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Author Topic: Cleaning sensitive high-impedance areas--methods/practice?  (Read 731 times)

soapfoot

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Cleaning sensitive high-impedance areas--methods/practice?
« on: September 14, 2022, 11:50:18 AM »

It's clear that, when dealing with the extremely-sensitive, ultra-high-impedance environments near condenser microphone capsules, any contamination (or compromise of insulation resistance) can impact the mic's operation.

What are the preferred methods for cleaning these sensitive areas--particularly acrylic plastic surfaces used on some historic microphones?

While I've often used 99.9% pure anhydrous isopropyl alcohol to clean electronic surfaces more-generally, it's known that isopropyl alcohol can have a deteriorating effect on acrylic surfaces (which is why it's recommended to never use solvents such as alcohol to clean plexiglas/lexan/acrylic windows or windshields/windscreens).

So what would be best to use? Could it be that occasional one-time cleaning of acrylic surfaces with 99% Isopropyl Alcohol is acceptable enough in practice? Or would it be better to use distilled or deionized water, or something else?

Will appreciate any insight!
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gtoledo3

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Re: Cleaning sensitive high-impedance areas--methods/practice?
« Reply #1 on: September 14, 2022, 01:14:58 PM »

Kunststoff makes perspex cleaner but I am definitely curious what anyone else has to say. Never used it, I only know that they make a few cleaning products for plastics.

I try to use suitable water but also dry methods first when possible.

If itís cleaning a newer made product I might ask if they had any thoughts about products or methods.
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soapfoot

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Re: Cleaning sensitive high-impedance areas--methods/practice?
« Reply #2 on: September 14, 2022, 08:27:35 PM »

I'd be hesitant to try any chemical or solution unless it had specifically been tested on microphone surfaces.

Most acrylic is used in applications where transparency (not insulation resistance) is the most important attribute.

The last thing we'd want is any kind of residue that would leave us worse-off than when we started!
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Kai

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Re: Cleaning sensitive high-impedance areas--methods/practice?
« Reply #3 on: September 15, 2022, 03:23:38 AM »

Kunststoff makes perspex cleaner but I am definitely curious what anyone else has to say. Never used it, I only know that they make a few cleaning products for plastics.
...
Most specific glass / plastic cleaners that head for a visually cleaning contain antistatic components.
This is the opposite of what we want!

For acrylic Iíd suggest deionized water with a bit of pure Isopropanol (to solve grease).
The Isopropanol does not harm, according to https://www.thyssenkrupp-plastics.de/de/acrylglas-richtig-reinigen
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gtoledo3

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Re: Cleaning sensitive high-impedance areas--methods/practice?
« Reply #4 on: September 15, 2022, 09:58:41 AM »

I'd be hesitant to try any chemical or solution unless it had specifically been tested on microphone surfaces.

Most acrylic is used in applications where transparency (not insulation resistance) is the most important attribute.

The last thing we'd want is any kind of residue that would leave us worse-off than when we started!

Yeah, thatís why Iím bringing it up, to ask if anyone had ever tried any of the products. :-) I thought maybe one of the Neumann people who sometimes chime in, or perhaps Klaus or someone who has encountered it, might have comment.

Iíve only used water.

Iíve heard the problem with alcohol is that it can disturb the plasticizers in the acrylic. Curious.

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gtoledo3

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Re: Cleaning sensitive high-impedance areas--methods/practice?
« Reply #5 on: September 15, 2022, 10:16:36 AM »

Most specific glass / plastic cleaners that head for a visually cleaning contain antistatic components.
This is the opposite of what we want!



Really?

You add conformal coating to things for similar purpose, right?


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soapfoot

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Re: Cleaning sensitive high-impedance areas--methods/practice?
« Reply #6 on: September 15, 2022, 11:19:07 AM »

For acrylic Iíd suggest deionized water with a bit of pure Isopropanol (to solve grease).
The Isopropanol does not harm, according to https://www.thyssenkrupp-plastics.de/de/acrylglas-richtig-reinigen

When you say "a bit" of isopropanol, what would be a typical solution?

Something like 4:1 deionized water:isopropanol, or more like "mostly water with just a splash of isopropanol"?

