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Help: Voltage Drop on +12v issue
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Help: Voltage Drop on +12v issue
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.
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).
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.
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.
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.
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.
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.
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!
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)
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 ?
Hi All,

Thanks for all help and suggestions so far ! SlayerBadger!

I tried out the new wall wart with 1,5a instead of 1a output, this one doesnt make any weird noises and looks to be way more stable and better quality.

I did have to reset the trimpot setting for the +12v rail when all modules were plugged in to be exactly +12v, this still changes with more or less modules plugged in, is this something i should worry about ?

I added 2 modules: befaco Even Vco and the Optomix, and it still runs smooth now after the adjustment so my guess is it was indeed the wall wart, just hope this is true and i'm not neglecting any other possible issues.

The heatsinks gets hotter but i can still easily put my finger on there for as long as i want without burning it so that should be allright i guess, even though i'll still replace them for bigger ones this week.

Anyway, Thanks for all help and insights, I'll be wiggling on for now It's peanut butter jelly time!
electric mist
I did have to reset the trimpot setting for the +12v rail when all modules were plugged in to be exactly +12v, this still changes with more or less modules plugged in, is this something i should worry about ?

Do you mean you have a voltage drop when you add some modules ? How many volts ?
Yes, if i add modules the +12v goes down a bit depending on the module it seems, around 0,75v averaged.

(-12 seems to alway stay on -12v)

But if i plug in all modules, and after that i adjust the trimmer to get back up to +12v again, it then will stay at +12v.

This would mean i need to adjust the trimmer every time i add a new module, which isn't a big issue for me but i'm wondering if this is correct like this or it's part of a defect or defunction?

I emailed frequency central about this, if i get a response or i've found the fix i'll put it up here as well!
electric mist
Doesn’t sound good. That means you’re psu doesn’t work properly. You should check if the voltage drop is before or after the regulator.
As I said in another post these regulators need to see a difference of 2v (or maybe 3v can’t remember) between the input and the output. Usually toroidal transformers with center tap deliver a higher voltage than the voltage they are rated for and after rectifying and filtering the voltage is usually high enough for the regulator to work properly. But I don’t know if it works like this with this small wallwart adapters. Simply check the voltage at the input of the regulator and see if it’s high enough.
I have this exact issue!!!

I believe it is to do with specification of the capacitors, possibly due to discharge due to the size of the load..

I have upgraded the heatsinks to 3.3c/w and am using a 30Vac 2.5a 12v ac/ac supply.

I have three routemasters connected in a daisy chain from one to the next.. I have set each +/-12v to exactly 12.00 using the pots "off load" I have then tested the incoming AC on the supply into the first Routemaster and then tested between ground and pin 3 on LM317 to give REG DC/in and compared with pin 2 on the LM317 to give REG DC/out.

headroom on the supply would definitely help however this does not explain the drop off in the voltage to REG DC/IN... looks to me like increasing the capacitors size would help as looks as if they are discharging too quickly with the load.. does anyone have any experience with this? please see attached table to show results of tests..

To get the "expected REG DC/IN" I was using (VAC IN * 1.4) (for DC rectification) - 1.4 for the diode drop..

The regulation is not possible with both modules running .. if this is a pure overload on the transformer what are the thoughts of switching to a 5 AMP/5000MA 12 VOLT 60VA AC/AC supply?

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