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Help: Voltage Drop on +12v issue
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Help: Voltage Drop on +12v issue
loresdef
HELP!? Voltage Drop on power rail +12v issue (Frequency central routemaster) / or modules?


Hello there all fello wigglers,

I’m kinda new here regarding posting although i’ve been reading up on here for quite a while. I did search a lot for solutions to my problem but couldn’t find any topics with this specific situation so here is my cry for help.

I’m having issues with voltage drops on the =12v rails if i add a 4th (active) module:

Basic problem: When i plug in all 4 modules the +12v rails drops about 2v, (the -12 always stays at -12). Which causes my oscillators to trip out of tune.

I’m not sure where to look for the solution and i really hope someone can point me in the right direction or advise on troubleshooting.

SET-UP: MI Tides, Dreadbox Lil Erebus, 2hp ARP, Frequency central Loop/env generator (DIY). ( My Power Consumption according to modulargrid: 195 mA +12V | 112 mA -12V | 0 mA 5V .)

PSU : Frequency central Routemaster (diy build) with 1a wall wart : Should be delivering (+12V 500mA, -12V 500mA)



Some context:

I have some basic knowledge of electronics but wouldn’t call myself anything more then a beginner, did a few repair projects and modules so far (old tape echo and some passive attenuators as well as the FC routemaster and Loopenv. which all seemed to work fine)

I started my rack 4/5 months ago, I wanted to do some modules diy since i like the process and i have experience with soldering and i liked to learn more about it + i like the new challenge / hobby side of it.

I first bought a Lil erebus (completely build module) from dreadbox and the Frequency Central Routemaster (DIY PSU+busboard) with corresponding WallWart from schneidersladen.

As i went on having a jolly time combining this with my microbrute, i added a few others to spice things up : MI Tides + 2HP ARP + FC LoopEnv .

This all worked eand me was happy patching away, untill i noticed that when i connected all 4 modules my wall wart started making a weird noise and my erebus kept doing weird stuff with pitch and sounded like sh*t, hhmmm that wasnt happening before.

I narrowed down the issue to the following situation:

Im guessing its a problem with my power;

When i plug in different combinations of three modules it seems to work fine, but when i add the 4th it drops V and starts making a vibrating noise on the wall wart.
(this noise also occurred when i accidentally shorted the +12v to GND pins on the busboard when measuring with my DMM)

Having built the routemaster power myself i’m concerned i made a mistake although it works perfectly fine with 3 modules connected.

When i plug in all 4 modules the vibrating noise happens from the wall wart and the voltage (+12v) drops between 1-2 V. from +12 to +/- 10,4-11,2 V



The Frequency Central Routemaster has two trim pots on the board which are used to set exact +/-12v.

When i plug in 3 modules it stays nicely around +12v, and i can trim it to be 12v again if it drifts a bit. But when i add the 4th module the trim doesnt seem to have any effect anymore and i cant turn it up from the dropped +/- 10/11 to 12V.



So i thought it could be that my psu isn’t delivering enough mAmp to power all modules, and because of this the voltage drops (dont know if this is right to assume) but the specs tell me that i should have around 300 mAmps left.

The build doc states :
- “ I’m recommend assuming that you ask about 500mA of each power rail (+12V 500mA, -12V 500mA) from the supply, assuming a 1A wallwart. The 5V source is rated at 100mA. “ -

I have a 1a Wallwart so i should be getting 500mA at +12v.



Some Notes from testing :

The -12v always stays nicely intact.

All modules work fine without the noise off the wallwart when connected “solo”`; +12v stays at 12v.
I believe all combinations of 2 and 3 modules work fine as well. with some i do get the vibrating wall wart but 12v stays where its at.
Whenever i add a 4th the +12v drops voltage.
I tried putting the digital modules (2hp + Tides) at the “end” of the bus board, no fix..


FC Loopenv + Tides = fine 12v
FC Loopenv + Tides + 2HP Arp = 12v but with the noise from wall wart.
FC Loopenv + Tides + 2HP Arp -> when i add the Lil erebus =12v drops to 11,22v
FC Loopenv + 2HP Arp + Erebus = fine 12v.
FC Loopenv + 2HP Arp + Erebus + Tides -> =when i add tides 12v drops to 11v



So now, i’m pretty stuck as to what to do to solve the issue, and i’d love to be patching with my whole (little) rack again.
What do you guys recommend to check or do from here on ?

