Moving Coil Prepre PSU: Basic Questions, What am i missing?
- By speedgeil
- Power Supplies
- 3 Replies
I won't lie, most of the time when i built DIY audio stuff, i'm blindly following ready made schematics. So i did 20 years ago when building my 2sk170 PrePre and the following RIAA stage. Now, over the years i have gathered crates full of electronic components stuff, often MIL spec parts, which i wanted to use some day to rebuild things that actually work, but have some flaws, maybe only optical, sometimes it was just me modifying into a wrong direction because i didn't have parts at hand, no money or whatsoever.
Now the time has come, the amount of parts in my garage is getting annoying. So i decided to "build it away" and get my final stereo setup done.
One of the DIY devices that has a flaw is the PSU of my phono amp. It humms a little bit. It is basically only LM7824/LM7812 with some filtering caps. So i thought to myself i had to go look into the crates what i have.
What i found is a nice little Collins choke with 2,5H/100R at 0,11A. I thought it could be a good idea to use it with a decent 30V toroid, some 4,7mF caps and two LM317 regulators for creating a dual power supply. The needed voltages are +12V@40mA and +24V@60mA.
I turned on PSU designer to simulate that and... wow... i'm getting 30V @ 1,4mV of ripple only? Can that be correct? I mean plus the additional rejection of the LM317s which should be around 60dB for each stage that should make a very quiet phono PSU in the nanoVolts region right?
Now what i would do is adding a LM317 stage to regulate for 24V for the MM stage (approx 60mA) and behind it another LM317 to regulate for 12V for the MC stage (approx 40mA). Maybe add another RC in front of the second LM 317. Should take off some heat from the reg's shoulders and should reduce ripple even more. Maybe something like 20R with 4,7mF or so.
Ok, so i'm not the smartest guy when it comes to designing circuits (and living with women). So i have some basic questions.
Everyone is building shunt regulated PSUs etc. No doubt they work good, but for me they are hard to understand and build. If i interpret PSU designer correctly, i wouldn't need more than these few parts plus etching a little PCB for regulators etc to get away with it? Does that mean all the effort put in shunts, low noise regs, huge filter caps etc is only for cost reasons because of rather expensive chokes? I mean actually you can get a choke with these values around USD 10 to 20 used or so. Can this be true?
Also another basic question: I would like to build a test setup. Do i have to worry inrush current could destroy the choke? Maybe should i add a current limiting resistor?
Thanks for your help!
Now the time has come, the amount of parts in my garage is getting annoying. So i decided to "build it away" and get my final stereo setup done.
One of the DIY devices that has a flaw is the PSU of my phono amp. It humms a little bit. It is basically only LM7824/LM7812 with some filtering caps. So i thought to myself i had to go look into the crates what i have.
What i found is a nice little Collins choke with 2,5H/100R at 0,11A. I thought it could be a good idea to use it with a decent 30V toroid, some 4,7mF caps and two LM317 regulators for creating a dual power supply. The needed voltages are +12V@40mA and +24V@60mA.
I turned on PSU designer to simulate that and... wow... i'm getting 30V @ 1,4mV of ripple only? Can that be correct? I mean plus the additional rejection of the LM317s which should be around 60dB for each stage that should make a very quiet phono PSU in the nanoVolts region right?
Now what i would do is adding a LM317 stage to regulate for 24V for the MM stage (approx 60mA) and behind it another LM317 to regulate for 12V for the MC stage (approx 40mA). Maybe add another RC in front of the second LM 317. Should take off some heat from the reg's shoulders and should reduce ripple even more. Maybe something like 20R with 4,7mF or so.
Ok, so i'm not the smartest guy when it comes to designing circuits (and living with women). So i have some basic questions.
Everyone is building shunt regulated PSUs etc. No doubt they work good, but for me they are hard to understand and build. If i interpret PSU designer correctly, i wouldn't need more than these few parts plus etching a little PCB for regulators etc to get away with it? Does that mean all the effort put in shunts, low noise regs, huge filter caps etc is only for cost reasons because of rather expensive chokes? I mean actually you can get a choke with these values around USD 10 to 20 used or so. Can this be true?
Also another basic question: I would like to build a test setup. Do i have to worry inrush current could destroy the choke? Maybe should i add a current limiting resistor?
Thanks for your help!