Crackles in output?

Someone I know is having an issue with an Ambika and thought I would ask for him over here. This is his issue:

"The ambika goes from voice card one being quiet and crackles in main out and it’s associated output being quiet and cracked with the rest of the outputs clear loud outputs in mix out. After a reboot the whole main output is quiet unlike before but voice one is ok in associated out but now the mix output is all at a quiet level. This makes me think something wasn’t done correctly on the motherboard level and I’m not finding any associated threads on the topic. It just alternates like this occasionally and is fine after some reboots but the behavior alternates from quiet to loud with exception to voice one in mix out to rebooting with all voice fine but now all voices quiet in main mix. I wouldn’t have been able to spot something like this immediately and am convinced something wasnt right with the build on the motherboard level.

The sum output is way more quiet then single outputs. Not sure if this is interfering or causing the crackles as it looks like some function for the network feed around the main sum tl072 output op amp"

Any ideas I can pass along to him?

I’d think crackles would be a poor connection. There will be capacitance there and it causes all sorts of odd behaviour.

Is this a problem that could develop over time?

If a soldered joint is marginal it can change over time, the expansion and contraction of some components as they warm up and cool down can do that.

The summed output will be quieter than the individual outs btw.

hi heath pointed me to this forum conversation.

i got the ambika fairly recently 2nd hand and have strange alternating behaviour in output which alternates between two different states between power cycles. crackling behaviour seems less likely on some reboots as it generally goes away on several reboots.

1. state one- all voices no crackle from main mix out or individual outs. however from the main mix all voices sound like they do from individual outputs but much more quiet.
2. state two- voice card one crackles and is lower in output both in main mix and from its dedicated output. what is strange is that the main mix out now outputs all voices as loud as individual outs from the mix out but the crackled quiet output remains as quiet as it’s individual out.

typically a reboot has been correcting the behaviour but not sure why it would alternate or sound okay once it boots up fine. i haven’t had the ambika for long so i don’t have any long running observations of the behaviour.

the only thing i can notice from a visual inspection is a kluge of a piggybacked resistor (the one marked 10k on the motherboard that feeds into a pin of the tl072 mix output. i’ll have to open it up and read the value.

do you think the piggybacked resistor might have anything to do with it?

or more like the loose connections from what 6581punk might of mentioned?

any other ideas to check in on?

measurement on the piggybacked resistor feeding into IC1- tl072 is showing 5k. gonna replace that and see what else might be suspect in the meanwhile while it’s opened up.

You do know that you can’t get reliable resistance measurements of a resistor that’s been soldered into a circuit, don’t you? It’s probably connected to all sorts of things in series and parallel, not to mention the inputs of various ICs.

hm. seems to add up though to 5k. i clipped a 10k resistor off and saw that there was a 10k resistor underneath it. not sure why the original builder might have done this since the reisistor called for was a 10k.

did all the other obvious stuff while in there. cleaning connectors, reflowed the output joints, swapped voice cards in the suspect voice port, checked all the joints in suspect card, checked ic seating and reseated voice cards for solid connection.

thanks for the suggestions. i’ll report back if it gives me any issues from here out!

Hi , with the 10 Kohm it can be that he TL 072 overload in some cases . Specially if you play all Voices it can be that you hear a distortion .
So 2x 10 Kohm wasn’t bad . Or use a 4,7kOhm .