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ALWSR Build Thread

Discussion in 'd.i.y.' started by timH, Apr 5, 2019.

  1. john.luckins

    john.luckins pfm Member

    Tricky. Have you got the Zener the right way round? The circuit diagram recommends an LED for D2 so I would give that a try. Make sure it has a resistive load to sink at least 5ma. I'd recommend 100 ohms or lower especially if you are using the tracking pre reg. Is the LED D1 alight?
  2. martin clark

    martin clark pinko bodger

    Good point well made and ultimately I found even the LM329 a bit susceptible to such effects in my preamp - the 329 has a pretty poor transient response, and gets markedly worse in the midrange and above - so I now prefer a CCS instead of the resistor to feed it or whatever's convenient (eg split the feed resistor in two and tie one end to 0v at the reference with a decent cap 10-100uF - but actually I usually use the 2mA ATI Semitec CRDs Rapid stock, for all sorts of things (excellent for all sorts of purposes, with 250Kohm min dynamic impedance from 5-100v input...). These parts ..:
  3. IDM

    IDM pfm Member


    I haven't put the pre-reg in yet as I am just testing the S.reg part.

    D1 does light up (not bright). I just added a 100R load and the output drops to approx 2.6V. I did try a blue LED (Vf 3.36V) instead of D2 and this gave me 4.2V out of the reg

    I am now a little stumped.
  4. timH

    timH pfm Member

    Shouldn’t r5 be 2.49k?
  5. IDM

    IDM pfm Member

    I just saw in the component changes table that pin 1 and 3 of the tl431 should be soldered together (which I hadn’t!). Made the change and it had no effect. I will try replacing the tl431 see if that helps
  6. timH

    timH pfm Member

    Pin 1 is the cathode which on the negative version goes to 0v sense which is the middle hole on the pcb. Pin 2 is the anode which goes to R5/R7 which is the upper hole on the pcb. Pin 3 is Ref which has to join pin 1 which is probably easiest to do above the pcb. I think this is correct but please check.
  7. john.luckins

    john.luckins pfm Member

    Not according to the manual Tim. It states 249R for the 5v reg. Having 10mA going through the TL431 rather than the 1mA it needs once everything is started up is of no benefit in terms of noise/performance as far a I can tell. Dynamic impedance is specified from 1 to 10 ma. Can't tell if higher current helps lower noise as it does with zeners and I've used 2K4 in 5 volt regs before so I don't think it effects the ability of the entire reg to start up. That would only happen if too high an R5 was used so unlikely to be causing IDM's problem. 2k4 for R5 gives the best rejection of rail noise without resorting to a CCS.

  8. john.luckins

    john.luckins pfm Member

    I would stick to using 249 ohms for R5 for now and get a new TL431 in place with two of its pins shorted. Double check it does what you want it to by putting circa 5 volts between the top of R5 and 0v and seeing that it gives a 2.5 volt reference. I do think that 3.3 volts is too much for D2 to drop. A red or green LED will be better, 1.6 or 1.8 volts each roughly. If you haven't got either of them then just a couple of forward biased 1N4148 diodes would do the job for now. If after that you get no joy then we will need some voltages to diagnose the issue or failing that post a photo the board in question and we can see if we can spot something.


    PS I'm building a 5 volt one now. I do also think that D1 hasn't got enough current going through it with R4 set to 10k. Am reducing this to 3K3. Don't think this is critical for operation.
  9. timH

    timH pfm Member

    Hmmm, just noticed in the parts list it says 2k49 but on the schematic and component overlay 249r is shown
  10. john.luckins

    john.luckins pfm Member

    I've just checked and all my 5v builds started with 2K4 for R5. The extra 20dB of rail rejection from using 2K4 is worth having.
  11. IDM

    IDM pfm Member

    I got the -5V reg working last night. The problem being my own stupidity. I naively didn't think to check the datasheet of the TL431 versus the LM329. If I had done that I would have realised that the pinout is different so you cannot simply reverse it in the holes in the PCB. I would also have realised that pin1 and 3 needed to be tied together (this is mentioned in the build guide in the table of component changes. So I strongly recommend having a really good look at the PCB tracks versus the datasheet before using the TL431 in order to not make my stupid mistake.

