Cad Equitek E100 Capsule

[k brown]

ME-50 has entirely different, non-removable, and much lower quality capsule; rather noisy, too. It is made by Primo, but a much lower end product - the long-discontinued EM68. It was used in a lot of inexpensive mics around that time, including a Radio Shack model.

Audio Technica used a much higher-spec'd version (I imagine made to AT's specs) in their first condenser mics. Had a gold rather than alum diaphragm, and different FET and circuit.

 

[Gus]

I traced it, and it's actually quite similar to the generalized schematic in the manual. What confused me was that the gate and drain of the input FET looked like they were soldered together, but it was actually just a small bead of glue -- no continuity. I don't know the value of the gigohm+ resistors, as they are SMT parts stood on end that look like terminals, and are unlabeled. My meters all max out at 1 Gohm or less, so these are probably 2.2G or more.

BTW that is the correct orientation of the 2SK170; it appears to have its drain and source flipped relative to what you'd expect. Does that actually make a difference here?

I may have XLR pins 2 and 3 reversed here, not sure.

I like how the transformer is driven.
The cascode allows the use of the 170 or other higher input capacitance JFET .

 

[bremusound]

I traced it, and it's actually quite similar to the generalized schematic in the manual. What confused me was that the gate and drain of the input FET looked like they were soldered together, but it was actually just a small bead of glue -- no continuity. I don't know the value of the gigohm+ resistors, as they are SMT parts stood on end that look like terminals, and are unlabeled. My meters all max out at 1 Gohm or less, so these are probably 2.2G or more.

BTW that is the correct orientation of the 2SK170; it appears to have its drain and source flipped relative to what you'd expect. Does that actually make a difference here?

I may have XLR pins 2 and 3 reversed here, not sure.

Could you determine which 170 and 369 variants are used? BL/GR?
Thanks a lot!

 

[jamesmafyew]

Could you determine which 170 and 369 variants are used? BL/GR?
Thanks a lot!

BL in both cases.

 

[bremusound]

BL in both cases.

Thank you!
BTW: I read somewhere that Josephson uses 10G resistors

 

[Gus]

I made a sim of the cascode section and got what look to be reasonable drain and source voltages in the range of 9.1VDC to 12VDC. Is that close to what is in the circuit?

 

[Icantthinkofaname]

Anybody know how much noise to expect from the Universum 381? A couple pairs on eBay for cheap enough. Thinking about picking up some cheap electrets that have cardioid, omni, and shotgun (and ideally hypercardioid non-interfence tube) capsules for flexibility. I'm also considering the Sennheiser K6 system.

 

[Gus]

One thing I notice is that there is no reservoir capacitor for the FET supply voltage upstream of the regulator. I don't have the equipment available to test, but it seems conceivable for the regulator to drop out if there is a sudden demand for current. I notice that the C715 schematic shows a cap ahead of the regulator, but there is none here.

Looking at the C715 schematic do C1 and C2 go to the place shown in the schematic?

 

[jamesmafyew]

Looking at the C715 schematic do C1 and C2 go to the place shown in the schematic?

I don't know if they're connected there in the 715 or not, but they're definitely not connected that way in the e22S. The e22S is as in its own schematic and in my trace.

 

[abbey road d enfer]

One thing I notice is that there is no reservoir capacitor for the FET supply voltage upstream of the regulator.

You mean downstream...?
Indeed it seems the designer considered the regulator's output is clean enough to allow dispensing with an output cap.

I don't have the equipment available to test, but it seems conceivable for the regulator to drop out if there is a sudden demand for current. I notice that the C715 schematic shows a cap ahead of the regulator, but there is none here.

The FET operates in class A, I don't think the demand on the regulator can in any circumstance be excessive. If it was the case, the input FET would be much more affected than the one in the regulator.

 

[Gus]

jamesmafyew

The E22 schematic makes sense.

Anyone
I was asking about the 715 because I do not understand why the transformer coupling caps are connected at the JFETs as drawn.
That junction voltage does not "move" alot being "held in place" by the source resistance of the "top" JFET.

Is that a mistake in the schematic?
Or am I missing something about the 715 schematic in post 155 in this thread?

 

[abbey road d enfer]

Is that a mistake in the schematic?

Very likely. However, considering the low side of the primary goes to the FET's source, it could work as a unity-gain Z-converter.

 

[Khron]

You probably still don't want DC going through the primary of that transformer..?

 

[Migs 31]

I traced it, and it's actually quite similar to the generalized schematic in the manual. What confused me was that the gate and drain of the input FET looked like they were soldered together, but it was actually just a small bead of glue -- no continuity. I don't know the value of the gigohm+ resistors, as they are SMT parts stood on end that look like terminals, and are unlabeled. My meters all max out at 1 Gohm or less, so these are probably 2.2G or more.

BTW that is the correct orientation of the 2SK170; it appears to have its drain and source flipped relative to what you'd expect. Does that actually make a difference here?

I may have XLR pins 2 and 3 reversed here, not sure.

CAD Equitek E100...
Amazing microphone, smooth on voice.
Unfortunately, one we had, the battery leaked.

Josephson e22s.
I wonder what that Diode (circled Red does) is that a Zener Diode?
And if yes, what Value is that !?!
6V, 9V or higher... ?

M

 

[abbey road d enfer]

I wonder what that Diode (circled Red does) is that a Zener Diode?

It's the voltage reference for the regulator circuit.

And if yes, what Value is that !?!
6V, 9V or higher... ?

Considering it powers the cascode input stage, I would think it's more than 6V.

 

[Migs 31]

It's the voltage reference for the regulator circuit.

Considering it powers the cascode input stage, I would think it's more than 6V.

Ok. Thank you for shedding light on this, Sir.

I made a sim of the cascode section and got what look to be reasonable drain and source voltages in the range of 9.1VDC to 12VDC. Is that close to what is in the circuit?

I think Gus might have solved the "mystery" of the voltage from the regulator in his simulation?
Clever, very clever.
M

 

[Gus]

I am bumping this thread because the E22 is an interesting circuit

 

[jamesmafyew]

CAD Equitek E100...
Amazing microphone, smooth on voice.
Unfortunately, one we had, the battery leaked.

Josephson e22s.
I wonder what that Diode (circled Red does) is that a Zener Diode?
And if yes, what Value is that !?!
6V, 9V or higher... ?

M

The zener is 18V, a 1N5248 specifically.

 

[Dylan W]

And since they were asked for, here are some gut pics of the e22S. There seems to be a diode-connected 2SK170 in series with the capsule coupling cap & ferrite, and the 2 cascode FETs are 2SK369s. EDIT: the 170 is not diode connected, it just looks that way because of the glue bead. The 170 is the input FET. One of the 369s is the regulator, the other is the "upper" FET in the cascode.

Any idea about the specs/ratio on the transformer? Looks like one of their amorphous cores

 

[jamesmafyew]

Any idea about the specs/ratio on the transformer? Looks like one of their amorphous cores

It is, custom-made for Josephson by Lundahl with a 4:1 step-down ratio. Here is David Josephson talking about it on another forum:
https://repforums.prosoundweb.com/index.php/topic,2967.msg23449.html#msg23449
And another reference:
https://repforums.prosoundweb.com/index.php/topic,26709.msg383159.html#msg383159