Turret boards in microphones

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tardishead

Well-known member
Joined
Aug 11, 2004
Messages
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Been trying to use acrylic both 2mm and 3mm to make turret boards for tube mics with limited success.
Acrylic seems to crack under very little stress. Can install the turret lugs fine but as soon as I start to install components - the heat and pulling stress of the components seems to make cracks. I think IPA when used too much can also encourage crazing and eventual cracking as well.
I see that old mics use acrylic boards and turrets so I cant think what I am doing wrong here. Although I've read reports of old boards crumbling and failing in Elam 251 etc.
Is there a special grade of acrylic that needs to be used? Also a lot of materials are called acrylic - including Plexiglass and Perspex. I'm a bit confused as to what to use here.

Also is there any other kind of board that might be more suitable for turret lugs in mics. I've read that acrylic is preferred because it has a very high electrical resistivity. That Garolite does not have as high resistivity. What about PTFE or something which is easy to machine but maintains strength without being brittle
What about FR4 without copper clad?

 
Be very careful machining PTFE - the fumes are quite nasty (as in potentially lethal) if you burn some of it by accident (and the dust ain't great either, especially if you smoke).

Sheets of FR4 aren't very expensive.
 
Intresting search, I've used opaque materials only for this kind of thing, micarta is the name here, is like a fiberglass sheet but brown. No problems, very good electrical properties AFAIK and will take any abuse for this application.

For a clear finish I don't know what to say, maybe doing holes by burning the acrylic instead of drilling may give a better resistance to cracking when you reheat the thing, the problem is you may have loose turrets easier, I don't know. Looking for a softer clear material may be the way to go or using some tubing between the turret and the acrylic, maybe heat shrink is a good option, always a perfect fit in size, really good insulator and soft material that would allow some movement dampening vibrations and making it harder to crack the board.

JS
 
I use FR4 PCB material and turrets from Keystone. I made an anvil by drilling a hole in a piece of aluminum. I used a center punch to swage the pin in place.

Patchbay_2-1.jpg
 
There are various russian small tag strips, various sizes available . Perhaps it can be used in diy mics. Very reliable, made of carbolite.
 
Also, solder components in with a bit of a curve in the leads. They expand as you heat them in the soldering and then contract as they cool down, pulling against the turrets and hence the board. If they are straight and tight already, then you get a lot more distortion than if there is some curve that allows a little slack.
 
I have used PTFE in a couple of guitar amps with good results. Not in microphones though, don't know if they are better or worse for high impedance circuits...
Got the idea from ampmaker (.com).
 
slimvince said:
I have used PTFE in a couple of guitar amps with good results. Not in microphones though, don't know if they are better or worse for high impedance circuits...
Got the idea from ampmaker (.com).
PTFE is perfect for mic circuits. It's what I use. Somewhat less rigid than polycarbonate though.
 
I've used PTFE as well, very easy to machine (if you take care not to breath the dust, like said before). It's perfect (especially) for high imp parts of the circuit in mics. I used FR4 "blank" 3mm boards wich can be found from tube guitar-amp makers suppliers (for turret boards!) for less sensitive stages. I had no success with regular Acrilic, plexiglass and polycarbonate, too brittle, and the turrets tend to get loose as you heat them for soldering. Perpex is better, and I think this is what was used in some old mics.
Laurent.
 
And, if you smoke, be extremely careful with PTFE - having the dust on your cigarette can, apparently, be fatal.
 
ok tried some polycarbonate - seems much better than regular acrylic. Well so far have drilled and soldered some point to point circuits on turrets. No crazing or cracking yet.
 
Do not use any alcohols on acril, it will crack the structure of the material. If you have one side only with turrets, put the turrets on the foiled side of the acril(you can remove the foil later) I made several c12 clones to 3mm acril boards without problems.
 
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