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goldenreference low voltage power supply


kevin gilmore
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7 minutes ago, Pars said:
  1. Steve,

I hadn't read that regarding a 4.5 digit DMM, but I would assume you would be able to see something? I've never used the trimpots for adjusting the voltages (I usually use either matched resistors using my HP bench meter, or 0.1% resistors and live with the results.)

That's what I was thinking.  Is there any harm leaving it as is?  I'm ok with the results

6 minutes ago, mwl168 said:

Judging by the photo you should definitely see output voltage change as you adjust the pots. If not, I would first check to see if the pins of the pot are soldered in correctly - is it possible you soldered pin 1 and 3 of the pots to the fixed resistor positions?

 

I'll check it tonight, anything is possible

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1 hour ago, Pars said:

I don't think you're going to get any closer than that :)

I'd agree...  I was quite pleased when I fired it up.  I'm inclined to just leave it.

Compared to the TPA bipolar supply it immediately sounded better.  The sound stage seems more dynamic and I hope it gets better.

Edited by sbelyo
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I've read a few parts of this thread but would like to confirm the following:

For a 24VDC output to power 2CFA boards I should use a 22-24VAC 50-60VA transformer right? 

How important is led and resistor matching? Do I really need 5 decimals of precision in the output voltages? 

 

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joke {

5 digits is too low accuracy, you need at least a 8.5 digit multimeter calibrated monthly in a sealed controlled environment and Faraday cage. 

The resistors should all be 0.01% 5ppm or better and the leds need to be curve traced from 0V to 5V and matched within 0.01% on current.

This should make the LV psu board more expensive and time consuming than the rest of the amp. 🙂 

} /joke

I don't know if the cfa has any special requirements but for both my blue hawaii and mini t2 builds I went for 1% 50ppm resistors, - koa brand. I did not match the leds other than they where all from the same reel and so had the same nominal specs. I aim for voltages within 1% of the target given I use 1% resistors. The ppm of the resistors will effect voltage drift with temperature, if you want good accuracy and stable voltages build the board with low ppm 1% resistors, measure the voltages, calculate the error and replace just the resistors that set the output voltage. I don't see any point in spending lots of money on better resistors everywhere when I can spend the money I save on music or other vices 😉 ... 

Edited by jamesmking
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Based on my experience, 24vac and 60va transformer is the minimum for 24VDC rails to supply a pair of CFA boards. 
I use two 100va transformers for my dual mono, balanced CFA amp running 30VDC rails. 

For GRLV, I did match the 4 resistors that determine the regulated voltage. No need for 5 decimal precision though. The LT1021 voltage reference has its own tolerance as well. 

Edited by mwl168
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On 3/4/2019 at 2:56 AM, kevin gilmore said:

someone needs to check this, works as single rectifier with center tapped transformer, or a pair with dual secondaries. Up to 72vdc, perfect for GRLV

caps are 100v rated, 1uf is 0805 size, 10uf is 2220 size

I can certainly do a bigger version with different fets for higher currents and lower voltages. .9 x 1.1 inches

 

syncrectifier.jpg

 

syncrectifier.zip

Hi Kevin,

Tried to upload the above files to PCBWay to order but couldn't . Any tip to do this will be appreciated as I am not familiar with GERBER or other file formats and this is my first go to get fabrication done.

 

Cheers!

Ravi

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You normally just upload the .zip, not the individual files. I don't use PCBWay and didn't want to go thru their registration bullshit, but tried the file with seeedstudio and it worked fine. The Gerber viewer picked it up just fine, and it didn't look like it would be any problem.

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I have had no trouble using the zip with jlcpcb in china, I have sync rectifiers in my grlv in my blue hawaiis, mini t2s, psus I made for my dacs and a preamp I made,. Please be aware the sync rectifier will not work with centre tapped windings . so if you are making a grLV you need two independent windings  and two sync rectifiers,. you cant use the  GRLV option for centre tap and one rectifier I have tested it myself the sync rect does not work in this configuration but a normal  diode rectifier does.

