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PostPosted: Wed Feb 21, 2024 9:58 am 
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Walnut
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First name: Daniel
Last Name: Russin
City: TUCSON
State: AZ
Zip/Postal Code: 85743
Country: US
Focus: Repair
Status: Amateur
I have an oval-hole mandolin with no pickguard, and use an ATM350 condenser mic to amplify it. Right now I use a DPA body clamp and clip the mic to that, but it's not terribly secure - no body-clamps are.

I've been sketching out an idea - getting a pair of neodymium magnets and using them as a mounting point for the microphone clip. I'd put one inside the mandolin with double stick foam tape, and have one outside onto which I could attach a mount for the microphone.

I know a lot of you use magnets for clamping so I'm hoping you can help me -
- do you think this is a viable idea?
- if so, how much clamping force do you think would be needed for something like this? Looking at countersunk magnets on KJ Magnetics, I can calculate the pull force through a mandolin side and tape (approx 0.1") and get something like 10lb of force for a reasonably sized magnet pair. You can spend more and get thicker magnets to substantially increase this.
- am I going to pull the side off my mandolin trying to remove it?

Any thoughts appreciated!


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PostPosted: Thu Feb 22, 2024 4:44 am 
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Old Growth Brazilian Rosewood
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Location: Ann Arbor, Michigan
First name: Hesh
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Interesting idea Daniel but I don't see in my mind's eye how you could slide a transducer on top of a magnet against the underside of the top without the transducer coming off. I also don't see how to get the transducer off when you want to.

Instead I see an idea that my business partner David Collins is using where he made a special purpose, small, long reach C-clamp made from a Waverly clamp. The transducer sits on the business end of the clamp and is held in place by a nipple-like membrane and he's got vacuum running to the nipple and his bench vacuum pump.

The clamp with the transducer reaches into the instrument and you can position things using what it looks like top side of the instrument since the top of the clamp has the same reach as the inside of the clamp. Put a small (small is important...) drop of medium, quality CA on the side of the transducer that will be glued to the underside of the top of the instrument and the other side of the transducer is held to the clamp with vacuum. Position things, close the clamp, wait 20 seconds and release by unscrewing the clamp and turning off the vacuum.

It works great we are using it to install K&K pups in instruments these days.

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PostPosted: Thu Feb 22, 2024 5:33 am 
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City: Lenoir City
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Hesh, I think the OP wants to use the magnets as a mount for the mic, I don’t think he is trying to glue it in permanently.

For the OP. Microphones generate signal when an internal element moves in a magnetic field. It may not operate properly or even be damaged with the neodymium magnet near it.


Steve

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These users thanked the author SteveSmith for the post: Hesh (Fri Feb 23, 2024 7:41 am)
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PostPosted: Thu Feb 22, 2024 9:57 am 
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Walnut
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Joined: Thu Sep 19, 2019 4:56 pm
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First name: Daniel
Last Name: Russin
City: TUCSON
State: AZ
Zip/Postal Code: 85743
Country: US
Focus: Repair
Status: Amateur
Thanks for the responses - you're correct Steve, I want to use the magnets to temporarily create a place to clip the mic, which looks like the below picture.

This is a phantom-powered condenser mic and I'm familiar with how they work, but I find conflicting information about whether it would be affected by magnets a few inches away and if so, what that effect would be!

I threw some cheap neo magnets in my amazon cart to try out a proof of concept. If I destroy the mic, I guess I'll get a K&K...


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PostPosted: Thu Feb 22, 2024 3:20 pm 
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I’ve done some work with magnets designing digital encoders and the field strength drops off pretty quickly with distance. I think being a few inches away will probably be ok.

I’m a big fan of K&K’s and have installed quite a few. I also use them on my guitars when I perform; I run it through a Red-Eye preamp to the sound board.


Steve

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PostPosted: Mon Mar 25, 2024 3:45 pm 
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Walnut
Walnut

Joined: Thu Sep 19, 2019 4:56 pm
Posts: 31
First name: Daniel
Last Name: Russin
City: TUCSON
State: AZ
Zip/Postal Code: 85743
Country: US
Focus: Repair
Status: Amateur
Following up on this, I have a super-crude proof-of-concept. This consists of two 1/2x1/2x1" countersunk neodymium block magnets, a scrap of ebony, a couple random wood screws, a pad of stickynotes (approximating the thickness of a mandolin side), and a scrap of leather from my local friendly furniture store.

I believe this could work. I can shake the left (inside) magnet around and it does not come loose. The outside may slide or rotate a little, but it quickly reorients itself. Having been nothing but frustrated with mandolin body clamps, I'm encouraged. With a thin strip of double-stick tape like 3m VHB to hold the inside magnet in place, you could put on/take off the outside part at will. I could wrap and glue the leather around the outside magnet, protecting the instrument from directly touching it.

It's not without its dangers. The two magnets are predictably very lively, and it would be really easy to dent or crack an instrument (or your fingers) if you're not careful. It's impossible to get the magnet inside the mandolin without taking off all the strings, and it still wants to suck over to the neck bolts (breedlove).

All that to say, I'm probably just going to install a K&K or JJB in this, since I have another instrument I just bought that has one. I didn't want to leave this question hanging out there and had already bought the magnets, so here we are. Thoughts welcome, or maybe someone will dredge this up in another 10 years and want to give it another try.


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PostPosted: Mon Mar 25, 2024 6:01 pm 
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I'd encourage you to try. The magnets are fairly heavy though and will probably effect the tone of the instrument.

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