Nothing but loud Hum coming from Shruthi-1

hey MI community. i finally just finished building my first kit having ordered it near the beginning of the year. everything seemed to be fine as i near finished the assembly, the LEDs all seem to be working and switches/encoder fully functional. but when i went to plug it into my mixer before soldering the screen into place i ran into a problem. hopefully its something small, but i plug in a midi cable, an audio cable then put the power supply in i get a loud hum. i cant seem to make any noise myself besides this humming constantly coming out of it. i have the spacers in so nothing should be touching inside. dont want to touch anything else untill i figure out why its making this noise. thanks for your help MI! hopefully can figure it out soon

  • It might be worth checking that you are not using a stereo cable, and that you are not plugging the cable in the signal input!
  • Post photos of your boards so that we can check part values, IC orientations etc.
  • The loud hum is usually a sign that there’s a short or wrongly oriented part somewhere - try removing the ICs one by one and see if removing one of them make the hum disappear.

Grounding issue? Check / reheat all solder joints? Do signal probe tests according to the build instructions. See where the hum starts.

i think im using a stereo cable, ill try to find a mono one. also ill take pics of my boards but my camera is not the best. im pretty sure my ICs are facing the right way accept maybe one of the last smaller ones that goes in the control board. there was no small cutaway on the chip but only the small dot, so i put the dot on the side the ridge is printed on the PCB.

i thought i found the source of the problem. one of the ICs on top had a connection outside the socket, seems it was bent a little as i put it in and as the rest set in it bent into itself, i thought it was broken at first but its in place now. i re checked all teh ICs and they seem to be fine. but when i plug in my shruthi i still get silence then a loud buzz followed by what seems like loud static. im guessing there is a short somewhere ? im taking pictures but the quality isnt the best im not sure if it will help but ill upload them

hey guys, i cant get a clear picture of my boards, i have blurry ones clear enough to see what resistors are where but thats about it. should i upload these or wait untill i can get a friends camera to help me take better pics?

Post them anyway.

sorry theyre so bad and for being so slow, ive been really busy lately.

Remove all ICs except the LT1054 and do the voltage test. What do you get?

Insert the ICs one by one and redo the test. Is there any IC that causes things to go wrong when inserted?

sorry to be such a noob but you want me to do the voltage test presented in the filter board instructions correct?

Yes.

sorry im not sure im doing this right. my numbers seem to always changing, i think they’re climbing? i plug in the power and put COM to GND then touch the green on TL072 and the number just climbs untill its in the positives and keeps climbing. ive removed all ICs except 1054. maybe a power supply issue? it was fine when i did the power test when first assembling but i was using a 100ma supply which i dont think will work for the final build

You need a power supply able to deliver at least 300mA.

Don’t the numbers ultimately stabilize?

yeah the power supply im using now is a 9v DC 300MA center positive.
but no, they just seem to keep rising. it went from about -6 to +3 before i unplugged the board again.
should i not have C1 attached ?

C1 should be there, but it’s hard from your blurry pictures to see if something is badly soldered. Is the C1 correctly polarized? Does the LT1054 get hot?

i know im really sorry im going to try to find a way to get clearer pictures.
which way should C1 be facing? it might be reversed. i have the label on it facing C2, should they be facing the input/output? and yes lt1054 seems to get hot not long after plugin.

From the assembly instructions:

“C1 is polarized. The positive lead is marked with a + and a band (see this picture”)

mmmm, i believe from what im looking at i have it reversed. i take it i need a solder sucker to remove this component and put it in correctly? also would this have damaged anything else on the board?

Why didn’t you perform the voltage test before continuing soldering the other parts? There’s a reason why the voltage test is early in the assembly process - to prevent you from frying too many parts in case of assembly error in the power supply section!

You might have damaged the 1054 too. One thing you could try is directly cutting the cap and try without it.

i did do the voltage test, i just didnt solder the C1 cap untill i was about to attach the two boards, so everything was fine the first tests. the C1 was actualy the last component i soldered after i finished the filter and control board so my brain was probably a little tired. hopefully i didn’t damage the 1054 as i never had it plugged in for very long.