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Old 2nd January 2012, 11:36 AM   #141
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Thanks stormsonic I've updated the blog entry. Note that it has always had a credit for Fred (and pointer to this thread). excerpt here (the blog entry is very dense so you may not spot it)

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One useful thread here on diyAudio was this one from Fred DieckMann. Post 34 in that thread is what the LM317 part of my circuit is based on. Another one was This thread from jbau, although it steered me in the direction of NOT using a negative regulator at all. The thing that struck me was his subjective evaluation that symmetry in the supply rails made a big difference to the sound of the amplifier. One person commented why don't you just use two LM317's (which in his application wasn't possible) but for me the decision was clear
On the 2A if needed, I assume that is the unofficial "pushing it to the limit" figure Data sheets I've read all said 1.5A even for the T03 versions.

Tony.
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Last edited by wintermute; 2nd January 2012 at 11:37 AM. Reason: minor edit
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Old 2nd January 2012, 12:10 PM   #142
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Great blog
It is time to improve your regulator to tracking regulator with additional LM317. Look into Using 3-pin regulators off-piste: part 4, last picture (tracking regulator with LED).
Keep using your schematic with BC560C in place, just add preregulator.
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Old 2nd January 2012, 03:21 PM   #143
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Quote:
Originally Posted by wintermute View Post
The schematic for my overkill realisation of this idea attached below. You can ignore the CRC front end if all you want is a working version of the reg part of the circuit and if you only want a single rail just use the top half of the circuit The more traditional approach (for dual rail) would be to use an LM337 for the bottom reg, and I think you would then need to use an npn transistor for the negative part of the circuit.
Tony,


I do not think the CRC front end would be overkill for a properly noise-free raw supply. Either that or a an CLC should be included. Though I am not sure about R2/R4 and R102/R104 being necessary. Only a test on a scope might show if they are. Did you test that?

What about the 511 ohm output resistors? Did you put them to increase performance?
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Old 2nd January 2012, 09:16 PM   #144
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Hi Carlmart, This blog entry has some scope measurements which clearly show what a difference the resistors in the CRCRC network make to the ripple pre reg --> http://www.diyaudio.com/forums/blogs...-progress.html It doesn't show only having the resistor in one leg of the supply though. I did test that as well and it did make a difference to the final pre-reg ripple (from memory it was significantly higher without the r2/r4 and r102/r104).

Thoese extra resistors were one of the things I was unsure about when I first simmed it, because I had not ever seen a PS with resistors in both the +ve and -ve legs.

I may have documented that in my measurements thread, I can't remember. --> LM317 experiments and measurements
Unfortunately now that I have made the final circuit it will not be easy to test the difference, as I don't really want to desolder the resistors from the board. However I can show the difference in the sim

Yes the pre-load resistors are to improve performance, I think it was Jan Didden that pointed out that LM317s perform better with a higher current draw, so this ensures a minimum of about 40mA of constant current draw

Tony.
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File Type: png ripple_nor2_r4.png (11.8 KB, 753 views)
File Type: png ripple_r2_r4.png (12.0 KB, 743 views)
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Old 3rd January 2012, 09:45 AM   #145
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Seeing those scope measurements, it's incredible why such a mod is not the first thing that is provided on any DIY job. At least on low current stages on preamps and power amps.

Even if ripple rejection specs are good, having less to reject should always be better.
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Old 3rd January 2012, 10:29 AM   #146
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Yes it was an eye opener for me as to just how much difference CRCRC made to the ripple. As you say though low current. Even with a very modest current draw (the sim output above is 250mA) the voltage drop is quite significant. The higher the current the bigger the drop. the difference between having or not having R2/R4 is about 1.5V pre reg in the above sim.

I ended up using a 15-0-15 toroidal for my +/- 10V output. The main reason for this was I wanted to have at least 5V difference in to out. This is another area that makes a difference to the final output performance.

Any less than 5V difference in to out and the ripple increases on the output. I don't think it is a coincidence that all of the data sheet measurements showing ripple rejection are with 5V in to out differential

So it is a bit of a balancing act. If you have too much voltage drop to reduce the ripple pre-reg, you may end up with worse ripple on the output if the in - out differential drops below the 5V threshold.

Tony.
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Last edited by wintermute; 3rd January 2012 at 10:30 AM. Reason: minor fixes
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Old 3rd January 2012, 11:05 AM   #147
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Yes, current draw is significant with series resistors.

What you could try is using lower value resistors on the simulation and tests, and see if ripple is affected (increased) for what value. I think you could go down to 1R2 with no problems.

Also, yes, the 3X7 needs more input voltage than other regulators to perform better. Which is not something that is not mentioned often.
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Old 3rd January 2012, 12:00 PM   #148
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Hi Tony,

Haven't forgotten the Xover project, just being slow!

If you reduce the ripple CRCRC to the simpler C-R-C and then add a simple C multiplier, you can radically change the sound of this simple reg - sort of like a reversed Teddy-Reg (Pink Fish Media) - will suck up another volt or 2, but this is quite manageable.

Curiously, both Patrick (EUVL) uses simple single pole reg for his balanced F5 power supply and John Brown (EC Design) has used a rather sophisticated combination for his newest power supply for the 1541A dac chip power supply - interesting!
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Old 3rd January 2012, 12:29 PM   #149
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Hi Jh, no I haven't forgotten I'm just very slow!!! Now that this is built it is time to start breadboarding the Synergy This was the pre-requisite. It was my goal to have both done before the end of 2011, unfortunately I only got one done. Hopefully the synergy will be a bit quicker now

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Old 8th January 2012, 08:13 AM   #150
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@Wintermute

What are R12 R13 for (after the regulator) in your diagram of the improved 317?

I'm guessing after that is the cap that sometimes comes after a 317 normally and a snubber?

-Zack
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