First time - Schoeps CMC5 schematics

[Karl-0_0-]

Hi,
I've been been wanting to learn how to create schematics and ultimately creating my own PCB. Since I'm a totalt novice and don't really know anything, I thought it best to start copying existing PCBs (for learning purposes obviously). So here is my first attempt at making a schematic copied of a certain well known DIY company's Schoeps style PCB. There are some path's I haven't figured out where to rout yet, because the components on the PCB obscures the view on some places:

R10 to C4 or perhaps C6
C7?
D1 to C5 (or perhaps D2 or R4)

In addition there are some routes on the back side not showing on the schematic, and there is no PWR or GND.

Ps. I know there are some professionals out there who probably gets cold shiver from looking on the schematic. Sorry about that!
There's some paths crossing each other - I wanted the schematic and symbols to be an image of the model PCB, and that created some routing issues.

Any advice or tips in "ogah-bogah" is very welcome.

 

[Khron]

Umm... Why necessarily reverse-engineer that, as opposed to copying the widely-available original schematic?

And then, of course, changing component designators to reflect what's on the physical board, of course...

A more useful / practical way would be to have both the schematic AND board view on-screen at the same time. You want to draw the schematic as clearly / readably as possible, and in parallel, you can lay out & route the board just as the one you're investigating, as a "sanity check".

Also, NOT a good idea to use the JFET symbol for ALL transistors there - (N-channel) JFETs, NPN BJTs and PNP BJTs have different symbols for a very good reason: to be able to tell them apart, because they're (obviously..?) VERY different animals.

Also, you might want to find and use the "ground" symbol in your libraries, and connect all the relevant component terminals, to that.

 

[Karl-0_0-]

Umm... Why necessarily reverse-engineer that, as opposed to copying the widely-available original schematic?

I wanted to use a readily available PCB. That way I have something visual to reference. If I only have the original schematic, I wouldn't understand what I was looking at. But I guess I could use the original and then convert in into a PCB. Only problem then is I don't know/understand anything about the components I'm supposed to use. I guess I need to study up on that part.

And then, of course, changing component designators to reflect what's on the physical board, of course...

A more useful / practical way would be to have both the schematic AND board view on-screen at the same time. You want to draw the schematic as clearly / readably as possible, and in parallel, you can lay out & route the board just as the one you're investigating, as a "sanity check".

Didn't know that existed. Seems like a pretty useful thing to have. I'll check it out!

Also, NOT a good idea to use the JFET symbol for ALL transistors there - (N-channel) JFETs, NPN BJTs and PNP BJTs have different symbols for a very good reason: to be able to tell them apart, because they're (obviously..?) VERY different animals.

Yeah, I'm aware there are some funky symbols used. I don't know what type of transistors I'm looking at, except for the JFET, so I just used the same symbols on everything to have something at least. I'll correct it!

Also, you might want to find and use the "ground" symbol in your libraries, and connect all the relevant component terminals, to that.

On it.

 

[Khron]

I don't know what type of transistors I'm looking at

Google is your friend Looking up the part numbers, more often than not, leads you to at least one version of the manufacturer's datasheet (usually in PDF format).

 

[Karl-0_0-]

Google is your friend Looking up the part numbers, more often than not, leads you to at least one version of the manufacturer's datasheet (usually in PDF format).

I took your advice and started sketching up a schematic from the original, but stumbled a bit on one symbol.

The attached picture - the explanation on the schematic says "ferrite bead" on Dr5, but I have not seen a symbol version of a ferrite bead like the one in the picture. Are these perhaps inductors?

 

[rogs]

I took your advice and started sketching up a schematic from the original, but stumbled a bit on one symbol.

The attached picture - the explanation on the schematic says "ferrite bead" on Dr5, but I have not seen a symbol version of a ferrite bead like the one in the picture. Are these perhaps inductors?

Yes, DR1 and DR2 are inductors. The values are likley to be within the range 45uH - 150uH, with DR1 being around twice the value of DR2.
Pages 5,6 and 7 of THIS PDF show a hobby version of the Schoeps voltage multiplier Hartley oscillator, with component values shown...

 

[Karl-0_0-]

Yes, DR1 and DR2 are inductors. The values are likley to be within the range 45uH - 150uH, with DR1 being around twice the value of DR2.
Pages 5,6 and 7 of THIS PDF show a hobby version of the Schoeps voltage multiplier Hartley oscillator, with component values shown...

Thank you, I'll check that out!

 

[bremusound]

What Schoeps used:

Dr1 680uH

Dr2 120uH

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

 

[Karl-0_0-]

What Schoeps used:

Dr1 680uH

Dr2 120uH

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

Thank you, I'll check out that thread.

 

[Karl-0_0-]

Anyone know what symbol to use in KiCad to create a trim res with three connection points? The R_Trim only allows me to connect to top and bottom. Not the joint on the left.

Should I use the R_Potentiometer symbol instead?

... and a another one. What is the symbol on the second picture? Ground? Diode?

 

[Karl-0_0-]

What Schoeps used:

Dr1 680uH

Dr2 120uH

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

Hmm.. I'm certainly no expert, but don't you think it might be 68uH instead of 680uH?

 

[micolas]

DC/DC:
The oscillator works with a very wide range of values, both for inductors and capacitors. Experiment with what components you have. I prefer smaller values for miniaturization reasons. Certain combinations allow obtaining a higher voltage polarization. It also varies the oscillation frequency, I prefer it to be higher, usually above 2Mhz. They are personal decisions. It's nice to experiment

 

[dai h.]

hi,

I am a bit confused on that since many people (and Schoeps circuit copying mics such as Rode NT2, etc.) seem to have no issues using 68uH, but I have a pic (1980s? CMC guts (internals)) and factory schematic (with some hand annotated parts values) appearing to show 680uH. Does the circuit work with both 68uF and 680uH?

 

[micolas]

hi,

I am a bit confused on that since many people (and Schoeps circuit copying mics such as Rode NT2, etc.) seem to have no issues using 68uH, but I have a pic (1980s? CMC guts (internals)) and factory schematic (with some hand annotated parts values) appearing to show 680uH. Does the circuit work with both 68uF and 680uH?

The capsule does not care how the necessary high voltage is produced, with a Hartley oscillator, with CMOS, through a voltage divider in the case of tubes, or from batteries (U87i).
The capsule is only interested in the value of this polarization voltage.
So you can build any DC/DC you want.
Microphone sound will not be affected.

 

[Karl-0_0-]

hi,

I am a bit confused on that since many people (and Schoeps circuit copying mics such as Rode NT2, etc.) seem to have no issues using 68uH, but I have a pic (1980s? CMC guts (internals)) and factory schematic (with some hand annotated parts values) appearing to show 680uH. Does the circuit work with both 68uF and 680uH?

The pic of the internals answered one of my earlier questions about the trim pot(s). Thanks!

Now I need to figure out how to modify the schematic so a nose cone can be applied.

 

[Karl-0_0-]

Yes, DR1 and DR2 are inductors. The values are likley to be within the range 45uH - 150uH, with DR1 being around twice the value of DR2.
Pages 5,6 and 7 of THIS PDF show a hobby version of the Schoeps voltage multiplier Hartley oscillator, with component values shown...

Is the "DC OUT" where you would connect for example the pogo pin on a nose cone?