Should i be checking to see if my bus board actually delivers the 500mA, and how can i measure this without modules being plugged in ? Can i just plug both sides of a ribbon cable in 2 slots of the bus board and put the DMM in between the +12v wire and measure the mA?

Should i try a different wall wart (1,5a instead of 1a) to see if it helps? - i should then add bigger heatsinks probably.
DozenCrows
As it seems you've eliminated the possibility of it being one of your modules, I would recommend trying a different wall-wart - especially as you're getting noises from it.

Maybe it got damaged when you shorted +12 to ground, so trying a different 1A one would tell you that.

Alternatively though it is rated at 1A, it is possibly not up to the job so worth trying one with a higher current to give you more headroom. For testing purposes, you probably won't need bigger heatsinks.

If the voltage is still dropping after trying that, there then could be an issue with the busboard. The voltage regulators could also be at fault; then it would be worth replacing those one by one to see (as they're inexpensive).
DozenCrows
Actually if you're planning to draw a total of 1A (500mA per rail), definitely worth having a higher rated wall-wart than that to give you headroom - stop it heating up and reduce the risk of voltage drop.
djs
DozenCrows wrote:
Alternatively though it is rated at 1A, it is possibly not up to the job


This is my thought.. it "says" 1A, but is it really? Especially as it's noisy, it's probably not the best quality?

The issues you're describing (4th module causing problems, doesn't matter which one) leads me to believe it's a PSU problem. Since you're getting proper voltages on the distribution, I'd look more to the wallwart.
DIY_geek
Here's another vote for overloading the wall wart - these are all classic symptoms. Prove it to yourself by measuring the AC volts into your Routemaster and watch it drop when you add the 4th module. Or, measure the DC voltage on the input pin of your regulators.
Starspawn
Ive been having the same problem using LM317 and LM337 recently, basically the same result, shutting down far to soon, seemingly before 300ma with 1A adapter, and the AC power runs fine. Bought from local electronics store from their cheap shit china parts imports line, so I dont trust them. Im going to try a more reputable regulator source first.
djs
To the OP- I have a variable DC benchtop power supply that I use for testing modules. I don't remember the amperage on the one I have, but it's at least 3 amps. You could use something like this to power the bus board (without the wall wart) and see if the behavior is the same.

Not sure where you're located, but I got mine for approximately $40 USD off ebay.
loresdef
Hi All!

First of all Thanks for al the responses, advice and help so far !! SlayerBadger!

Im glad to see I was probably sort of on the right track looking for the problem around the power supply!

My assumption that voltage drops can occur from insufficient mA’s i guess is correct reading ur comments which would clarify it so thanks for the confirmation!

So I ordered a 1,5a wall wart to test out if this resolves the issue, although I wonder for how long (new modules are on their way to be build) that will solve the problem until I hit the next mA “ceiling”. Assuming it’s the wall wart...

I will measure the ac going in to the routemaster later today, was thinking about how to go about this but I guess just adding the DMM in the + line between wall wart and power pcb.

Also will check the voltage regulators v going to the bus board, if these are “broken” how would I recognize or test for a faulty? Does someone know if there Would there be a better replacement instead of the LM317/LM337 possible in this circuit which or just replace em with new ones?
Maybe i’m Too far ahead, I’ll try the wall wart first anyway!

Thanks again, i’ll Post the results of my tests tonight!
djs
loresdef wrote:
I will measure the ac going in to the routemaster later today, was thinking about how to go about this but I guess just adding the DMM in the + line between wall wart and power pcb.

Also will check the voltage regulators v going to the bus board, if these are “broken” how would I recognize or test for a faulty?


you're correct on the DMM- just set it to AC voltage measurement, not DC. Note- this will only give you voltage, not amperage that it's outputting. However, you can maybe measure it's voltage as you add modules.

As far as v-regs.. I've only heard of them going bad where they just don't work. If the voltage is drooping, it's usually because the input voltage isn't sufficient- not a fault of the vreg.

Now you could probably argue that some voltage regulators are more accurate than others, but clearly your issue isn't an accuracy issue (i.e. 11.98v instead of 12v)
djs
Forgot to mention- when you're measuring the wallwart voltage, please be careful that you aren't in contact with mains voltage. I highly doubt this would happen, but I'd feel safer in warning you than not smile
electric mist
Hi, these Vreg are not so happy if they don’t see a 2v difference between input and output. Maybe this is something to investigate. What is the voltage of you’re Ac with no load ?
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