VA with secondaries for 19v for pc, 2x 12v and one for 5v rails. Will see in future how is the performance and sound, and then decide wheter it is worth to change it for 3 x R Cores in future. I also ordered milled steel boxes and resin for encapsulation of the Lundahls. I have four of them. For now only two will be employed for 4 dac bords (not ordered yet) with Tent shunts. For now I’m focusing mainly on the psu. As for dac, there will be also tall case to house in future 8 boards for low impedance (4 mono power amps to feed with passive volume control). All will be attenuated with Transformer Volume Control, ones I’ll get it to understand
. Please, if anyone has some experience with TVC working with the dddac, please share info, tips, anything! The 5V supply boards will be moved from power case to the dac case. Both cases will be connected with military plugs (very hq pins)The rest parts which is main board and dac boards are to be ordered ones I'll be done completely with psu. I silently hope that until then Doede will launch updated version of the boards
I have attached some photos to make an idea of my work up to now.
An externally hosted image should be here but it was not working when we last tested it.
http://www.divshare.com/download/26855889-90c
An externally hosted image should be here but it was not working when we last tested it.
http://www.divshare.com/download/26855890-766
An externally hosted image should be here but it was not working when we last tested it.
http://www.divshare.com/download/26855891-a34
An externally hosted image should be here but it was not working when we last tested it.
http://www.divshare.com/download/26855892-cc7
PS.
Honestly, I'm in trouble with that image posting hehe. Just click the links.
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Salas Analog Power Supplies
The Salas power supply/voltage regulators have 4 rectifying diodes on each board. No place for a choke. The on board main supply cap and shunt current create a 3mohm output impedance up to 30Khz without the need for a big-@$$ transformer. I use a 56VA transformer with dual secondaries rated at 2 amps at 14VAC each. This is more than four times the .45 amps my Salas boards draw supplying 8V to the PCM1794 analog sections and +/-12V to the DAC output buffer.
I just want to let forum readers know that there is more than one power supply path to great sound. My DAC sounds far better than I ever imagined possible without using lots of iron. I will explain my Salas power supplies in greater detail with pictures on my Upgrade Thread if there is interest.
The Salas power supply/voltage regulators have 4 rectifying diodes on each board. No place for a choke. The on board main supply cap and shunt current create a 3mohm output impedance up to 30Khz without the need for a big-@$$ transformer. I use a 56VA transformer with dual secondaries rated at 2 amps at 14VAC each. This is more than four times the .45 amps my Salas boards draw supplying 8V to the PCM1794 analog sections and +/-12V to the DAC output buffer.
I just want to let forum readers know that there is more than one power supply path to great sound. My DAC sounds far better than I ever imagined possible without using lots of iron. I will explain my Salas power supplies in greater detail with pictures on my Upgrade Thread if there is interest.
My WaveIo will be powered from Salas Reflector D psu board. Very interesting unit, you can also provide DC current to it. Instead of mounting onboard diodes and big cap, you mount only a wire port and ready to go with DC. I thought to pull the current from 12Vdc main unregulated rail to increase inductance on chokes and at the same time to have exellent clean current for usb board.
Share it please, any other good alternative is interesting. Especialy when it comes to Salas boards.
I am using 4 chokes in my dddac. Two for the dac, and two for WaveIo. Both choke psu's have a bleeder resistor for current stability. The sound is very good now, when playing well know music, I discover details that I have never heard before.
My dac is a 4 deck with stock parts and no shunts. ( almost stock, changed to Elna cerafine caps on the analog side on dac boards ).
My dac is a 4 deck with stock parts and no shunts. ( almost stock, changed to Elna cerafine caps on the analog side on dac boards ).
Would you mind sharing your ps with photos? I particularly interested in your connection of the bleeder resistor and appropriate value?
I plan using 2 separate choke input ps for each Analog and digital...! Appreciate any feedbacks from those have already gave this a trial?
Cheers.
Hi Chanh.
I will try to take some fotos later. The bleeder resistor are in paralell at the end , after the chokes and caps and before mainboard. I have the psu set up as an LCLC. Remember I have only 4 deck and this represents a volt drop around 1.5v. So 13.6v before connecting the psu to the mainboard is perfekt for me. In your case things are quite different with 11 boards . So the value of your bleeder is not going to be the same as mine. I guess it also depends on how much capacitance and what kind of chokes you are using.
Per Lundahl told me that a bleeder resistor is very important for a stabil psu. When measuring the psu, it seems that Mr Lundahl is right.
Good luck
I will try to take some fotos later. The bleeder resistor are in paralell at the end , after the chokes and caps and before mainboard. I have the psu set up as an LCLC. Remember I have only 4 deck and this represents a volt drop around 1.5v. So 13.6v before connecting the psu to the mainboard is perfekt for me. In your case things are quite different with 11 boards . So the value of your bleeder is not going to be the same as mine. I guess it also depends on how much capacitance and what kind of chokes you are using.
Per Lundahl told me that a bleeder resistor is very important for a stabil psu. When measuring the psu, it seems that Mr Lundahl is right.
Good luck
bleeder
Hello,
i think when using shunts the current draw will be very stable. I think in that situation the bleeder is only needed to create the current that is needed to make it work as a choke input all the time in case the dac doesnt work.
so now we are wai ting for the boards that will have some space for mounting shunts like tent or salas.
buying a 4 board dac with shunts installed true diy way and then seeing new boards arrive is not my favourite thought.
let us hope we will get some info on this soon.
greetings edward
Hello,
i think when using shunts the current draw will be very stable. I think in that situation the bleeder is only needed to create the current that is needed to make it work as a choke input all the time in case the dac doesnt work.
so now we are wai ting for the boards that will have some space for mounting shunts like tent or salas.
buying a 4 board dac with shunts installed true diy way and then seeing new boards arrive is not my favourite thought.
let us hope we will get some info on this soon.
greetings edward
My guess would be, that thee is some kind of optimum load for the chokes.... Now depending on what load the dddac is for the ps, you could add current with the bleeder. So for a 11 deck like chahn's may be none need. Also may be already beyond optimum. Now this a question Luhdahl should be able to answer ? Just my 2 cents
minimum current
Hello Chanh,
There is a minimum current flow necessary to make it work like a choke input. The bigger the inductance the less current is needed.
If you have 14 volts at the cap after the input choke and you are using ll1694 which will be 160mH. You will need a current of about 87,5mA. ( 14 divided by 0,16). If something would go wrong with the dac the voltage will go up to much ( if you are using 25 voltrs caps) if there is no bleeder.
To be sure you can draw a little more current like 125mA no need to draw 0,5A.
Still didnt get answer about possible new boards from audio creative.
New boards will surely reactivate this thread lol
Sincere greetings, edward
Hello Chanh,
There is a minimum current flow necessary to make it work like a choke input. The bigger the inductance the less current is needed.
If you have 14 volts at the cap after the input choke and you are using ll1694 which will be 160mH. You will need a current of about 87,5mA. ( 14 divided by 0,16). If something would go wrong with the dac the voltage will go up to much ( if you are using 25 voltrs caps) if there is no bleeder.
To be sure you can draw a little more current like 125mA no need to draw 0,5A.
Still didnt get answer about possible new boards from audio creative.
New boards will surely reactivate this thread lol
Sincere greetings, edward