Hello everybody,

Maybe this will be usefull for someone.

Here are pictures and schematics of the PSU of STELLAR CM-2 (APEX 460 copy - 165 USD on Evilbay)





The zener diodes d5, d6, are 1N4760A (2 x 68 volts)!!!

About the microphone himself it's identical to an Apex 460. Absolutely no difference !

eD

EDITED 23/07/08 : on my schematic I wrote : D1 to D11 = 1N4007 it's with the exception of D5 and D6 (the zenners)

Don't buy that. You can buy a brand new Nady 1050 supply directly from them for about $49 plus shipping. It's the same supply. I bought one last year because I wanted an extra one around to experiment on.

Maybe I wasn't clear... the $165 USD is for the complete kit : MIC, PSU, shockmount, case, etc.
You can do a search on Evilbay for Stellar CM-1.

I've just post the pic and the schematics of the PSU because it's a little bit different than the Apex one.

The mic is identical...

eD

Question about the polarization voltage !

Is it wrong to say, according the schematics of the Apex 460, that the polarization voltage is 50% of B+ ?

As long as R3 and R4 have the same values, it's a simple voltage divider, isn't it ?

My "understanding" of this part of the circuit is : there is no DC voltage drop accross R5 and R10 (there is no path to the ground for DC current, only 2 caps : the capsule and C4) so the polarization voltage must be V+ just after R4 ? Am I crazy ???

eD

Hi guys, a newbie around here trying to resurrect the thread.

Im getting crazy trying to understant some things a about the C12, lets see:

1.LDT2 said: Panasonic for C1 and C2, C6 black gate, and Auricap on C8.
the values are the one in the schematics or another ???

2.whitch components to remove ???

3.Im trying to find the differences between
each valve, so whitch one you like most and
how does it sound ???

4.Do I have to change something in the power supply ???

5.And...Ive solder the cinemag like Ashton said:
Apex 460 Cinemag CM-2480

Red Red

White Brown

Green Yellow

Black Orange

Is it right with the other modifications ???

sorry to be a pain guys, but im a bit lost,
Im just trying to build the best combinations.

Im just waiting for your answers to start the war....regards

1. For C1, C2, and C6, I left the values the same. C8 can also be left the same, but a larger value increases bass response. However, if you have an Apex 460 or Nady 1150 (as opposed to a Nady 1050), space might be limited.
2. Are you removing the cathode followed part of the circuit?
3. I've only used the 6072.
4. No, but a few people have. I've changed two diodes in one of my power supplies to lower values.
5. yes

There is more than one variation on these mods. List the ones that you're interested in, and we'll be able to answer your questions better.

Craig

I think that you're confusing me with MPCNYC who uses the Auricaps. I don't think they'll fit into the 460. I haven't changed C1 and C2 in either of my mics and only have a Black Gate in C8 of my 1050/U47ish mic.

Check out page 12 of this thread for my mod schematics. The 1st schematic is the one to follow for a C12ish mic. All values are the closest match to the C12 schematic that were available with the only difference being the cathode section, which matches the C24 schematic.

Remove the cathode follower which includes R8. Then remove R1, R5, C3, C7, C9 and C10.

All other resisters and caps were changed to the values on my schematic, although I've since changed C8 to a 1uf. The original C12 used a 0.5uf in the C8 position. C1, C2 and R9 are the original parts.

The Apex PS is fine as far as the voltage goes, the Nady uses a higher voltage.

As for the tranny colors it should be:

Red > Red
White > Brown
Green > Orange
Black > Yellow

You're not a pain because it's quite easy to get lost with this stuff if you haven't done it alot. Hope this helps.

Lucio

Hi,

BTW Lucio, about the polarization voltages you wrote on your schematics, how did you measure them ?

I confirm there is no way to put an Auricap 1uF in a 460 without loosing one of the PCBs. (The size of the Auricap 1uF 400V is .77"D x .90"L)

eD

eD,

I used a multimeter set to voltage and put the red lead at the points shown on the schematic with the black lead on the mic chassis/ground.

Lucio

I used a Ansar at C8 in a 1050. Will that fit into the 460?

quote:

Originally posted by LDT2:
eD,

I used a multimeter set to voltage and put the red lead at the points shown on the schematic with the black lead on the mic chassis/ground.

Lucio

Hi lucio,

I'm a bit confused (as usual )
after reading this thread :

Klaus Heyne's mic lab

It seems it's not possible to measure the polarization voltage with a traditional volmeter. I asked for precisions and I'm waiting for the answer.

It seems the polarization is given by the calculation of the resulting voltage after the 1st resistor of the voltage divider.
The same explanation is given by Jakob in the description of the G7
microphone.

On my 460 (Stellar CM-1) I measured 65.4 Volts (before R5) for a B+ of 133.5 Volts.

