lovelyworldsound

Neumann W492 project - PSU help needed
« on: February 18, 2021, 05:59:59 AM »
Hi,

Hope that someone can help me out here :-)
10 years ago I was on my way building a W492 (audiox clone) - and now I finaly have gotten time to finish the project  ;D
Boards are populated, switches and pots are in place, frontplate and rearplate drilled, torroid and all component sourced and suddenly I remember why I left the project unattended in the first place - the PSU!

I have a PSU board vari+ from Gustav (PCB Grinder) and need to get +-15v out of it - but then I have to calculate the resistor values on the trails, and that is a very weak spot in my personality  :'(.

Anyone made this build or have the values needed? Any help greatly appreciated  :)





TwentyTrees

Re: Neumann W492 project - PSU help needed
« Reply #1 on: February 18, 2021, 04:09:23 PM »
Here you go:

http://www.reuk.co.uk/wordpress/electric-circuit/lm317-voltage-calculator/

This should get you going on the LM317, can't remember off the top of my head of the calculations are the same for a 337 (negative voltage regulator) but if not then googling "lm337 calculator" or similar should sort you out. It's worth the digging - it's a great EQ to my ears (I use a heavily modified one on my mix bus).

lovelyworldsound

Re: Neumann W492 project - PSU help needed
« Reply #2 on: February 18, 2021, 05:20:28 PM »
Thank you a tonne, TwentyTrees! Very usefull calculator :) - and thank you for your reply.

But I still kind of don´t get it, though.
In each of the trails going to LM317 and LM337 (on Gustavs PCB) there is both a "R" and a "K" in pairs.I believe that "R" stands for resistor - and that "K" could be some kind of relay? Do you know what that could be?
Every other PSU I´ve checked out, (Mnats f.ex.) has a R1 to the negative side, and a R2 to the positive - but in the calculator that you link to, it seems that you need 2 resistor values (R1 and R2) to make any given output voltage (ex: 15.31V, R1 = 240, R2 = 2700).

I can not really get my noodle around it  :o

TwentyTrees

Re: Neumann W492 project - PSU help needed
« Reply #3 on: February 18, 2021, 05:44:20 PM »
Both the "R" and "K" on Gustav's Vari-PSU are resistors - they're they R1 and R2 shown in the calculator and in data sheets. I forget whether R1=R+ and R2=K+, or the other way round, but following the PCB traces should make it clear. There's also documentation on the PCB Grinder website which should help you make sense of it, might be a schematic in there too which should clear everything up if you reference against the LM317 and LM337 data sheets for pinouts.

Once you've figured out which resistor is which, it really is just a matter of putting those in place and going from there. Good luck!

PS - just found this PSU from Mnats, is this the one you mean? R1 and R2 on the calculator are R4 and R3 here, if that helps. http://mnats.net/files/MNATS_PSU.pdf

JMan

Re: Neumann W492 project - PSU help needed
« Reply #4 on: February 18, 2021, 05:46:41 PM »
In each of the trails going to LM317 and LM337 (on Gustavs PCB) there is both a "R" and a "K" in pairs.I believe that "R" stands for resistor - and that "K" could be some kind of relay? Do you know what that could be?

Looking at the schematic that I pulled from Gustav's files recently (I am planning to build this soon as well), the R and K designations both seem to be resistors (R89, R90 on positive side, R83, R84 on negative).  I am also unsure about what the letters R and K actually stand for there -- though stumping me is no big task -- but these DO appear to be resistors.

EDIT: TwentyTrees beat me to it, and was more helpful lol

JMan

Re: Neumann W492 project - PSU help needed
« Reply #5 on: February 18, 2021, 05:53:31 PM »
For the LM317 Calculator, on a quick glance, I believe that R+ is R1 and K+ is R2.  Probably worth double checking me here, but that appears to be correct.

lovelyworldsound

Re: Neumann W492 project - PSU help needed
« Reply #6 on: February 18, 2021, 05:54:38 PM »
Thanks!! Dunno who beats who - but it was extremely kind of the both of you :-)
Can´t wait to get this thing up and running.

JMan

Re: Neumann W492 project - PSU help needed
« Reply #7 on: February 18, 2021, 06:03:01 PM »
I actually have a related question, if anyone wants to chime in.  It seems that there is a fairly wide range of resistor values that can be used here (for example, the calculator above allows for R1 to be any value between 100r and 1k, with R2 simply adjusting its value in kind).  Assuming that I have the appropriate resistors/trimpots to work anywhere within the range, is there a reason to choose a given R1 value over another?  Or is this a fairly arbitrary choice and more about making sure the R1/R2 values are appropriately calculated?

