Sampler issues, hiss on line, temperature related

[Amiga1992]

I just noticed one of my samplers doing some annoying hiss that later disappears.
Today I thought that this could be related to temperature so I opened it up and blew hot air to it while it was making the noise. A few seconds later and the noise was gone!

Does this sound to you like capacitor fault? All the other components seem to be ICs so it has to be some of the analogue stuff.
The thing is pretty old and I bet it could use a cap replacement, but I want to make sure before I go all the way to do such work, don't really want to do it for nothing.

[hooverphonique]

is it hissing with no signal connected? what happens when you short the inputs to ground?

[voyager]

bad transistors can hiss like that..

[Amiga1992]

Yeah, with nothing connected, it gives this hiss. Shorting the inputs still gives the hiss.
When I warm it up, it goes away.

Maybe it is transistors. Let me take a photo of the PCB so you can see more or less what's inside.

Here:



I pretty much focused the hot air on the top left part of the unit, where those caps are, right by the inputs, because I thought it made sense. But maybe that was just a coincidence.

[hooverphonique]

I'm pretty sure it's not the ac coupling capacitors at the input.. could be a power supply problem at the A/D converter (ZN449) or an opamp.. Do you have access to an oscilloscope?

I also spot a DAC in there (AD7520).. If that's used for software controlled attenuation/amplification of the sampler input, that could be related to the problem as well.

Does this sampler have a midi interface, or what is all that unrelated stuff on the right?

[Amiga1992]

Yep, it also has a MIDI interface.
I don't have an oscilloscope

THere's no software control of the amplification, that I know of. PErhaps I should look for the AMAS2 software, if any at all, and find out.

Any other way I can diagnose this without an oscilloscope? Should I just change all teh components you mentioned?

Which one is the opamp?

[hooverphonique]

the 3 ic's on the left are opamps..

does the problem happen regardless of if you sample in stereo or mono?

[Amiga1992]

I don't have any software to sample in stereo, Protracker doesn't do it. Will look into it.

[voyager]

If the problem occurs spray the opamps one by one with some freeze spray.

[robinsonb5]

Have you checked for cracked solder joints?

[Amiga1992]

I wouldn't know how to check for cracked solder joints. Pressing teh chips?
But my instinct tells me that if I had cracked solder joints, I would get intermittent hiss instead of solid operation after the unit has warmed up.

Once the unit had time to warm up, it just keeps going great.

[robinsonb5]

Originally Posted by Akira

I wouldn't know how to check for cracked solder joints. Pressing teh chips?

Or just looking at them with a magnifying glass.

But my instinct tells me that if I had cracked solder joints, I would get intermittent hiss instead of solid operation after the unit has warmed up.

Could be - but remember that warming up = expansion = potentially closing up microscopic gaps or cracks.

[daxb]

AudioMasterIV is able to handle mono and stereo. You can switch them with menu "Project" -> Mode.

I guess you have alread checked cable and connection.

[Amiga1992]

Thanks to you both, I will check both stereo sampling and for cracked joints! Need to get a nice magnifying glass though, the one on my helping hand is shit of course.

Cables aren't the problem as I tried others, yeah.

[hooverphonique]

if you already sample in mono (and assuming the channel selection is controlled from the amiga), it's alright.. The reason I asked was to get an idea about if the 4066 chip could be involved in the problem - it contains 4 cmos switches which are used to pass either left or right channel to the ADC.

but yeah, as others mentioned, remove the pcb and check solder joints..

[Hewitson]

I'm willing to be proven wrong but I think we're barking up the wrong tree here. A piece of equipment needing to "warm up" before working properly is almost definitely bad caps.

[Stedy]

Hi,

Can you take a photo of the other side of the PCB.

As an electronic item heats up the following changes happen:
Solder joints expand, very commonly this causes intermittent connections to re-connect.
Capacitance increases slightly.
Resistance increases slightly.
Digital logic and clocks run slower.

I suspect a bad solder joint but would want to see the solder side of the PCB. Freezer spray is fun

Ian

[Amiga1992]

Here's something I'll say that would help:
I am not getting an intermittent connection. When the unit is heated up, the hiss GRADUALLY disappears. This is why I don't think it's a cold joint, that would be on or off.
Also it's not like "disconnecting ground hum", it's a particular hiss. I'm pretty sure it's a component being faulty. I can record the hiss for you to hear, and how it changes when heat is applied.

Here's a pic of the other side anyway!

[voyager]

Just replace the 7 caps they cost next to nothing, if the problem remains it's one of the opamp's. you can use a spray duster upsite down to get a nice freeze spray ;-)

[Amiga1992]

Explain the freezer stuff, because I never heard of it.
I think I will do as you say indeed, just change the caps and see if that fixes it!