1 voicecard crackle (SOLVED- in a really embarrassing way)

Hi!
My Ambika has been working perfectly for the past week but today a weird thing showed up:
Third SMR voice card has some weird crackle noise and it “builds up” depending on how long Ambika is powered on. When it’s powered off for a while and on again, it’s fine. But during some playing, it becomes a bit crackled and distorted. I recorded the sound when it was at it’s worst (ambika was on for quite a long time):
http://audiour.com/playlist/ftjltbtr

Also the card lacks a bit in volume:
http://audiour.com/playlist/wqvsfvbe - two voice cards activated, the quieter sound is the crackling one.

So what could be the problem? just the headers not transfering the signal properly, or something wrong with some component?

I don’t know, you should investigate more…

  • If you use individuals outputs, could this be the cable/audio interface?
  • Does the problem appear on the individual output too or only on the mix?
  • When the problem happens, can you probe the signal output on the voicecard (middle pin of the upper A/B jumper) and see if the crackle is there too?

1,2) The crackled sound comes from the mix output and from the output 3.
So it can’t be some outer problem.

3) Is this probing done with an oscilloscope? Sorry, I’m from the farthest depths of n00bland, does someone deign to explain how’s it done?

Probing is explained on the build page of the shruthi smr4 filter
The Ambika SMR is of course different but very similar to the shruthi version.
Did you build the Ambika yourself?

One thing i would suggest to start with is take out the voicecard that gives the crackles and check if all the ic’s are firmly pressed and exchange it for another voicecard in a different slot. If your problem stays in the same slot the problem is on the main board. If it moves along with your voicecard it’s one your voicecard.

I swapped the 1st and 3rd voice card, now the first one is the duller and one (not crackling though), so the reason must be only in the card. It’s not the same card as in “this”:www.mutable-instruments.net/forum/discussion/4987/two-problems-with-ambika-and-smr4-solved#Item_21/ (why the hell does my linking not work) thread, so no replaced resistors or wrong value caps, but if needed, I can take the pictures also.

I built this Ambika by myself, but purely just following instructions and putting it together like some legos. So no deep technical understanding from me…
I’ll just ask that is the probing done just from the solderpoint side? I mean that if the A layer middle and upper pin are connected with the jumper, what’s the difference?

> what’s the difference?

The difference is that we want to measure the signal straight out of the voicecard, rather than through the stack of headers and the output jack, in case the problem is a loose connection with the headers or the jack!

Yes I understand that but my question was rather that should I remove the jumper that connects the "A "and “sel” or just probe the middle one? If latter, then the middle pin (sel) is also connected with the A and therefore what’s the difference in probing the middle or the upper pin if they’re connected anyway?
sorry for my stupid questions…
Edit: After changing the port of the voice card, I can’t seem to recreate the crackling sounds like before, but the card is lacking volume the way it did before… Should I still probe this card and for example the some properly working card and compare their volumes?

It doesn’t matter if you test the middle pin with the jumper in place or not.

> Should I still probe this card and for example the some properly working card and compare their volumes?

Yes.

I’ve now probed the middle pin on the faulty and working card, and the volume difference is like 8db…

Ouch!

This deserves a high-res photo… But first compare all parts with a working voicecard.

Funny thing is that this occured after one week period. I would have noticed it before, if it was the case from the start.
I’ll try to get the pictures soon.

Okay, you may wanna ban me from this forum after I’ve told this-
Rather than first watching myself what could be the problem, I come here crying like a baby…
So I started to look the solder joints of that card and didn’t find anything. Then I did it again and saw, and rubbed my eyes and saw again that… BASICALLY ALL THE PINS OF THE TL072 WERE UNSOLDERED!?
Only some corner ones were attached. So I must’ve been soldering all the sockets at once, first attaching the corners and then going over all of them and forgeting to solder the TL072.
But I’m kind of baffeled about the fact that it still worked for a week… So were the legs of the socket touching the edges of the holes and over time bent away from them? (that’s where the crackling probably came)
Don’t know… but at least it works again :slight_smile:
Really embarrassed about that, sorry…

It happens. My Ambika voice card was only producing clicks and after looking at the boards and resoldering numerous times I finally saw I missed a few solder joints on some resistors. I have missed sockets in the past as well.

The partial socket solder type of incident has happened to me too. It’s kind of cute, after a while you can join the battle-scarred veterans. Just tilt your head and say naww…

Glad you found it!

Yup, I’ve done it too… on sockets…

yes that’s quite a common scenario i’d say. but be happy your TL072 has survived.

I wont comment on this. And yes, i buy TL07xs by 50s……