3U Warbler IV issues

[micolas]

Well, the audio board miiiiiiiight be a U87A clone type deal, possibly? Since the transformer is a 12:1, it shouldn't need that second transistor as an emitter follower for low-impedance drive, so that might be a capacitance multiplier?

The "PSU" board is more interesting though. The pair of inductors and capacitors near the bottom edge must be between the transformer secondary and the XLR output. Otherwise, it kinda-sorta looks like a Schoeps-type oscillator, but i'm only seeing ONE inductor, instead of the usual two

That being said, manual labor must be dirt-cheap in China - i wouldn't exactly call this "design(ed) for manufacture", with those dozens of wires flying all over the place...

We'll know when we see the other sides of the PCBs

 

[micolas]

That being said, manual labor must be dirt-cheap in China - i wouldn't exactly call this "design(ed) for manufacture", with those dozens of wires flying all over the place...

Regarding the internal build quality, someone reported the presence of PCBs/components identical to the 3U in a WarmA microphone. I really don't remember more details(offtopic posts impossible to locate in case of need)

 

[Voyager10]

From the photos posted, it looks like the impedance converter/preamp is a common JFET + emitter follower + transformer circuit, with a Schoeps-style DC voltage converter for polarisation voltage(s).

It's a similar arrangement to the CAD 3000, see https://groupdiy.com/threads/cad.61526/post-1125665

 

[micolas]

From the photos posted, it looks like the impedance converter/preamp is a common JFET + emitter follower + transformer circuit, with a Schoeps-style DC voltage converter for polarisation voltage(s).

It's a similar arrangement to the CAD 3000, see https://groupdiy.com/threads/cad.61526/post-1125665

Yes, it can be jFET+BJT+Transformer
It seems the same circuit with transformers gzt-12 and gzt-47
We are waiting to see other pcbs pictures

 

[Voyager10]

Just guessing here, but it would be useful to know the DC voltage at the end of this diode:



We only have 3 diodes here, one of them might be a zener so there's only one stage of voltage multiplier? Would be interesting to know what voltage we're getting - most multi-pattern mics either have 0/60/120V or +/-60V available.

 

[micolas]

Just guessing here, but it would be useful to know the DC voltage at the end of this diode:

View attachment 131645

We only have 3 diodes here, one of them might be a zener so there's only one stage of voltage multiplier? Would be interesting to know what voltage we're getting - most multi-pattern mics either have 0/60/120V or +/-60V available.

Warbler MKIV is cardioid only.
But there the polarization voltage of the capsule is measured, on the positive terminal of a diode (highest voltage)

 

[Voyager10]

You're right, I was looking at the wrong one of the many Warblers.

The single inductor is another mystery too - is there another on the other side of the board? Is it a Colpitts oscillator??

 

[micolas]

You're right, I was looking at the wrong one of the many Warblers.

The single inductor is another mystery too - is there another on the other side of the board? Is it a Colpitts oscillator??

That's why I insisted on posting pictures of the other side of the PCBs.
To be able to draw the diagram.

 

[mattrico]

OK here are a few more pics so you guys can work out what might be happening here.

 

[Voyager10]

Here's what I think the circuit looks like:


(I'm currently travelling, so back to pen and paper).

It does appear to be a Colpitts oscillator, in a common-base configuration. I've also annotated the circuit board view with component positions. Green = R, Red = C, Blue = L, Black = semiconductors.

Hope it helps, corrections welcome.

 

[Voyager10]

Best guess at the circuit on the other board:

 

[Voyager10]

C2 looks like it's a charge-amplifier style circuit, and my guess is that the 'voicing' switch couples somewhere via C8 or C9 to ground, to effect an HF rolloff.

From the power supply board, my guess would be that the pad works by reducing capsule voltage using the 2.2M / 1.0M divider, and possibly the OP's problems revolve around this in some way?

It would be useful to have some clear photos of the wiring to the pad switch.

 

[mattrico]

Thanks again for all your help guys. Guosheng finally got back to me, but didn't offer any light unfortunately.
It seems like it probably is all related to that top section where the switches are, so I'll try and get that photo uploaded in the next day or so.