    John, I notice that you mentioned that D2 dropping 3.3V was too much, yet in the original BOM it uses a 1N5333B, which is 3.3V zener. Do you think a green LED is better? I do note that in some of my earlier builds I have used a green LED in that position. Also should R5 be changed from 249R to 2k4 as you mention above?
  12. john.luckins

    john.luckins pfm Member

    Great that you got it working. With regard to the 3.3 volt Zener, ideally you want the opamp to be working as close to mid rail as possible, i.e. at 2.5 volts at its output. that means that you really want circa 2.5 volts across D2. It is slightly better to have the opamp output higher than 2.5 volts as it is sinking current and green LED's (circa 1.8 volts) are also quieter than zeners. I would change to a green LED if it is convenient. I would certainly recommend changing R5 to 2.4k. I think the 249R is simply an error.

    By the way, do you find that you get just less than 5 volts. The TL431 gives slightly less than 2.49 volts and I always get 4.97 volts at the 5v reg output. A suitable high value resistor across the lower feedback resistor will solve that.

  13. timH

    timH pfm Member

    Hmmm. I’ve got a positive reg feeding 3.3v to the digital part of an ES9038 DAC board. Seems like I should definitely change the zener to an led.
  14. john.luckins

    john.luckins pfm Member

    The change to a quieter LED will be a minor improvement in a 3.3v reg. More tricky is making sure the opamp gets enough supply voltage and is operating in where it works best. Feedng your opamp from the TPR output at the top end of C1 rather than the SR output may be advantageous. This involves cutting a track or lifting a pin. A series resistor or even a cap multiplier can be used to improve this supply if you have the voltage headroom. Which Opamp are you using?

    Variations to the standard ALWSR builds might be best dealt with in a separate thread. I'll kick one off at the weekend, starting with what must be an increasingly common role for the device, the 5v reg for digital circuits. The aim will be getting concensus on the optimum practical implementation for each role.

  15. timH

    timH pfm Member

    I’m using the ad817 but I’ll wait for the new thread. 3.3v seems quite common for digital as well
  16. chrisn

    chrisn pfm Member

    "Soldering Surface Mount Components" by ALW. Updated!
    It is on page 3 in the reference section and it's taken me an hour to find it again. Good stuff Andy! It is a must do for ALWSRs above 5V. I thought I was going to get away with a TTHole mount. :(
    Questions :- Can I get it right first time with the real thing or do I need to practice? Am I going to have to buy x5 RS Flux Pens?
  17. timH

    timH pfm Member

    I’d definitely get a flux pen. They’re available singly on eBay.
    It’s possible to solder the chip pin by pin using a very small pointed tip.
    Either way you do it have a go at one as the first item you solder on the board. That way you might be able to rescue it if you go wrong. They’re expensive to practice on :)
  18. andrewsutton

    andrewsutton pfm Member

    Use a flux pen, place the chip in the right place, pin it down (I use a wooden skewer), solder a leg that is not connected ( there are 3) and then the others.
    Hot iron and be quick. I don’t use a fine tip because I find a 3mm chisel tip fine.
    Cheers Andy.
  19. geoturbo

    geoturbo pfm Member

    Thank you very much for your reply timH, I had found the SNAPS mod manual earlier, just trying to figure out the best way (it would be good to know if anyone has done it before and if feasible..) to put 4 ALWSR in the SNAPS using the 5 pin SNAIC to 32-5 for the boards . Thinking about a dedicated plastic/metal holder - or something like that - to hold the 4 ALWSR populated boards and screw to the standard bottom holes of SNAPS.. I'll report back in case I'll be able to figure out something.. just not wanting to continue with personal project in this thread.. that's it for now, thanks,

  20. Andrew L Weekes

    Andrew L Weekes Reverse Engineer

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