If it's true the voltage polarization can only be measure with an electrostatic voltmeter, it must be true for the pattern voltage as well (voltage after R9). In cardio mode you need to "mute" the back capsule by applying a polarization voltage equal to the one applied on the center electrode. So in cardio mode, the voltage potential between R9 and the capsule should be the same of the voltage potential between R10 and the capsule.
On your "C12 schematic" you have : 0-25-50 volts for the pattern voltages. 25 volts for a the cardioid figure is a bit low... ?

The other thing which bugs me is : if the polarization voltage is brought by 2 divider resistors and if R5, R10 ha no influence, it would mean the Apex 460/1050 which have 182 volts stock at B+ would have 91 volts of capsule polarization ? I thing I even read someone had two zeners of 100 volts stock, meaning 100 volts at the capsule...

It's very "funny" to see that the stock B+ voltages vary from 133 Volts to 200 for the exact same microphone circuit...

eD

On my C12 schematic it shows 55volts in the same location, before the last resister leading to the capsule. John Peluso recommends between 60-64volts for his capsules. I have 62v with 154v at B+. The C12 used 120v at B+ so that would drop the voltage to the capsule. Your voltages are different because you probably still have the 270k resisters which will allow more voltage through compared to the 500k resisters used in the C12, not to mention the extra resister and cap at R5/C3.

If you look at the 2nd quote from that link, it says to measure the resistance after you power down the mic. All of my measurements are with the mic powered up.

For me, if those measurements were good enough for AKG then they're good enough for me.

As for the pattern voltages being low, I was concerned about that at 1st, but both mics measured the same. I recently read that the PS voltages can be measured with the mic disconnected to check the voltage at the PS, which may show the higher numbers, I don't know as I haven't done that.

As for the different PS voltages, we're dealing with different companies here. Apex using 150v (2x75v zeners), Nady using 182v (100v + 82v zeners) and your CM-1 at 138v (2x 68v zeners). The actual voltages vary slightly as we've seen.

2 100v zeners resulting in 200v to the mic will not result in 100v to the capsule because you don't check the voltage resistance until you shut the mic down, according to that link. Personally, I wouldn't over think this.

If you only have 65.4v before R10, how can that possibly increase when there's another resister to drop the voltage after the measurement?

For me, it's about the sound of the mic, not the theory behind it and if AKG designed this mic with those parts, then the only issue is the incoming voltage to achieve it. Slightly higher voltage will make the mic a bit brighter and increase the gain. Slightly less the opposite.

Hope that helps some,

Lucio

quote:

Originally posted by LDT2:
On my C12 schematic it shows 55volts in the same location, before the last resister leading to the capsule. John Peluso recommends between 60-64volts for his capsules. I have 62v with 154v at B+. The C12 used 120v at B+ so that would drop the voltage to the capsule. Your voltages are different because you probably still have the 270k resisters which will allow more voltage through compared to the 500k resisters used in the C12, not to mention the extra resister and cap at R5/C3.

Actually, that the center of this discussion : for getting a voltage drop, you need a current and the ONLY path to ground for a DC voltage after R4 is the point when R3 is connected to the ground. If R3=R4, the half of the B+ voltage is lost with R4, and the second half is lost with R3.
After R4, if you go to the left, you've got R5, C3, R10 and the capsule, NO path to ground for DC, so no current and no power dissipated and no voltage drops.

quote:

Originally posted by LDT2:
If you look at the 2nd quote from that link, it says to measure the resistance after you power down the mic. All of my measurements are with the mic powered up.

He said : "You can check you polarisation voltage by measuring the incoming voltage at the mike end (approx. 105V)(*)and then (after powering down!) measuring the resistance of each of the two divider resistors (2 and 3MOhms). Finally calculate the resulting voltage from the resistance ratio. Replace resistors if needed.(**)

(*))--> to me it means, the B+ value under load (when the mic is connected)

(**) --> to me that's just mean, you have to know the resistors's values for your making your calculations. With the Ohm laws, once you know the values of R3 and R4 you are able to calculate the current in this part of the circuit : current=B+/(R3+R4)
Once you know the current value, you can calculate the voltage dropped by R4 V=R4xcurrent. If R3=R4, 50% of the B+ is dropped by each of them.


[QUOTE]Originally posted by LDT2:
For me, if those measurements were good enough for AKG then they're good enough for me.

You're talking bout the 55 Volts ?
Is this "the official" capsule polarization of a C12 ? Or something "added by hand" ?
I've been searching for hours the CK12 polarization voltage / capsule bias voltage on several forums, and I'm not able to find anything but 55 volts (posted by you) and the "I have a tech note somewhere that shows a C12 schematic with about 61 volts polarizing the capsule posts." posted by Dave Thomas.
I don't understand why this info is so hard to find.

quote:

Originally posted by LDT2:
As for the pattern voltages being low, I was concerned about that at 1st, but both mics measured the same. I recently read that the PS voltages can be measured with the mic disconnected to check the voltage at the PS, which may show the higher numbers, I don't know as I haven't done that.

