DC-DC Converter for Multi-Pattern Phantom powered mic.

[SparkleBear]

Hey all,

Im working on making a little SMD daughter board much like the one found in the u87ai. I have been building the bom on mouser and came upon a symbol in the schematic that I cannot identify...
What is the component circled in green?



Also, how much more after t2 needs to be included... I imagine the feedback resistor r112 is included... do I need to go all the way to r109? I want to use this just like i'd use matador's dc-dc board but it will be MUCH smaller... to be integrated into smaller designs or used as a daughter board on header pins.

Any advice would be appreciated. CHEERS!

-Eric

 

[Khron]

Wouldn't the Schoeps type be a bit simpler?

And that mystery component is a transformer, or coupled inductor.

 

[Drosselmeier]

Chinese manufacturers often change this transformer with two inductors.

 

[ccaudle]

Chinese manufacturers often change this transformer with two inductors

Is it more efficient with both coils on the same core, or just smaller? I would have thought the tight coupling was needed to ensure it always oscillates properly.

 

[Khron]

More efficient? Maybe, but also more expensive / labor-intensive, since you'd either have to wind your own, or have them custom-wound.

 

[ccaudle]

Do you happen to remember what that oscillator circuit is named? Is that a Baxandall oscillator, such as these:
Baxandall sine oscillator paper, 1959

 

[SparkleBear]

Wouldn't the Schoeps type be a bit simpler?

And that mystery component is a transformer, or coupled inductor.

I suppose I could go for the schoeps type. I never considered that... do you have a link to the schema? I definitely want to make it SMD and tiny...

 

[Khron]

https://groupdiy.com/threads/schoeps-cmc5-inductor-values.73321/

 

[rogs]

As it's surface mount, why not consider something along the lines of fig. 9 in this article: https://gyraf.dk/schematics/Voltage_multipliers_with_CMOS_gates.pdf
(Maybe using 2 separate devices to get the extra stages for the voltages you need? )
No inductors involved...

 

[Khron]

No mandatory need for two devices, "just" enough diodes and caps connected the right way. Works well enough for Rode...

 

[rogs]

I only suggested 2 devices because of the need for the dual polarity in this case...
I've used a single device to get up to 80v (schematic about half way down this page: http://www.jp137.com/lts/OPIC.41.pdf ).
Works very well - and no inductors involved!
I just thought it might be easier to use a separate second device to generate the negative supply? .....

 

[doqmemory]

I have used the version of the DC bias supply from Henry Spragens site. It works well for both +60V and -60V with 18 parts, I think, and easily fits on a small board. BTW, he has some great articles for DIYers.

 

[Gus]

I see EJD audio
Do you have an audio company?

 

[SparkleBear]

I see EJD audio
Do you have an audio company?

I'm aspiring to start an audio company... its still in the budding stages. More of a dream at this point... Right now i've just been taking commissions for mic builds in my local community of musicians and engineers. I'm working on my design chops right now...

 

[Thetro1an]

hello, it’s rather strange that there are different denominations in 2 photos, as I understand it, where 0.22 mH is closer to the original

 

[SparkleBear]

Hey all,

I started working on this dc-dc project again. My idea is to make a little daughter board that lives on headers so I can use this in various designs. Looking at Henry Spragen's circuit schematic I was wondering if I would need more than the highlighted portion.





Mostly curious if I would need Q6 and the surrounding passives... Or what i have mapped out would be enough to get the capsule bias voltages.

Thanks friends.

-Eric

 

[Khron]

- You won't (and shouldn't) have 48v at the input of that circuit
- You mixed up the signs of the two output voltages

 

[ccaudle]

Mostly curious if I would need Q6

Q6 looks like an emitter follower for the 9V zener, essentially a regulator circuit with about 8.5V output.

 

[SparkleBear]

- You won't (and shouldn't) have 48v at the input of that circuit
- You mixed up the signs of the two output voltages

Thanks mate, always helping me catch my mistakes. Appreciate it..

Q6 looks like an emitter follower for the 9V zener, essentially a regulator circuit with about 8.5V output.

So, the input for that specific dc-dc bias circuit is 8.5v coming off of Q6? If i understand correctly from your guidance.

The first mic I want to bring this into is my km84-47 LDC mic. Basically a km84 circuit with a k47...



I imagine putting this dc-dc after R5 (and modifying mic circuit for multi patterns if wanted)... Is it important to regulate down to the lower voltages before going up to +/- 60v?

Thanks for the guidance, wise friends.

 

[SparkleBear]

So far making progress...

Still not sure if I need to add Q6 and passives but I wanted to start layout and can expand board if I need to do so.