The pin pitch is rather small and you need to check very carefully for shorts between pins 3 and 4,  (pins 1-3 are internally connected together) and between the metal base and pins 1-4.

 

_MG_6138.thumb.jpg.da3672d4ed7248a273cf211b13397d9a.jpg

 

syncrectifier.JPG.3f665968ebe122196f8a054d70ef8f6c.JPG

 

I created a small test rig for the sync rect, I used a spare grlv board, put a female header where the rectifier solders in, added a largish value smoothing cap and bring the sync rectifier under test up slowly using a current limited dc supply and when I believe its ok, I swap the polarity of the dc supply and repeat so all 4 psmn040 are tested. I then use a 15v transformer and bring the sync rectifier up slowly on a variac. So far I have had one psmn040 smoke, I think I had a soldering short between the metal base and pins 1 or 2 or 3 or 4. Fortunately the expensive lt4320 survived without issue and I was able to reuse it. the test rig also includes wire loops for attaching a multi meter, scope and electronic dc load. I populated the diode next to the cap and one led partly to help drain the cap and to give a visual indication the board is live. Once the board has passed variac tests, I test switch on with no variac so the cap will cause a reasonable inrush, then I test with an electronic DC load up to 2A.

._MG_6135.thumb.jpg.fa09c8c07dcc9425041246e845ff1c7b.jpg

 

 

 

Edited by jamesmking
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On 7/17/2015 at 5:14 PM, kevin gilmore said:

2 watt transformer... no

 

22 watt, just barely

 

30 watt transformer is about right

 

one of the mounting holes is 25th off of square.

 

current posted boards (dual and singles) have the mounting

holes one size smaller, the silk screen fixed, and 1 resistor

each moved by 25th.

 

done

 

measurements this morning in a screen room is about 800picovolts

of noise. and voltage stability exceeding 6.5 digit meter.

 

anything better is going to require stupidly expensive test gear.

Hi Kevin,

Could you please provide description of your measurement setup? What kind of LNA could provide such low noise to not mask the claimed noise of this regulator? What was the bandwidth of this measurments?

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a pile of metrology gear owned by the university. not sure what the bandwidth was, but probably only a few khz at best.

front end gear was peltier cooled to get the noise down.

I really want the 8.5 digit agilent unit, but $5k for a toy with known issues seems a bit much especially since the screen room part is not possible at home.

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Thanks for info! IMHO the $5k DMM/voltmeter doesn't help much with this sort of measurements because self noise even best of them is more than 1 nV (in practice > 10 nV). The only solution could be to use some unknown to me LNA.

Its good to know that this is possible. 

https://www.analog.com/media/en/technical-documentation/application-notes/an159fa.pdf

https://www.analog.com/media/en/technical-documentation/application-notes/an83f.pdf

Thank you very much for the answers! BTW do you see any reason not to replace huge input capacitors for the HV regulator with reasonable capacitance multiplier (e.g. 10u pre + 10u in cap.mult. + 10u post)? 

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  • 3 weeks later...

Apparently mouser forgot to send me the opa134 needed so I plugged a pair of opa445 for the CFA servo. 

No smoke. Voltages are +25.02 and -25.11 I didn't match any of the LEDs or resistors so this seems pretty good to me and probably won't make a difference in real life. 

20200602_234954.jpg

Edited by MASantos
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  • 1 month later...
On 4/28/2020 at 10:19 AM, bravi said:

Hi James, Pars,

 

Thanks a lot for the tips. Will try again and report back on progress.

 

Cheers!

Hi All,

Soldered the first lot of 4 pcbs of Sync rectifier with all components. Tested with 12 v transformer . Got around 16.1v on the output with a 10mF capacitor. With a test resistor load of 48ohms the current would have been around 330ma. Great start for me with learnings on soldering smd device.

Any views on the max current that can be drawn with this sync rectifier board without stressing the components?

Cheers!

 

Ravi

 

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