EDIT: after translating the above web page within Google, I ran across something that's a little incongruous-seeming, to me.

It could be my lack of chemistry knowledge, but here's some text from the site:

Quote
For heavier dirt, especially greasy dirt, you can use a plastic intensive cleaner. Benzene-free pure petrol (white spirit, light petrol) or isopropanol is also possible.

It is important that the cleaning agent does not contain benzene, ethanol, alcohol, organic substances or thinners. These can damage the acrylic glass.

(Emphasis mine).

Is isopropanol not an alcohol?
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Kai

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Re: Cleaning sensitive high-impedance areas--methods/practice?
« Reply #7 on: September 15, 2022, 04:45:20 PM »

Isopropanol is explicitly mentioned as usable for acrylics.

You don’t need much, 10% is enough (the exact value doesn’t matter) to eliminate water’s surface tension an solve greasy contaminations.

In my experience the whole process isn’t critical at all.
Once washed, any conductivity is gone.

Tip: don’t dry-wipe, or you will bring back contamination.
If necessary I use a water-capable vacuum cleaner to suck the fluid away.
Of course, don’t vacuum close to a mounted capsule.
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soapfoot

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Re: Cleaning sensitive high-impedance areas--methods/practice?
« Reply #8 on: September 16, 2022, 09:50:13 AM »

Isopropanol is explicitly mentioned as usable for acrylics.

You donít need much, 10% is enough (the exact value doesnít matter) to eliminate waterís surface tension an solve greasy contaminations.

In my experience the whole process isnít critical at all.
Once washed, any conductivity is gone.

Tip: donít dry-wipe, or you will bring back contamination.
If necessary I use a water-capable vacuum cleaner to suck the fluid away.
Of course, donít vacuum close to a mounted capsule.

Thanks Kai!

One more questionóif isopropanol is safe for acrylic, would there be any disadvantage to using 99.9% pure anhydrous isopropanol?
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gtoledo3

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Re: Cleaning sensitive high-impedance areas--methods/practice?
« Reply #9 on: September 16, 2022, 10:22:41 AM »

https://repforums.prosoundweb.com/index.php/topic,25594.msg445867.html#msg445867

Not necessarily disagreeing with anything said, but going to reiterate that the cautious thing to do is to contact FLEA and ask what they advise instead of going on advice that is possibly not fully based on the relevant parameters you are dealing with.

Neumann has also advised to keep alcohol away from all plastic parts in their mics in the past, aside from this comment I have linked about Oliver finding it to result in fractured on the plastics FLEA has used in the past.
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Kai

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Re: Cleaning sensitive high-impedance areas--methods/practice?
« Reply #10 on: September 16, 2022, 12:16:29 PM »

One more questionóif isopropanol is safe for acrylic, would there be any disadvantage to using 99.9% pure anhydrous isopropanol?
Yes, because most of the dirt is more water than isopropanol solvable.
Specially all kinds of salts do not dissolve in isopropanol.

A low amount of isopropanol would largely reduce the risk of adverse effects too.
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gtoledo3

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Re: Cleaning sensitive high-impedance areas--methods/practice?
« Reply #11 on: September 16, 2022, 01:18:51 PM »

If you donít know how the plastic has been processed you really donít know if alcohol will cause cracks or not. It is extremely easy to find numerous reports of alcohol causing cracks on this general type of plastic.

Alcohol definitely stops surface tension, and I suppose that is an advantage in some contexts.

If it is possible to use alcohol on this specific plastic used in FLEA mics, which people specifically report cracking with, which generally causes cracking on other acrylics, which Neumann has suggested not to use on their former pinboard, I will definitely be glad to know that this is now the case for some currently unknown reason.

I guess the feeling that having it be mostly water, but just a little alcohol, makes a difference as far as safety of the materials goes?
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soapfoot

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Re: Cleaning sensitive high-impedance areas--methods/practice?
« Reply #12 on: September 16, 2022, 07:41:33 PM »

A bit more research into the chemistry (e.g. here indicates that temperature may make a difference, with isopropanol attacking PMMA (acrylic) at higher temps
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