When I made the measurements of my polarization voltages, it's the contrary, they increase under load ! I've upgated my schematic with the values a few posts above.

quote:

Originally posted by LDT2:
As for the different PS voltages, we're dealing with different companies here. Apex using 150v (2x75v zeners), Nady using 182v (100v + 82v zeners) and your CM-1 at 138v (2x 68v zeners). The actual voltages vary slightly as we've seen.

Aren't all those different microphones brands are supplied by the same company Chinese named Alctron ?

quote:

Originally posted by LDT2:
2 100v zeners resulting in 200v to the mic will not result in 100v to the capsule because you don't check the voltage resistance until you shut the mic down, according to that link. Personally, I wouldn't over think this.

I've explained that above. I think the reason he suggests to shut the power off and measure the resistors value it's because it can be hard to read the values on the body of the resistors : vintage resistors, old codes, erased chiffers, etc...

quote:

Originally posted by LDT2:
If you only have 65.4v before R10, how can that possibly increase when there's another resister to drop the voltage after the measurement?

I'm not sure I follow you here...

quote:

Originally posted by LDT2:
For me, it's about the sound of the mic, not the theory behind it and if AKG designed this mic with those parts, then the only issue is the incoming voltage to achieve it. Slightly higher voltage will make the mic a bit brighter and increase the gain. Slightly less the opposite.

You're right, it's about the sound.
I'm maybe tooooooooo obssessed with the theory.

I just want to understand as much as I can before starting swapping resistors, capacitors, and make test. I want to know for example : "what will happen if I decrease the values of this cap or this resistor" : will I have more gain, more basses, more mid ? I will make the fine tuning by ears, but I would like to know the "big lines" before plugging my solering iron.
The Apex 460 is inspired by the C12 and the C24, but the C12 and the C24 are different as explained here so I don't feel comfortable by picking one value there and another there before I know exactly what I do.

I don't want to be right, I just want the truth !

If it's true, the polarization cannot be measured with a traditional volmeter I WANT to know how to get the 62-64 volts recommended by Peluso at the capsule...

Oh man... when I go to bed and when I close my eyes... I saw all these schematics...

Thank you for your time Lucio !

eD

eD,

Yes a the 55v was written on the page and the 61v that Dave spoke of was from a C12A schematic, also written by hand.

I think it's difficult to find because it's a factor of everything that comes before it, which may be why they list the incoming voltages for reference.

My reference to 65.4v before R10 is just that, if you have 65.4v before R10 then R10 will add resistance.

Even though the mics are made at the same factory they're not 100% the same. The individual companies may specify slight differences. I know that the Nady and Apex did use some different resister parts as well as caps and zeners. My Apex PS uses 1000uf caps for C9 & C10 and the Nady PS has 10,000uf caps in the same spots as well as different caps for C7. I tried switching out the PS with each mic and didn't hear a difference.

I'm not sure what truth you're looking for. We've mentioned the differences between the C12 and C24 from the beginning. The ELA M251 uses a similar circuit to the C24 as far as the cathode bias goes. You could easily go in that direction with these mic's also.

Check out the C12VR schematic and you'll see different values of resisters and caps, but the voltages are about the same.

I really can't help you with the theory behind all this because I'm not a mic designer.

You might want to check out Prodigy Pro forums. They've got enough info to keep you reading for awhile just from the META's. I've tried to join they're forum for over a year at least, but never got an activation email. Maybe you'll have better luck. I'd definitely do some reading over there and search the forums for the answers you want.

Sorry I couldn't help you more. I just know that my mic's sound excellent.

Lucio

Sorry if this has already been covered. I'm just wondering if the a AMI Tab transformer can work with this mod? I believe this is the one that's used in the MKII M16..

V314 same size than BV308 but with T14 ratio ECC81, 6072/12AY7, EC92, AC701

I also notice that the canadiandistributors kit lists a BV11P Transformer. I cannot find any other information on this model number or maker other than their site. Anyone have info?

I've used it. It sounds really nice....but...it barely fits in there. You have to do without the little plastic bracket which sits on top of the can (which is discarded) that the original trannie is in. So, it'll fit in a 460, oddly it wont fit in a 1050.

It's expensive but I feel like it sounds great.

quote:

BV11P Transformer. I cannot find any other information on this model number or maker other than their site. Anyone have info

I think BV11P is the Peluso transformer...not really sure.

Yes the BV11P is from Peluso...

eD

quote:

Originally posted by MPCNYC:
I've used it. It sounds really nice....but...it barely fits in there. You have to do without the little plastic bracket which sits on top of the can (which is discarded) that the original trannie is in. So, it'll fit in a 460, oddly it wont fit in a 1050.

It's expensive but I feel like it sounds great.

Just to clarify, you're responding in regard to the AMI TAB tranny?

Thanks

Yep