# Odd oscillator on sound card



## mwaurelius (Jan 1, 2015)

So, I'm working away from home, except we aren't working on New Year's Day. I spent a lot of the day stripping some boards by hand and watching Geo's YouTube videos. (Thanks, Geo! Great stuff!) One of the sound cards had three oscillators on it. Two were the ordinary (at least I assume from my limited exposure) rectangle/oval capsules with an enclosed crystal and silver sandwich - know that from the videos, yeah, got a lot to learn. Anyway, the third oscillator was a rectangle with six legs and I wish I'd thought to write down the numbering on the top cover before I mangled it; I do remember it said Rakon and gave a kHz range frequency. I got it open and :shock: is that gold??

I THINK that I'm looking at what's left of the crystal with silver on both sides (don't have a good method of opening these without breaking the crystal yet), silver solder on the contacts on either side and some sort of gold spring. It's GOT to be plated or overlayed; I can't think of any reason to make it solid or even a solid alloy.

There are also what's left of an MLCC and an itty bitty chip which should have a few bond wires in it and I'm betting the solder is a silver alloy. The white substrate is ceramic.

Thoughts? Comments? Ideas? I've got the resolution turned down on the camera to keep the file size down; let me know if finer detail will make a difference. I'd go in closer, but the camera on the phone doesn't have a macro feature.


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## solar_plasma (Jan 2, 2015)

> but the camera on the phone doesn't have a macro feature.



You can use a DVD drive laser lense or any other convex lense and place/tape it in front of your camera lense.


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## Geo (Jan 2, 2015)

Thanks for the kind words. I try to include as much useful information as I can in my videos. There are parts and components that I didn't mention or have any knowledge of myself. I'm still learning like everyone else.


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## the iron dwarf (Jan 2, 2015)

I have a few of those, mostly they are silver coloured on the bottom but sometimes you get gold plated ones and can be spotted by the gold showing just on one corner from the top, on these the base plate is gold plated inside too


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## mwaurelius (Jan 2, 2015)

solar_plasma said:


> You can use a DVD drive laser lense or any other convex lense and place/tape it in front of your camera lense.



That's a great idea and I'll see about extracting one from a scrap drive here, but I'll do it next week. I have the weekend off and my wife's cousin is visiting from overseas.

I tried the loupe - 10x and 20x sides - but the picture just comes out grainy on zoom.


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## mwaurelius (Jan 9, 2015)

Been busy here and only just got to things with the somewhat improved picture. No matter what I do I cannot seem to get pictures which remain clear on zooming. The best result I've managed to get is with the magnifying glass on a Victorinox Swiss army knife. :lol: The bit of crystal broke and it's in the silver bag now.

The real item of interest, like I indicated in the OP, is the gold-colored spring. I realize it's not big and the only place I've seen this style of oscillator is on sound boards, so it's not like there will ever be a large mass of them to harvest; I'm just curious and I'm on the steep side of the learning curve so I'm trying to learn everything.

So, as far as the spring goes: A) do any of the experienced members have an idea of the typical composition and B) what is the purpose of using a spring anyway? I have a (very old and dated) military background in electronics and I'm an electrician professionally so my guess at why there would be springs in an oscillator is to use them for inductors; if that is the case, gold plating/overlay might be used to enhance the surface effect of the conductor IF the interior is a base metal. Gold plating/overlay on a silver wire would decrease the effectiveness of that as silver has a lower resistance - that's probably shooting in the dark.

On a side note: I'm processing the boards from a 10-15 year old fire alarm system and I've found some very interesting things in it. Would it be better if I started a new thread or continued this one? I'd like patnor's input once I post.


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## g_axelsson (Jan 9, 2015)

Since an oscillator works with mechanical waves it is a bit sensitive to external forces, especially high frequency vibrations. The springs holds up the crystal so I would guess it is just a suspension for the crystal. Gold plated for solderability and beryllium copper or phosphor brass for rigidity and flexibility.

Put a drop of nitric on the spring and watch the gold foils after the base metal has been dissolved. Then you know.

There is no reason to have solid gold or gold plated silver in this application, the signal current is so small that resistivity is of very low concern, especially in an oscillator. The mechanical suspension of the crystal on the other hand is of greater concern. If the sampling frequency would change up and down in sync with an external vibration this would add a modulation on top of the output (or input) signal from the sound card. I don't know if this is a word in English but I would call it to be michrophonic. That effect is sometimes found in tube amplifiers.

Göran


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## auratus72 (Jan 11, 2015)

Hi,
It looks like a "VCXO" (voltage controlled crystal oscillator) and I would like to share material composition sheet of a typical VCXO made by BOMAR'XTALS.


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## mwaurelius (Jan 11, 2015)

> share material composition sheet of a typical VCXO made by BOMAR'XTALS



THAT is really cool! It's like having a combination assay and treasure map for cherry picking parts. Tells you what to process and what to skip.

Obviously it doesn't apply to the pictured chip, but is it possible to find these sheets on older assemblies, chips, etc?

Interesting that they choose to list the gold bonding wire in the IC as "Aurum."


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