user 37518
Well-known member
Well, those SSL consoles are full of SMPS and people just worship them.... I am not denying (nor affirming) what you say, but people don't care or don't know...
Should phantom power be supplied by a linear supply?
- Thread starter Lerok
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user 37518
Well-known member
I once reached the conclusion that between good converters you can definitely hear a difference when comparing them A/B, but when used in isolation, it doesn't matter, I know I will get some heat for saying this from people claiming otherwise, among with arguments including a lot of adjectives such as "openness", "forward", "bold", "sterile", "warm" and my personal favorite: "musical".
RogerAF
Well-known member
Wow! I think you're going to be blowing that 0.5A fuse every time the rectifier filter caps have to charge, I've seen power amps with less capacitance. I also suggest that C7 and C14 are not necessary and that C6, C16 and C8, C16 (Whoops, look like you have some numbering errors.) Anyway the smaller caps should be right next to the regulators.
Also I agree with Abbey Road re LM3x7 devices.
Having just looked at a bunch of TI's regulators, there are versions of LM3x7 with noise below 50µV.
If you are going to use 10,000µF caps at the rectifier filter, I suggest you implement some kind of inrush current limiting.
Regarding the SMPS for 48V phantom supply, recommended practice for keeping switching noise to a minimum is to use a linear regulator following the SMPS. So bump the +15V up to 52V with a boost converter, then use something like a LM317HV (60V adj regulator see: https://www.ti.com/lit/gpn/lm317hv). These are noisy, so some kind of circuit like Thor talks about would be good to figure out.
Couldn't find any... TI's parametric search is a mess.
RogerAF
Well-known member
https://www.ti.com/product/LM317A/part-details/LM317AT/NOPBhttps://www.ti.com/product/LM337-N/part-details/LM337T/LF01From my shopping cart...
Better hurry on the 337s, only 508 left in inventory...
Note: These are direct from TI. Both DigiKey and Mouser have 0 (at least for 337s).
Cheers
I don't see any difference with the historic 317/337 in terms of noise.
Still rated at 0.003% of output voltage.
IINM, for 48V output, noise is about 1.6mVrms
RogerAF
Well-known member
Yes, totally in contradiction with the datasheet. Which one is right?
I have told this story before but back last century when I was using 3 terminal regulators by the truckload, I traced a noise floor issue to noisy 3-terminal regulators. Checking the spec file (data sheet) there was no guaranteed max noise spec. I contacted the rep, it was a major company and their response was that they do not specify output noise. Apparently their way to deliver six-sigma reliability was to open up the definition of what good is. 
After they declined to provide a guaranteed noise spec, I declined to purchase any more from them (I black balled them from future purchases).
JR
After they declined to provide a guaranteed noise spec, I declined to purchase any more from them (I black balled them from future purchases).
JR
RogerAF
Well-known member
They only have the TO220 types left at TI, I wonder if it might depend on package and layout
But they are cheap
Well yeah; as compared to what?
If you go backwards through the math, they should meet the 38uV feature list number for output noise at the minimum output voltage of 1.2V. Seems like the line in the feature list is incomplete enough to argue it is dishonest. Also a reminder to read all of the datasheet, don't design in devices based on the marketing copy at the top of the web page.
Yes, it is the voltage reference's noise.
As you say, dishonest and misleading.
Actyally, these "new" parts are no better than the old ones, in that respect.
RogerAF
Well-known member
Before I knew about "noise" I made several linear supplies for one-offs for various studios. I used a LM723 DIP-8 and a series pass as per the data sheet https://www.ti.com/product/LM723JAN-SP one for the + rail and 1 for the - rail. Everybody was happy and I never had a complaint. I will note however, that all of these dealt with line level signals and analog consoles and tape machines, so the noise floor was probably below the tape hiss.
I once had to rebuild 3) SSL 4000 series PSUs. They had a very similar circuit with several series-pass transistors in parallel. Talk about high current capacity!
The 723 is a real old dog, but riddle me this: why is there a radiation-hardened-space version that's currently active?
I think someone is still using these. (Starlink?)
Who knew?
BTW I just looked at the price. Holy S**t! the space grade is almost $200 a pop in lots of 1000. The Mil grade is just under $8. I think I still have some regular plain vanilla versions from the 80s in one of my parts drawers. Hmmm...Ebay?
I once had to rebuild 3) SSL 4000 series PSUs. They had a very similar circuit with several series-pass transistors in parallel. Talk about high current capacity!
The 723 is a real old dog, but riddle me this: why is there a radiation-hardened-space version that's currently active?
I think someone is still using these. (Starlink?)
Who knew?
BTW I just looked at the price. Holy S**t! the space grade is almost $200 a pop in lots of 1000. The Mil grade is just under $8. I think I still have some regular plain vanilla versions from the 80s in one of my parts drawers. Hmmm...Ebay?
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RogerAF
Well-known member
Follow up. Jameco has 'em for $1.39. Not sure of manufacturer. Probably not Mil spec
Best way for clean power is Funk-Tonstudiotechnik : SCMS-Copyprossesoren/Konverter
lowest noise ever.....and precise
Best regards!
lowest noise ever.....and precise
Best regards!
