The Mic

[analag]

I have some skinny enclosures like the AKG stuff those will get the UTMs but for larger bodies like the U47 I will not hesitate to use the Chinese transformer, if I have learned anything from winding transformers for 49yrs I fully expect them to do good. Ordering another as we speak. Also currently waiting on this one to arrive. poor documentation also but I'm up for the challenge.
https://www.aliexpress.us/item/3256...t_main.23.76161802XytPGX&gatewayAdapt=glo2usa

 

[micolas]

Secondary is 4.3H from me physically testing the thing. Next question.
Unfortunately their documentation sucks and as I stated earlier I had to use my impedance meter to series up the coils correctly. I also stated that the UTM and the Chinese transformer read similar impedances...

Hi @analag !
I am glad that you are persistent and You are going tot test both transformers. I am sure you will make an objective, fair comparison. I'm also a little intrigued by the specifications published by the Chinese manufacturer (probably the guys in suits from the marketing office messed things up)
I can't wait for you to share your findings with us.

 

[analag]

Hàha, I'm not testing them in the same mic. Let's see how the UTM do with an active loaded 5703wb. Pushing forward into the experimentation bs.

 

[analag]

I'm going try and make this thread as pic heavy as I can. BTW I can have them operational in a few hours if I choose. But if I finish them too quick I will get bored again, so I'm slowing it down a lil bit.
I have parts for two more mics on the way and I'm a little undecided on what direction to take with them. But I will by the time everything shows up.

 

[micolas]

I'm going try and make this thread as pic heavy as I can. BTW I can have them operational in a few hours if I choose. But if I finish them too quick I will get bored again, so I'm slowing it down a lil bit.
I have parts for two more mics on the way and I'm a little undecided on what direction to take with them. But I will by the time everything shows up.

Ha, ha! You perfectly described our problem. We want to extend as much as possible the state of happiness that our hobby produces.
It's called DIY

 

[analag]

Quick check before final assembly. I only had to reduce the LED current. No other adjustment was needed.

 

[analag]

It's alive!!! Super quiet, nice even huge flattering sound, the transient response is noticably good and I'm going to attribute that to the biasing scheme and the transformer core size. Overall I am very very satisfied. Now on to the next one. Did I mention I reodered another one of those Chinese transformers. I'm moving quick before the tariffs hit, lol.

 

[lampas]

Quick check before final assembly. I only had to reduce the LED current. No other adjustment was needed.

View attachment 143585

What kind of topology did you use? M49 or U47? Is it transistor or fet near LED?

 

[analag]

What kind of topology did you use? M49 or U47? Is it transistor or fet near LED?

Inspired by the U48. What you see there is a depletion mode MOSFET holding a steady 2mA through the LED

 

[analag]

Next is this with MOSFET loaded anode, I'm also toying with the idea of fixed biasing her for a more dynamic performance. The beauty of perf boarding is being able to switch it up just like that.
There is your UTM mounted, for all you defenders of it, lol. Big transformers for big enclosures and small transformers for small enclosures, is what I say!

 

[analag]

Almost done

 

[analag]

Little bit of a layout jig saw puzzle getting things where I wanted it without interfering with the enclosure, closure...get it?

 

[analag]

The saga continues....

 

[analag]

I fired up the second mic this morning. Adjusted the active load until I got 62V or half the B+ at the anode. I am going to compare the noise level with and without the cathode bypass cap. I am hoping the superior PS rejection and increased gain of the CCS will make it possible to not bypass the cathode. But I can also fix bias the tube if I choose. A 100K resistor and a green LED should get me where I want to be. The MOSFET remained cold to the touch during testing. I eventually swapped the capsule to a sub $30 China edge terminated thing. I'm sure it will sound good, the edge terminated capsule is not as difficult to get right, me thinks. I will know in the morning.

 

[analag]

Three wires to connect

 

[terry setter]

If you end up using the circuit with a green LED, watch out for noise. LED's are NOT quiet. Better to stack something like two UF4007s, which are impressively quiet and not at all sensitive to having light strike them (which, of course, is not something too likely to happen inside of your microphone).