JMan

Re: Neumann W492 project - PSU help needed
« Reply #8 on: February 18, 2021, 06:05:44 PM »
By the way, what torroid do you recomend for this? I got an 30, 0, 30 for this build, is that too much?

I think this wants 2x15 secondaries (looking at the schem), like this one: https://www.pcbgrinder.com/produktside/power-trafo

Maybe someone who has built it can weigh in?  I'm just looking at the docs.

lovelyworldsound

Re: Neumann W492 project - PSU help needed
« Reply #9 on: February 18, 2021, 06:09:12 PM »
Ah yes - you´re right on that one - and I had the wrong glasses on  ;D
It is a 2x15v I got on the secondary :-)

Thanks again


lovelyworldsound

Re: Neumann W492 project - PSU help needed
« Reply #10 on: February 19, 2021, 05:04:49 AM »
Just to update, if anyone in the future should have the same question:

Calculated R-values seems to be the same for both the negative and the positive rail (ex. -15v = R- (R1) 240 ohm, and K- (R2) 2.640 ohm / +15v = R+ (R1) 240 ohm, and K+ (R2) 2.640 ohm).

Manufacturer recommend a R1 value of 240 ohm at default.


PS - just found this PSU from Mnats, is this the one you mean? R1 and R2 on the calculator are R4 and R3 here, if that helps. http://mnats.net/files/MNATS_PSU.pdf

In Gustavs PSU board vari+ layout, the trails are very clear - but on the Mnats PSU, I can´t make head or tail in what goes where. It seems to me, that the resistors R1 and R2 are placed as R1 to negative out, and R2 to positive out.
Mnat writes in his PSU schematic:
"R1, R2 -- SELECT FOR PROPER LED CURRENT GIVEN SELECTED OUTPUT VOLTAGE
R3, R5 -- CALCULATE VALUES OR USE OPTIONAL TRIMPOTS FOR VARIABLE SUPPLY VOLTAGE"

Anyone see this clear?

Anyway - think I go with Gustavs board :-)

lovelyworldsound

Re: Neumann W492 project - PSU help needed
« Reply #11 on: February 19, 2021, 09:13:27 AM »
Anyone knows what the symbol means on the attached image? Some kind of transistor? On the PCB it has 4 legs and diagonal -/+.

TwentyTrees

Re: Neumann W492 project - PSU help needed
« Reply #12 on: February 19, 2021, 10:57:11 AM »
It's a diode bridge rectifier - 4 diodes. Often done using discrete diodes, but from what you say it sounds like the VariPSU uses an integrated diode bridge. If there's a bill of materials (BOM) for the project, that should say what you need.

lovelyworldsound

Re: Neumann W492 project - PSU help needed
« Reply #13 on: February 19, 2021, 12:29:25 PM »
Thanks TwentyTrees - Yeah, you are right. It seems to be a "Round bridge rectifier". Maybe like this:

https://www.tme.eu/gb/details/w01m/round-single-phase-diode-bridge-rectif/dc-components/

But I don´t know the value, since there are no BOM on the project. I´ll make a BOM, as soon as I get sourced all I need :-)

JMan

Re: Neumann W492 project - PSU help needed
« Reply #14 on: February 20, 2021, 03:09:44 PM »
Thanks TwentyTrees - Yeah, you are right. It seems to be a "Round bridge rectifier". Maybe like this:

https://www.tme.eu/gb/details/w01m/round-single-phase-diode-bridge-rectif/dc-components/

But I don´t know the value, since there are no BOM on the project. I´ll make a BOM, as soon as I get sourced all I need :-)

I think this one should work, but again, I suggest double checking me.  Looking at the pcb layout, it seems like the W0xG form factor will not fit.

https://www.mouser.com/ProductDetail/Diodes-Incorporated/KBP204G/?qs=sGAEpiMZZMtQ8nqTKtFS%2FNgL6ac11fJuOgO4GrxUCBM=


EDIT: I looked again and I was totally wrong about this, I don't know why my brain mixed that up lol.  I'll probably try out a W04G, as I've got several extra lying around.  Can't imagine it'll require anything bigger than that.
« Last Edit: February 20, 2021, 03:26:23 PM by JMan »

lovelyworldsound

Re: Neumann W492 project - PSU help needed
« Reply #15 on: February 20, 2021, 03:33:02 PM »
Thanks, JMan :-)


 

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