Has anyone else found this site or used the bias generator circuit? (halfshavedyaks.xyz)

[daschnoz]

(not my site, the google just finally returned a good result)
https://halfshavedyaks.xyz/pcb/BM700-polarisation.php

I'm looking to put the FET based C12 topology that I built a couple of weeks ago into a larger mic body, with a charged backplate capsule and 3-way pattern switch.

Has anyone used the circuit at the link above? I've sim'd it and it looks to work perfectly fine, even with the parts swaps that I made - because it's what I have in the parts bin (1N4007, 2N2222). The sim comes in at +62, -55 (ish), so it's close enough to a 120V differential to get it done. It runs at about 130kHz.

I'm hoping to get some feedback on it before I do the layout work and get the boards made.

 

[Khron]

The 1N4007's will NOT be too happy or effective at 130kHz. Really no 1N4148 / 1N4448's in your stash at all?

 

[daschnoz]

Nope. I do have some "switching diodes" that I bought at RadioShack many years ago. I don't remember the specs on them and the package is long lost to time, so I've been using them as 50V, 50mA max (perfect for fixing the bias on something or cheating another 600mV or so out of a 3-pin regulator). Kinda like a 1N914, but not really. They are glass, but they're short and fat with a white anode marking. There are no numbers on them.

I need to put in an order to Mouser for the zener and some caps anyway, so I'll add some 4148s to the order.

 

[rogs]

(not my site, the google just finally returned a good result)
https://halfshavedyaks.xyz/pcb/BM700-polarisation.php

I'm looking to put the FET based C12 topology that I built a couple of weeks ago into a larger mic body, with a charged backplate capsule and 3-way pattern switch.

Has anyone used the circuit at the link above? I've sim'd it and it looks to work perfectly fine, even with the parts swaps that I made - because it's what I have in the parts bin (1N4007, 2N2222). The sim comes in at +62, -55 (ish), so it's close enough to a 120V differential to get it done. It runs at about 130kHz.

I'm hoping to get some feedback on it before I do the layout work and get the boards made.

I've done a similar voltage multiplier circuit for my OPIC.45 project
The one you linked to - and mine - are based on the oscillator in the 'famous' Schoeps CMC5 schematic
The only thing you might have to physically experiment with - layout wise - is the relative positions of the 2 inductors .
The amount of 'mutual coupling' between the inductors in a Hartley oscillator can sometimes make the difference between the oscillator running - reliably - or not!
I found laying 2 Bourns 78F style inductors side by side - on a 0.1" spacing and orientated in the same direction - produced my most reliable results.
But that was on stripboard. A PCB layout should produce similar results, but I think I would check a PCB layout with a prototype first, to confirm that you get what you're expecting!

And further to Khron's diode comment, Hartley oscillators built with the component values you show will run at a couple of MHz, rather than the c.150KHz of the more common 'charge pump' multipliers found in many of todays' mics.
Not a problem with suitable components, but the frequency differences are quite significant...

 

[daschnoz]

So it is a known design and does work, sweet. Thanks for the heads-up on the component selection and layout. I think I'm going to use the component values in rogs's design.

Thanks guys.

I have been on a mic kick recently and have expanded my locker with various mics (most were pretty cheap to start, none are factory stock any longer), including a rebuilt EV V-1 ribbon to use for my son who plays trumpet. (Mike Farabee did the rebuild on this one)

This new mic is going to be for my daughter. She's 13, so she wants a pink mic. I could repaint a $20 stock BM800 if I wanted to and she wouldn't care, it just needs to be pink. She sings and plays violin, so I want to build something for her that she can use for everything. Solo, duet, or the whole string ensemble - just stick the mic in the right spot and flip the pattern switch.

When she and I were doing a small mic shoot-out, she liked the mini-mod'd Apex 460 the best, but I have that one painted OD green, not pink. I'm going to use the left-over capsule from my Apex 460 --> chunger C12 conversion for this pink mic. Sure, I could have just repainted the mod'd 460, but she's a kid; "dad, I don't need to know all the technical garbuldy-gook", so I want to give her something that is simple to use. Standard XLR cable, one switch that is easy to understand, no additional power supply, plug it in to the board and it just works. This will likely end up under the Christmas tree this year.